阅读说明：本技术 硫酸锂与碳酸钠（钾）直产碳酸锂降低硫酸根含量新方法 (New method for directly producing lithium carbonate from lithium sulfate and sodium (potassium) carbonate to reduce sulfate radical content ) 是由 王庆生 于 2019-09-30 设计创作，主要内容包括：从硫酸锂净化完成液液和碳酸钠(钾)净化完成液热沉淀工序产出粗碳酸锂开始,到产出精碳酸锂湿品为止,已有祛除硅、铝、铁、镁、钙、重金属的方法大部分不变,但可选用本发明2“预沉淀补充除杂”辅助,检测方法不变；采用本发明1“反向加料、不循环母液”和3“高效解吸附”,可使工业级碳酸锂硫酸根下降到0.03％、主含量升高到2.5N,电池级硫酸根下降到0.010％-0.008％、主含量稳定上3N甚至触及3.5N-4N极限位。“高效解吸附”由‘微提温热沉淀暨热搅洗’(105-115摄氏度)与‘中高温强力解吸附’(140-160-170摄氏度)释放包晶核心部位被深度包裹的硫酸根等杂质,再由“旋液分离”液相有效带离。热沉淀改求小晶体并后移热陈化时长至‘中高温强力解吸附’。(From the beginning of the production of crude lithium carbonate in the process of liquid-liquid heat precipitation after the purification of lithium sulfate and the purification of sodium (potassium) carbonate, until the production of a refined lithium carbonate wet product, most of the existing methods for removing silicon, aluminum, iron, magnesium, calcium and heavy metals are unchanged, but the method 2 'pre-precipitation supplement impurity removal' can be selected for assistance, and the detection method is unchanged; by adopting the invention 1 'reverse feeding, non-circulating mother liquor' and 3 'high-efficiency desorption', the industrial-grade lithium carbonate sulfate radical can be reduced to 0.03%, the main content can be increased to 2.5N, the battery-grade sulfate radical can be reduced to 0.010% -0.008%, and the main content can be stabilized to 3N and even reach 3.5N-4N limit. The high-efficiency desorption releases the impurities such as sulfate radical and the like deeply wrapped at the peritectic core part from micro-temperature-raising thermal precipitation and thermal agitation washing (105 ℃ and 115 ℃) and medium-high temperature strong desorption (140 ℃ and 160 ℃ and 170 ℃), and then the impurities are effectively carried away by the liquid phase of the hydrocyclone separation. The thermal precipitation is changed into small crystals, and the crystals are moved back for thermal aging for a long time to be strongly desorbed at a medium-high temperature.)

1. The new method for directly producing lithium carbonate from lithium sulfate and sodium (potassium) carbonate to reduce the content of sulfate radical is characterized in that: 1) the method adopts 3 technical contents from the step of obtaining crude lithium carbonate from the thermal precipitation reaction of the lithium sulfate purification finished solution and the sodium (potassium) carbonate purification finished solution to the step of obtaining a refined lithium carbonate wet product: 1 'reverse feeding, no circulation of mother liquor', 2 'pre-precipitation supplement impurity removal' and 3 'high-efficiency desorption'; 2) most of the prior art for removing impurities such as silicon, iron, aluminum, magnesium, calcium and heavy metals before the thermal precipitation process is unchanged, but the 2 nd 'pre-precipitation supplement impurity removal' technology of the invention can be selected for assistance; 3) the existing technology of drying, crushing, metering and packaging the refined lithium carbonate wet product is not changed; 4) various detection methods are unchanged; 5) other characteristics are as follows: the lithium-containing raw material for producing lithium sulfate comprises: spodumene, lepidolite, carbonate type primary lithium carbonate of salt lake lithia, lepidolite, phospholithite, petalite and other lithiated ores and lithium batteries and other lithium-containing wastes; the sulfur-containing raw materials comprise various sulfur-containing substances such as sulfuric acid, sulfate, sulfur oxide, sulfide, elemental sulfur and the like, when the coarse lithium carbonate is thermally precipitated, the dosage of sodium carbonate (potassium) is 5 percent more than the theoretical quantity, the thermal aging time of the thermal precipitation operation is shifted backwards, the charging time is shortened by more than 50 percent, and a pressurized shower atomization spraying mode is adopted to obtain the coarse lithium carbonate with small particle size (large-particle-size crystals are not obtained temporarily), so that the high-efficiency desorption operation is facilitated to release impurities such as chemical adsorption at the core part and deeply-wrapped sulfate radicals, and the like, namely the sulfate radical content of the lithium carbonate can be respectively reduced to be 0.03 percent at the lowest industrial level and 0.008 percent at the lowest battery level, the main content can be respectively increased to be 99.5 percent at the industrial level, the battery level is 99.90 percent, and part of products can be.

2. The technique of "reverse feeding without mother liquor circulation" as claimed in claim 1, which is characterized in that, taking spodumene sulfate process lithium carbonate as an example: the traditional mode that the sodium carbonate purification finished solution is added into the lithium sulfate purification finished solution in the thermal precipitation process is reversed, and the lithium sulfate purification finished solution is added into the soda purification finished solution to greatly reduce the chemical adsorption and deep wrapping of the lithium carbonate particles on sulfate radicals; the primary hot mother liquor for obtaining the crude lithium carbonate 1 by centrifugal leaching is operated in the following three ways respectively, and does not return to the acidified material leaching process: firstly, cooling to 0-15 ℃ for crystallization and centrifuging to obtain mirabilite, then, creating another process route, concentrating the secondary cold mother liquor to the beginning of a sodium sulfate crystallization membrane, filtering out crude lithium carbonate 1 which is separated out again while the secondary cold mother liquor is hot, merging and crystallizing mirabilite … … with the tertiary hot mother liquor, alternately carrying out the operations of ' cold separating mirabilite and heat separating crude lithium carbonate ', recovering lithium from the secondary cold mother liquor in a manner of precipitating water-insoluble lithium salts such as lithium phosphate, lithium fluoride or lithium stearate, and the like, multi-effect vacuum concentration for recovering anhydrous sodium sulfate, directly carrying out multi-effect vacuum continuous concentration for recovering anhydrous sodium sulfate from the primary hot mother liquor after recovering the water-insoluble lithium salts such as lithium phosphate, lithium fluoride or lithium stearate, and the like, merging the mother liquor which is centrifuged to the anhydrous sodium sulfate into the primary hot mother liquor for recovering lithium, thus, the sodium sulfate concentration of a heat sink reaction liquor system can be greatly reduced, and the beneficial effects of ' reverse feeding, and the primary yield of the crude lithium carbonate 1 is increased due to the reduction of the salt effect.

3. The "high efficiency desorption" technique of claim 1, wherein: it is composed of 'strong desorption' technique and 'cyclone separation' technique, and the 'strong desorption' is composed of 'micro-temperature-raising thermal precipitation and thermal agitation washing' and 'middle-high temperature strong desorption': the former means that under the condition that the allowable pressure in a jacket and a kettle of a thermal precipitation and thermal agitation washing jacket reaction kettle is respectively allowed to be more than 0.6 MPa and 0.2 MPa, the saturated vapor pressure in the kettle is selected to be 0.13-0.18-0.20 MPa, the corresponding temperature of a material liquid is 105 ℃ and 115-120 ℃ at the highest, thermal precipitation and thermal agitation washing (the thermal agitation washing is matched with 3 times of deionized water) are carried out, the sulfate radical content of the obtained crude lithium carbonate 2 can be properly reduced, the primary yield of lithium can be properly improved, and the using amount of the thermal agitation washing deionized water can be properly reduced; the latter means: the crude lithium carbonate 2 is matched with deionized water with 3-4-5-6 times of the weight of the crude lithium carbonate and is placed into a pressure reaction kettle, the saturated vapor pressure in the kettle is 0.5-0.6-0.7-0.8-1.2 MPa at the highest, the corresponding temperature is 152 ℃, 159 ℃, 165 ℃, 170 ℃ to 188 ℃ at the highest, and under the condition of low-speed stirring, the strong desorption and thermal aging is carried out for more than 1 hour, because the thermal motion of various molecules, ions and atomic groups in a material liquid system is intensified, the sulfate radical which is deeply wrapped on the core part of the crude lithium carbonate particles due to chemical adsorption in the initial stage of the thermal precipitation reaction and most of other water-soluble, slightly water-soluble and water-insoluble impurities are released into a large amount of deionized water, a large amount of small-diameter lithium carbonate crystals or completely disintegrated, and are recrystallized into large crystals with extremely low sulfate radical content in the environment, such a key innovation; "hydrocyclone separation" means: the 'middle-high temperature strong desorption' operation separates out lithium carbonate particles to dissolve (including water dissolution and peptization) and most of impurities such as sulfate radical suspended in a large amount of deionized water are directly carried away by a liquid phase of rotary flow, and the impurities are not trapped in refined lithium carbonate particles much like various solid-liquid separation technologies using filter cloth.

4. The 'micro-heating up thermal precipitation and hot washing with stirring' technique as claimed in claim 3, wherein: after sodium carbonate is added into the thermal precipitation reaction kettle to complete the purification solution, the jacket is opened to raise the temperature, the manhole of the reaction kettle is covered, and the reaction kettle is totally closed after air in the kettle is completely exhausted; the temperature is raised to a selected value, the stirrer is started and is always kept to be effectively stirred, and the lithium sulfate purification completion liquid is pumped in a spraying mode through a pressurizing shower nozzle arranged at multiple points (the feeding speed is controlled to be improved by more than 50% compared with the existing thermal precipitation reaction so as to obtain coarse lithium carbonate with small particle size) to carry out the thermal precipitation reaction; and (3) after the addition is finished, immediately starting pressure relief and temperature reduction (steam heat is recovered by a pipeline), and immediately discharging and centrifugally leaching to obtain crude lithium carbonate 1 when the temperature of the materials in the reactor is reduced to 95 ℃.

5. The 'micro-heating up thermal precipitation and hot washing with stirring' technique as claimed in claim 3, wherein: and (2) moving the crude lithium carbonate 1 obtained by hot precipitation into a hot agitation washing reaction kettle which is filled with deionized water with selected multiple, such as 3-4-5 times and 5-6 times of industrial grade and battery grade respectively, heating to 95 ℃, starting a stirrer, covering a manhole, continuously heating, fully sealing the reaction kettle after air in the kettle is completely exhausted, heating to a selected place value, keeping the hot agitation washing for 15 minutes, releasing the pressure of the reaction kettle, cooling (preferably taking a pipeline to recover steam heat) to 95 ℃, discharging, centrifuging and washing, and controlling sulfate radicals of the industrial grade and battery grade crude lithium carbonate 2 to be respectively reduced to 0.30-0.20 percent and 0.15-0.10 percent.

6. The 'medium-high temperature strong desorption' technique according to claim 3, which is characterized in that: pumping deionized water (for producing grade lithium carbonate with the weight of more than 99.950%, deionized water with the mass of more than 18 megaohms.cm) which is selected according to the weight of the crude lithium carbonate 2 into the medium-high temperature strong desorption kettle, starting a jacket to heat, starting low-speed stirring, and adding the crude lithium carbonate 2; heating to a selected position, maintaining low-speed stirring, keeping a slurry solid phase in a low-speed motion state, strongly desorbing and thermally aging for more than 1 hour to release water-soluble impurities, slightly water-soluble and water-insoluble impurities mainly comprising sodium sulfate in the core part of the lithium carbonate particles in deionized water, so that a large amount of small-particle-size crystals are disintegrated, and the small-particle-size crystals are recrystallized into large crystals with extremely low sulfate radical content in an environment where the sulfate radical concentration is far lower than the thermal precipitation reaction concentration.

7. The hydrocyclone separation technique according to claim 3, characterized in that: after the high-medium temperature strong desorption operation detects that the sulfate radical residual content of the lithium carbonate in the desorption kettle reaches the standard, closing a heating valve, maintaining low-speed stirring, releasing pressure, introducing cooling water for cooling, increasing the stirring speed until the slurry maintains a strong stirring state when the pressure in the kettle is reduced to 0.05-0.06 MPa, controlling the speed, pumping the slurry out, feeding the slurry into a hydrocyclone separator, and continuously separating liquid phase and solid phase; the separated liquid phase can not be circularly used for the operation started by the working procedure of thermally precipitating crude lithium carbonate generally, and returns to the leaching working procedure for use or cleaning filter cloth and equipment for use; allowing only a part of the separation liquid which is fully condensed with impurities and is subjected to precise filtration to be used in the deionized water for hot agitation washing of industrial-grade crude lithium carbonate 1, but the subsequent process is forbidden; after solid phase centrifugal leaching (if necessary, stirring and washing for 1 time), the refined lithium carbonate wet product is obtained, the industrial-grade sulfate radical should be 0.03-0.02%, the battery-grade sulfate radical can be as low as 0.010-0.008% or even-0.005%, and the main content reaches the limit value of 4N grade.

8. The 'mid-high temperature forced desorption' technique, the 'hydrocyclone separation' technique according to claim 3 or 8, characterized in that: the pipeline type desorption device is adopted to automatically and continuously carry out 'middle-high temperature strong desorption' operation, the pressure of slurry is reduced to 0.05-0.06 MPa through a decompression storage tank with a stirrer and a cooling water jacket, the speed is controlled, and the slurry is pumped out and enters a hydrocyclone separator for separation operation.

9. The 'medium-high temperature strong desorption' technique according to claim 3, which is characterized in that: the shape of the desorption main body device can be selected from a vertical pressure reaction kettle with a stirring jacket, a low-rotation-speed spherical or cylindrical horizontal pressure reaction kettle and a pipeline type reactor; uniformly dividing the wall for heating and cooling; the contact part of the material liquid, such as the inner wall, the stirrer, the pipeline pipe fitting and the container, is made of titanium material, 0Cr18Ni9Ti stainless steel, 0Cr18Mo2Ti stainless steel and glass lining, but crude lithium carbonate produced by lithium ore containing halogen, fluorine and chlorine, such as fluorine lithium mica, and the lining is made of polytetrafluoroethylene material; if the 2 stainless steel materials are selected, because the battery-grade product has the strict limit that the content of magnetic metal chromium is less than or equal to 3ppm, a small pressure kettle with the pressure resistance of 1.6 MPa is required to be used, the lithium carbonate slurry is subjected to a long-time (more than 100 hours recommended) soaking test under the condition that the saturated vapor pressure in the kettle is 0.8-1.0-1.2 MPa to detect the chromium leaching amount, and as long as the chromium content of the lithium carbonate is increased by 1 ppm after the soaking test than before the soaking, the batch of materials are rejected, and the substitution is carried out; the inner wall glass lining designer needs a pre-strip test to detect the dissolving amount of elements such as boron, aluminum, silicon, lead, antimony and the like in the glass lining under the conditions of lithium carbonate alkaline slurry, long time (more than 100 hours are recommended), high temperature (the saturated vapor pressure is 0.8-1.0-1.2 MPa) and low-speed stirring, and once the dissolving of the elements and other elements which can be dissolved in alkali and have limited battery-grade lithium carbonate impurity indexes and cause the elements to be unqualified, the material formula of the inner wall glass lining should be denied and alternative selected; the material of the part of the hydrocyclone separation device contacting the feed liquid is the same as that of the desorption kettle and the desorption device.

10. The "high efficiency desorption" technique of claim 1, wherein: the operation parameters required for the design and control are specially explained, in the whole operation processes of 'micro-heating thermal precipitation and hot agitation washing', 'middle-high temperature strong desorption' and 'hydrocyclone separation', all technical parameters, such as deionized water dosage and purity, reactor saturated steam pressure-temperature control index, sulfate radical content control index of crude lithium carbonate 1 and 2, stirring speed or rotating speed of spherical and cylindrical horizontal desorption kettles, desorption thermal aging duration, hydrocyclone separation operation parameters and the like, form a whole, but are not invariable stiff parameters, but can be reasonably and properly adjusted within a certain range according to the grade of the produced lithium carbonate, order quality requirements, raw material composition characteristics, yield and cost control, safety production management and the like, such as deionized water quantity, producing industrial-grade lithium carbonate, and stirring and washing according to heat as appropriate: 'medium-high temperature strong desorption': centrifugal leaching is 2.5: 5: 0.5 or 1.5 × 1.5: 5.5: 0.5 distribution, and the total amount of the three is enough to be added according to 8-9 times of finished lithium carbonate; battery grade, at 2.5: 6: 0.5 or 1.5 × 1.5: 6.5: 0.5 distribution, the total amount of the three is 9-10 times enough; for example, the saturated steam pressure-temperature parameter control range of a reaction kettle and a reactor, namely 'micro-heating thermal precipitation and thermal agitation washing' operation is suitable at 104.8-0.13 MPa or 115.2-0.18 MPa and at most 120.2-0.20 MPa, 'middle-high temperature strong desorption' operation is suitable at 159 ℃ and 170 ℃ (0.6-0.8 MPa), and the pipeline type desorption device is automatically and continuously produced and can exceed 170 ℃ (0.8 MPa) and be increased to 180 ℃ (1.00 MPa) -at most 188 ℃ (1.20 MPa) without necessarily exceeding 200 ℃ (1.60 MPa) and enters the medium-pressure container management range; therefore, all technical parameters mentioned in the "efficient desorption" are included in the scope of the present invention.

11. The "preliminary precipitation supplement impurity removal" technology as claimed in claim 1, which is characterized in that: the optional technology can be applied under the following three conditions that 1) when the operation of removing impurities such as aluminum, iron, magnesium, calcium, heavy metals and the like by a successive precipitation method from the beginning of the primary leaching operation is delayed until the beginning of the thermal precipitation process, colloid particles formed by hydroxides of aluminum, iron, magnesium and certain heavy metals are not sufficiently condensed and incompletely precipitated, or filter cloth is damaged and improperly placed to cause cross filtration, or other impurity removal accidents occur, and the impurity indexes of the lithium sulfate purifying solution are detected to exceed the standard, so that the method can be used and efficiently saved; 2) only industrial grade 0 lithium carbonate is produced, only the invention contents 1 and 2 can be used, if necessary, the part of 'micro-heating thermal precipitation and thermal agitation washing' of the invention content 3 can be used, and a plurality of existing impurity removal technologies are added, so that the lithium carbonate with the sulfate radical content as low as 0.15 percent, even 0.10 percent is produced; 3) when battery-grade lithium carbonate (including other types of high-purity lithium carbonate) is produced, if a process of circularly leaching and not concentrating lithium sulfate is adopted, the phenomenon that hydroxide colloid impurities of aluminum, iron, magnesium and certain heavy metals are not heated for a long time or surface charges of colloid particles are not eliminated, and are not fully condensed, co-precipitated and filtered can occur, and the method can also be applied before formal hot precipitation operation for saving.

12. The method as claimed in claim 11, wherein the method comprises the following steps: the specific operation method comprises the following steps: adding lithium sulfate purification liquid into a thermal precipitation reaction kettle, starting stirring, slowly adding a small amount of sodium carbonate purification completion liquid from a pressurized sprinkler spray nozzle in a spray form under close observation or online detection of a turbidity meter at about 90 ℃, stopping feeding once the feed liquid generates turbidity and separates out white fine substances (with yellow and red light when iron exceeds a standard), continuing stirring for about a while, sampling, precisely filtering, detecting the contents of iron, aluminum, magnesium, calcium and heavy metals, and spraying a small amount of sodium carbonate purification completion liquid until the contents of iron, aluminum, magnesium, calcium and heavy metals do not reach the standard, and detecting again until the contents of iron, aluminum, magnesium, calcium and heavy metals reach the standard; filtering the qualified lithium sulfate purified solution, temporarily putting the initial filtrate into a small turbid liquid tank (the total volume is about 20% of the volume of the lithium sulfate purified solution), circularly re-filtering until the filtrate sample is detected again and reaches the standard, namely, judging that the filter cake is successfully bridged, and continuously filtering the filtrate together with the lithium sulfate purified solution in the turbid liquid tank to obtain the lithium sulfate purified solution; the filter residue is fine and fine with coarse particles (lithium carbonate) which is good.

13. The present description is only intended to illustrate and explain the contents of the present invention by taking as an example the spodumene-sulfuric acid process, which is still the largest scale production at present, and should not be interpreted as limiting the scope of protection of the present invention; in fact, the invention of claim 3 is also applicable to these similar fields of technology, in addition to the substantial reduction of the impurity sulfate content by precipitation of lithium carbonate from the lithium sulfate solution and sodium (potassium) carbonate solution exemplified: 2 or more soluble inorganic substances, the target product precipitated by the precipitation reaction, the crystal (or called particle) core part of the target product is chemically adsorbed and deeply wrapped to remove impurities which are difficult to remove by a conventional washing method, a large amount of the impurities are released into a strong desorption feed liquid by a method of properly increasing the temperature and intensifying the thermal motion of molecules, ions and atomic groups, and the impurities are purified by rotary liquid separation, so the content of the invention is covered; therefore, the technical content based on the description of the present application is covered in the protection scope of the present invention.

14. A method of reducing the concentration of sulfate ions in a lithium ion-containing solution, the method comprising: 1) gradually adding the lithium ion-containing solution into the stirred soda solution with the temperature of 90-95 ℃, and precipitating crude lithium carbonate.

15. The method of claim 14, further comprising a "pre-precipitation supplement impurity removal" step before the step 1),

the step of pre-precipitation supplement impurity removal comprises the following steps: slowly adding a soda solution into the lithium ion-containing solution, stopping feeding when white fine precipitates are observed, detecting the lithium sulfate purifying solution which is discharged from the sampling port and carefully filtered, if the lithium sulfate purifying solution is not qualified, adding the soda solution again until the lithium sulfate purifying solution is qualified, stopping feeding once the impurity indexes are qualified, continuously stirring, pumping the mixture into a filtering barrel for micro-vacuum filtration, pumping out the initial filtrate for circular filtration until the filter cake is successfully bridged, and stopping the circulation of the filtrate after the filtrate is completely clear after the filtrate is sampled and observed.

16. The method of claim 15, wherein the continuing agitation comprises: and continuously stirring for more than about one quarter of a second to ensure that the excessive aluminum, iron, magnesium, heavy metal hydroxide and calcium carbonate are fully coagulated and coprecipitated.

17. The method of claim 14, further comprising, after said step 1):

heating and concentrating the lithium ion-containing solution until a sodium sulfate crystallization film on the liquid surface starts, keeping a small excess of sodium carbonate in the mother solution, gradually precipitating crude lithium carbonate in the concentration process, filtering out the crude lithium carbonate while the crude lithium carbonate is hot, and returning the crude lithium carbonate to an acidification material leaching process or elutriating the crude lithium carbonate into an industrial grade 2 product; and (3) merging the tertiary hot mother liquor obtained by filtering out the crude lithium carbonate while the tertiary hot mother liquor is hot into the new primary hot mother liquor obtained by precipitating lithium, freezing and separating out mirabilite, and alternately performing the operations of 'cold separating out mirabilite-hot separating out crude lithium carbonate'.

18. The method of claim 17, wherein the lithium ion solution is a secondary cold mother liquor containing 10 to 15 grams per liter as lithium carbonate.

19. The method of claim 14, further comprising, after said step 1): recovering lithium from the cold mother liquor, even the hot mother liquor, by precipitating lithium phosphate, lithium fluoride, and organic acid lithium such as lithium stearate, and directly vacuum concentrating to recover anhydrous sodium sulfate.

20. The method as set forth in claim 14, wherein said operation of precipitating crude lithium carbonate in said step 1) is carried out without obtaining large-sized crude lithium carbonate particles, wherein the feeding speed is increased appropriately, and the aging period is shifted backward.

21. The method of claim 14 wherein after step 1), said precipitated crude lithium carbonate is thermally agitated with 3 times deionized water for 1 centrifugation to reduce the sulfate levels to below 0.40% and 0.30% for industrial and battery grades, respectively; then 0Cr with low-speed stirring, heating and cooling jacket₁₈Ni₉Heating a composite board desorption kettle made of Ti stainless steel or a lining titanium plate by 6-7 times of deionized water, wherein the saturated steam pressure in the kettle is 0.4-0.6 MPa and at the temperature of 150-;

preferably, if a stainless steel material is selected, a small pressure kettle with pressure resistance of 1.6 MPa is used, and a soaking test is firstly carried out on lithium carbonate slurry for more than 100 hours under the condition of 0.8-1.0-1.2 MPa of saturated vapor pressure in the kettle to detect the chromium leaching amount: as long as the chromium content of the lithium carbonate after the soaking test is increased by 1 ppm compared with that before the soaking, the batch of materials cannot be selected and needs to be replaced.

22. The method of claim 21, wherein when the pressure in the desorption kettle is reduced to 0.05 mpa, the desorption kettle is slowly pressed into the hydrocyclone separator; and according to the turbidity of the separated liquid phase, performing final purification treatment on the lithium carbonate slurry in a centrifugal leaching or hot-churning centrifugal mode respectively to obtain refined lithium carbonate.

23. The method of claim 21, wherein a low speed spherical or cylindrical desorber of 0Cr is used₁₈Ni₉Ti or titanium lined composite panels; or a continuous external heating type desorption device is adopted; the glass lining design scheme of the inner wall of the desorption device is detected in advance by carrying materials, the elution amount of elements such as boron, aluminum, silicon, lead, antimony and the like in the glass lining under the conditions of alkaline slurry and long-time high-temperature stirring is detected, and if the elution amount is large, the glass lining is not adopted.

A, the technical field

The invention relates to a method for producing lithium salt. Specifically, the invention relates to a novel method for reducing the sulfate radical content in lithium carbonate obtained by the thermal precipitation reaction of a lithium sulfate solution and a sodium (potassium) carbonate solution. More specifically, the invention relates to a method for greatly reducing the sulfate radical content in each level of lithium carbonate directly produced by a sulfuric acid method, a sulfate method or other sulfide methods (namely, not converted by expensive lithium hydroxide) from lithium ores such as spodumene, lepidolite, carbonate type salt lake lithium ore primary lithium carbonate, phosphoaluminite, petalite, carbonate sedimentary rock lithium ore and the like. The present invention, particularly the similar field to which "high efficiency desorption" of item 3 can naturally extend, is further described in paragraph [ 0083 ]; the present specification will be described in detail with reference to the spodumene-sulfuric acid method as an example, so as not to be unduly complicated.

Second, background Art

In the first century, the content of impurity sulfate radical in industrial grade lithium carbonate produced in europe is generally 0.70-0.80 wt%, which is equivalent to 1.035% -1.183% of sodium sulfate, and the arithmetic mean value is 1.109%, which is much higher than that of other water-insoluble and slightly soluble carbonate products.

In the fourth and fifties of the last century, the original American Lithium company (Lithium of America) invented the Lithium carbonate process by spodumene sulfate process, and a factory with annual production of 0.9 ten thousand tons was built in Bismarck City, North Carolina, and in the industrial-grade Lithium carbonate standard, the content of impurity sulfate radicals is reduced by a lot compared with the early European products, and reaches 0.35% of first-grade products and 0.50% of second-grade products, but the industrial standard is still high for middle-grade and high-grade Lithium-containing glass and other industries.

Lithium carbonate with a sulfate content as low as 0.20% (standard of Corning glass company) is required for producing medium-high grade lithium-containing glass such as microcrystalline glass, and then purified by a Texte Method (carbonization Method). The method comprises the steps of pressing carbon dioxide into lithium carbonate water slurry prepared by 20 times of deionized water, acidifying (sometimes called hydrogenating) lithium carbonate into lithium bicarbonate with the solubility of 5% in water, diluting sodium sulfate impurity into a large amount of water, then heating to decompose lithium bicarbonate, removing carbon dioxide, and precipitating lithium carbonate again in a low-concentration sulfate radical environment to achieve the aim of reducing the sulfate radical to 0.20%. However, the purification process has long flow, large equipment investment and much higher cost.

The chemical components of the industrial-grade lithium carbonate specified by the current Chinese national standard GB/T11075-2013 are shown in the following table 1:

TABLE 1

The moisture content of the product should meet the specifications as given in table 2 below:

TABLE 2

Product brand	Li2CO3-0	Li2CO3-1	Li2CO3-2
				Water content of not more than	0.3％	0.3％	0.5％

The chemical composition table specified in the current Chinese nonferrous metal industry standard YS/T582-2013 of the battery-grade lithium carbonate is shown in the following table 3:

TABLE 3

From the lithium carbonate chemical composition tables specified in GB/T11075-2013 and YS/T582-2013, industrial grades 0, 1 and 2 (corresponding to Li in the tables above) can be seen₂CO₃-0、Li₂CO₃-1、Li₂CO₃-2) the indexes of the impurity sulfate radicals in the grade lithium carbonate are 1 to 2 orders of magnitude higher than the indexes of other impurities Fe, Ca, Mg and Cl; this difference is much larger for the cell grade, 2-3 orders of magnitude higher than Mg, Ca, Fe, Zn, Cu, Pb, Si, Al, Mn, Ni, Cl. It is clear that the reason for this is that the technical difficulty of reducing the sulfate content is greater than that of reducing the content of other impurities. It should be noted that in the industrial lithium carbonate produced by the earliest sulfate process in europe, the impurity sulfate radical content is reduced to 0.50% -0.35% of the original american lithium company sulfuric acid process industrial grade lithium carbonate for about 40 years; now to 0.20% of the common industrial grade, 0.08% of the battery grade (essentially also an industrial grade), for over 100 years, it is sufficient to see the difficult.

Chinese patent application CN107915240A (published japanese 2018.04.17) discloses a method for producing battery grade lithium carbonate by a sulfuric acid process. The method adopts 'circular leaching', so that the concentration of a leached lithium sulfate solution can be effectively improved; the EDTA is adopted to complex calcium and magnesium to precipitate lithium, so that the content of impurity calcium and magnesium in the crude lithium carbonate obtained by the thermal precipitation reaction can be effectively reduced. There is a problem that the contents of impurities of sulfate and sodium are still very high, 0.08% and 0.025%, respectively, which is disadvantageous in improving the quality of the lithium battery.

Third, the invention

All percentages or ratios stated herein are by weight unless otherwise stated; the present invention is described by way of example only with respect to the spodumene-sulfuric acid process, and it is to be understood that this is not to be construed as limiting the scope of the invention, as any technique that can be practiced based on the teachings of the present invention is intended to be covered by the scope of the present application.

The technical problem to be solved by the invention is as follows: (1) on the basis of the existing production technology for directly manufacturing battery-grade lithium carbonate by using a lithium sulfate purified liquid and sodium (potassium) carbonate purified liquid thermal precipitation process and the product standard YS/T582-2013, part of processes are innovated to greatly reduce the content of impurity sulfate radicals to 0.010-0.008 percent and slightly reduce the content of other impurities simultaneously, so that the main content of the battery-grade lithium carbonate stably reaches 3N grade, under the optimized condition, part of products reach 3.5N grade, and part of products approach, finally or even reach 4N grade. The inventors of the present application believe that the limit of the main content value of lithium carbonate produced directly by the thermal precipitation method of lithium sulfate solution and sodium (potassium) carbonate solution may be 4N.

(2) On the basis of the existing production technology for manufacturing industrial-grade lithium carbonate by using a lithium sulfate purifying solution and a sodium (potassium) carbonate purifying solution thermal precipitation process and the product standard GB/T11079-2013, part of processes are innovated to greatly reduce the content of impurity sulfate radicals to lower 'new zero-order' 0.03%, and simultaneously reduce the content of sodium and other impurities to ensure that the main content is increased to 99.50%; 0.10% of new first-stage sulfate radical and the main content is increased to 99.35%. Other low-grade industrial lithium carbonates are not considered any more, because once the three aspects of the invention are fully implemented, the sulfate content in the produced industrial lithium carbonate is no longer thousands of bits, and the sulfate content is unified into ten thousands of bits.

The technical scheme for solving the technical problem is as follows: the invention uses the following three items: 1, "reverse feeding, no mother liquor circulation"; 2, "pre-precipitation supplement impurity removal"; 3, high-efficiency desorption, and the aim of the paragraphs [ 0010 ] to [ 0011 ] is achieved in two stages. The following paragraphs [ 0013 ] to [ 0073 ] are combined with an example of direct production of lithium carbonate by the spodumene-sulfuric acid process, and are given progressively deeper descriptions:

items 1 and 3 of the present invention are essential technologies, which are used from a step of obtaining crude lithium carbonate by a hydrothermal precipitation reaction of a lithium sulfate purification completion solution and a sodium (potassium) carbonate purification completion solution to a step of obtaining each level of refined lithium carbonate wet products; the existing technology of drying, crushing and packaging the refined lithium carbonate is not changed; the prior art for removing impurities such as silicon, iron, aluminum, magnesium, calcium, heavy metals and magnetic metals before the thermal precipitation process is basically unchanged; all detection methods were unchanged. The invention of claim 2 is an alternative technique, used immediately before the thermal precipitation reaction, and mainly used for producing industrial-grade lithium carbonate, and also used for battery-grade lithium carbonate if necessary.

By applying the technologies of items 1 and 2 of the present invention and the existing technologies for removing impurities such as silicon, iron, aluminum, magnesium, calcium, heavy metals, magnetic metals, etc., various solid lithium ores such as spodumene, lepidolite, carbonate type primary lithium carbonate (produced in zabunya tea, dragon wood, and zakha salt lake), lepidolite, phospholithite, petalite, and (future) carbonate type sedimentary rock lithium ore in the middle of Yunnan can be purified into a purified liquid in the form of lithium sulfate, and then the purified liquid is subjected to a thermal precipitation reaction with a purified and purified liquid of sodium carbonate (potassium), so that the content of impurity sulfate radicals in each level of lithium carbonate directly produced is first reduced to an industrial level of 0.20% -0.15%; at the battery level, when the thermal precipitation and thermal agitation washing operation is performed by the partial technology of the invention 3, namely, the micro-temperature-raising thermal precipitation and thermal agitation washing operation (see paragraphs [ 0027 ] to [ 0029 ] and [ 0041 ]), the sulfate radical can be reduced to 0.08%.

And secondly, the comprehensive application of the ' high-efficiency desorption ' technology in the item 3 of the invention can further greatly reduce the content of the impurity sulfate radicals to the industrial grade of 0.03-0.02% and the battery grade of 0.01-0.008% in the ' 0010 ' -0011 ' section. And due to the powerful desorption function of 'efficient desorption', the sulfate radical content can be further greatly reduced, and other water-soluble, slightly water-soluble and water-insoluble impurities which are chemically adsorbed and deeply wrapped in the lithium carbonate particles can be simultaneously reduced, so that the main content can be favorably improved, and the main content targets in the sections [ 0010 ] to [ 0011 ] of battery-grade and industrial-grade products can be realized.

From this paragraph to paragraph [ 0072 ], the three inventions are further detailed by taking the spodumene-sulfuric acid method as an example for directly producing lithium carbonate:

the invention of 'reverse feeding without mother liquor circulation' is invented by the inventor of the application in 1978-:

1, from the working procedures of crude lithium carbonate thermal precipitation of lithium sulfate purification finished liquid and sodium carbonate purification finished liquid, the classical operation process of spodumene-sulfuric acid method invented by original American lithium company, namely, as shown in figure 1, Na as precipitator₂CO₃To "20% of Li₂SO₄In the solution (this mode can be called as 'forward feeding'), the reverse direction is carried out, and the lithium sulfate purification completion liquid is added into the strongly stirred sodium carbonate purification completion liquid with the temperature of 90-95 ℃ in a mode that the feeding point is moderately dispersed, so as to precipitate coarse lithium carbonate particles with less chemical adsorption and less deep coating of sulfate radicals.

2, simultaneously, not according to the classic operation process of the original American lithium company, freezing the primary hot mother liquor of sodium sulfate for centrifugally separating crude lithium carbonate while the mother liquor is hot to 0-15 ℃, crystallizing the mirabilite, and returning the secondary cold mother liquor to the acidification material leaching process to recover lithium; but another process route is adopted, the secondary cold mother liquor containing lithium (converted into lithium carbonate) up to 10-15 g/L is heated and concentrated until the liquid surface sodium sulfate crystallization film starts (the mother liquor retains a small excess of sodium carbonate, and crude lithium carbonate is gradually precipitated in the concentration process), the crude lithium carbonate is filtered out when the mother liquor is hot, and the crude lithium carbonate is returned to the acidification material leaching process (or is elutriated into an industrial grade 2 product); the tertiary hot mother liquor from which the crude lithium carbonate is filtered out is merged into the new primary hot mother liquor from which the lithium is precipitated for freezing and separating out the mirabilite, and the operation of 'cold separating out the mirabilite-hot separating out the crude lithium carbonate' is alternately carried out; or (only the content of the part is tested), after lithium is recovered from the secondary cold mother liquor (even the primary hot mother liquor) by precipitating lithium phosphate, lithium fluoride and organic lithium (such as lithium stearate), the anhydrous sodium sulphate is directly recovered by vacuum concentration.

The 'mother liquor circulation is not needed', namely, a large amount of lithium-containing sodium sulfate mother liquor is not returned to the leaching process, so that the harmful sodium sulfate content in a lithium sulfate solution system leached out is reduced to the maximum extent, the sulfate radical concentration of the reaction material liquid of the thermal precipitation lithium carbonate is further reduced, and the beneficial technical effects of reducing the chemical adsorption of sulfate radicals and deeply wrapping (hereinafter referred to as 'peritectic') by 'reverse feeding' are mutually superposed; and the concentration of the sodium sulfate liquid after the lithium sulfate purification is finished is reduced more, the salt effect is reduced, and the primary yield of the coarse lithium carbonate subjected to thermal precipitation is improved.

The beneficial technical effects generated by reverse feeding and non-circulating mother liquor are realized at the cost of very low equipment and cost investment; however, an economical and effective method does not exist in the field, and the sulfate radical in the lithium carbonate directly produced by the spodumene-sulfuric acid method can be reduced to be below 0.35 percent; moreover, the invention is still another creative improvement which is produced later and further greatly reduces the sulfate radical content, namely, the necessary matching and foundation technology of the invention 3 of 'high-efficiency desorption'.

Item 2 of the present invention, "preliminary precipitation supplement impurity removal" is an optional means, and includes three uses: 1) If the operation of leaching at the early stage and the operation of removing impurities such as aluminum, iron, magnesium, calcium, heavy metals and the like by a successive precipitation method are not successful until the thermal precipitation process begins, so that some impurities are incompletely precipitated, formed colloid particles are not sufficiently agglomerated, or filter cloth is damaged and improperly placed, and penetration filtration is carried out, and the indexes of the impurities of the lithium sulfate purifying solution exceed the standards, the feeding is suspended in a forward feeding mode before the thermal precipitation process, a small amount of sodium carbonate purification completion solution is slowly added into the lithium sulfate purifying solution under stirring, visual inspection and turbidimetric observation are closely carried out, when white fine precipitates in the lithium sulfate purifying solution just appear, the feeding is suspended, the lithium sulfate purifying solution which is discharged from a sampling port and carefully filtered is detected, and when the indexes of the impurities are qualified, the feeding is stopped (if the indexes of the impurities are not qualified, a small amount of sodium carbonate purification completion solution is added, until the filtrate is qualified), continuously stirring for more than one quarter of a second to ensure that the excessive aluminum, iron, magnesium, certain heavy metal hydroxides and calcium carbonate are fully coagulated and coprecipitated, then pumping out, putting into a suction filtration barrel for micro-vacuum filtration, wherein the initial filtrate is always turbid, pumping out for circulating filtration until the filter cake is successfully bridged, the filtrate is completely clear after sampling observation, and stopping the circulating filtration of the filtrate. When the filter cake was observed, it was found that the filtrate was fine and smooth (mainly comprising magnesium hydroxide and aluminum), and a small amount of coarse particles (lithium carbonate) were mixed, indicating that the impurities were purified well, and the purified solution of lithium sulfate which had been successfully filtered was confirmed by detection and was identified as a purified solution. Compared with the method that the unqualified lithium sulfate purified solution is returned to the leaching process to remove the impurities again, the method has the advantages of simple error correction and obvious cost effect, and is especially suitable for small-sized manufacturers with poor conditions such as equipment and management.

After the pre-precipitation supplement impurity removal is completed, the thermal precipitation operation is carried out according to a reverse feeding mode (and a non-circulating mother liquor mode) for producing industrial-grade lithium carbonate and producing battery-grade lithium carbonate with the current technical standard or higher technical standard in the future.

2) By using the invention of items 1 and 2, the thermal precipitation and thermal agitation washing operation is supplemented with the 'micro-heating thermal precipitation and thermal agitation washing' part of the invention of item 3 if necessary, and a plurality of existing impurity removal technologies are added, so that the industrial-grade lithium carbonate can reach the large threshold of 0.35 percent, and the successfully produced sulfate radical content is as low as 0.15 percent (the analytical purity standard), even 0.10 percent (namely the standard of special-grade lithium carbonate produced by reconversion of lithium hydroxide produced by spodumene-lime method in Xinjiang lithium salt works); now measured, very close to battery level standards).

3) Once in the production process, the completely clear lithium sulfate purified solution is often observed, and iron, aluminum and magnesium hydroxides are often flocculated and precipitated in the concentration process, which is consistent with the phenomenon recorded in the spodumene-lithium sulfate process technical literature published by the original American lithium company, and the situation that the colloid impurities remained in the lithium sulfate purified solution due to percolation are necessary to be fully flocculated, coprecipitated and removed for multiple times is shown; particularly, when battery-grade lithium carbonate (including other types of high-purity lithium carbonate) is produced, if a process of circularly leaching and not concentrating lithium sulfate is adopted, the hydroxide colloid impurities of aluminum, iron, magnesium and certain heavy metals are not heated for a long time or the surface charges of colloid particles are not eliminated, and are not sufficiently condensed, so that the lithium carbonate can be removed by parallel supplement and removal by using a technology of 'pre-precipitation supplement impurity removal' before the coarse lithium carbonate is thermally precipitated.

The term "high-efficiency desorption" in the summary of the invention of item 3 is a general term of two-part constituting techniques of "strong desorption" and "hydrocyclone separation". The method is a powerful new technology which is required by reducing the sulfate radicals to the maximum extent from 0.20-0.15-0.10% of industrial-grade lithium carbonate sulfate radicals and 0.08% of battery-grade lithium carbonate, and realizing the second-stage aim that the industrial-grade lithium carbonate and the battery-grade lithium carbonate are respectively reduced to 0.03-0.02% and 0.01-0.008%, and the main contents are respectively increased to 99.50% and 3.5N-4N.

The strong desorption also contains 2 parts of contents, namely 'micro-temperature-raising thermal precipitation and thermal agitation washing' and 'medium-high temperature strong desorption'.

The 'micro-temperature-raising thermal precipitation and thermal agitation washing' is also an improvement to the technical principle explanation according to the two items 1 and 3 of the invention according to paragraphs [ 0057 ] to [ 0072 ]: in the whole process of removing sulfate radicals in peritectic by a thermal precipitation, thermal agitation and powerful desorption operation system, adsorption and desorption are in a dynamic equilibrium state, adsorption heat release and desorption heat absorption are realized, the temperature balance is increased to move towards the desorption direction (Lexhlet principle), desorption is facilitated, namely the desorption effect is positively correlated with the temperature, and the continuous change process is realized, and by referring to data of a [ 0032 ] small experiment 1), the obvious effect of increasing the sulfate radical desorption can be approximately predicted even if the thermal precipitation and thermal agitation temperature is increased by 10 degrees centigrade. Moreover, the curvature of the lithium carbonate solubility-temperature curve is negative, and the primary yield can be improved as the temperature is increased.

The allowable pressure of the existing universal jacket reaction kettle design is mostly 0.6 MPa of the jacket and 0.2 MPa in the kettle, so that the sulfate radical content of the crude lithium carbonate can be effectively reduced by performing hot precipitation and hot agitation washing operation only by changing part of operation modes and operation parameters under the premise of not changing the existing main equipment, a better technical cushion is provided for the subsequent high-temperature strong desorption operation, and the possibility of producing 4N-grade lithium carbonate with the sulfate radical far less than 0.008 percent and close to 0.005-0.003 percent (50-30ppm) is increased. This effect can be predicted by referring to the trial result data of paragraph 1) of paragraph [ 0032 ]. In addition, the process is improved, and the content of sulfate radical of crude lithium carbonate entering the kettle is reduced, so that the using amount of expensive deionized water can be reduced. For this purpose, it is recommended to operate at 104.8 degrees celsius (0.13 mpa), or 115.2 degrees celsius (0.18 mpa), up to 120.2 degrees celsius (0.20 mpa).

But without excessively raising the temperature. After all, in a high-concentration sulfate radical environment, the technical effect of reducing the sulfate radical is still limited, and a jacket reaction kettle with higher allowable stress does not need to be replaced.

By 'moderate to high temperature strong desorption' is meant: for the part of sulfate radicals in the core peritectic crystal of the coarse lithium carbonate particles which are difficult to continue to be reduced by the conventional hot agitation washing centrifugation method, the temperature is greatly increased to intensify the thermal motion of various molecules, ions and atomic groups in a coarse lithium carbonate-deionized water slurry system, the coordination bonds between the sulfate radicals and lithium ions in the nuclear crystal inclusion of the lithium carbonate particles are loosened, and the lithium carbonate particles are strongly promoted to be largely separated from the lithium carbonate particles and released and dissolved in a large amount of deionized water; a significant portion of the other water soluble, slightly soluble and water insoluble impurities are also released, dissolved and suspended in larger amounts of deionized water due to increased thermal motion, a key inventive invention. The method is based on the technical principle of adsorption and desorption, and is described in detail in paragraphs [ 0057 ] to [ 0072 ]; for a detailed description, please refer to paragraphs [ 0042 ] to [ 0043 ].

The following two easily-repeated verification small-scale test results of 'strong desorption' by gradually increasing the pressure and the temperature by the inventor of the application prove that the invention has a strong desorption effect on sulfate radicals in the lithium carbonate particles:

1) adding a proper amount of tap water into a household cooking pressure cooker, putting industrial-grade crude lithium carbonate which is produced by the process of firstly using 3 times of hot distilled water for primary washing for 1 time, reducing sulfate radicals to be below 0.40 percent and carrying out reverse feeding and mother liquor non-circulation into a placed stainless steel cup, adding 3 times of distilled water, covering the stainless steel cup to prevent tap water outside the cup from being polluted, externally heating to the pressure of 0.12 MPa (the highest pressure of the household cooking pressure cooker corresponds to the saturated steam pressure of about 105 ℃, and is characterized in that the jet nozzle suddenly emits steam), and carrying out static strong desorption and concurrent thermal aging for 1 hour. Naturally cooling, reducing pressure, removing liquid phase by using a pouring washing method, adding 1 time of distilled water, and stirring and washing for 1 time, wherein the sulfate radical of the obtained refined lithium carbonate is reduced to below 0.15% by chemical method, and the reduction range is beyond expectation.

2) Then, a simple stainless steel hot-pressing cylinder is used for increasing the pressure and the temperature for testing: firstly, the industrial-grade lithium carbonate is primarily washed by 3 times of hot distilled water for 1 time, the sulfate radical is reduced to 0.35 percent, then the 6 times of distilled water and the pressure of 0.4-0.6 MPa (the corresponding saturated steam pressure is about 146-.

According to the results of the above-mentioned pilot plant, it can be expected that, after adding the "strong desorption" and "hydrocyclone separation" impurity removal techniques, the sulfate radical can be further reduced to 0.03% -0.02% of industrial grade for the existing process, equipment and lithium carbonate manufacturers in the spodumene-sulfuric acid process managed generally; it is possible for the advanced manufacturers to reduce the level to 0.008% of battery grade lithium carbonate. This is because the principles of the "strong desorption" technique on which they are based are identical.

"hydrocyclone separation" means: can efficiently separate impurities such as sulfate radical and the like which are separated from lithium carbonate particles and dissolved and suspended in a large amount of deionized water by 'strong desorption' operation, and is simple, convenient, low in investment and easy to operate. It is superior to various solid-liquid separation techniques using filter cloth because the majority of the particulate water-insoluble impurities that are removed and suspended in a large amount of deionized water are carried away directly from the liquid phase flowing in rotation; and the solid-liquid phase is separated by using a filter cloth, so that more water-insoluble impurities with micro-particle sizes can be retained, and the beneficial technical effect of 'strong desorption' is achieved.

The technical problem of the present invention is further, systematically and completely explained by taking the direct production of industrial-grade and battery-grade lithium carbonate by the spodumene-sulfuric acid method as an example in the following:

(1) for the direct production of industrial zero-level lithium carbonate and battery-level lithium carbonate by adopting a lithium sulfate solution and sodium carbonate solution thermal precipitation method (after the 'high-efficiency desorption' technology is applied, industrial secondary products and primary products of lithium carbonate have no significance), the existing technology for removing impurities such as silicon, aluminum, iron, magnesium, calcium, heavy metals, magnetic metals and the like before the thermal precipitation process is basically unchanged; the technology of 'pre-precipitation supplement impurity removal' can be used for supplement; the prior art of drying, crushing, metering and packaging the refined lithium carbonate wet product is not changed; all detection methods were unchanged. Taking the attached figure 1 as an example: FIG. 1 shows a schematic process flow diagram of the conventional spodumene-sulfuric acid process of original Li America Inc. for producing industrial grade lithium carbonate. In this specification, the term "conventional technique for removing impurities such as silicon, aluminum, iron, magnesium, calcium, heavy metals, and magnetic metals before the thermal precipitation step" means that "20% of Li is obtained in FIG. 1₂SO₄Solution "all the preceding steps include impurity removal techniques.

(2) The excess of sodium carbonate formula in the thermal precipitation process is 5%.

(3) The lithium sulfate and sodium carbonate purification completion liquid must be subjected to thermal precipitation and related operations thereafter in a 'reverse feeding, mother liquor not circulating' manner. If necessary, a technology of 'pre-precipitation supplement impurity removal' is applied.

(4) The operation of the thermal precipitation process is greatly modified, namely, large-particle-size coarse lithium carbonate particles are not obtained for the moment, and the thermal aging time is shifted to the 'strong desorption' process to be completed together. This is a technical support for "strong desorption" to effectively release impurities such as sulfate radicals contained in the peritectic crystals formed at the initial stage of the thermal precipitation reaction, and the technical principle of the improvement is described in the paragraphs [ 0069 ] to [ 0072 ].

(5) The operation method of the thermal precipitation and the thermal agitation washing adopts the operation method of the micro-temperature-raising thermal precipitation and the thermal agitation washing technology, and comprises the following steps: after sodium carbonate is added into the reaction kettle to complete the purification liquid, the temperature is raised, a manhole of the reaction kettle is covered, and the reaction kettle is closed after air in the kettle is completely removed; and (4) when the temperature rises to a selected place value, starting the stirrer and keeping effective stirring all the time, and pumping the pumped lithium sulfate purification completion liquid into the reaction tank in a spraying mode through a pressurizing shower nozzle. And (3) after the addition is finished, immediately releasing the pressure of the reaction kettle (recovering steam heat by a pipeline), immediately discharging and centrifugally leaching when the temperature of the materials in the kettle is reduced to 95 ℃, and obtaining crude lithium carbonate 1.

(6) Moving the crude lithium carbonate 1 obtained by hot precipitation into a reaction kettle which is provided with deionized water with selected times, such as 3-4-5 times and 5-6 times of industrial grade and battery grade respectively, heating to 95 ℃, starting a stirrer, covering a manhole, continuously heating, sealing the reaction kettle after air in the kettle is completely removed, heating to the same position as the thermal precipitation reaction in the [ 0041 ] stage, keeping hot agitation for 15 minutes, releasing pressure of the reaction kettle (preferably taking a pipeline to recover steam heat), cooling to 95 ℃, discharging, centrifuging, and controlling sulfate radicals of the industrial grade and battery grade crude lithium carbonate 2 to be 0.30-0.20% and 0.15-0.10% respectively for later use.

(7) Pumping deionized water with a selected multiple of the weight of the crude lithium carbonate 2 into a medium-high temperature strong desorption kettle, starting low-speed stirring, adding the crude lithium carbonate 2, heating to a selected position such as 159 ℃ plus 170 ℃ (the saturated vapor pressure is 0.6-0.8 MPa), carrying out strong desorption and concurrent thermal aging for more than 1 hour under the state of low-speed stirring and keeping the solid phase of the slurry moving at a low speed, so as to release water-soluble impurities, slightly water-soluble and water-insoluble impurities which mainly comprise sodium sulfate in the peritectic crystal at the core part of the lithium carbonate particles into the deionized water, and recrystallizing into large crystals with extremely low sulfate radical content under the condition that the sulfate radical concentration is far lower than the thermal precipitation reaction concentration.

(8) After the sulfate radical content is detected to reach the standard, the desorption kettle is decompressed (a pipeline is required to be connected for recycling and steam heat is utilized), when the pressure is reduced to 0.05-0.06 MPa, the stirring speed is increased until the slurry is maintained in a strong stirring state, the speed is controlled, the slurry is pumped out and enters a hydrocyclone separator, and liquid and solid phases are continuously separated; separating out the liquid phase with the released water (micro) soluble and water insoluble micro-particle size impurities, returning the liquid phase to the leaching process to recover lithium, and using a part of the liquid phase to clean filter cloth and equipment; only a portion of the solution, which has been sufficiently coagulated and fine-filtered, is allowed to be used for hot-washing crude lithium carbonate 1 to produce a technical grade product, and the process is disabled thereafter. Centrifugally leaching the solid phase (if necessary, performing one more battery-grade agitation washing), thus obtaining a battery-grade refined lithium carbonate wet product with the sulfate radical reduced to 0.03-0.02% and the sulfate radical reduced to below 0.008%.

(9) The pipeline type desorption device is adopted to automatically and continuously carry out 'middle-high temperature strong desorption' operation, the pressure of slurry is reduced to 0.05-0.06 MPa through a decompression storage tank with a stirrer and a cooling water jacket, the speed is controlled, and the slurry is pumped out and enters a hydrocyclone separator for separation operation.

The 'middle-high temperature strong desorption' operation end point judgment method comprises the following steps: sampling is carried out through a continuous sampling pipe orifice specially arranged on the desorption kettle and the desorption device, the liquid phase sulfate radical content is intermittently and repeatedly sampled and detected or continuously and online detected, the residual sulfate radical content of the solid-phase lithium carbonate (dry basis) is calculated by a program control computer according to the content data, the amount of the input crude lithium carbonate, the sulfate radical content of the input crude lithium carbonate and the amount of the added deionized water, and the desorption end point can be determined after the residual sulfate radical content reaches the standard.

Specific remarks regarding "forced desorption" technical parameters: designing and regulating various operation parameters, such as crude lithium carbonate 1 initial washing water distribution amount, initial washing times, crude lithium carbonate 2 sulfate radical content control indexes in a 'micro-temperature-raising thermal precipitation and thermal agitation washing' stage, 'middle-high temperature strong desorption' stage desorption water distribution amount, desorber saturated steam pressure-temperature control indexes, stirring rotating speed or desorber rotating speed, desorption and thermal aging duration and the like, and is a normal and completely necessary technical means determined according to the grade of the produced lithium carbonate, order quality requirements, raw material component characteristics, yield and cost control, safety production management and other factors; the parameters exemplified in the summary and the embodiments of the present invention are an integer, they are not a constant stiffness parameter, and they can be flexibly adjusted and controlled by themselves when in actual use, so they are all covered in the protection scope of the present invention.

For example (but not limited to) deionized water usage: when industrial-grade lithium carbonate is produced, 'micro-temperature-raising thermal precipitation and thermal agitation washing', 'medium-high temperature strong desorption' and centrifugal washing, the total amount of the three is enough to be recommended to be added according to 8-9 times of finished lithium carbonate, and the total amount of the three can be 2.5 according to specific conditions: 5: 0.5 or 1.5 × 1.5: 5.5: 0.5 distribution; and battery grade, the total amount of the three is recommended to be 9-10 times, and the weight ratio is 2.5: 6: 0.5 or 1.5 × 1.5: 6.5: 0.5 allocation. These parameters are all included in the scope of the present invention.

Also for example (without limitation) desorption kettle, temperature-saturated vapor pressure within the vessel: although the desorption effect is positively correlated with temperature-pressure, the higher the pressure, the easier and more about, and the shorter the time required for the removal of sulfate and other impurities, the higher the equipment cost and maintenance costs, and the more complex the enterprise is to manage. Comprehensively considering factors such as product quality requirements, technical effects, investment amount, production capacity, cost, safety management of pressure vessels, existing equipment conditions of various manufacturers and the like, when industrial grade 0 lithium carbonate is produced, 0.5-0.6 MPa is adopted and is not necessarily exceeded, only a pipeline type desorption device is automatically and continuously produced and can exceed 0.8 MPa, and the pipeline type desorption device is not limited but is not necessarily exceeded by 1.0 MPa; the battery grade is recommended to adopt 0.7-0.8-1.0 MPa, but not necessarily exceeding, but the automatic and continuous production of the pipeline type de-adsorber can exceed 1.0-1.2 MPa, and the low pressure/medium pressure container limit of the current 1.6 MPa is not limited but is not necessarily exceeded. These parameters are also included in the scope of the present invention.

For this reason, the paragraphs [ 0028 ], [ 0032 ] - [ 0033 ], [ 0041 ] - [ 0045 ], [ 0048 ], [ 0049 ], and [ 0053 ] - [ 0054 ], which refer to the "efficient desorption" technique, should be covered by the scope of protection of the present invention.

Separating the liquid phase of water-soluble impurities, slightly water-soluble impurities, other colloidal impurities and other micro-particle water-insoluble impurities which are separated from the coarse lithium carbonate particles in the desorption process by a hydrocyclone separator, wherein the liquid phase is good in solid-liquid separation equipment type selection for large-scale industrial, automatic and continuous production by medium-high temperature strong desorption; if a liquid-solid-phase separation mode (such as centrifugal separation) with filter cloth is used, a large number of suspended particle diameter water-insoluble impurities can be mixed into a solid phase, and the original excellent impurity removal effect of 'medium-high temperature strong desorption' is greatly reduced.

The optional structure types of the desorption kettle and the desorption device used for the medium-high temperature strong desorption comprise: 1) a pressure reaction kettle with a low-speed stirring, heating and cooling jacket and a shaping device; or 2) a low-rotating speed spherical or horizontal cylindrical desorption device, a shaping device or self-design; or 3) designing a manufacturer with large capacity, which is most suitable for adopting a pipeline type desorption device and is designed by self; 4) no matter what type of desorption kettle or device is selected, the way of dividing wall type heating and cooling is adopted, and the direct steam heating can not be adopted, so as to avoid polluting the dye slurry.

The inner surface structure material of the contacting material of the desorption kettle and the desorption device used for the middle-high temperature strong desorption is preferably titanium plate, and the material can also be stainless steel plate of 0Cr18Ni9Ti or 0Cr18Mo2 Ti. However, in the production of battery grade, if stainless steel is to be selected, because the content of magnetic metal chromium in the product is strictly limited to be less than or equal to 3ppm, a small pressure kettle with pressure resistance of 1.6 mpa is used, and a long-time (more than 100 hours is recommended) soaking test is firstly carried out on lithium carbonate slurry under the condition of 0.8-1.0-1.2 mpa saturated vapor pressure in the kettle to detect the chromium leaching amount: as long as the chromium content of the lithium carbonate after the soaking test is increased by 1 ppm compared with that before the soaking, the batch of materials cannot be selected and needs to be replaced. In addition, this immersion test is also required for lithium sulfate obtained from a fluorine (chlorine) -containing raw material such as fluorolepidolite, but the purpose of the test is to measure the corrosiveness of fluorine (chlorine) to these two materials, and if there is corrosion, a composite steel sheet lined with polytetrafluoroethylene is selected as the structural material.

The scheme of using the glass lining design of the inner wall of the desorption device needs a material pre-carrying test to detect the release amount of elements such as boron, aluminum, silicon, lead, antimony and the like in the glass lining under the conditions of lithium carbonate alkaline slurry, long time (more than 100 hours are recommended), high temperature (the saturated vapor pressure is 0.8-1.0-1.2 MPa) and low-speed stirring: once the elements with limited impurity indexes of the battery-grade lithium carbonate which can be dissolved in alkali dissolve out and are unqualified, the formula of the inner wall glass lining material is rejected and needs to be replaced. Lithium sulfate obtained from fluorine (chlorine) -containing raw materials such as fluorohectorite is not suitable for use in glass-lined reaction vessels or vessels.

The hydrocyclone separation uses a setting device or a self-designed hydrocyclone separator, and the material selection mode of the hydrocyclone separation is the same as that of the desorption kettle and the inner surface structure material of the contact material used in the desorption kettle and the device used in the middle-high temperature strong desorption.

The technical scheme of the invention has the following general beneficial effects: the method has the advantages that the content of impurity sulfate radicals and other impurities in industrial-grade and battery-grade lithium carbonates directly produced from lithium sulfate liquid and sodium (potassium) carbonate liquid extracted from various lithium ores and sulfur-containing raw materials in paragraph [ 0001 ] is greatly reduced by a relatively simple technical scheme and lower cost, and the main content of the two types of lithium carbonates is improved; the original huge quality, cost and price differences of the industrial-grade and battery-grade lithium carbonates directly produced by a sulfuric acid method, a sulfate method and a sulfur compound method and the high-purity-grade lithium carbonates produced by various methods are greatly reduced, the boundaries are fuzzy, and the technical standard of lithium carbonate modified in the future can be simplified. The beneficial effects are very beneficial to promoting the rapid development of high-end lithium industries such as lithium batteries and the like, and are very beneficial to the long-term parallel of the lithium salt in the ore and the lithium salt in the salt lake.

The technical principle of 'reverse feeding, non-circulating mother liquor' and 'high-efficiency desorption' is jointly based on, and the analysis is as follows from the section to the section [ 0072 ]:

the paragraphs [ 0002 ] to [ 0008 ] have indicated the historical aeipathia of the high difficulty in removing impurity sulfate radicals in lithium carbonate produced directly by the lithium ore sulfuric acid process and the sulfate process. The essential reason for this is that lithium ions are likely to form coordinate bonds with oxygen acid groups containing silicon, carbon, and sulfur due to their structural characteristics, i.e., the coarse lithium carbonate is likely to undergo chemisorption of sulfate groups during thermal precipitation, thereby forming inclusions (peritectic crystals). Particularly, the adsorbed sulfate radicals at the initial stage of thermal precipitation grow with coarse lithium carbonate particles and are even deeply wrapped, so that the sulfate radicals are extremely difficult to remove according to the existing thermal agitation washing method and the harm is the greatest. Although not having a transition element, both the alkali metal and the alkaline earth metal elements are strong in polarizability, but can form a complex (complex) with a coordinating atom as a central atom, particularly a lithium atom, and the smallest radius among all the metal elements is advantageous for forming a complex having a slightly larger stability constant. And sulfate has two coordinated oxygen atoms, so that the sulfate is also favorable for forming a complex with a slightly large stable constant with lithium ions in lithium carbonate, and the generated coordination bond has slightly high energy and stronger chemical adsorption force (the carbonate and silicate are also the same).

According to langevi theory of solid surface adsorption in physical chemistry, precipitating and washing coarse lithium carbonate particles at a relatively high temperature of 90-95 degrees celsius, the physical adsorption force based on van der waals force is weak, and the desorption tendency is large. Since two coordinated oxygen atoms in the sulfate radical can be used as coordination sites of the complex, the probability is very high that a sulfate radical complex with a slightly large stability constant is generated under the condition that the concentration of the sulfate radical is high when crude lithium carbonate is precipitated. The adsorption of the surface of the coarse lithium carbonate particles to sulfate radicals is mainly chemical adsorption, the adsorbent is lithium ions, and the adsorbate is sulfate radicals. Several additional features of chemisorption are: a, the selectivity is very high. During the thermal precipitation reaction, the lithium carbonate particles have strong adsorption to sulfate radicals and carbonate radicals, so that the probability of adsorption of the lithium carbonate particles is high, the quantity of the lithium carbonate particles is large, and the lithium carbonate particles mainly depend on the concentration of the adsorbate, because the Fleinedxle adsorption formula shows that the adsorption quantity is increased along with the increase of the concentration of the adsorbate. b, only monolayer adsorption occurs. This is because the chemical adsorption is accomplished by forming a new chemical bond with the adsorbate by the residual bond force of the molecules on the surface layer of the solid molecules, and thus when the surface of the solid molecules is saturated and adsorbed, the adsorbate with the same charge is no longer adsorbed to form the second adsorption layer. And c, heat is released during adsorption, and the reverse direction is difficult, namely, desorption is difficult and heat absorption is needed. The chemical adsorption also promotes the coating of sulfate radicals in the crystal growth process, because once sulfate radicals are adsorbed on the lithium carbonate particles and are not easy to desorb, lithium carbonate molecules coordinated with the sulfate radicals are adsorbed outside to form the coating of the sulfate radicals, namely peritectic crystals are formed, so that the conventional washing mode is difficult to desorb and remove the sulfate radicals in the lithium carbonate particles, the content of the sulfate radicals is higher, and the conventional washing mode is naturally inevitable.

From the two aspects of the adsorbate and the adsorbent, the production practice proves that the former has greater influence on the high and low content of the sulfate radical as the impurity.

According to the theoretical analysis, the content of impurity sulfate radicals is reduced, most importantly, the concentration of adsorbed sulfate radicals in a thermal precipitation reaction system is reduced as much as possible, and then coarse lithium carbonate particles with large particle size are obtained in a slow, hot and old operation mode so as to reduce the sulfate radicals in the inclusion crystal (which is the theoretical basis of the first-stage technical measures for reducing the sulfate radicals in the specification); in the second stage, a new desorption technology which is simple, low in cost and powerful must be found to release sulfate radicals in peritectic crystals which are difficult to remove by the existing hot-agitation centrifugal method.

Based on the above knowledge, the inventor of the present application proposes a technical scheme of 'reverse feeding, without circulating mother liquor'. The reverse feeding is deduced according to the principle that the chemical adsorption has selective adsorption, single-layer adsorption and difficult desorption at the same time: at the initial stage of feeding, the nascent lithium carbonate micro particles are in the environment of high-concentration carbonate and low-concentration sulfate radicals, so that the probability of carbonate adsorption on the surfaces is high, the probability of sulfate radical adsorption is low, and only individual parts adsorb sulfate radicals (and silicate radicals); due to the characteristic of single-layer adsorption, after the surface of the lithium carbonate particles is saturated and adsorbs carbonate, electronegative sulfate and carbonate are not adsorbed any more. Because the absorbed carbonate is not easy to reversely desorb, the carbonate can quickly absorb free electropositive lithium ions (sodium ions) and cross-absorb carbonate and lithium ions, lithium carbonate particles can quickly grow in an environment with lower concentration of sulfate radicals, and the amount of the adsorbed sulfate radicals is greatly reduced compared with that of a forward feeding process.

A layer of carbonate adsorbed by the precipitated lithium carbonate particles, a part of which adsorbs sodium ions to become sodium carbonate, does not cause a great trouble: the carbonate radicals can be chemically adsorbed with lithium ions dissociated from the continuously added lithium sulfate to further perform chemical reaction to generate lithium carbonate with solubility much lower than that of sodium carbonate and more firm bonding, so that lithium carbonate particles are enlarged, and sodium ions which are extruded and exchanged by the lithium ions added into a thermal precipitation system later are absorbed by sulfate radicals in a reaction solution and transferred into the reaction solution; sodium carbonate and lithium carbonate do not generate double salt, and the sodium carbonate and the lithium carbonate are relatively easy to wash when being stirred and washed by hot water in the subsequent process. Naturally, a small amount of sodium ions and sulfate radicals are close to each other to form sodium sulfate, and the sodium sulfate is wrapped by lithium carbonate adsorbed later and is difficult to wash; it is sometimes found that the product lithium carbonate has a slightly lower amount of sodium than the equivalent amount of sulfate, indicating that there are also traces of other metal elements, such as calcium sulfate, which are more difficult to wash.

The 'reverse feeding' process uses high-concentration adsorbate carbonate to perform pre-complexing on lithium ions in the primary lithium carbonate particles, prevents sulfate radicals from being coated by complexing a large amount of absorbent lithium ions in the lithium carbonate particles, and successfully reduces the content of the sulfate radicals in the product. After the reverse feeding is adopted, the coarse lithium carbonate is only required to be added according to the proportion of 1: 2-3 (mass ratio) of the lithium carbonate is added with deionized water, the mixture is heated, stirred, washed and centrifuged for 3 times, and then a product with 0.15% -0.20% of sulfate radical can be obtained, 30 kg of refined lithium carbonate is obtained after each reaction in one kettle, only 5 kg of sodium carbonate is added compared with the original process, part of the refined lithium carbonate is mixed into the primary sodium sulfate hot mother liquor (part of the refined lithium carbonate is added into washing water), and then part of the refined lithium carbonate is automatically consumed when the secondary cold mother liquor 'crude lithium carbonate' is concentrated and thermally precipitated, so that the economic value is.

The reason for the operation of 'slow stirring, hot heating and aging' in the process of thermally precipitating the coarse lithium carbonate is to obtain large-particle-size lithium carbonate particles to reduce the adsorption and the coating of sulfate radicals. The theory on which this is based is: 1, the adsorption quantity is less when the surface of the adsorbent is smaller, namely the particle size is larger according to the Lange-spurious theory; 2, according to a Kelvin formula, small crystals can be automatically converted into large crystals (the free energy of a system is reduced and tends to be stable) by aging, and sulfate radicals and sodium ions which are adsorbed and coated can release part of the sulfate radicals and the sodium ions into a reaction solution under the conditions of stirring and heating in the conversion process; however, because the sulfate radical adsorbed by the primary lithium carbonate particle is deeply coated in the early stage of the reaction, the concentration of the sulfate radical in the reaction solution is very high in the later stage of the reaction, and the amount of the sulfate radical adsorbed and coated in the lithium carbonate particle is still very high in the dynamic reversible state of adsorption-desorption, the problem is solved by means of new technological breakthrough; the le chatler principle, raising the temperature, favors desorption.

In the initial stage of thermal precipitation of lithium carbonate, particularly under the conditions of rapid charging and poor stirring, the thermal precipitation is often very viscous for the following reasons: a, four main ion concentrations of two feed liquids of lithium sulfate and sodium carbonate used in the thermal precipitation reaction are high, the reaction trend is strong, lithium ions of primary lithium carbonate are easily coordinated with carbonate, sulfate radicals and silicate radicals to form complex salts, and a layer of acid radicals outside the lithium ions, a layer of lithium ions outside the acid radicals and a layer of acid radicals … … are rapidly self-adhered to each other to form a group; the lithium ions can also be adhered to the inner wall of a glass lining reaction tank or a stirrer (also a laboratory glass instrument and a tool) formed by silicate, which is a rapid entropy increasing process and has great driving force. However, as time goes on, the adhesive groups are loosened and broken up due to the continuous adjustment of various chemical bonds in the adhesive groups, lithium carbonate particles in the adhesive groups are continuously precipitated and automatically grow into large-particle crystals, sulfate radicals are continuously combined with sodium ions to be dissolved in hot water, and only a few or very few adhesive groups are continuously adhered to the wall of the vessel or the stirrer. And b, if the desiliconization of the lithium sulfate and the soda liquid is not sufficient, lithium silicate is generated during the hot precipitation, the viscosity of the lithium silicate is very strong, the self-adhesion of lithium carbonate particles is increased, and the lithium silicate is easy to agglomerate after being dried. Taking high modulus (4-5 model, up to 8-9 model) liquid lithium silicate of concrete sealant as an example, the concrete sealant is very firm after being dried and cured in construction, and does not need to be soaked in water for a long time. This is because liquid lithium silicate has a characteristic of never re-dissolving in water once dehydrated, and is very different from water glass, i.e. sodium silicate.

Lithium carbonate is agglomerated in the early stage of thermal precipitation and is very harmful. Therefore, the lithium sulfate and the soda ash must be strictly and effectively removed of silicon in advance; under the condition of strong and effective stirring, the material is sprayed and fed at a proper speed through a reasonably-arranged pressurized sprinkler feeding port; the inner wall of the stainless steel reaction tank and the surface of the stirrer should be smooth and have no scratch or spot welding slag so as to prevent lithium carbonate particles from being bonded.

The above technical principles also illustrate that the application of the "high efficiency desorption" content in item 3 of the present invention to further reduce the sulfate and sodium contents in lithium carbonate still needs to be based on these adsorption-desorption technical principles.

Supplementary explanation is given to the technical principle that the feeding speed of the lithium sulfate purification completion liquid is moderately increased and the thermal aging time is shifted backwards in the thermal precipitation working procedure in the [ 0040 ] section so as to obtain the coarse lithium carbonate with small particle size: in a liquid-solid system, the general technical principle is also applicable to crude lithium carbonate obtained by the thermal precipitation reaction of a lithium sulfate solution and a sodium carbonate solution by providing conditions of dilution, slowness, stirring, heat and aging to obtain crystals with large particle size so as to reduce the total surface area of the crystals and reduce the adsorption of other harmful impurities on the surfaces of the crystals. The lithium carbonate is thin, the primary yield of the lithium carbonate is reduced, the production cost is too unfavorable, and the lithium carbonate is suitable for use; the slow stirring, heating and aging are adopted, effective and error-free in the first stage of reducing the sulfate radical content, namely, the industrial grade is reduced to 0.20-0.15-0.10 percent, and the battery grade is reduced to 0.08 percent. However, to further reduce sulfate radical to a large extent to achieve the second stage of goal, i.e. 0.03% -0.02% industrial grade, 0.008% battery grade, even if 4N grade product is to be produced, it is necessary to modify "slow" to "moderate speed" and move back to the "old" operation position to obtain small grain size crystals.

In the high concentration environment of the thermal precipitation system, the impurities such as sulfate radicals and sodium ions in the peritectic crystal formed in the initial stage of thermal precipitation are generated at the core part of the large crystal and are extremely difficult to be thermally stirred and washed, and even released by 'strong desorption' (the thermal stirring is also a desorption operation in essence, and the strength is greatly lower than that of the 'strong desorption'), and the sulfate radicals form the battery grade index of 0.08 percent. The method for obtaining the crystal with small grain diameter by thermal precipitation is used as a technical bedding, and the working procedure of 'high-temperature strong desorption' can be carried out in the next step, thereby solving the technical problem.

The particle size of the crystal is reduced, namely the distance between the core part and the outer surface of the crystal is reduced to the range of a shallow layer, and the sulfate radicals and other impurities remained in the peritectic crystal are easy to be released during the operation of 'high-temperature strong desorption'; wherein most of the small crystals can be largely and thoroughly disintegrated during 'middle-high temperature strong desorption' and thermal aging operation, and are recrystallized into large-particle-size crystals in an environment with low-concentration impurities, so that sulfate radicals and other impurities are released to the maximum extent. Therefore, the technology can improve 'middle-high temperature strong desorption', further greatly reduce the reliability of sulfate radicals, shorten the pressure operation time, reduce the volume of a pressure kettle and reduce the equipment investment. The first stage needs large-particle-size crystals and the second stage needs small-particle-size crystals, which are only seemingly contradictory; the different occurrence states of sulfate radicals are different, and the corresponding technical measures are correspondingly different and have different potentials.

It is not to be considered that the quantity of the lithium carbonate with small particle size is greatly increased, the total surface area is greatly increased, and the impurities such as sodium carbonate and sulfate radicals are adsorbed on the surface layer of the lithium carbonate with small particle size temporarily, because the impurities are buried shallowly, and are easily released in the processes of primary hot-washing centrifugation and strong desorption of the crude lithium carbonate.

Description of the drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings of the embodiments will be briefly described below, and it is obvious that the drawings in the following description only relate to some embodiments of the present invention, and are not limiting on the present invention.

FIG. 1 is a schematic process flow diagram of the spodumene-sulfuric acid process of original Li America;

FIG. 2 is a washing curve for a pilot product sulfate according to the conventional process of original lithium America;

FIG. 3 is solubility data for lithium phosphate, lithium fluoride, lithium carbonate in water;

fig. 4 is a sulfate content reduction curve of lithium carbonate after 3 technical contents included in the technical solution of the present application are implemented.

The drawings 1-4 are described in detail as follows: FIG. 1 is a schematic diagram of a process flow for producing lithium carbonate by the conventional spodumene-sulfuric acid process of original lithium America. FIG. 1 is a drawing of a publication of "chemistry and technology of lithium" by Osterroshko et al, published by Chinese Industrial Press, Beijing, first edition, 5 months 1965, page 160.

FIG. 2 is a graph showing the washing curve of pilot product sulfate radical by the inventor of the present application in 1978-79-80, in accordance with the "forward feed" process of original American lithium corporation, at the initial stage of small-scale spodumene-sulfuric acid process lithium carbonate production. The curve is sufficient to show that the greatest disadvantage of this conventional process is the high level of impurity sulfate. The washing conditions were: crude Li₂CO₃: distilled water 1: 1.5, the temperature is 90-95 ℃, the stirring time is 30 minutes, and the SS-800 tripod type centrifuge is spin-dried at the speed of 1,300 revolutions per minute.

FIG. 3 is a graph showing the large difference in solubility data of lithium phosphate, lithium fluoride, and lithium carbonate in water, which is one order of magnitude larger, indicating that the lithium yield is the highest when lithium-containing sodium sulfate mother liquor is recovered as lithium phosphate.

FIG. 4 shows the descending curves of sulfate radicals in cliff-broken falling state after reverse feeding, mother liquor non-circulation and pre-precipitation supplement impurity removal of the invention and industrial grade and battery grade crude lithium carbonate produced by thermal precipitation operation are subjected to efficient desorption impurity removal. In the figure, the character A represents the 'micro-heating thermal precipitation and thermal agitation washing' stage, and the character B represents the 'high-efficiency desorption' stage; the horizontal line represents that the crude lithium carbonate 2 is transferred to a strong desorption kettle; the left one represents the industrial grade and the right one represents the battery grade.

Fifth, detailed description of the invention

The present invention will be further described with reference to specific embodiments. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies implemented based on the above-mentioned contents of the present invention are covered within the protection scope of the present invention.

1, taking the spodumene-sulfuric acid method to directly produce lithium carbonate as an example: when the technical scheme of the application is implemented, the existing impurity removal method before the 'micro-temperature-raising thermal precipitation and thermal agitation washing' process is not changed in principle, but the 'pre-precipitation supplement impurity removal' technology of the invention item 2 can be used; the working procedures of micro-temperature-raising thermal precipitation and thermal agitation washing must adopt the technology of 'reverse feeding and no circulation of mother liquor' in the invention 1; the existing technology of drying, crushing, metering and packaging the refined lithium carbonate wet product is unchanged; all detection methods are unchanged; the 'strong desorption' end point judgment method in the paragraph [ 0046 ] only relates to a sampling measure and a calculation method of sulfate radical content in solid-phase lithium carbonate, and does not relate to the change of a detection method of sulfate radical.

2, when the technology of 'preliminary precipitation supplement impurity removal' is confirmed to be needed, adding lithium sulfate purifying liquid into a thermal precipitation reaction kettle, starting stirring, spraying a small amount of sodium carbonate purifying liquid at a medium speed from a material spraying pipe orifice of a pressurized shower head in a mist shape, once the material liquid is found to be turbid by naked eyes and a turbidity meter, separating white fine substances (with yellow and red light when iron exceeds the standard), stopping feeding, continuing stirring for a few minutes, sampling and precisely filtering, detecting the contents of iron, aluminum, magnesium, calcium and heavy metals, and spraying a small amount of sodium carbonate until the contents reach the standard.

3, filtering the qualified lithium sulfate purified solution, temporarily putting the initial filtrate into a small turbid liquid tank (the total volume is about 20% of the volume of the lithium sulfate purified solution), circularly re-filtering until the filtrate sample is detected again, and reaching the standard, namely, judging that the filter cake bridging is successful, and continuously filtering (together with the lithium sulfate purified solution in the turbid liquid tank) if the filtrate sample is confirmed to be the purified finished solution; then, according to the technical specification of 'reverse feeding and no mother liquor circulation' in the '0017' to the '0019' section and the '0032' to the '0033' section, the '0041' to the '0045' section and the '0048' section, the crude lithium carbonate 1 is produced.

4, the thermal precipitation is implemented according to the technology of 'micro temperature-raising thermal precipitation and thermal agitation washing' in the paragraph [ 0078 ], without applying 'pre-precipitation supplement impurity-removing' technology, directly according to 'reverse feeding, mother liquor-not-circulating' technology, to produce crude lithium carbonate 1, and the feeding speed is doubled compared with that before the technology of the invention is not adopted because of the need of obtaining the crude lithium carbonate particles with small particle size.

And 5, after the charging is finished, releasing the pressure to 95 ℃, immediately discharging and centrifuging, and leaching with deionized water at 90-95 ℃ (the water amount, the rotating speed of a centrifuge and the centrifugal time length are controlled), so that the sulfate radical content of the discharged crude lithium carbonate 1 is as follows: 0.50-0.40% of industrial grade and 0.30-0.20% of battery grade; the primary sodium sulfate hot mother liquor is used for recovering lithium salts such as crude lithium carbonate or lithium phosphate according to the method explained in the process of 'non-circulating mother liquor', and recovering mirabilite or anhydrous sodium sulphate.

And 6, immediately transferring 1 time of crude lithium carbonate to a reaction kettle which is charged with deionized water with 3 times (industrial grade) or 4 times (battery grade) of the weight of the lithium carbonate and has a temperature of 90-95 ℃, starting stirring, covering a manhole, sealing the reaction kettle after air is exhausted, continuously heating to a selected position such as 115.2 ℃, performing agitation washing for 15 minutes, releasing pressure, starting discharging and centrifugal leaching after the temperature returns to 95 ℃, controlling the content of sulfate radicals of the discharged crude lithium carbonate for initial washing to be 0.30-0.20%, and controlling the battery grade to be 0.15-0.10%.

7, under the low-speed stirring, transferring the primary-washing crude lithium carbonate 2 into a strong desorption kettle which is 3-4-5 times (industrial grade) or 5-6 times (battery grade) of the weight of the primary-washing crude lithium carbonate while hot, pumping deionized water (18 megaohms. cm for producing the battery grade, self-made and preheated to 90-95 ℃) and starts the low-speed stirring; continuously heating to drive out the air in the reaction kettle, and then completely sealing the reaction kettle; in the production industry level, the temperature is raised to 144-159 ℃ (the saturated steam pressure in the kettle is 0.4-0.6 MPa), in the battery level, the temperature is raised to 165-170-180 ℃ (the saturated steam pressure in the kettle is 0.7-0.8-1.0 MPa), the low-speed stirring, the temperature and the pressure are maintained, and the middle-high temperature strong desorption and thermal aging operation is continued for more than 1 hour; during the process, a small amount of liquid phase is extruded out through a specially arranged sampling pipe orifice at regular time, the sulfate radical content of the liquid phase is rapidly detected (online continuous detection is performed as far as possible), the sulfate radical residual content of the lithium carbonate in the kettle is calculated according to the content, after the lithium carbonate reaches the standard, the heating valve is closed, low-speed stirring is maintained, cooling water is introduced, the stirring speed is increased until the slurry is maintained in a strong stirring state when the pressure in the kettle is reduced to 0.05-0.06 MPa, the speed is controlled, the slurry is pumped out and enters a hydrocyclone separator, and liquid and solid phases are continuously separated; the separated liquid phase contains slightly water-soluble impurities and particle-diameter water-insoluble impurities adsorbed and wrapped in the crude lithium carbonate, cannot be circularly used for the operation started by the process of thermally precipitating the crude lithium carbonate, returns to the leaching process for use, or is used for cleaning filter cloth and equipment, and only allows part of separation liquid which is fully coagulated, subjected to precise filtration to be used in deionized water for thermally agitating and washing the crude lithium carbonate 1. After solid phase centrifugal washing, the refined lithium carbonate wet product is obtained, the industrial-grade sulfate radical should be 0.03% -0.02%, the battery-grade (if necessary, the product is stirred and washed for 1 time) sulfate radical can be expected to be 0.010% -0.008% -0.005%, and the product reaches the limit value of 4N grade of main content.

In summary of the invention in claim 3, in addition to the precipitation of lithium carbonate from the exemplified lithium sulfate solution and sodium (potassium) carbonate solution to substantially reduce the impurity sulfate content, the following similar technical fields apply: 2 or more soluble inorganic substances, the target product precipitated by precipitation reaction, the crystal (or called particle) core part of which is chemically adsorbed and deeply wrapped to remove the impurities which are difficult to remove by the conventional washing method, can be greatly released into the strong desorption material liquid by a method of moderately raising the temperature and intensifying the thermal motion of molecules, ions and atomic groups, and is purified by rotary liquid separation, therefore, the invention is covered in the content of the invention.