阅读说明：本技术 一种溶剂萃取净化湿法磷酸的方法 (Method for purifying wet-process phosphoric acid by solvent extraction ) 是由 杜招鑫 高有飞 赵远方 王长岭 侯玉兰 李燕凤 孙国超 张继生 梁石生 于 2021-03-24 设计创作，主要内容包括：本发明公开了一种溶剂萃取净化湿法磷酸的方法,该方法将原料酸依次进行萃取、洗涤和反萃得到净化稀磷酸,其中,上述原料酸来自洗涤产生的洗余酸经浓缩得到的浓缩酸与湿法磷酸工艺生产得到的粗磷酸。由于浓缩酸杂质离子浓度较低,与粗磷酸混合能降低萃取单元原料酸的杂质离子浓度,从而减少萃取剂中杂质离子浓度,有助于降低净化酸杂质离子浓度。(The invention discloses a method for purifying wet-process phosphoric acid by solvent extraction, which comprises the steps of sequentially extracting, washing and back-extracting raw material acid to obtain purified dilute phosphoric acid, wherein the raw material acid is concentrated acid obtained by concentrating washing spent acid generated by washing and crude phosphoric acid obtained by wet-process phosphoric acid process production. Because the concentration of impurity ions of the concentrated acid is lower, the concentration of the impurity ions of the raw material acid of the extraction unit can be reduced by mixing the concentrated acid with the crude phosphoric acid, so that the concentration of the impurity ions in the extracting agent is reduced, and the concentration of the impurity ions of the purified acid is reduced.)

1. A method for purifying wet-process phosphoric acid by solvent extraction is characterized by comprising the following steps: and sequentially extracting, washing and back-extracting the raw material acid to obtain purified dilute phosphoric acid, wherein the raw material acid is a concentrated acid obtained by concentrating a washing spent acid generated by washing and a crude phosphoric acid obtained by wet-process phosphoric acid process production.

2. The method of claim 1, comprising: extracting crude phosphoric acid obtained by a wet-process phosphoric acid process through an extraction unit, and washing through a washing unit to obtain spent acid and an extractant rich in phosphoric acid; concentrating the washing residual acid by a concentration unit to obtain concentrated acid, and then mixing the concentrated acid with the crude phosphoric acid to obtain mixed acid serving as raw material acid of the extraction unit; and carrying out back extraction on the extractant rich in phosphoric acid in a back extraction unit to prepare purified dilute phosphoric acid.

3. The method according to claim 2, characterized in that the crude phosphoric acid is pretreated before extraction, the pretreatment being: mixing the wet-process phosphoric acid with a defluorinating agent to remove fluoride ions, and then decoloring by active carbon and decoloring by hydrogen peroxide to remove the fluoride ions and pigments.

4. The method of claim 2, wherein the extraction unit uses a rotating disc tower as the extraction device,

preferably, the raw material acid enters a rotating disc tower from a heavy phase inlet, the extracting agent enters the rotating disc tower from a light phase inlet, the raw material acid and the extracting agent are subjected to countercurrent contact mass transfer, after the mass transfer is finished, raffinate acid is discharged from a heavy phase outlet, and the first extracting agent rich in phosphoric acid is discharged from a light phase outlet and enters a washing unit;

preferably, the ratio of the extracting agent to the raw material acid is 3: 1-6: 1, the extraction temperature is 35-50 ℃.

5. The method of claim 4, wherein the extractant is a mixture of one of tributyl phosphate and butyl phosphate and a diluent which is one of kerosene, MIBK, n-butanol, and diisopropyl ether.

6. The method according to claim 2, wherein the washing unit uses a first centrifugal extractor as washing equipment,

preferably, the first phosphoric acid-rich extractant obtained in the extraction unit enters a first centrifugal extractor from a light phase inlet, is in countercurrent contact with the washing acid entering from a heavy phase inlet for mass transfer, the second phosphoric acid-rich extractant obtained after washing is discharged from a light phase outlet and enters a back extraction unit, and the washing spent acid is discharged from a heavy phase outlet and enters a concentration unit;

preferably, the first phosphoric acid-rich extractant compared to the wash acid is 15: 1-25: 1, the washing temperature is 45-55 ℃.

7. The process according to claim 6, wherein the scrubbing acid is derived from a second phosphoric acid-rich extractant which is discharged through a light phase outlet and enters a stripping unit for stripping to obtain a partially purified dilute phosphoric acid.

8. The method according to claim 2, characterized in that the stripping unit uses a second centrifugal extractor as stripping equipment,

preferably, the second phosphoric acid-rich extractant obtained by washing in the washing unit enters a second centrifugal extractor from a light phase inlet and is in countercurrent contact with pure water entering from a heavy phase inlet for mass transfer, the second phosphoric acid-rich extractant is subjected to back extraction and then returns to the extraction unit as a lean solvent, the back-extracted pure water is changed into purified dilute phosphoric acid, one part of the purified dilute phosphoric acid enters the washing unit as washing acid, and the other part of the purified dilute phosphoric acid is sent to a subsequent unit for concentration and desulfurization;

preferably, the second phosphoric acid-rich extractant compared to the pure water is 3: 1-8: 1, the back extraction temperature is 40-55 ℃.

9. The method according to claim 8, wherein the first centrifugal extractor and the second centrifugal extractor are both multi-stage extraction mechanisms with two or more centrifugal extractors connected in series.

10. The method according to any one of claims 1 to 9, characterized by the following steps:

pretreatment: mixing the wet-process phosphoric acid with a defluorinating agent to remove fluoride ions, and then decoloring with activated carbon and decoloring with hydrogen peroxide to remove fluoride ions and pigments to obtain crude phosphoric acid;

and (3) extraction: feeding the raw material acid into a rotating disc tower from a heavy phase inlet, and feeding an extracting agent into the rotating disc tower from a light phase inlet for countercurrent extraction;

washing: feeding the first phosphoric acid-rich extractant obtained by extraction into a first centrifugal extractor from a light phase inlet, and washing the first centrifugal extractor and the washing acid fed from a heavy phase inlet in a counter-current manner;

back extraction: the washed second extractant rich in phosphoric acid enters a second centrifugal extractor from a light phase inlet and is reversely extracted with pure water entering from a heavy phase inlet;

concentration: and taking part of purified dilute phosphoric acid obtained by back extraction as washing acid, feeding washing residual acid obtained by washing the washing acid into a concentration unit to be concentrated into concentrated acid, and taking mixed acid obtained by mixing the concentrated acid and crude phosphoric acid as raw material acid of an extraction unit.

Technical Field

The invention relates to the technical field of phosphorus chemical industry, in particular to a method for purifying wet-process phosphoric acid by solvent extraction.

Background

In the production of wet-process phosphoric acid, especially the wet-process phosphoric acid produced by using medium-low grade phosphate ore, a large amount of solid substances are produced after the wet-process phosphoric acid is concentrated, secondary precipitates are produced along with the reduction of the temperature of the concentrated acid, organic substances are carbonized during the leaching of the phosphate ore and the abrasion of the phosphate material on a graphite evaporator during the concentration is added, so that 50 percent P is generated₂O₅The solid matter content of the wet-process phosphoric acid can reach more than 8 percent at most, and the acid liquid is black. These solids are collectively referred to as sludge. Meanwhile, the phosphoric acid also contains SO₃F, etc., which must be removed by purification. However, the quality of the purified acid obtained varies depending on the species of ore and the purification method. In order to ensure the quality of the product and control the production cost, most producers can produce qualified products only by matching purified wet-process phosphoric acid with a certain amount of hot-process phosphoric acid. However, the cost of the thermal phosphoric acid is far higher than that of the wet phosphoric acid, and the higher the proportion of the thermal phosphoric acid, the higher the cost. Meanwhile, waste residues generated in the wet-process phosphoric acid purification process generally contain a large amount of useless impurities and are directly discarded, so that the phosphorus loss is large and the environmental pollution is serious.

The solvent extraction is a mass transfer separation method widely applied to the fields of petrochemical industry, nuclear industry, medicine, environmental protection and the like, and the working principle of the method is that a liquid extractant which is immiscible or partially miscible with the mixed solution to be separated is added into the mixed solution to form a mixed solution-extractant two-phase system, and the distribution difference of each component in the mixed solution in two phases is utilized to enable more components in the mixed solution to enter the extracted phase, so that the separation of the mixed solution is realized. The solvent extraction method has the advantages of continuous operation, high mass transfer rate, short production period, large solute concentration multiple, high purification degree and the like when multi-stage extraction is adopted.

In the process of purifying wet-process phosphoric acid by solvent extraction, waste acid is inevitably generated. One part of waste acid comes from the extraction unit, and the other part comes from the washing unit, wherein the extraction unit has high content of raffinate acid impurities, high viscosity and high recycling difficulty. The spent acid is generated after the dilute phosphoric acid is purified to wash the solvent, has the characteristics of lower phosphoric acid concentration and lower impurity content, and is generally used as a waste acid and a raffinate acid of an extraction unit to be discharged together to be used as a raw material for producing a phosphate fertilizer. Along with the reduction of the grade of the phosphorite and the continuous increase of the impurity content of the crude phosphoric acid, the requirement of recycling the waste acid is more and more urgent. The existing wet-process phosphoric acid purification process has some defects in recycling of the washing residual acid, and the reasonable recycling of the washing residual acid has important significance in improving the utilization rate of phosphorus resources in the wet-process phosphoric acid purification process.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a method for purifying wet-process phosphoric acid by solvent extraction.

The invention is realized by the following steps:

the invention provides a method for purifying wet-process phosphoric acid by solvent extraction, which comprises the following steps: and sequentially extracting, washing and back-extracting the raw material acid to obtain purified dilute phosphoric acid, wherein the raw material acid is a concentrated acid obtained by concentrating a washing spent acid generated by washing and a crude phosphoric acid obtained by wet-process phosphoric acid process production.

The invention has the following beneficial effects:

the invention provides a method for purifying wet-process phosphoric acid by solvent extraction. The method comprises the following steps: and sequentially extracting, washing and back-extracting the raw material acid to obtain purified dilute phosphoric acid, wherein the raw material acid is a concentrated acid obtained by concentrating a washing spent acid generated by washing and a crude phosphoric acid obtained by wet-process phosphoric acid process production. Because the concentration of the impurity ions in the concentrated acid is lower, the concentration of the impurity ions in the raw material acid can be reduced by mixing the concentrated acid with the crude phosphoric acid, so that the concentration of the impurity ions in the extracting agent is reduced, and the concentration of the impurity ions in the purified acid is reduced.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.

FIG. 1 is a flow chart of the method for purifying wet-process phosphoric acid by solvent extraction.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.

Aiming at the problems and the defects of the recycling of the washing spent acid in the existing wet-process phosphoric acid purification process, the inventor researches and develops a method for purifying the wet-process phosphoric acid by solvent extraction, and the concentrated acid obtained by concentrating the washing spent acid is used as a raw material, so that the purity of the purified acid, the removal rate of impurity ions and the utilization rate of phosphorus resources can be effectively improved. In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

the embodiment of the invention provides a method for purifying wet-process phosphoric acid by solvent extraction, which comprises the following steps: and sequentially extracting, washing and back-extracting the raw material acid to obtain purified dilute phosphoric acid, wherein the raw material acid is a concentrated acid obtained by concentrating a washing spent acid generated by washing and a crude phosphoric acid obtained by wet-process phosphoric acid process production.

In the method, because the concentration of impurity ions of the concentrated acid is lower, the impurity ion concentration of the raw material acid of the extraction unit can be reduced by mixing the concentrated acid with the crude phosphoric acid, so that the concentration of the impurity ions in the extracting agent is reduced, and the concentration of the impurity ions of the purified acid is reduced.

In an alternative embodiment, a method for solvent extraction purification of wet-process phosphoric acid comprises: extracting crude phosphoric acid obtained by a wet-process phosphoric acid process through an extraction unit, and washing through a washing unit to obtain spent acid and an extractant rich in phosphoric acid; concentrating the washing residual acid by a concentration unit to obtain concentrated acid, wherein the extraction process is to perform extraction operation on mixed acid obtained by mixing the concentrated acid with crude phosphoric acid; then the extractant rich in phosphoric acid is subjected to back extraction in a back extraction unit to prepare purified dilute phosphoric acid.

In an alternative embodiment, the crude phosphoric acid is pre-treated prior to extraction, the pre-treatment being: mixing wet-process phosphoric acid and a defluorinating agent to remove fluoride ions, and then decoloring by active carbon and decoloring by hydrogen peroxide to remove fluoride ions and pigments.

In an alternative embodiment, the extraction unit has a rotating disc column as the extraction device;

preferably, raw material acid enters a rotating disc tower from a heavy phase inlet, an extracting agent enters the rotating disc tower from a light phase inlet, the raw material acid and the extracting agent are subjected to countercurrent contact mass transfer, raffinate acid after mass transfer is discharged from a heavy phase outlet, and a first extracting agent rich in phosphoric acid is discharged from a light phase outlet and enters a washing unit;

preferably, the ratio of the extractant to the starting acid is 3: 1-6: 1, the extraction temperature is 35-50 ℃;

in an alternative embodiment, the extraction agent is a mixture of tributyl phosphate or one of butyl phosphate with one of the diluents kerosene, MIBK, n-butanol or diisopropyl ether.

In an alternative embodiment, the washing unit has a first centrifugal extractor as the washing device;

preferably, a first extractant rich in phosphoric acid enters a first centrifugal extractor from a light phase inlet, is in countercurrent contact with washing acid entering a heavy phase inlet for mass transfer, a second extractant rich in phosphoric acid obtained after washing is discharged from a light phase outlet and enters a stripping unit, and washing residual acid is discharged from a heavy phase outlet and enters a concentration unit;

preferably, the first phosphoric acid-rich extractant compared to the wash acid is 15: 1-25: 1, the washing temperature is 45-55 ℃.

In an alternative embodiment, the scrubbing acid is derived from a second phosphoric acid-rich extractant which is discharged through a light phase outlet and enters a stripping unit to strip a portion of the purified dilute phosphoric acid.

In an alternative embodiment, the stripping unit takes a second centrifugal extractor as stripping equipment;

preferably, the second phosphoric acid-rich extractant enters a second centrifugal extractor from a light phase inlet and is in countercurrent contact mass transfer with pure water entering from a heavy phase inlet, the second phosphoric acid-rich extractant is subjected to back extraction and then is used as a lean solvent to return to the extraction unit, the back extracted pure water is changed into purified dilute phosphoric acid, one part of the purified dilute phosphoric acid is used as washing acid to enter a washing unit, and the other part of the purified dilute phosphoric acid is sent to a subsequent unit for concentration and desulfurization;

preferably, the second phosphoric acid-rich extractant is 3: 1-8: 1, the back extraction temperature is 40-55 ℃.

In an alternative embodiment, the method further comprises: washing acid is fed into a concentration unit after passing through a washing unit, and the concentrated acid is mixed with crude phosphoric acid to be used as raw material acid of an extraction unit.

In an alternative embodiment, the method comprises the following steps:

pretreatment: mixing wet-process phosphoric acid and a defluorinating agent to remove fluoride ions, and then decolorizing with activated carbon and hydrogen peroxide to remove fluoride ions and pigments to obtain vinegar phosphoric acid;

and (3) extraction: feeding the raw material acid into a rotating disc tower from a heavy phase inlet, and feeding an extracting agent into the rotating disc tower from a light phase inlet for countercurrent extraction;

washing: feeding the first phosphoric acid-rich extractant obtained by extraction into a first centrifugal extractor from a light phase inlet, and washing the first centrifugal extractor and the washing acid fed from a heavy phase inlet in a counter-current manner;

back extraction: the washed second extractant rich in phosphoric acid enters a second centrifugal extractor from a light phase inlet and is reversely extracted with pure water entering from a heavy phase inlet;

concentration: and (3) taking part of purified dilute phosphoric acid obtained by back extraction as washing acid, washing the washing acid, then concentrating the washing acid into a concentration unit, and mixing the concentrated acid and the crude phosphoric acid to be used as raw material acid of the extraction unit.

Referring to fig. 1 again, the embodiment of the invention provides a method for purifying wet-process phosphoric acid by solvent extraction, and the method comprises a flow path for purifying the wet-process phosphoric acid, which comprises an extraction unit, a washing unit, a stripping unit and a concentration unit. Wherein:

the extraction unit takes a rotating disc tower as extraction equipment, and the rotating disc tower has the important advantage that an extraction system containing a small amount of solid particles can be treated.

The washing unit uses a centrifugal extractor as washing equipment, washing acid and rich solvent do not contain solid particles, the centrifugal extractor has the advantages of high extraction efficiency, fast mass transfer balance, small occupied area and the like, and the washing effect can be improved and the washing time can be reduced by selecting the centrifugal extractor to wash the rich solvent.

The back extraction unit takes a centrifugal extractor as back extraction equipment and pure water as heavy phase feed.

The concentration unit is used for concentrating the washing residual acid, and mixed acid obtained by mixing the concentrated acid and the crude phosphoric acid is used as extraction raw material acid and enters the extraction unit. The concentration of impurity ions of the concentrated acid is low, and the concentration of the impurity ions of the raw material acid of the extraction unit can be reduced by mixing the concentrated acid with the crude phosphoric acid, so that the concentration of the impurity ions in the extracting agent is reduced, and the purity of the purified acid is improved; the washing residual acid is mixed with the crude phosphoric acid after being concentrated, the concentration of the crude phosphoric acid can not be reduced, and the utilization rate of phosphorus resources can be improved.

The method for purifying wet-process phosphoric acid by solvent extraction provided by the embodiment of the invention comprises the following steps:

pretreatment: adding defluorinating agent into wet phosphoric acid to remove fluoride ions, and then adding active carbon for decolorization and hydrogen peroxide for decolorization to remove fluoride ions and pigments.

And (3) extraction: the raw material acid enters the rotating disc tower from the heavy phase inlet, the extracting agent enters the rotating disc tower from the light phase inlet, the raw material acid and the extracting agent are subjected to countercurrent contact mass transfer, the raffinate acid after the mass transfer is discharged from the heavy phase outlet and enters a fertilizer grade product system, and the extracting agent is discharged from the light phase outlet at the top of the tower and enters a washing unit. The raw material acid of the extraction unit is formed by mixing crude phosphoric acid and concentrated acid, and the ratio of the extracting agent to the raw material acid is 3: 1-6: 1, the extraction temperature is 35-50 ℃.

Washing: the extractant rich in phosphoric acid from the extraction unit enters a washing unit centrifugal extractor from a light phase inlet, is in countercurrent contact with washing acid entering a heavy phase inlet for mass transfer, the extractant rich in phosphoric acid after washing is discharged from a light phase outlet and enters a back extraction unit, and washing residual acid is discharged from a heavy phase outlet and enters a concentration unit. The extractant compared to the washing acid was 15: 1-25: 1, the washing temperature is 45-55 ℃.

Back extraction: the extractant rich in phosphoric acid enters a back-extraction unit centrifugal extractor from a light phase inlet, and is in countercurrent contact mass transfer with pure water entering from a heavy phase inlet, the extractant is subjected to back extraction and then enters an extraction unit as a poor solvent, the pure water after back extraction is changed into purified dilute phosphoric acid, one part of the purified dilute phosphoric acid enters a washing unit as washing acid, and the other part of the purified dilute phosphoric acid enters a subsequent unit for concentration and desulfurization treatment. The extractant compared with pure water is 3: 1-8: 1, the back extraction temperature is 40-55 ℃.

Concentration: washing acid enters the concentration unit after passing through the washing unit, and the concentrated acid is mixed with crude phosphoric acid to be used as raw material acid of the extraction unit.

The features and properties of the present invention are described in further detail below with reference to examples.

Example 1

The index of the crude phosphoric acid after pretreatment is shown in Table 1.

TABLE 1

Components	H3PO4％	CaO％	MgO％	Fe2O3％	Al2O3％	F％
							Mass fraction	50.04	0.07	1.34	0.38	0.15	0.062

And (3) extraction: the diameter of a rotating disc tower is 100mm, the height of an extraction section is 1000mm, the rotating speed of a rotating disc is 300r/min, the flow of raw material acid is 5L/h, the flow of an extracting agent MIBK is 20L/h, the feeding temperatures of two phases are both 45 ℃, and the extracting agent is 4: 1. two-phase countercurrent contact mass transfer, wherein after mass transfer is finished, extraction spent acid is discharged from a heavy phase outlet, and a fertilizer grade product removing system is adopted; the first acid-containing extractant MIBK is withdrawn from the light phase outlet and enters a scrubbing unit.

Washing: the washing unit is formed by connecting two centrifugal extractors in series, the rotating speeds of the centrifugal extractors are 3500r/min, and the ratio of an extracting agent to washing acid is 20: both phases were fed at 50 ℃. The first acid-containing extractant MIBK enters the first-stage centrifugal extractor from a light phase inlet, the washing acid enters the second-stage centrifugal extractor from a heavy phase inlet, after two-stage countercurrent contact mass transfer, the second acid-containing extractant MIBK is discharged from a light phase outlet of the second-stage centrifugal extractor and enters a back extraction unit, and the washing acid is discharged from a heavy phase outlet of the first-stage centrifugal extractor and enters a concentration unit for concentration.

Back extraction: the back extraction unit is formed by connecting two centrifugal extractors in series, the rotating speeds of the centrifugal extractors are both 2500r/min, and the feeding temperatures of the two phases are both 50 ℃. Leading the second acid-containing extractant MIBK to enter a first-stage centrifugal extractor from a light phase inlet, leading pure water to enter a second-stage centrifugal extractor from a heavy phase inlet, discharging the MIBK from a light phase outlet of the second-stage centrifugal extractor as a lean solvent to an extraction unit after two-stage countercurrent contact mass transfer; the pure water is changed into purified dilute phosphoric acid and is discharged from a heavy phase outlet of the primary centrifugal extractor, one part of the purified dilute phosphoric acid is used as washing acid and enters a washing unit, and the rest of the purified dilute phosphoric acid is concentrated in a subsequent device. The extractant compared with pure water is 7: 1.

concentration: the concentration unit takes a vacuum evaporation tube still heat exchanger as concentration equipment. The concentration of the washing residual acid is about 20.5 percent, concentrated acid with the concentration of 50.1 percent is prepared by a vacuum evaporation tubular heat exchanger, and the concentrated acid is mixed with the crude phosphoric acid to be used as raw material acid of an extraction unit.

After the device is operated for 6 hours, 45.42kg of crude phosphoric acid is consumed, 16.37kg of raffinate acid is produced, the utilization rate of the phosphorus element is 86.36%, and the specific conditions are shown in Table 2.

TABLE 2

The indexes of the obtained purified diluted phosphoric acid are shown in Table 3.

TABLE 3

Components

H3PO4％

CaO％

MgO％

Fe2O3％

Al2O3％

F％

Mass fraction

20.51

Not detected out

Not detected out

0.0002

0.0002

0.004

Compared with the prior art, the method provided by the embodiment of the invention has the following advantages:

1. compared with the prior art, the method has the advantages that the purification effect is good, the concentration of the washing residual acid and the crude phosphoric acid are mixed to serve as the raw material acid for extraction, the impurity ion concentration of the raw material acid is reduced, the purity of the purified acid can be effectively improved, and the impurity ion removal rate is improved by about 10%;

2. the utilization rate of phosphorus resources is high, and compared with the prior art, the utilization rate of phosphorus resources can be improved by about 15% by using the spent acid as the raw material;

3. the device has long running period, and the rotating disc tower is adopted as the extraction equipment in the extraction unit, thereby avoiding the abrasion of the rotating drum of the centrifugal extractor, reducing the maintenance frequency and improving the running period of the device.

The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.