阅读说明：本技术 一种大修渣湿法浸出液中盐提纯回收工艺 (Process for purifying and recovering salt in wet-process leaching solution of overhaul residues ) 是由 宋海农 林宏飞 周郁文 丘能 杜建嘉 慕俊豪 于 2021-08-18 设计创作，主要内容包括：本发明公开了一种大修渣湿法浸出液中盐提纯回收工艺,具体涉及固体危险废弃物处理技术领域,包括步骤：(1)沉氟；(2)浸出液中和、回收铝成分；(3)制备聚合铝；(4)深度除氟及去除悬浮物；(5)吸附除钙；(6)回收钠盐。本发明通过对浸出液沉氟,得到的沉氟后液加入无机酸中和及pH调节,固液分离得到氢氧化铝胶体和除铝后液,得到的氢氧化铝用于制备聚合铝,通过回收铝制备聚合铝作为混凝剂进行深度除氟,实现以废治废,回收钠盐的纯度也得到进一步提升,使浸出液中的无机盐类得到资源化回收；处理后的浸出液可返回大修渣湿法浸出工艺循环利用,实现了浸出液废水的零排放,符合节能减排的环保政策。(The invention discloses a process for purifying and recovering salt in wet leachate of overhaul residues, and particularly relates to the technical field of solid hazardous waste treatment, which comprises the following steps: (1) fluorine precipitation; (2) neutralizing the leachate and recovering aluminum components; (3) preparing polymeric aluminum; (4) deeply removing fluorine and suspended matters; (5) adsorbing and removing calcium; (6) recovering the sodium salt. According to the invention, the leachate is subjected to fluorine precipitation, the obtained fluorine-precipitated liquid is added with inorganic acid for neutralization and pH adjustment, solid-liquid separation is carried out to obtain an aluminum hydroxide colloid and a liquid after aluminum removal, the obtained aluminum hydroxide is used for preparing polyaluminium, the polyaluminium is prepared by recovering aluminum and used as a coagulant for deep fluorine removal, the waste treatment by waste is realized, the purity of the recovered sodium salt is further improved, and the inorganic salts in the leachate are recycled; the treated leachate can be returned to the overhaul slag wet leaching process for recycling, so that zero discharge of leachate wastewater is realized, and the environmental protection policy of energy conservation and emission reduction is met.)

1. A process for purifying and recovering salt in wet leachate of overhaul residues is characterized by comprising the following treatment steps:

(1) fluorine deposition: adding a calcium agent into the overhaul residue leaching solution, carrying out fluorine precipitation reaction, and carrying out solid-liquid separation to obtain a calcium fluoride mixed precipitate and a fluorine precipitation solution;

(2) neutralizing the leachate and recovering aluminum components: adding inorganic acid into the fluorine-precipitated liquid obtained in the step (1), adjusting the pH value to 6.5-7.5 to enable aluminum components in the fluorine-precipitated liquid to generate aluminum hydroxide, and performing solid-liquid separation to obtain an aluminum hydroxide colloid and a liquid after aluminum removal;

(3) preparing the polymeric aluminum: adding inorganic acid into the aluminum hydroxide colloid obtained in the step (2), adding water for reaction, curing, filtering and drying to obtain polymeric aluminum;

(4) deeply removing fluorine and suspended matters: adding the polyaluminium prepared in the step (3) into the liquid obtained in the step (2) after aluminum removal, adsorbing, condensing and removing fluorine, removing suspended matters in the leachate, and performing solid-liquid separation to obtain deep fluorine removal clear liquid;

(5) adsorption and calcium removal: adding cation exchange resin into the deep defluorination clear liquid obtained in the step (4), and carrying out solid-liquid separation to obtain high-purity sodium salt clear liquid;

(6) and (3) recovering sodium salt: and (5) treating the high-purity sodium salt clear liquid obtained in the step (5) by a crystallization system, recovering a solid phase to obtain refined sodium salt, and returning a liquid phase to the overhaul residue leaching process for recycling.

2. The process according to claim 1, wherein in the step (1), the calcium agent is one of calcium sulfate, calcium chloride, calcium oxide and calcium hydroxide, and the addition amount of the calcium agent is 0.6-1.2 times of the molar amount of the fluoride ions in the leachate.

3. The process according to claim 1, wherein the inorganic acid added in the steps (2) and (3) is sulfuric acid or hydrochloric acid.

4. The process according to claim 3, wherein the inorganic acid added in the steps (2) and (3) is sulfuric acid, and the calcium agent is one of calcium sulfate, calcium oxide and calcium hydroxide.

5. The process according to claim 3, wherein the inorganic acid added in the steps (2) and (3) is hydrochloric acid, and the calcium agent is one of calcium chloride, calcium oxide and calcium hydroxide.

6. The process according to claim 1, wherein the amount of the inorganic acid added in the step (3) is 0.2 to 0.25 times the molar amount of the aluminum hydroxide.

7. The process for purifying and recovering the salt in the wet leachate of the overhaul slag as claimed in claim 1, wherein the reaction temperature in the step (3) is 100-150 ℃.

8. The process for purifying and recovering the salt in the wet leachate of the overhaul residue according to claim 1, wherein the reaction pressure in the step (3) is 3 to 4 MPa.

9. The process for purifying and recovering the salt in the wet leachate of the overhaul residue according to claim 1, wherein the reaction time of the step (3) is 2 to 5 hours.

10. The process according to claim 1, wherein the amount of polyaluminium added in step (4) is 50-250 times of the concentration of fluoride ions in the solution after aluminum removal.

Technical Field

The invention relates to the technical field of solid hazardous waste treatment, in particular to a process for purifying and recovering salt in wet-process leachate of overhaul residues.

Background

In recent years, with the annual increase of aluminum yield in China, the amount of dangerous solid waste generated by the aluminum electrolysis industry is also increasing year by year. The overhaul slag is solid dangerous waste inevitable in the aluminum electrolysis production, and 15-25kg of overhaul slag is discharged per 1 ton of aluminum produced by a tank for 7-8 years of production, wherein the waste cathode carbon block accounts for about 55%, and the waste refractory material accounts for about 45%. The main toxic substances are soluble fluoride and soluble cyanide, which have great harm to the environment including soil, water area and atmosphere, so the harmless treatment of the overhaul slag is urgently needed to be solved and is not slow.

The domestic treatment mode of the waste refractory materials mainly comprises a fire method, a wet method, stockpiling, landfill and hazardous waste conveying center, the fire method and the wet method can thoroughly and harmlessly treat the waste refractory materials, but the fire method is not industrialized so far, and the investment is large. Therefore, wet processing of overhaul slags is a hot spot of recent research.

At present, the wet-process leaching process of the overhaul residues at home and abroad mainly comprises water leaching, alkali leaching, water leaching, acid-base combined leaching and the like, the leaching solution contains a large amount of soluble sodium fluoride and excessive acid-base, but a specific treatment and salt recovery process aiming at the overhaul residue leaching solution does not exist, so the application of the wet-process treatment of the overhaul residues is limited to a certain extent. When the overhaul residues are treated by adopting a water leaching and alkaline leaching process, the pH value of the leaching solution reaches more than 13, and the following reactions can occur: (1) na (Na)₃AlF₆+4NaOH＝6NaF+NaAlO₂+2H₂O，(2)Al₂O₃+2NaOH＝2NaAlO₂+H₂And O, generating a large amount of sodium fluoride and sodium aluminate in the leachate and generating excessive sodium hydroxide, thereby influencing the reutilization of the leachate. Therefore, the leachate needs to be treated, purified and recycled, so that on one hand, the leachate can be recycled, zero discharge of wastewater is realized, and transfer of dangerous substances is reduced; on the other hand, the additional value of the salt is greatly improved by purifying the salt, and the operation cost of an enterprise can be shared.

Disclosure of Invention

The invention aims to overcome the defects in the prior art and provide a process for purifying and recovering salt in wet leachate of overhaul residues, which comprises the steps of carrying out fluorine precipitation, leachate neutralization, aluminum component recovery, polymeric aluminum preparation, deep fluorine removal, calcium adsorption removal and sodium salt recovery on the leachate of overhaul residues treated by a water leaching and alkali leaching process, so that inorganic salts in wastewater are recycled, and zero discharge and cyclic utilization of wastewater are realized.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a process for purifying and recovering salt in wet leachate of overhaul residues comprises the following treatment steps:

(1) fluorine deposition: adding a calcium agent into the overhaul residue leaching solution, carrying out fluorine precipitation reaction, and carrying out solid-liquid separation to obtain a calcium fluoride mixed precipitate and a fluorine precipitation solution;

(2) neutralizing the leachate and recovering aluminum components: adding inorganic acid into the fluorine-precipitated liquid obtained in the step (1), adjusting the pH value to 6.5-7.5 to enable aluminum components in the fluorine-precipitated liquid to generate aluminum hydroxide, and performing solid-liquid separation to obtain an aluminum hydroxide colloid and a liquid after aluminum removal;

(3) preparing the polymeric aluminum: adding inorganic acid into the aluminum hydroxide colloid obtained in the step (2), adding water for reaction, curing, filtering and drying to obtain polymeric aluminum;

(4) deeply removing fluorine and suspended matters: adding the polymeric aluminum prepared in the step (3) into the aluminum-removed liquid obtained in the step (2), carrying out adsorption and coagulation deep fluorine removal, removing suspended matters in the leachate, and carrying out solid-liquid separation to obtain a deep fluorine-removed clear liquid;

(5) adsorption and calcium removal: adding cation exchange resin into the deep defluorination clear liquid obtained in the step (4), and carrying out solid-liquid separation to obtain high-purity sodium salt clear liquid;

(6) and (3) recovering sodium salt: and (5) treating the high-purity sodium salt clear liquid obtained in the step (5) by a crystallization system, recovering the solid phase part to obtain refined sodium salt, and returning the liquid phase part to the overhaul residue leaching process for recycling.

Preferably, in the step (1), the calcium agent is one of calcium sulfate, calcium chloride, calcium oxide and calcium hydroxide, and the addition amount of the calcium agent is 0.6-1.2 times of the molar amount of the fluorine ions in the leachate.

Preferably, the inorganic acid added in the step (2) and the step (3) is sulfuric acid or hydrochloric acid.

Preferably, the inorganic acid added in the step (2) and the step (3) is sulfuric acid, and then the calcium agent is one of calcium sulfate, calcium oxide and calcium hydroxide.

Preferably, the inorganic acid added in step (2) and step (3) is hydrochloric acid, and then the calcium agent is one of calcium chloride, calcium oxide and calcium hydroxide.

Preferably, the amount of the inorganic acid added in the step (3) is 0.2 to 0.25 times of the molar amount of the aluminum hydroxide.

Preferably, the reaction temperature of the step (3) is 100-150 ℃.

Preferably, the reaction pressure of the step (3) is 3-4 MPa.

Preferably, the reaction time of the step (3) is 2 to 5 hours.

Preferably, the adding amount of the polymeric aluminum in the step (4) is 50 to 250 times of the concentration of the fluorine ions in the aluminum-removed liquid.

The invention treats the leachate of the overhaul residues after water leaching and alkali leaching treatment, wherein after calcium is added in the step (1) for fluorine precipitation, the concentration of fluorine ions in the liquid after fluorine precipitation can be reduced to 40-50mg/L from 3000-10000mg/L, and the obtained calcium fluoride mixed precipitate is dried to obtain a crude calcium fluoride product.

The fluorine-precipitated liquid obtained in the step (1) is alkaline, and inorganic acid is added in the step (2), so that on one hand, excessive sodium hydroxide in the fluorine-precipitated liquid is neutralized and converted into sodium salt for recycling; on the other hand, the pH value of the solution is adjusted to be between 6.5 and 7.5, the aluminum component in the solution after fluorine precipitation is sodium aluminate, a large amount of aluminate ions can be dissociated, and the aluminate ions can be hydrolyzed when the pH value is between 6.5 and 7.5, so that aluminum hydroxide is generated and recovered, and the aluminum component in the leachate can be recovered.

The polymeric aluminum prepared in the step (3) is an oligomer aluminum salt and contains excessive aluminum hydroxide, the polymeric aluminum is added into the solution after aluminum removal, the fluorine ions and the oligomer aluminum salt generate an aluminum fluorine complex, and simultaneously partial aluminum ions are hydrolyzed to generate aluminum hydroxide colloid, the aluminum hydroxide colloid existing in the solution after aluminum removal can increase the basicity of the oligomer aluminum salt, the coagulation effect of the polymeric aluminum is improved, the aluminum fluorine complex is swept down by the aluminum hydroxide colloid, so that the fluorine ions are removed, and the fluorine concentration in the solution can be reduced to 0.8-1.5mg/L through the coagulation effect of the polymeric aluminum.

And (5) adding cation exchange resin to adsorb impurities such as excessive calcium ions generated in the fluorine precipitation process, softening the water quality of the deep fluorine removal clear liquid, and reducing the calcium ion concentration in the high-purity sodium salt clear liquid obtained after solid-liquid separation to below 1mg/L or even not detecting the calcium ion concentration.

Adding sulfuric acid in the step (2) and the step (3), preparing polyaluminium sulfate in the step (3), obtaining high-purity sodium sulfate clear liquid in the step (5), and concentrating and crystallizing the high-purity sodium sulfate clear liquid in the step (6) by the following steps: and (3) carrying out variable temperature crystallization on the high-purity sodium sulfate clear liquid by using a freezing crystallization system, filtering the low-temperature crystal slurry to obtain sodium sulfate decahydrate crystals, drying the sodium sulfate decahydrate crystals to obtain refined sodium sulfate salt, and returning the filtrate to the overhaul residue leaching process for recycling.

Hydrochloric acid is added in the step (2) and the step (3), polyaluminum chloride is prepared in the step (3), high-purity sodium chloride clear liquid is obtained in the step (5), and the method for concentrating and crystallizing the high-purity sodium chloride clear liquid in the step (6) comprises the following steps: and (3) carrying out evaporative crystallization on the clear liquid through an evaporation system to obtain sodium chloride crystals, returning evaporative condensed water to the overhaul residue leaching process for recycling, and drying the sodium chloride crystals to obtain refined sodium chloride salt.

Due to the adoption of the technical scheme, the invention has the following beneficial effects:

1. the invention prepares polymeric aluminum by carrying out fluorine precipitation, neutralization and aluminum component recovery on leachate of overhaul residues treated by water leaching and alkaline leaching, deeply removes fluorine and adsorbs and removes calcium to obtain high-purity sodium salt clear solution, and then recovers salt through crystallization, a solid phase can obtain refined sodium salt, and the liquid phase returns to the overhaul residue leaching process for recycling; the obtained sodium sulfate refined salt product meets the national standard GB/T6009-2014 industrial anhydrous sodium sulfate standard, and the sodium chloride refined salt product meets the national standard GBT 5462-2016 industrial salt standard, so that on one hand, the leachate can be recycled, the zero discharge of wastewater is realized, and the transfer of dangerous substances is reduced; on the other hand, the additional value of the salt is greatly improved by purifying the salt, and the prepared refined sodium salt is sold as a product and can also share the operation cost of enterprises.

2. The invention firstly adopts the calcium agent to precipitate the fluorine in the leaching solution, so that the concentration of the fluorine in the leaching solution is reduced to 40-50mg/L from 3000-10000mg/L, thereby reducing the treatment load of further fluorine removal in the next step, and simultaneously obtaining a crude calcium fluoride product for sale, and realizing the resource recovery of the fluorine.

3. According to the invention, inorganic acid is added into the fluorine-precipitated liquid, so that on one hand, excessive sodium hydroxide in the fluorine-precipitated liquid can be neutralized and converted into sodium salt for recycling; on the other hand, the pH value of the solution can be adjusted to be between 6.5 and 7.5, the aluminum component in the leaching solution is recovered, the obtained aluminum hydroxide is used for preparing the polyaluminium hydroxide, and the polyaluminium hydroxide is used as a coagulant for deep defluorination, so that the aim of treating wastes with processes of wastes against one another is achieved, and the operation cost of enterprises is reduced.

4. The prepared polymeric aluminum contains excessive aluminum hydroxide, and is added into the aluminum-removed liquid, fluorine ions and oligomer aluminum salt generate aluminum fluorine complex, and the complex is swept down by aluminum hydroxide colloid generated by hydrolysis of the aluminum ions and the excessive aluminum hydroxide colloid, so that the fluorine ions are removed. The fluorine concentration in the aluminum-removed liquid can be reduced from 40-50mg/L to 0.8-1.5mg/L by adsorption and condensation for fluorine removal, and meanwhile, solid suspended matters in the leachate are also removed; excessive calcium ions generated in the fluorine precipitation process are adsorbed by adopting cation adsorption resin, the water quality is softened, and the calcium ion concentration of the filtered water can be reduced to below 1mg/L or even not detected. According to the invention, the leachate is subjected to deep defluorination and decalcification, so that the purity of sodium salt in the leachate is further improved, and the recycling of sodium salt and the improvement of the additional value of the sodium salt are facilitated.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to preferred embodiments. It should be noted, however, that the numerous details set forth in the description are merely for the purpose of providing the reader with a thorough understanding of one or more aspects of the present invention, which may be practiced without these specific details.

Example 1

A process for purifying and recovering salt in wet leachate of overhaul residues comprises the following treatment steps:

(1) fluorine deposition: adding calcium sulfate with the molar weight of fluoride ions of the leaching solution being 1.2 times that of the leaching solution into the leaching solution of the water leaching and alkali leaching treatment overhaul residues, carrying out fluorine precipitation reaction, carrying out solid-liquid separation to obtain a calcium fluoride mixed precipitate and a fluorine precipitation solution, and drying the calcium fluoride mixed precipitate to obtain a crude calcium fluoride product;

(2) neutralizing the leachate and recovering aluminum components: adding sulfuric acid into the fluorine-precipitated liquid obtained in the step (1), adjusting the pH to 7.0 to enable aluminum components in the fluorine-precipitated liquid to generate an aluminum hydroxide mixed suspension, and performing solid-liquid separation to obtain an aluminum hydroxide colloid and a liquid after aluminum removal;

(3) preparation of polyaluminium sulfate: adding sulfuric acid with 0.25 time of molar weight of aluminum hydroxide into the aluminum hydroxide colloid obtained in the step (2), adding water for reaction at the reaction temperature of 150 ℃, the reaction pressure of 4MPa and the reaction time of 4 hours, and curing, filtering and drying to obtain polyaluminum sulfate;

(4) deeply removing fluorine and suspended matters: adding the polyaluminum sulfate prepared in the step (3) into the liquid after aluminum removal obtained in the step (2), wherein the adding amount of the polyaluminum sulfate is 250 times of the concentration of fluorine ions in the liquid after aluminum removal, the polyaluminum sulfate is used as a coagulant for adsorption, coagulation and deep fluorine removal, suspended matters in the leachate are removed, and a deep fluorine removal clear liquid is obtained through solid-liquid separation;

(5) adsorption and calcium removal: adding cation exchange resin into the deep defluorination clear solution obtained in the step (4) to adsorb impurities such as calcium ions and the like, softening water, carrying out solid-liquid separation, and obtaining high-purity sodium sulfate clear solution from a liquid phase;

(6) and (3) recovering sodium salt: and (5) treating the high-purity sodium sulfate clear liquid in the step (5) by using a freezing and crystallizing system, carrying out variable temperature crystallization, controlling the temperature of the freezing and crystallizing to be 0 ℃, filtering the low-temperature magma to obtain sodium sulfate decahydrate crystals, returning the filtrate to the overhaul residue leaching process for recycling, and drying the sodium sulfate decahydrate crystals to obtain sodium sulfate refined salt.

Example 2

A process for purifying and recovering salt in wet leachate of overhaul residues comprises the following treatment steps:

(1) fluorine deposition: adding calcium chloride with the molar weight of fluoride ions of the leaching solution being 1.0 time that of the leaching solution into the leaching solution of the water leaching and alkali leaching treatment overhaul residues, carrying out fluorine precipitation reaction, carrying out solid-liquid separation to obtain a calcium fluoride mixed precipitate and a fluorine precipitation solution, and drying the calcium fluoride mixed precipitate to obtain a crude calcium fluoride product;

(2) neutralizing the leachate and recovering aluminum components: adding hydrochloric acid into the fluorine-precipitated liquid obtained in the step (1), adjusting the pH to 6.5 to enable aluminum components in the fluorine-precipitated liquid to generate an aluminum hydroxide mixed suspension, and performing solid-liquid separation to obtain an aluminum hydroxide colloid and a liquid after aluminum removal;

(3) preparing polyaluminum chloride: adding hydrochloric acid with the molar weight 0.2 time that of aluminum hydroxide into the aluminum hydroxide colloid obtained in the step (2), adding water for reaction at the reaction temperature of 100 ℃, the reaction pressure of 3MPa and the reaction time of 5 hours, curing, filtering and drying to obtain polyaluminum chloride;

(4) deeply removing fluorine and suspended matters: adding the polyaluminum chloride prepared in the step (3) into the liquid after aluminum removal obtained in the step (2), wherein the adding amount of the polyaluminum chloride is 200 times of the concentration of fluorine ions in the liquid after aluminum removal, the polyaluminum chloride is used as a coagulant for adsorption, coagulation and deep fluorine removal, suspended matters in the leachate are removed, and a deep fluorine removal clear liquid is obtained through solid-liquid separation;

(5) adsorption and calcium removal: adding cation exchange resin into the deep defluorination clear solution obtained in the step (4) to adsorb impurities such as calcium ions and the like, softening water quality, carrying out solid-liquid separation, and obtaining high-purity sodium chloride clear solution from a liquid phase;

(6) and (3) recovering sodium salt: and (5) evaporating and crystallizing the high-purity sodium chloride clear liquid in the step (5) through an evaporation system to obtain sodium chloride crystals, returning evaporation condensate water to the overhaul residue leaching process for recycling, and drying the sodium chloride crystals to obtain sodium chloride refined salt.

Example 3

A process for purifying and recovering salt in wet leachate of overhaul residues comprises the following treatment steps:

(1) fluorine deposition: adding calcium sulfate with the molar weight of fluoride ions of the leaching solution being 0.6 times that of the leaching solution into the leaching solution of the water leaching and alkali leaching treatment overhaul residues, carrying out fluorine precipitation reaction, carrying out solid-liquid separation to obtain a calcium fluoride mixed precipitate and a fluorine precipitation solution, and drying the calcium fluoride mixed precipitate to obtain a crude calcium fluoride product;

(2) neutralizing the leachate and recovering aluminum components: adding sulfuric acid into the fluorine-precipitated liquid obtained in the step (1), adjusting the pH to 7.5 to enable aluminum components in the fluorine-precipitated liquid to generate an aluminum hydroxide mixed suspension, and performing solid-liquid separation to obtain an aluminum hydroxide colloid and a liquid after aluminum removal;

(3) preparation of polyaluminium sulfate: adding sulfuric acid with 0.22 time of molar weight of aluminum hydroxide into the aluminum hydroxide colloid obtained in the step (2), adding water for reaction at the reaction temperature of 140 ℃, the reaction pressure of 3.5MPa and the reaction time of 2 hours, and curing, filtering and drying to obtain polyaluminum sulfate;

(4) deeply removing fluorine and suspended matters: adding the polyaluminum sulfate prepared in the step (3) into the liquid after aluminum removal obtained in the step (2), wherein the adding amount of the polyaluminum sulfate is 50 times of the concentration of fluorine ions in the liquid after aluminum removal, the polyaluminum sulfate is used as a coagulant for adsorption, coagulation and deep fluorine removal, suspended matters in the leachate are removed, and a deep fluorine removal clear liquid is obtained through solid-liquid separation;

(5) adsorption and calcium removal: adding cation exchange resin into the deep defluorination clear solution obtained in the step (4) to adsorb impurities such as calcium ions and the like, softening water, carrying out solid-liquid separation, and obtaining high-purity sodium sulfate clear solution from a liquid phase;

(6) and (3) recovering sodium salt: and (5) treating the high-purity sodium sulfate clear liquid in the step (5) by using a freezing and crystallizing system, carrying out variable temperature crystallization, controlling the temperature of the freezing and crystallizing at 0 ℃, filtering the low-temperature crystal mush to obtain sodium sulfate decahydrate crystals, returning the filtrate to the overhaul residue leaching process for recycling, and drying the sodium sulfate decahydrate crystals to obtain sodium sulfate refined salt.

Comparative example 1

A wet-process leaching wastewater treatment and salt purification recovery process for overhaul residues comprises the following treatment steps:

the difference from the example 1 is that the steps of preparing polyaluminium sulfate, deeply removing fluorine and removing suspended matters are not carried out, and fluorine is precipitated through the step (1) under the same conditions as other steps in the example 1; (2) neutralizing the leachate and recovering aluminum components; (3) adsorbing and removing calcium; (4) and recovering the sodium salt to finally obtain the sodium sulfate.

The applicant carried out purity tests on the products obtained by recovering sodium salts in step (6) of examples 1 to 3 and step (4) of comparative example 1 by treating the same batch of overhaul residue leachate by the methods of examples 1 to 3 and comparative example 1, respectively, and the results are shown in table 1.

TABLE 1 index of purity of product obtained in each example

From the above results, it can be seen that the sodium salt content obtained in examples 1-3 is 96.19% on average, which exceeds the sodium salt content obtained in comparative example 1 by more than 10%, wherein the sodium sulfate content of the refined sodium sulfate product obtained in example 1 is 98.39%, which meets the first class II standard of anhydrous sodium sulfate in GB/T6009-2014 industry; the sodium chloride content of the sodium chloride refined salt product obtained in the embodiment 2 reaches 97.82 percent, and meets the secondary standard of industrial dry salt in the national standard of GBT 5462-2016 industrial salt; the sodium sulfate content of the sodium sulfate refined salt product obtained in the embodiment 3 reaches 92.37%, and meets the III-type standard (the sodium sulfate is more than or equal to 92.0%) in the anhydrous sodium sulfate in GB/T6009-2014 industry, and is higher than the sodium sulfate content of the sodium sulfate salt product obtained in the comparative example 1, so that the purity of the salt recovered from the overhaul residue leachate is further improved.

Compared with the example 1, the sodium sulfate product obtained in the comparative example 1 has a lower sodium sulfate content than the example 1 and cannot meet the international GBT 5462-.

Therefore, by adopting the overhaul slag leachate treatment and salt purification and recovery process, the aluminum hydroxide is obtained by fluorine precipitation, leachate neutralization and aluminum component recovery in the overhaul slag leachate, the polyaluminium prepared from the obtained aluminum hydroxide is used as a coagulant for deep fluorine removal, and then calcium removal and sodium salt recovery are carried out through adsorption, so that the treatment of waste by waste is realized.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications can be made without departing from the principle of the present invention, and these modifications should also be construed as the protection scope of the present invention.