A method for synchronous de-cyanation and lithium extraction from overhaul slag

Abstract

The present invention provides a method for synchronous de-cyanation and lithium extraction from overhaul slag, belonging to the technical field of waste resource utilization. This method first mixes the overhaul slag evenly with an oxidant and a reconstruction agent, and then mixes it with water to obtain a mineral-phase reconstructed slurry; the mineral-phase reconstructed slurry is mixed with sulfuric acid, and after leaching and separation, a leaching solution and a filter cake are obtained; the filter cake is mixed with water, and after solid-liquid separation, a washing solution and a leaching residue are obtained; potassium sulfate is added to the leaching solution, and after reaction and solid-liquid separation, potassium alum crystals and an aluminum-removed solution are obtained; lime milk is added to the aluminum-removed solution, and after solid-liquid separation, a purified solution and neutralization slag 1 are obtained; trisodium phosphate is added to the purified solution, and after solid-liquid separation, a crude lithium phosphate product and wastewater are obtained; the crude lithium phosphate product is washed with deionized water and dried to obtain a lithium phosphate product; lime milk is added to the wastewater, and after solid-liquid separation, purified wastewater and neutralization slag 2 are obtained. This method has a short process flow, low cost, good lithium recovery effect, and high comprehensive resource utilization rate.

Description

Technical Field

[0001] The present invention relates to the technical field of waste resource utilization, and particularly to a method for synchronous de-cyanation and lithium extraction from overhaul slag. Background Art

[0002] A large amount of waste slag is generated in the aluminum electrolysis industry every year. The waste slag includes waste cathodes, electrolytes, cell lining, refractory bricks, carbon slag, etc., and their mixture is called overhaul slag. Since the raw material alumina used in aluminum electrolysis contains trace amounts of lithium elements, and a certain amount of lithium electrolyte needs to be added during the aluminum electrolysis production process, the introduced lithium elements gradually accumulate, resulting in the aluminum electrolysis waste slag containing lithium elements. Usually, the lithium content in the overhaul slag is between 0.2% and 2.5%, which has a high separation and recovery value.

[0003] Overhaul slag is highly poisonous due to the presence of harmful impurities such as cyanide and belongs to hazardous waste. At present, the process for de-cyanation and harmless treatment of overhaul slag is relatively mature. After the overhaul slag is treated harmlessly, it is usually used as a raw material for cement or bricks, and the valuable elements such as lithium, aluminum, fluorine, and silicon in it have not been effectively utilized for resource recovery. Therefore, it is of great significance to synchronously de-cyanate and extract lithium from overhaul slag and comprehensively recover valuable metals.

[0004] The prior application CN105293536 A discloses a method for extracting lithium from aluminum electrolysis waste slag. The lithium-containing aluminum electrolysis waste slag is leached with concentrated sulfuric acid and then water and filtered. The filtrate is added with sodium carbonate for alkali hydrolysis reaction. The filter residue of the alkali hydrolysis reaction is added with water and lime for causticization reaction. CO2 is introduced into the filtrate of the causticization reaction for carbonization reaction to obtain battery-grade lithium carbonate.

[0005] The prior application CN109179457A discloses a method for extracting lithium from aluminum electrolysis waste slag. The aluminum electrolysis waste slag is reacted with concentrated sulfuric acid, then water is added and filtered. Calcium oxide is added to the filtrate and then filtered. The further obtained filtrate is heated and evaporated to concentrate. Saturated sodium carbonate solution is added to the concentrated filtrate to obtain a suspension. The suspension is filtered and dried to obtain a lithium carbonate product.

[0006] The prior application CN116005006A discloses a method for extracting lithium from aluminum electrolysis waste slag and its application. The aluminum electrolysis waste slag is dried, ground, and impurity-removed, and then reacted with calcium carbonate, water, and concentrated sulfuric acid. The leachate is separated; calcium oxide is added, and the filtrate is separated; the filtrate is cooled and crystallized, separated and concentrated to obtain a concentrated solution; sodium carbonate and a flocculant are added to the concentrated solution, stirred and allowed to stand for separation to obtain a lithium sulfate solution; sodium carbonate solution is added to the lithium sulfate solution for reaction and then separated to obtain crude lithium carbonate and mother liquor. The mother liquor and the above filtrate are cooled and crystallized together, separated and concentrated to obtain the above concentrated solution; the obtained crude lithium carbonate is washed, dried, and crushed to obtain battery-grade lithium carbonate.

[0007] The prior application CN115216645A discloses a method for extracting lithium from electrolytic aluminum waste residue by mixed salt calcination method. Using electrolytic aluminum waste residue as raw material and potassium and calcium salts as auxiliary materials, through the mixed salt calcination method, industrial lithium hydroxide and lithium carbonate are extracted and separated.

[0008] The prior application CN116081658A discloses a purification method for preparing industrial-grade lithium carbonate from electrolytic waste residue. The electrolytic aluminum waste residue is added to a crusher for crushing to obtain fine powder. The fine powder is mixed evenly with sodium carbonate and then calcined. The calcined fine powder is stirred and leached with an alkaline solution to obtain a leachate; an adsorbent is added to the leachate to obtain a saturated adsorbent. The saturated adsorbent is added to an aqueous hydrochloric acid solution, filtered, and an aqueous sodium carbonate solution is added to the filtrate, and heated and stirred to obtain industrial-grade lithium carbonate.

[0009] The prior application CN115652097A discloses a method for resource utilization of electrolytic aluminum waste-containing electrolyte. Mineral acid and aluminum-containing inorganic compound are added to the waste-containing electrolyte, filtered, washed, and the filter residue is dried to obtain regenerated cryolite electrolyte. The washing water and the filtrate are mixed; after evaporation and concentration, filtration is carried out, and the filter residue is dried to obtain industrial sodium salt, and the filtrate is a concentrated salt solution; sodium carbonate is added to the concentrated salt solution, and after reaction, filtration is carried out at room temperature, and the filter residue is dried to obtain industrial lithium carbonate.

[0010] It can be seen that the above-mentioned prior technologies all consider how to obtain lithium carbonate in the utilization of electrolytic aluminum slag, and completely do not mention the treatment problem of cyanide in electrolytic aluminum slag. Moreover, from the disclosed content, except for the mixed salt calcination method in CN115216645A, the other methods are roughly similar, with a low lithium recovery rate, and do not consider the recovery problem of other valuable metals, and the resource recovery is not thorough.

[0011] In summary, the existing technologies for extracting lithium from overhaul slag mainly first carry out harmless treatment and then extract lithium, which have the characteristics of long process flow, high cost, poor lithium recovery effect, and uncomprehensive utilization of resources. Summary of the Invention

[0012] The present invention provides a method for synchronous cyanide removal and lithium extraction from overhaul slag. This method has a short process flow, low cost, good lithium recovery effect, and high resource comprehensive utilization rate.

[0013] To achieve the above-mentioned invention purpose, the technical solution provided by the present invention is as follows:

[0014] A method for synchronous cyanide removal and lithium extraction from overhaul slag, comprising the following steps:

[0015] S1. Mix the overhaul slag evenly with an oxidant and a reconstructing agent to obtain the overhaul slag to be treated;

[0016] S2. Mix the to-be-treated overhaul slag obtained in step S1 with water. After the stirring reaction is completed, a mineral phase reconstructed slurry is obtained.

[0017] S3. Mix the mineral phase reconstructed slurry obtained in step S2 with sulfuric acid, stir for leaching, and after solid-liquid separation, a leachate and a filter cake are obtained.

[0018] S4. Mix the filter cake obtained in step S3 with water at a mass ratio of 1:1 evenly, stir at room temperature for 1-2 h, and after solid-liquid separation, a washing liquid and a leaching residue are obtained; the washing liquid is returned to step S2 for water reuse, and the leaching residue is sold to a cement plant for use.

[0019] S5. Add potassium sulfate to the leachate obtained in step S3, stir at 60-90 °C for 1-2 h, then cool down to 0-10 °C for crystallization. After solid-liquid separation, potassium alum crystals and aluminum-removed liquid are obtained.

[0020] S6. Add lime to the aluminum-removed liquid obtained in step S5, adjust the pH to 10-11, and after solid-liquid separation, a purified solution and a neutralization residue 1 are obtained; the neutralization residue 1 is sold to a cement plant and a brick factory as building material raw materials for use.

[0021] S7. Add trisodium phosphate to the purified solution obtained in step S6, stir, precipitate, and after solid-liquid separation, a crude lithium phosphate product and wastewater are obtained.

[0022] S8. Wash the crude lithium phosphate product obtained in step S7 with deionized water, perform solid-liquid separation, and after gradient drying, a lithium phosphate product is obtained.

[0023] S9. Add lime to the wastewater obtained in step S7, adjust the pH = 9-10, stir at room temperature for 1-2 h, and after solid-liquid separation, purified wastewater and a neutralization residue 2 are obtained; the purified wastewater is returned to step S2 for water reuse; the neutralization residue 2 is sold to a cement plant and a brick factory as building material raw materials for use.

[0024] The lithium grade of the overhaul slag in step S1 is ≥0.2%, and the particle size -0.10 mm accounts for 100%.

[0025] The oxidant in step S1 is one or more of sodium m-nitrobenzenesulfonate, sodium percarbonate, sodium peroxide, hydrogen peroxide, sodium hypochlorite, calcium hypochlorite, and ozone.

[0026] The reconstructing agent is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide.

[0027] The mass ratio of the overhaul slag, the oxidant, and the reconstructing agent is 1:(1-3):(1-3).

[0028] In the step S2, the mass ratio of the overhaul slag to be treated to water is 1:(1 - 3), the reaction temperature is 80 - 98°C, and the reaction time is 3 - 6 h.

[0029] In the step S3, the mass concentration of sulfuric acid is 50 - 98%, the addition amount of sulfuric acid is 30 - 50% of the mass of the ore phase reconstruction pulp, the leaching reaction temperature is 80 - 98°C, and the stirring time is 3 - 6 h.

[0030] In the step S5, the addition amount of potassium sulfate ensures that the molar ratio of potassium ions to aluminum ions is 1:(0.5 - 1).

[0031] In the step S5, it is replaced by adding lime to the leaching solution obtained in the step S3, stirring evenly, adjusting the pH to 5 - 5.5, and after solid-liquid separation, aluminum hydroxide and the solution after aluminum removal are obtained.

[0032] In the step S7, the molar ratio of lithium ions to phosphate radicals of trisodium phosphate in the purification solution is 1:(0.3 - 1), the precipitation temperature is 80 - 98°C, and the stirring time is 1 - 4 h.

[0033] In the step S8, the mass ratio of the crude lithium phosphate product to deionized water is 1:1, the washing temperature is 80 - 98°C, and drying is carried out in three gradients, with the temperatures being 60°C, 85°C, and 110°C respectively, and the drying time for each time is 1 h.

[0034] The above technical solution has at least the following beneficial effects compared with the prior art:

[0035] (1) In the present invention, by adding an oxidizing agent and a reconstructing agent to the overhaul slag, on the one hand, the oxidizing agent can oxidize and decompose cyanide radicals, and on the other hand, the reconstructing agent can convert lithium that is insoluble in acid in the overhaul slag into lithium that is soluble in acid, thereby simultaneously realizing the harmless treatment of the overhaul slag and the ore phase reconstruction of lithium, and having the characteristic of a short process flow.

[0036] (2) In the present invention, the transformed overhaul slag is subjected to sulfuric acid leaching, and the pH of sulfuric acid is controlled at 2 - 3, which can ensure the efficient leaching of lithium, and at the same time, the molecular structure of the original cryolite and other ore phases is damaged as little as possible, realizing the efficient leaching of lithium; after the lithium leaching solution is purified and enriched, by adding trisodium phosphate, lithium is recovered in the form of lithium phosphate, realizing the efficient precipitation of lithium, and having the characteristic of good lithium recovery effect.

[0037] (3) In the present invention, when adding a reconstructing agent to the overhaul slag, on the one hand, calcium hydroxide can destroy the structure of lithium under strong alkaline conditions, making lithium easy to recover, and on the other hand, the excess calcium ions can form calcium fluoride precipitation with fluoride ions, and the components in the leaching residue are mainly calcium fluoride and calcium sulfate, which can be sold as cement raw materials; the aluminum in the leaching solution is recovered in the form of potassium alum or aluminum hydroxide through low-temperature crystallization or hydrolysis for aluminum recovery, and has the characteristic of high comprehensive resource utilization rate.

[0038] (4) Through processes such as synchronous harmless treatment and mineral phase reconstruction, sulfuric acid leaching, comprehensive aluminum recovery, neutralization for impurity removal, and chemical precipitation, the present invention can achieve efficient lithium recovery and comprehensive utilization of resources such as fluorine and aluminum. Lithium is recovered in the form of lithium phosphate, and the purity of the lithium phosphate product reaches over 98%, and the lithium recovery rate reaches over 90%.

[0039] Therefore, the present invention has the characteristics of short process flow, low cost, good lithium recovery effect, and high comprehensive resource utilization rate. Specific Embodiments

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, rather than all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the described embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0041] The present invention provides a method for synchronous cyanide removal and lithium extraction from overhaul slag.

[0042] The method includes the following steps:

[0043] S1. Mix the overhaul slag evenly with an oxidant and a reconstructing agent to obtain the overhaul slag to be treated;

[0044] S2. Mix the overhaul slag to be treated obtained in step S1 with water, and after stirring and reacting, obtain a mineral phase reconstructed pulp;

[0045] S3. Mix the mineral phase reconstructed pulp obtained in step S2 with sulfuric acid, stir and leach, and after solid-liquid separation, obtain a leachate and a filter cake;

[0046] S4. Mix the filter cake obtained in step S3 with water at a mass ratio of 1:1 evenly, stir at room temperature for 1 - 2 h, and after solid-liquid separation, obtain a washing liquid and a leaching residue; the washing liquid is returned to step S2 for reuse as water, and the leaching residue is sold to a cement plant for use;

[0047] S5. Add potassium sulfate to the leachate obtained in step S3, stir at 60 - 90 °C for 1 - 2 h, then cool down to 0 - 10 °C for crystallization, and after solid-liquid separation, obtain potassium alum crystals and an aluminum-removed liquid;

[0048] S6. Add lime to the aluminum-removed liquid obtained in step S5, adjust the pH to 10 - 11, and after solid-liquid separation, obtain a purified solution and a neutralization residue 1;

[0049] S7. Add trisodium phosphate to the purified solution obtained in step S6, stir, precipitate, and after solid-liquid separation, obtain crude lithium phosphate product and wastewater;

[0050] S8. Wash the crude lithium phosphate product obtained in step S7 with deionized water, perform solid-liquid separation, and after gradient drying, obtain lithium phosphate product;

[0051] S9. Add lime to the wastewater obtained in step S7, adjust the pH to 9 - 10, stir at room temperature for 1 - 2 h, and after solid-liquid separation, obtain purified wastewater and neutralization residue 2; the purified wastewater is returned to step S2 for water reuse.

[0052] Example 1

[0053] For the overhaul slag generated by an aluminum electrolysis plant with a lithium grade of 0.25%, synchronous cyanide removal and lithium extraction are achieved according to the following steps.

[0054] S1. Grind the overhaul slag to 100% of -0.10 mm, and mix it evenly with an oxidant (sodium peroxide) and a reconstructing agent (sodium hydroxide) in a mass ratio of 1:1:1 to obtain the overhaul slag to be treated;

[0055] S2. Mix the overhaul slag to be treated obtained in step S1 with water in a mass ratio of 1:2, stir evenly at 85°C, and after reacting for 4 h, obtain a mineral phase reconstructed pulp;

[0056] S3. Mix the mineral phase reconstructed pulp obtained in step S2 with sulfuric acid with a mass concentration of 80%, stir and leach at 85°C, and after stirring for 4 h, perform solid-liquid separation to obtain a leaching solution and a filter cake;

[0057] S4. Mix the filter cake obtained in step S3 with water in a mass ratio of 1:1 evenly, stir at room temperature for 2 h, and after solid-liquid separation, obtain a washing solution and a leaching residue; the washing solution is returned to step S2 for water reuse, and the leaching residue is sold to a cement plant for use;

[0058] S5. Add potassium sulfate to the leaching solution obtained in step S3, stir at 80°C for 1 h, then cool down to 5°C, crystallize, and after solid-liquid separation, obtain potassium alum crystals and aluminum-removed solution;

[0059] S6. Add lime to the aluminum-removed solution obtained in step S5, adjust the pH to 10, and after solid-liquid separation, obtain a purified solution and neutralization residue 1;

[0060] S7. Add trisodium phosphate to the purified solution obtained in step S6, ensure that the molar ratio of lithium ions to phosphate radicals of trisodium phosphate in the purified solution is 1:0.3, stir at 85°C for 2 h, then precipitate, and perform solid-liquid separation to obtain crude lithium phosphate product and wastewater;

[0061] S8. Add deionized water to the crude lithium phosphate obtained in step S7 at a mass ratio of 1:1 and wash it at 85°C. After solid-liquid separation, dry it at 60°C, 85°C, and 110°C for 1 hour respectively to obtain lithium phosphate products.

[0062] S9. Add lime to the wastewater obtained in step S7, adjust the pH to 9, stir at room temperature for 1 hour, and after solid-liquid separation, obtain purified wastewater and neutralization residue 2; the purified wastewater is returned to step S2 for water reuse.

[0063] The purity of the lithium phosphate product obtained according to the above steps is 98.5%, and the lithium recovery rate reaches 95%.

[0064] Example 2

[0065] For the overhaul slag generated by an electrolytic aluminum plant with a lithium grade of 0.23%, synchronous de-cyanation and lithium extraction are achieved according to the following steps.

[0066] S1. After grinding the overhaul slag to 100% of -0.10mm, mix it evenly with an oxidant (hydrogen peroxide) and a reconstructing agent (sodium hydroxide) at a mass ratio of 1:1:2 to obtain the overhaul slag to be treated.

[0067] S2. Mix the overhaul slag to be treated obtained in step S1 with water at a mass ratio of 1:3, stir evenly at 90°C, and after reacting for 5 hours, obtain a mineral phase reconstruction slurry.

[0068] S3. Mix the mineral phase reconstruction slurry obtained in step S2 with sulfuric acid with a mass concentration of 60%, stir and leach at 90°C, and after stirring for 5 hours, perform solid-liquid separation to obtain a leachate and a filter cake.

[0069] S4. Mix the filter cake obtained in step S3 with water at a mass ratio of 1:1 evenly, stir at room temperature for 2 hours, and after solid-liquid separation, obtain a washing solution and a leaching residue; the washing solution is returned to step S2 for water reuse, and the leaching residue is sold to a cement plant for use.

[0070] S5. Add lime to the leachate obtained in step S3, stir evenly at a constant speed, adjust the pH to 5 - 5.5, and after solid-liquid separation, obtain aluminum hydroxide and the solution after aluminum removal.

[0071] S6. Add lime to the solution after aluminum removal obtained in step S5, adjust the pH to 10, and after solid-liquid separation, obtain a purified solution and neutralization residue 1.

[0072] S7. Add trisodium phosphate to the purified solution obtained in step S6 to ensure that the molar ratio of lithium ions to phosphate radicals of trisodium phosphate in the purified solution is 1:0.5, stir at 90°C for 3 hours, then precipitate, and perform solid-liquid separation to obtain crude lithium phosphate products and wastewater.

[0073] S8. Add deionized water to the crude lithium phosphate obtained in step S7 at a mass ratio of 1:1 and wash it at 90°C. After solid-liquid separation, dry it at 60°C, 85°C, and 110°C for 1 h respectively to obtain the lithium phosphate product;

[0074] S9. Add lime to the wastewater obtained in step S7, adjust the pH to 10, stir it at room temperature for 2 h, and after solid-liquid separation, obtain purified wastewater and neutralization residue 2; the purified wastewater is returned to step S2 for water reuse.

[0075] The purity of the lithium phosphate product obtained according to the above steps is 98.8%, and the lithium recovery rate reaches 96%.

[0076] The above is only the specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. The protection scope of the present invention shall be subject to the protection scope of the claims.

Claims

1. A method for synchronous de-cyanation and lithium extraction from overhaul slag, characterized in that, It includes the following steps: S1. Mix overhaul slag evenly with an oxidant and a restructuring agent to obtain the overhaul slag to be treated; S2. Mix the overhaul slag to be treated obtained in step S1 with water, and after the stirring reaction is completed, obtain a mineral phase restructured pulp; S3. Mix the mineral phase restructured pulp obtained in step S2 with sulfuric acid, stir and leach, and after solid-liquid separation, obtain a leachate and a filter cake; S4. Mix the filter cake obtained in step S3 with water at a mass ratio of 1:1 evenly, stir at room temperature for 1-2 h, and after solid-liquid separation, obtain a washing liquid and a leaching residue; the washing liquid is returned to step S2 for water reuse, and the leaching residue is sold to a cement plant for use; S5. Add potassium sulfate to the leachate obtained in step S3, stir at 60-90 °C for 1-2 h, then cool down to 0-10 °C, crystallize, and after solid-liquid separation, obtain potassium alum crystals and aluminum-removed liquid; S6. Add lime to the aluminum-removed liquid obtained in step S5, adjust the pH to 10-11, and after solid-liquid separation, obtain a purified solution and neutralization residue 1; the neutralization residue 1 is sold to a cement plant and a brick factory as a building material raw material for use; S7. Add trisodium phosphate to the purified solution obtained in step S6, stir, precipitate, and after solid-liquid separation, obtain a crude lithium phosphate product and wastewater; S8. Wash the crude lithium phosphate product obtained in step S7 with deionized water, perform solid-liquid separation, and after stepwise drying, obtain a lithium phosphate product; S9. Add lime to the wastewater obtained in step S7, adjust the pH = 9-10, stir at room temperature for 1-2 h, and after solid-liquid separation, obtain purified wastewater and neutralization residue 2; the purified wastewater is returned to step S2 for water reuse; the neutralization residue 2 is sold to a cement plant and a brick factory as a building material raw material for use; The restructuring agent is one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide; The mass ratio of the overhaul slag, the oxidant, and the restructuring agent is 1:(1-3):(1-3); In step S2, the mass ratio of the overhaul slag to be treated to water is 1:(1-3), the reaction temperature is 80-98 °C, and the reaction time is 3-6 h; In step S3, the mass concentration of sulfuric acid is 50-98%, the addition amount of sulfuric acid is 30-50% of the mass of the mineral phase restructured pulp, the leaching reaction temperature is 80-98 °C, and the stirring time is 3-6 h.

2. The method for synchronous cyanide removal and lithium extraction from overhaul slag according to claim 1, wherein In step S1, the lithium grade of the overhaul slag is ≥0.2%, and the particle size -0.10 mm accounts for 100%.

3. The method for synchronous de-cyanation and lithium extraction from overhaul slag according to claim 1, characterized in that In step S1, the oxidant is one or more of sodium m-nitrobenzenesulfonate, sodium percarbonate, sodium peroxide, hydrogen peroxide, sodium hypochlorite, calcium hypochlorite, and ozone.

4. The method for synchronous cyanide removal and lithium extraction from overhaul slag according to claim 1, characterized in that, In step S5, the addition amount of potassium sulfate ensures that the molar ratio of potassium ions to aluminum ions is 1:(0.5-1).

5. The method for simultaneous cyanide removal and lithium extraction from overhaul slag according to claim 1, characterized in that, In step S5, it is replaced by adding lime to the leachate obtained in step S3, stirring evenly, adjusting the pH to 5-5.5, and after solid-liquid separation, obtaining aluminum hydroxide and aluminum-removed liquid.

6. The method for synchronous de-cyanation and lithium extraction from overhaul slag according to claim 1, wherein In step S7, the molar ratio of lithium ions in the purified solution to the phosphate radical of trisodium phosphate is 1:(0.3-1), the precipitation temperature is 80-98 °C, and the stirring time is 1-4 h.

7. The method for synchronous de-cyanation and lithium extraction from overhaul slag according to claim 1, characterized in that In the step S8, the mass ratio of the crude lithium phosphate product to deionized water is 1:1, the washing temperature is 80-98 °C, and drying is carried out in three gradients at temperatures of 60 °C, 85 °C and 110 °C respectively, with each drying time being 1 h.