A method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps

Abstract

The present invention provides a method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps, and belongs to the technical field of waste resource utilization. The method firstly mixes the rare earth molten salt electrolytic slag with lime evenly, and then mixes it with water to obtain slurry; the slurry is mixed with sulfuric acid, and after solid-liquid separation, a leachate 1 and a leachate slag are obtained; lime is added to the leachate 1 for neutralization and impurity removal, and after solid-liquid separation, neutralized slag and purified liquid are obtained; trisodium phosphate is added to the purified liquid, and after solid-liquid separation, lithium phosphate crystals and lithium precipitation mother liquor are obtained; sulfuric acid is added to the leachate slag, and after solid-liquid separation, a leachate 2 is obtained; oxalic acid is added to the leachate 2, and after solid-liquid separation, oxalate rare earth and rare earth precipitation waste liquid are obtained. The method has a short process flow, low energy consumption, good lithium and rare earth recovery effect, and high comprehensive resource utilization rate.

Description

Technical Field

[0001] The invention relates to the technical field of waste resource utilization, and in particular to a method for extracting lithium and rare earth in steps from rare earth molten salt electrolytic slag. Background Art

[0002] In my country, rare earth metals are usually produced by electrolysis of rare earth fluoride molten salt system. Rare earth molten salt electrolytic slag is produced during high-temperature electrolytic volatilization, metal removal, anode replacement, furnace cleaning and dismantling. At present, the rare earth yield in the rare earth molten salt electrolysis process is only 95%, so the rare earth content in the rare earth molten salt electrolytic slag is usually 20-80%. In order to improve the melting point, conductivity, solubility and other properties of the electrolyte, a certain amount of lithium fluoride is added. Therefore, the rare earth molten salt electrolytic slag contains lithium elements. Under normal circumstances, the lithium content in the rare earth molten salt electrolytic slag is 0.8-2.5%, which has a high separation and recovery value.

[0003] At present, the treatment process for recovering rare earths from rare earth molten salt electrolysis slag is relatively mature. After the rare earth molten salt electrolysis slag is treated by physical method, acid method, alkali method and other methods, the recovery rate of rare earths reaches more than 95%. However, previous studies usually only recover rare earths in the slag, and do not pay much attention to the lithium element in it, and lithium has not been effectively utilized as a resource. Therefore, it is of great significance to extract lithium and rare earths from rare earth molten salt electrolysis slag step by step.

[0004] CN114457238 A discloses a method for simultaneously leaching rare earth, fluorine and lithium acid leaching solution from rare earth electrolysis molten salt slag, wherein the rare earth electrolysis molten salt slag is dried, crushed and ground, mixed with aluminum sulfate 18hydrate and calcium oxide and roasted, leached with hydrochloric acid, and filtered to obtain an acid leaching solution containing rare earth, fluorine and lithium.

[0005] CN111534701 A discloses a method for efficiently recovering valuable elements from rare earth molten salt electrolytic slag, which comprises uniformly mixing the rare earth molten salt electrolytic slag with industrial lithium hydroxide monohydrate to obtain a mixture, subjecting the obtained mixture to a first stage of vacuum roasting and a second stage of vacuum distillation to obtain high-purity lithium fluoride; the distillation slag obtained after the second stage of vacuum distillation is acid-leached with hydrochloric acid, and filtered to obtain a rare earth liquid for further recovery of rare earths.

[0006] CN111519020 A discloses a method for recovering valuable elements from rare earth electrolysis molten salt slag, which comprises mixing the rare earth electrolysis molten salt slag with lithium carbonate and then calcining the mixture to obtain calcined slag, vacuum distilling the calcined slag to collect lithium fluoride condensate and distillation slag, acid-leaching the distillation slag with hydrochloric acid, and filtering the resulting liquid material to obtain rare earth liquid.

[0007] CN116904750 A discloses a method for stepwise recovery of lithium and rare earth from rare earth molten salt electrolytic slag, which comprises leaching the rare earth molten salt electrolytic slag with sulfuric acid to obtain a lithium-containing solution and leached slag, wherein the lithium-containing solution can be used as a raw material for preparing lithium carbonate; the leached slag is mixed with alkali and activated carbon and then subjected to low-temperature roasting and transformation, the roasted product is leached with water to obtain water-leached slag and a fluorine-containing solution, and a reducing agent is added to the water-leached slag for acid leaching to obtain a rare earth leaching solution.

[0008] CN115959688 A discloses a method for recycling rare earth molten salt slag to prepare high-quality lithium salt, wherein the rare earth molten salt slag is ball-milled and sieved, and then reacted with water and concentrated sulfuric acid under heating conditions to obtain lithium-containing acid leaching solution and acid leaching slag, and the escaped hydrogen fluoride gas is treated with lithium hydroxide solution to finally obtain industrial-grade lithium fluoride. The pH of the lithium-containing acid leaching solution is adjusted twice with a compound containing calcium or magnesium and filtered to obtain a neutral lithium solution, and the pH of the neutral lithium solution is further adjusted with an inorganic base, and the lithium-containing purified solution obtained after filtration is heated and concentrated, and the concentrated lithium-containing concentrated solution is mixed with a sodium carbonate solution to react to obtain battery-grade lithium carbonate.

[0009] CN111593206 A discloses a method for extracting valuable metals from rare earth secondary resources, which comprises placing rare earth molten salt electrolytic slag of a fluoride salt system in a hydrochloric acid solution for leaching and filtering, adding hydrogen peroxide and sodium hydroxide to the filtrate for pretreatment and filtering again, evaporating the filtrate obtained after the pretreatment, slowly adding the evaporated supernatant to a hot sodium carbonate solution for reaction, filtering after the reaction to obtain a filter cake, and drying the filter cake to obtain lithium carbonate solid.

[0010] According to the disclosed content, in the above-mentioned prior art for recycling rare earth molten salt electrolytic slag, the method of directly subjecting the rare earth molten salt electrolytic slag to acid leaching has a low lithium recovery rate; except for CN114457238 A, the method of mixing the rare earth molten salt electrolytic slag with auxiliary materials and then roasting it mainly focuses on how to recover rare earth and fluorine elements, and the recovery of lithium is not taken seriously, and CN114457238 A does not separate the rare earth and lithium elements.

[0011] In summary, the existing technologies for extracting lithium and rare earths from rare earth molten salt electrolytic slag are mainly acid dissolution-lithium precipitation or roasting-distillation lithium extraction, which have the disadvantages of long process flow, high energy consumption, poor lithium recovery effect, and lack of comprehensive utilization of resources. Summary of the invention

[0012] The present invention provides a method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps. The method has a short process flow, low energy consumption, good lithium and rare earth recovery effect, and high comprehensive resource utilization rate.

[0013] In order to solve the above-mentioned invention object, the technical solution provided by the present invention is as follows:

[0014] A method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps, comprising the following steps:

[0015] S1, mixing rare earth molten salt electrolytic slag and lime evenly to obtain rare earth molten salt electrolytic slag to be treated;

[0016] S2, mixing the rare earth molten salt electrolytic slag to be treated obtained in step S1 with water, and stirring to obtain slurry after the reaction is completed;

[0017] S3, mixing the slurry obtained in step S2 with sulfuric acid, stirring and leaching, and obtaining leachate 1 and leach residue after solid-liquid separation;

[0018] S4, adding lime to the leachate 1 obtained in step S3, adjusting the pH to 10-11 to neutralize and remove impurities, and obtaining purified liquid and neutralized slag after solid-liquid separation;

[0019] S5, adding trisodium phosphate to the purified liquid obtained in step S4, stirring at 60-90° C. for 1-2 hours, precipitating, and obtaining a crude lithium phosphate product and a lithium precipitation mother liquor after solid-liquid separation; the lithium precipitation mother liquor is returned to S2 for reuse as water;

[0020] S6, washing the crude lithium phosphate product obtained in step S5 with deionized water, separating the solid and the liquid, and drying to obtain a lithium phosphate product;

[0021] S7, adding sulfuric acid to the leached residue obtained in step S3, stirring and leaching, and obtaining leachate 2 after solid-liquid separation;

[0022] S8. Add oxalic acid to the leachate 2 obtained in step S7, stir at 30-60° C. for 30-60 min, and obtain rare earth oxalate and rare earth precipitation wastewater after solid-liquid separation.

[0023] In the step S1, the lithium grade of the rare earth molten salt electrolytic slag is ≥0.2%, the total rare earth content is ≥0.5%, and the particle size of -0.10 mm accounts for 100%.

[0024] Optionally, in step S1, the mass ratio of lime to rare earth molten salt electrolytic slag is 1:(3-5).

[0025] Optionally, in step S2, the mass ratio of the rare earth molten salt electrolytic slag to be treated to water is 1:(1-2), the reaction is carried out at room temperature, and the reaction time is 1-3 hours.

[0026] Optionally, in step S3, the volume concentration of sulfuric acid is 3-8%, the mass ratio of slurry to sulfuric acid is 1:(3-5), leaching is carried out at room temperature, and the leaching time is 20-40 min.

[0027] Optionally, trisodium phosphate is added in step S5 to ensure that the amount of trisodium phosphate in the purified liquid is 30-50 g / L.

[0028] Optionally, in step S6, the mass ratio of the crude lithium phosphate product to deionized water is 1:1, the washing temperature is 80-98° C., the drying temperature is 60-110° C., and the drying time is 3 hours.

[0029] Optionally, in step S7, the volume concentration of sulfuric acid added to the leached residue obtained in step S3 is 15-30%, the mass ratio of leached residue to sulfuric acid is 1:(3-5), the leaching temperature is 90° C., and the leaching time is 1-2 h.

[0030] Optionally, the oxalic acid in step S8 is added to the leachate 2 in the following amount:

[0031] The mass ratio of the leached residue obtained in S3 to oxalic acid is 1:(0.6-2).

[0032] The above technical solution provided by the present invention has at least the following beneficial effects compared with the prior art:

[0033] (1) The present invention adds lime and water to the rare earth molten salt electrolytic slag. On the one hand, calcium ions can convert fluoride ions into calcium fluoride, thereby playing a role in fixing fluorine. On the other hand, lime can convert lithium fluoride in the rare earth molten salt electrolytic slag that is insoluble in acid into lithium compounds that are easily soluble in acid, thereby simultaneously achieving the harmless treatment of the rare earth molten salt electrolytic slag and the mineral phase reconstruction of lithium, and has the characteristic of a short process flow.

[0034] (2) The present invention uses dilute sulfuric acid at room temperature to leach the transformed rare earth molten salt electrolytic slag, which can ensure efficient leaching of lithium while leaching as little rare earth elements as possible; after the lithium leaching solution is purified and enriched, trisodium phosphate is added to recover the lithium in the form of lithium phosphate, thereby achieving efficient precipitation of lithium, and having the characteristics of good lithium recovery effect and low energy consumption.

[0035] (3) The present invention can achieve efficient recovery of lithium and rare earth through harmless treatment and mineral phase reconstruction, sulfuric acid leaching, neutralization and impurity removal, chemical precipitation and other processes. Lithium is recovered in the form of lithium phosphate, the purity of lithium phosphate product is more than 98.5%, and the lithium recovery rate is more than 95%. Rare earth is recovered in the form of rare earth oxalate, the purity of rare earth oxalate is more than 98%, and the rare earth recovery rate is more than 95%, which has the characteristics of high comprehensive utilization rate of resources.

[0036] Therefore, the present invention has the characteristics of short process flow, low energy consumption, good lithium recovery effect and high comprehensive resource utilization rate. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The invention provides a method for extracting lithium and rare earth in steps from rare earth molten salt electrolytic slag.

[0039] The method comprises the following steps:

[0040] S1, mixing rare earth molten salt electrolytic slag and lime evenly to obtain rare earth molten salt electrolytic slag to be treated;

[0041] S2, mixing the rare earth molten salt electrolytic slag to be treated obtained in step S1 with water, and stirring to obtain slurry after the reaction is completed;

[0042] S3, mixing the slurry obtained in step S2 with sulfuric acid, stirring and leaching, and obtaining leachate 1 and leach residue after solid-liquid separation;

[0043] S4, adding lime to the leachate 1 obtained in step S3, adjusting the pH to 10-11 to neutralize and remove impurities, and obtaining purified liquid and neutralized slag after solid-liquid separation;

[0044] S5, adding trisodium phosphate to the purified liquid obtained in step S4, stirring at 60-90°C for 1-2h, precipitating, and obtaining a crude lithium phosphate product and a lithium precipitation mother liquor after solid-liquid separation; the lithium precipitation mother liquor is returned to S2 and reused as water;

[0045] S6, washing the crude lithium phosphate product obtained in step S5 with deionized water, separating the solid and the liquid, and drying to obtain a lithium phosphate product;

[0046] S7, adding sulfuric acid to the leached residue obtained in step S3, stirring and leaching, and obtaining leachate 2 after solid-liquid separation;

[0047] S8. Add oxalic acid to the leachate 2 obtained in step S7, stir at 30-60° C. for 30-60 min, and obtain rare earth oxalate and rare earth precipitation wastewater after solid-liquid separation.

[0048] Example 1

[0049] For the rare earth molten salt electrolytic slag produced by a rare earth electrolysis plant, in which the lithium grade is 1.97%, the rare earth and lithium are extracted step by step according to the following steps.

[0050] S1, mixing rare earth molten salt electrolytic slag and lime in a mass ratio of 1:4 to obtain rare earth molten salt electrolytic slag to be treated;

[0051] S2, mixing the rare earth molten salt electrolytic slag to be treated obtained in step S1 with water in a mass ratio of 1:1, and stirring without heating for 2 hours to obtain a slurry;

[0052] S3, mixing the slurry obtained in step S2 with sulfuric acid having a volume concentration of 5% at a mass ratio of 1:4, stirring and leaching at room temperature, and obtaining leachate 1 and leach residue after solid-liquid separation;

[0053] S4, adding lime to the leachate 1 obtained in step S3, adjusting the pH to 10-11 to neutralize and remove impurities, and obtaining purified liquid and neutralized slag after solid-liquid separation;

[0054] S5, adding trisodium phosphate to the purified liquid obtained in step S4 to make its concentration 30g / L, stirring at 70°C for 2h, precipitating, and obtaining a crude lithium phosphate product and a lithium precipitation mother liquor after solid-liquid separation; the lithium precipitation mother liquor is returned to S2 and reused as water;

[0055] S6, adding deionized water at a mass ratio of 1:1 to the crude lithium phosphate product obtained in step S5, washing at 90° C., separating the solid from the liquid, and drying at 80° C. for 3 h to obtain a lithium phosphate product;

[0056] S7, adding sulfuric acid with a volume concentration of 30% to the leached residue obtained in step S3 at a mass ratio of 1:3, stirring for leaching, and obtaining leachate 2 after solid-liquid separation;

[0057] S8. Add oxalic acid to the leachate 2 obtained in step S7 (the amount of oxalic acid is: the mass ratio of oxalic acid to the leaching residue obtained in S3 is 2:1), stir for 60 minutes at 30° C., and after solid-liquid separation, obtain rare earth oxalate and rare earth precipitation wastewater.

[0058] The purity of the lithium phosphate product obtained according to the above steps is above 98.5%, and the lithium recovery rate is above 95%. The purity of the rare earth oxalate product is above 98%, and the rare earth recovery rate is above 95%.

[0059] Example 2

[0060] For the rare earth molten salt electrolytic slag produced by a rare earth electrolysis plant, in which the lithium grade is 2.63%, the rare earth and lithium are extracted step by step according to the following steps.

[0061] S1, mixing rare earth molten salt electrolytic slag and lime in a mass ratio of 1:5 to obtain rare earth molten salt electrolytic slag to be treated;

[0062] S2, mixing the rare earth molten salt electrolytic slag to be treated obtained in step S1 with water in a mass ratio of 1:2, and stirring without heating for 2.5 hours to obtain a slurry;

[0063] S3, mixing the slurry obtained in step S2 with sulfuric acid having a volume concentration of 6% at a mass ratio of 1:5, stirring and leaching at room temperature, and obtaining leachate 1 and leach residue after solid-liquid separation;

[0064] S4, adding lime to the leachate 1 obtained in step S3, adjusting the pH to 10-11 to neutralize and remove impurities, and obtaining purified liquid and neutralized slag after solid-liquid separation;

[0065] S5, adding trisodium phosphate to the purified liquid obtained in step S4 to make its concentration 45g / L, stirring at 80°C for 2h, precipitating, and obtaining a crude lithium phosphate product and a lithium precipitation mother liquor after solid-liquid separation; the lithium precipitation mother liquor is returned to S2 and reused as water;

[0066] S6, adding deionized water at a mass ratio of 1:1 to the crude lithium phosphate product obtained in step S5, washing at 90° C., separating the solid from the liquid, and drying at 85° C. for 3 h to obtain a lithium phosphate product;

[0067] S7, adding sulfuric acid with a volume concentration of 25% to the leached residue obtained in step S3 at a mass ratio of 1:4, stirring for leaching, and obtaining leachate 2 after solid-liquid separation;

[0068] S8. Add oxalic acid to the leachate 2 obtained in step S7 (the amount of oxalic acid is: the mass ratio of oxalic acid to the leaching residue obtained in S3 is 0.6:1), stir for 60 minutes at 30° C., and after solid-liquid separation, obtain rare earth oxalate and rare earth precipitation wastewater.

[0069] The purity of the lithium phosphate product obtained according to the above steps is above 98.5%, and the lithium recovery rate is above 95%. The purity of the rare earth oxalate product is above 98%, and the rare earth recovery rate is above 95%.

[0070] The above are only specific embodiments 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 based on the protection scope of the claims.

Claims

1. A method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps, characterized in that: It consists of the following steps: S1, mixing rare earth molten salt electrolytic slag and lime evenly to obtain rare earth molten salt electrolytic slag to be treated; the lithium grade of the rare earth molten salt electrolytic slag in step S1 is ≥0.2%, the total rare earth content is ≥0.5%, and the particle size of -0.10 mm accounts for 100%; S2, mixing the rare earth molten salt electrolytic slag to be treated obtained in step S1 with water, reacting at room temperature, and stirring to obtain slurry after the reaction is completed; S3, mixing the slurry obtained in step S2 with sulfuric acid, stirring and leaching, and obtaining a leachate 1 and a leached residue after solid-liquid separation; the volume concentration of sulfuric acid in step S3 is 3-8%, the mass ratio of slurry to sulfuric acid is 1:(3-5), leaching is carried out at room temperature, and the leaching time is 20-40 min; S4, adding lime to the leachate 1 obtained in step S3, adjusting the pH to 10-11 to neutralize and remove impurities, and obtaining purified liquid and neutralized slag after solid-liquid separation; S5, adding trisodium phosphate to the purified liquid obtained in step S4, stirring at 60-90° C. for 1-2 hours, precipitating, and obtaining a crude lithium phosphate product and a lithium precipitation mother liquor after solid-liquid separation; the lithium precipitation mother liquor is returned to S2 for reuse as water; S6, washing the crude lithium phosphate product obtained in step S5 with deionized water, separating the solid and the liquid, and drying to obtain a lithium phosphate product; S7, adding sulfuric acid to the leached residue obtained in step S3, stirring for leaching, and obtaining leachate 2 after solid-liquid separation; the volume concentration of sulfuric acid added to the leached residue obtained in step S3 in step S7 is 15-30%, the mass ratio of leached residue to sulfuric acid is 1: (3-5), the leaching temperature is 90° C., and the leaching time is 1-2 h; S8. Add oxalic acid to the leachate 2 obtained in step S7, stir at 30-60° C. for 30-60 min, and obtain rare earth oxalate and rare earth precipitation wastewater after solid-liquid separation.

2. The method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps according to claim 1, characterized in that: In the step S1, the mass ratio of lime to rare earth molten salt electrolytic slag is 1:(3-5).

3. The method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps according to claim 1, characterized in that: In the step S2, the mass ratio of the rare earth molten salt electrolytic slag to be treated to water is 1:(1-2), and the reaction time is 1-3 hours.

4. The method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps according to claim 1, characterized in that: In step S5, trisodium phosphate is added to ensure that the amount of trisodium phosphate in the purified liquid is 30-50 g / L.

5. The method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps according to claim 1, characterized in that: In step S6, the mass ratio of the crude lithium phosphate product to deionized water is 1:1, the washing temperature is 80-98° C., the drying temperature is 60-110° C., and the drying time is 3 hours.

6. The method for extracting lithium and rare earth from rare earth molten salt electrolytic slag in steps according to claim 1, characterized in that: The oxalic acid in step S8 is added to the leachate 2 in the following amount: The mass ratio of the leached residue obtained in S3 to oxalic acid is 1:(0.6-2).