Preparation method of lithium hydroxide

Abstract

The invention relates to a lithium hydroxide preparation method, which comprises: re-dissolving a lithium salt to obtain a lithium-containing solution; carrying out nanofiltration impurity removal on the lithium-containing solution to obtain nanofiltration produced water and nanofiltration concentrated water; carrying out post-treatment on the nanofiltration produced water to obtain mother liquor and lithium hydroxide; the mother liquor is reused for redissolution; carrying out silicon removal treatment on the nanofiltration concentrated water to obtain filtrate and filter residues; the filtrate is reused for redissolution; a silicon removal agent adopted in the silicon removal treatment comprises barium hydroxide and lanthanum cerium carbonate. According to the method, the nanofiltration concentrated water is subjected to silicon removal treatment, so that the direct recovery rate of lithium can reach 99% or above, and the waste of auxiliary materials is reduced; the production cost is reduced through the cooperation of nanofiltration treatment and the silicon removal agent, and the silicon removal agent can be recycled and regenerated, and in addition, the silicon removal agent is relatively low in cost and has a good silicon removal effect; therefore, the preparation method provided by the invention greatly reduces the preparation cost of the lithium hydroxide.

Description

Technical Field

[0001] The invention belongs to the field of compound preparation and relates to a method for preparing a lithium salt, in particular to a method for preparing lithium hydroxide. Background Art

[0002] Liquid caustic soda and strong alkalis such as lithium hydroxide are important chemical raw materials. Lithium hydroxide is an indispensable raw material in the battery field, and the requirements for it are becoming more and more stringent. Lithium hydroxide can be prepared by the traditional causticizing method. The causticizing liquid produced by this process contains silicon, which causes the lithium hydroxide produced to contain a certain amount of silicon, affecting the quality of lithium hydroxide. If it is necessary to reduce production costs and reuse the mother liquor after one or two evaporations, it is necessary to deeply remove impurities from the dissolved silicon to avoid the enrichment of silicon during the circulation process, but the removal of silicon is difficult.

[0003] CN117963951A discloses a monohydrate lithium hydroxide and a preparation method and application thereof. The process needs to consider the cost and service life of a special alkali-resistant nanofiltration membrane, so the one-time lithium yield is less than 90%, and the concentrated high-silicon concentrated water needs to be open-circuited; moreover, the treatment of the high-silicon concentrated water requires lithium precipitation and pH adjustment in sequence before it can be adsorbed and removed using conventional silicon removal resins, resulting in very high treatment costs for the high-silicon concentrated water; moreover, the high-silicon concentrated water returns to the front-end treatment, which affects the lithium production capacity of the back-end and increases the unit consumption of auxiliary materials.

[0004] Therefore, it is necessary to provide a method for removing silicon under strong alkaline conditions so that high-silicon concentrated water can be reused in a short distance during the production of lithium hydroxide to reduce production costs. Summary of the invention

[0005] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing lithium hydroxide, which can make the direct recovery rate of lithium reach more than 99%, reduce the waste of auxiliary materials, and greatly reduce the preparation cost of lithium hydroxide.

[0006] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] The present invention provides a method for preparing lithium hydroxide, which comprises the following steps:

[0008] (1) Redissolve the lithium salt to obtain a lithium-containing solution.

[0009] (2) The lithium-containing solution in step (1) is subjected to nanofiltration to remove impurities to obtain nanofiltration product water and nanofiltration concentrated water.

[0010] (3) The nanofiltration water produced in step (2) is post-treated to obtain a mother liquor and lithium hydroxide; the mother liquor is reused for the re-dissolution in step (1).

[0011] (4) The nanofiltration concentrated water of step (2) is subjected to a desiliconization treatment to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution of step (1); and the desiliconization agent used in the desiliconization treatment includes barium hydroxide and lanthanum cerium carbonate.

[0012] Step (3) and step (4) are performed in no particular order.

[0013] The present invention can achieve a direct recovery rate of lithium of more than 99% by desiliconizing the nanofiltration concentrated water, thereby reducing the waste of auxiliary materials; the combination of nanofiltration treatment and desiliconizing agent reduces the production cost, and the desiliconizing agent has a low cost and has a good desiliconizing effect; therefore, the preparation method provided by the present invention greatly reduces the preparation cost of lithium hydroxide.

[0014] Preferably, during the silicon removal treatment in step (4), the molar amount of barium hydroxide used is 0.6 to 1 times the molar amount of sulfate in the nanofiltration concentrated water.

[0015] Preferably, based on the volume of the nanofiltration concentrate, during the silicon removal treatment in step (4), the mass of lanthanum cerium carbonate added to the nanofiltration concentrate is 1 g / L-20 g / L.

[0016] Preferably, the temperature of the desiliconization treatment in step (4) is 40°C-100°C.

[0017] Preferably, the desiliconization treatment in step (4) is carried out under stirring conditions at a rotation speed of 250 rpm-500 rpm.

[0018] Preferably, the desiliconization treatment time in step (4) is more than 15 minutes.

[0019] Preferably, the filter residue in step (4) is successively subjected to acid dissolution, solid-liquid separation and alkali precipitation to recover lanthanum cerium carbonate.

[0020] Preferably, the lithium content in the lithium-containing solution in step (1) is 25 g / L-36 g / L, the Si content is ≤35 mg / L, and the SO4 2- Content ≤2g / L.

[0021] Preferably, the temperature of the lithium-containing solution in step (1) is 75°C-90°C.

[0022] Preferably, before the nanofiltration impurity removal in step (2), the lithium-containing solution is cooled to below 60° C. and then subjected to microfiltration treatment.

[0023] Preferably, the Si content in the nanofiltration water produced in step (2) is ≤10 mg / L, SO4 2- ≤0.5g / L; Si content in the nanofiltration concentrated water of step (2) ≥25mg / L, SO4 2- Content ≥0.5g / L.

[0024] Preferably, the post-treatment in step (3) includes evaporative crystallization and centrifugal separation.

[0025] Preferably, the temperature of the evaporation crystallization is 80°C-100°C.

[0026] Preferably, the preparation method of the lithium salt in step (1) comprises: subjecting a crude lithium carbonate solution to a causticizing reaction to obtain a lithium hydroxide solution and calcium carbonate slag; and concentrating the lithium hydroxide solution by evaporation to obtain a mother liquor and a lithium salt.

[0027] Preferably, the temperature of the causticization reaction is 50°C-95°C.

[0028] Preferably, the causticizing reaction time is 1h-5h.

[0029] Preferably, the causticizing reaction is carried out under stirring conditions at a rotation speed of 250 rpm-500 rpm.

[0030] Preferably, during the causticizing reaction, the molar amount of causticizing calcium is 1.05 to 1.3 times the theoretical molar amount required for complete reaction of lithium carbonate.

[0031] Preferably, the Li content in the lithium hydroxide solution is 7 g / L-12 g / L.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention can achieve a direct recovery rate of lithium of more than 99% by desiliconizing the nanofiltration concentrated water, thereby reducing the waste of auxiliary materials; the combination of nanofiltration treatment and desiliconizing agent reduces the production cost, and the desiliconizing agent has a low cost and has a good desiliconizing effect; therefore, the preparation method provided by the present invention greatly reduces the preparation cost of lithium hydroxide. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A process flow chart of the preparation method is provided for Example 1 of the present invention. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0036] A certain embodiment of the present invention provides a method for preparing lithium hydroxide, the preparation method comprising the following steps:

[0037] (1) Redissolve the lithium salt to obtain a lithium-containing solution.

[0038] (2) The lithium-containing solution in step (1) is subjected to nanofiltration to remove impurities to obtain nanofiltration product water and nanofiltration concentrated water.

[0039] (3) The nanofiltration water produced in step (2) is post-treated to obtain a mother liquor and lithium hydroxide; the mother liquor is reused for the re-dissolution in step (1).

[0040] (4) The nanofiltration concentrated water of step (2) is subjected to a desiliconization treatment to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution of step (1); and the desiliconization agent used in the desiliconization treatment includes barium hydroxide and lanthanum cerium carbonate.

[0041] Step (3) and step (4) are performed in no particular order.

[0042] Simple nanofiltration impurity removal cannot obtain a high lithium yield. The present invention removes silicon from nanofiltration concentrated water so that the strongly alkaline lithium-containing solution can be reused in a short distance, so that the direct lithium recovery rate reaches more than 99%, which greatly reduces the waste of auxiliary materials. In addition, nanofiltration impurity removal concentrates the lithium-containing solution with a low silicon content, and then uses a silicon remover to remove silicon from the nanofiltration concentrated water with a high silicon content, which makes up for the defects of high water volume, low effect and secondary chemical pollution of traditional chemical agents for low-silicon strong alkaline solutions, and greatly reduces the production cost. The price of lanthanum cerium carbonate in the silicon remover is relatively low, which also reduces the production cost of lithium hydroxide. The filtrate is reused for re-dissolution, which can also reduce the waste of auxiliary materials and reduce the production cost.

[0043] In certain embodiments, the lanthanum cerium carbonate is a lanthanum cerium carbonate complex, and the lanthanum cerium carbonate complex is a complex of lanthanum carbonate and cerium carbonate, wherein the molar ratio of lanthanum to cerium is 1:1-1:3.

[0044] In certain embodiments, during the silicon removal treatment in step (4), the molar amount of barium hydroxide used is 0.6 to 1 times the molar amount of sulfate in the nanofiltration concentrate, for example, it can be 0.6, 0.7, 0.8, 0.9 or 1 times, but is not limited to the listed values, and the remaining values ​​not listed within the numerical range are also applicable.

[0045] In certain embodiments, based on the volume of the nanofiltration concentrate, during the silicon removal treatment in step (4), the added mass of lanthanum cerium carbonate in the nanofiltration concentrate is 1 g / L-20 g / L, for example, it can be 1 g / L, 3 g / L, 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L or 20 g / L, but is not limited to the listed values, and the remaining values ​​not listed in the numerical range are also applicable.

[0046] In some embodiments, the temperature of the desiliconization treatment in step (4) is 40°C-100°C, for example, it can be 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0047] In certain embodiments, the desiliconization treatment in step (4) is carried out under stirring conditions at a rotation speed of 250rpm-500rpm, for example, 250rpm, 300rpm, 350rpm, 400rpm, 450rpm or 500rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0048] In some embodiments, the time for the silicon removal treatment in step (4) is more than 15 minutes, for example, it can be 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 80 minutes or 100 minutes, but is not limited to the listed values, and other values ​​not listed in the numerical range are also applicable.

[0049] In certain embodiments, the filter residue in step (4) is sequentially subjected to acid dissolution, solid-liquid separation and alkali precipitation to recover lanthanum cerium carbonate.

[0050] Optionally, the acid used for the acid dissolution includes sulfuric acid. After the acid dissolution, the insoluble matter is subjected to solid-liquid separation and slag washing, and then scrapped; after the solid-liquid separation, 1 to 1.2 times the molar amount of soda ash required for complete precipitation of lanthanum and cerium is added to the acid solution, and the reaction is carried out for 20 minutes to 120 minutes at a temperature of 30°C to 90°C and a stirring speed of 250rpm to 500rpm to perform alkaline precipitation; the recovered lanthanum carbonate and cerium can be reused for silicon removal treatment.

[0051] In certain embodiments, the lithium salt comprises lithium hydroxide. The lithium-containing solution is obtained by re-dissolving the lithium salt comprising lithium hydroxide.

[0052] In some embodiments, the lithium content of the lithium-containing solution in step (1) is 25 g / L-36 g / L, the Si content is ≤35 mg / L, and the SO4 2- Content ≤2g / L.

[0053] The Li content in the lithium-containing solution in step (1) is 25 g / L-36 g / L, for example, 25 g / L, 28 g / L, 30 g / L, 32 g / L, 35 g / L or 36 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] The present invention adopts the combination of nanofiltration impurity removal, post-treatment and silicon removal treatment, and each step reuses the re-dissolved solution, which will not cause Si enrichment during the recycling process, so that the Si content in the lithium-containing solution is ≤35 mg / L.

[0055] In some embodiments, the temperature of the lithium-containing solution in step (1) is 75°C-90°C, for example, 75°C, 80°C, 85°C or 90°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0056] In certain embodiments, before the nanofiltration impurity removal in step (2), the lithium-containing solution is cooled to below 60° C. and then subjected to microfiltration treatment.

[0057] Nanofiltration membranes used for nanofiltration impurity removal are not resistant to high temperatures, so the lithium-containing solution needs to be cooled to below 60°C first. Since some crystals will precipitate during the cooling process, microfiltration treatment is required, and the filtered solution is then nanofiltration-removed. Nanofiltration impurity removal can intercept silicon ions, sulfate ions, calcium ions, and high-valent ions with a valence of more than two valences. Optionally, microfiltration treatment is performed using a precision filter.

[0058] In some embodiments, the Si content in the nanofiltration water produced in step (2) is ≤10 mg / L, SO4 2- ≤0.5g / L; Si content in the nanofiltration concentrated water of step (2) ≥25mg / L, SO4 2- Content ≥0.5g / L.

[0059] In certain embodiments, the post-treatment in step (3) includes evaporative crystallization and centrifugal separation.

[0060] Due to the nanofiltration impurity removal process, the mother liquor obtained by post-processing crystallization evaporation can be reused for re-dissolution. Optionally, the mother liquor is mixed with water in a volume ratio of 5:1-20:1 as a re-dissolution solvent, which can make the Si content in the lithium-containing solution ≤35mg / L, SO4 2- Content ≤2g / L.

[0061] In some embodiments, the temperature of the evaporation crystallization is 80°C-100°C, for example, 80°C, 85°C, 90°C, 95°C or 100°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0062] The lithium salt of the present invention can be lithium hydroxide. The present invention does not specifically limit the source of lithium hydroxide. As long as the Li content in the lithium-containing solution is 25g / L-36g / L, the Si content is ≤35mg / L, and the SO4 2- The content should be ≤2g / L.

[0063] In certain embodiments, the method for preparing the lithium salt in step (1) comprises: subjecting a crude lithium carbonate solution to a causticizing reaction to obtain a lithium hydroxide solution and calcium carbonate slag; and concentrating the lithium hydroxide solution by evaporation to obtain a mother liquor and a lithium salt.

[0064] In certain embodiments, the temperature of the causticizing reaction is 50°C-95°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 95°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] In some embodiments, the causticizing reaction time is 1 h-5 h, for example, 1 h, 2 h, 3 h, 4 h or 5 h, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0066] In certain embodiments, the causticizing reaction is carried out under stirring conditions at a rotation speed of 250 rpm-500 rpm, for example, 250 rpm, 300 rpm, 350 rpm, 400 rpm, 450 rpm or 500 rpm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] In certain embodiments, during the causticizing reaction, the molar amount of causticizing calcium is 1.05 to 1.3 times the theoretical molar amount of lithium carbonate, for example, it can be 1.05, 1.1, 1.15, 1.2, 1.25 or 1.3 times, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] In the present invention, the molar amount of calcium causticize is 1.05 times to 1.3 times the theoretical molar amount of lithium carbonate, which means that the molar amount of calcium causticize is 1.05 times to 1.3 times the molar amount required for complete reaction of lithium carbonate.

[0069] In certain embodiments, the Li content in the lithium hydroxide solution obtained after the causticization reaction is 7 g / L-12 g / L, for example, 7 g / L, 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0070] In certain embodiments, the calcium carbonate slag produced by the causticizing reaction is used to regenerate the causticizing calcium.

[0071] In certain embodiments, the mother liquor obtained by evaporating and concentrating the lithium hydroxide solution can be used to prepare crude lithium carbonate.

[0072] Example 1

[0073] This embodiment provides a Figure 1The preparation method of lithium hydroxide shown in the figure comprises the following steps:

[0074] (I) adding calcium hydroxide in an amount of 1.2 times the theoretical molar amount of lithium carbonate to a crude lithium carbonate solution, subjecting the solution to a causticizing reaction at a temperature of 80° C., a stirring speed of 400 rpm, and a time of 3 h to obtain a lithium hydroxide solution having a Li content of 10 g / L and calcium carbonate slag; the lithium hydroxide solution is concentrated by evaporation at 90° C., and then centrifuged to obtain a mother liquor and lithium hydroxide.

[0075] (II) Redissolving the lithium hydroxide obtained in step (I) to obtain a temperature of 85°C, a Li content of 32 g / L, a Si content of 18 mg / L, and a SO4 2- A lithium-containing solution with a content of 1250 mg / L.

[0076] (III) The lithium-containing solution in step (II) is cooled to 38° C., and then passed through a microporous filter for microfiltration treatment, and then subjected to nanofiltration to remove impurities with a lithium recovery rate of 90%, thereby obtaining nanofiltration product water and nanofiltration concentrated water.

[0077] The Si content in the nanofiltration produced water is 5.2 mg / L, SO4 2- The content is 260mg / L.

[0078] The Si content in the nanofiltration concentrated water is 75.9 mg / L, SO4 2- The content is 8466mg / L.

[0079] (IV) The nanofiltration water is evaporated and crystallized at 90° C. and centrifuged to obtain a mother liquor and a lithium hydroxide monohydrate product; the mother liquor is reused for the re-dissolution in step (II).

[0080] (V) the nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 75° C. and a rotation speed of 350 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution described in step (II); the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 2; sodium carbonate is added to the acid solution after solid-liquid separation to recover lanthanum cerium carbonate; the lanthanum cerium carbonate is reused for preparing the desiliconizing agent.

[0081] The silicon removal agent includes barium hydroxide and lanthanum cerium carbonate (commercial lanthanum cerium carbonate, the molar ratio of lanthanum to cerium is 1:2), the molar amount of barium hydroxide is 0.8 times the molar amount of sulfate in the nanofiltration concentrate; based on the volume of the nanofiltration concentrate, the added mass of lanthanum cerium carbonate in the nanofiltration concentrate is 8g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate lanthanum and cerium in the acid solution.

[0082] Example 2

[0083] This embodiment provides a method for preparing lithium hydroxide, the preparation method comprising the following steps:

[0084] (I) The step parameters for preparing lithium hydroxide are the same as those in Example 1.

[0085] (II) Redissolving the lithium hydroxide obtained in step (I) to obtain a temperature of 75°C, a Li content of 25 g / L, a Si content of 14 mg / L, and SO4 2- A lithium-containing solution with a content of 970 mg / L.

[0086] (III) The lithium-containing solution in step (II) is cooled to 38° C., and then passed through a microporous filter for microfiltration treatment, and then subjected to nanofiltration to remove impurities with a lithium recovery rate of 90%, thereby obtaining nanofiltration product water and nanofiltration concentrated water.

[0087] The Si content in the nanofiltration produced water is 7.5 mg / L, SO4 2- The content is 360.5mg / L.

[0088] The Si content in the nanofiltration concentrated water is 62.3 mg / L, SO4 2- The content is 6252.3 mg / L.

[0089] (IV) The nanofiltration water is evaporated and crystallized at 80° C. and centrifuged to obtain a mother liquor and a lithium hydroxide monohydrate product; the mother liquor is reused for the re-dissolution in step (II).

[0090] (V) the nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 40° C. and a rotation speed of 250 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution described in step (II); the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 3; sodium carbonate is added to the acid solution after solid-liquid separation to recover lanthanum cerium carbonate; the lanthanum cerium carbonate is reused for preparing the desiliconizing agent.

[0091] The silicon removal agent includes barium hydroxide and lanthanum cerium carbonate (commercial lanthanum cerium carbonate, the molar ratio of lanthanum to cerium is 1:2), the molar amount of barium hydroxide is 0.6 times the molar amount of sulfate in the nanofiltration concentrate; based on the volume of the nanofiltration concentrate, the added mass of lanthanum cerium carbonate in the nanofiltration concentrate is 4g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate lanthanum and cerium in the acid solution.

[0092] Example 3

[0093] This embodiment provides a method for preparing lithium hydroxide, the preparation method comprising the following steps:

[0094] (I) The step parameters for preparing lithium hydroxide are the same as those in Example 1.

[0095] (II) Redissolving the lithium hydroxide obtained in step (I) to obtain a temperature of 90°C, a Li content of 36 g / L, a Si content of 20 mg / L, and SO4 2- A lithium-containing solution with a content of 1400 mg / L.

[0096] (III) The lithium-containing solution in step (II) is cooled to 38° C., and then passed through a microporous filter for microfiltration treatment, and then subjected to nanofiltration to remove impurities with a lithium recovery rate of 90%, thereby obtaining nanofiltration product water and nanofiltration concentrated water.

[0097] The Si content in the nanofiltration produced water is 9.8 mg / L, SO4 2- The content is 425.3mg / L.

[0098] The Si content in the nanofiltration concentrated water is 92.2 mg / L, SO4 2- The content is 9560.0mg / L.

[0099] (IV) The nanofiltration water is evaporated and crystallized at 100° C. and centrifuged to obtain a mother liquor and a lithium hydroxide monohydrate product; the mother liquor is reused for the re-dissolution in step (II).

[0100] (V) the nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconization treatment is performed for 60 minutes at a temperature of 100° C. and a rotation speed of 500 rpm, and filter pressing is performed to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution described in step (II); the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 1; sodium carbonate is added to the acid solution after solid-liquid separation to recover lanthanum cerium carbonate; the lanthanum cerium carbonate is reused for the preparation of the desiliconizing agent.

[0101] The silicon removal agent includes barium hydroxide and lanthanum cerium carbonate (commercial lanthanum cerium carbonate, the molar ratio of lanthanum to cerium is 1:2), the molar amount of barium hydroxide is 1 times the molar amount of sulfate in the nanofiltration concentrate; based on the volume of the nanofiltration concentrate, the added mass of lanthanum cerium carbonate in the nanofiltration concentrate is 20g / L; the added molar amount of sodium carbonate is 1.2 times the molar amount required to completely precipitate lanthanum and cerium in the acid solution.

[0102] Comparative Example 1

[0103] This comparative example provides a method for preparing lithium hydroxide, which comprises the following steps:

[0104] Step (I) to step (IV) are the same as in Example 1.

[0105] (V) The nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 75° C. and a rotation speed of 350 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for re-dissolution; the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 2; sodium carbonate is added to the acid solution after solid-liquid separation to recover calcium carbonate.

[0106] The silicon removal agent includes barium hydroxide and calcium hydroxide; the molar amount of barium hydroxide is 1.2 times the molar amount of sulfate in the nanofiltration concentrated water; based on the volume of the nanofiltration concentrated water, the added mass of calcium hydroxide in the nanofiltration concentrated water is 20g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate calcium in the acid solution.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing lithium hydroxide, which comprises the following steps:

[0109] Step (I) to step (IV) are the same as in Example 1.

[0110] (V) The nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 75° C. and a rotation speed of 350 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for re-dissolution; the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 2; sodium carbonate is added to the acid solution after solid-liquid separation to recover lanthanum carbonate.

[0111] The silicon removal agent includes barium hydroxide and lanthanum carbonate; the molar amount of barium hydroxide is 1.2 times the molar amount of sulfate in the nanofiltration concentrated water; based on the volume of the nanofiltration concentrated water, the added mass of lanthanum carbonate in the nanofiltration concentrated water is 20g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate lanthanum in the acid solution.

[0112] Comparative Example 3

[0113] This comparative example provides a method for preparing lithium hydroxide, which comprises the following steps:

[0114] Step (I) to step (IV) are the same as in Example 1.

[0115] (V) The nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 75° C. and a rotation speed of 350 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for re-dissolution; the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 2; sodium carbonate is added to the acid solution after solid-liquid separation to recover iron hydroxide.

[0116] The silicon removal agent includes barium hydroxide and polyferric sulfate; the molar amount of barium hydroxide is 1.2 times the molar amount of sulfate in the nanofiltration concentrate; based on the volume of the nanofiltration concentrate, the added mass of polyferric sulfate in the nanofiltration concentrate is 20g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate iron in the acid solution.

[0117] Comparative Example 4

[0118] This comparative example provides a method for preparing lithium hydroxide, which comprises the following steps:

[0119] Step (I) to step (IV) are the same as in Example 1.

[0120] (V) The nanofiltration concentrated water is mixed with a desiliconizing agent, and desiliconized for 60 minutes at a temperature of 75° C. and a rotation speed of 350 rpm, and filtered to obtain a filtrate and a filter residue; the filtrate is reused for re-dissolution; the filter residue is mixed with sulfuric acid for acid dissolution to obtain an acid solution with a pH of 2; sodium carbonate is added to the acid solution after solid-liquid separation to recover magnesium carbonate.

[0121] The silicon removal agent includes barium hydroxide and magnesium hydroxide; the molar amount of barium hydroxide is 1.2 times the molar amount of sulfate in the nanofiltration concentrated water; based on the volume of the nanofiltration concentrated water, the added mass of magnesium hydroxide in the nanofiltration concentrated water is 20g / L; the added molar amount of sodium carbonate is 1.1 times the molar amount required to completely precipitate magnesium in the acid solution.

[0122] Performance Characterization

[0123] In the above embodiments and comparative examples, the mass percentage of each component in the obtained lithium hydroxide product and the single direct recovery rate of lithium are shown in Table 1; the concentration (mg / L) of each component in the nanofiltration concentrated water is shown in Table 2; the concentration (mg / L) of each component in the filtrate after desiliconization treatment is shown in Table 3.

[0124] Among them, in the composition of lithium hydroxide products, the main content is determined by acid-base titration, and other components are measured by ICP. The main content refers to the mass percentage of lithium hydroxide without crystal water in the monohydrate lithium hydroxide product; the single direct yield refers to the total volume of the filtrate recycled after silicon removal treatment and the nanofiltration water produced in a single cycle, which accounts for the volume percentage of the total water intake of nanofiltration impurity removal.

[0125] Table 1

[0126]

[0127]

[0128] Table 2

[0129]

[0130] Table 3

[0131]

[0132] In summary, the present invention can achieve a direct recovery rate of lithium of more than 99% by desiliconizing the nanofiltration concentrated water, thereby reducing the waste of auxiliary materials; the combination of nanofiltration treatment and desiliconizing agent reduces the production cost, and the desiliconizing agent can be reused and regenerated. In addition, the cost of the desiliconizing agent is low and has a good desiliconizing effect; therefore, the preparation method provided by the present invention greatly reduces the preparation cost of lithium hydroxide.

[0133] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing lithium hydroxide, characterized in that: The preparation method comprises the following steps: (1) redissolving the lithium salt to obtain a lithium-containing solution; (2) The lithium-containing solution in step (1) is subjected to nanofiltration to remove impurities to obtain nanofiltration product water and nanofiltration concentrated water; (3) The nanofiltration water produced in step (2) is post-treated to obtain a mother liquor and lithium hydroxide; the mother liquor is reused for the re-dissolution in step (1); (4) The nanofiltration concentrated water of step (2) is subjected to a desiliconization treatment to obtain a filtrate and a filter residue; the filtrate is reused for the re-dissolution in step (1); the desiliconization agent used in the desiliconization treatment includes barium hydroxide and lanthanum cerium carbonate; Step (3) and step (4) are performed in no particular order.

2. The preparation method according to claim 1, characterized in that: During the silicon removal treatment in step (4), the molar amount of barium hydroxide used is 0.6 to 1 times the molar amount of sulfate in the nanofiltration concentrated water; And / or, based on the volume of the nanofiltration concentrated water, during the silicon removal treatment in step (4), the added mass of the lanthanum cerium carbonate is 1g / L-20g / L.

3. The preparation method according to claim 1 or 2, characterized in that: The temperature of the desiliconization treatment in step (4) is 40°C-100°C; And / or, the desiliconization treatment in step (4) is carried out under stirring conditions at a rotation speed of 250 rpm-500 rpm; And / or, the time for the desiliconization treatment in step (4) is more than 15 minutes.

4. The preparation method according to any one of claims 1 to 3, characterized in that The filter residue in step (4) is successively subjected to acid dissolution, solid-liquid separation and alkali precipitation to recover lanthanum cerium carbonate.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The lithium content of the lithium-containing solution in step (1) is 25 g / L-36 g / L, the Si content is ≤35 mg / L, and the SO4 2- Content ≤2g / L; And / or, the temperature of the lithium-containing solution in step (1) is 75° C.-90° C.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Before the nanofiltration impurity removal in step (2), the lithium-containing solution is cooled to below 60° C. and then subjected to microfiltration treatment; And / or, the Si content in the nanofiltration water produced in step (2) is ≤10 mg / L, SO4 2- Content ≤ 0.5g / L; Si content in the nanofiltration concentrated water of step (2) ≥ 25mg / L, SO4 2- Content ≥0.5g / L.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The post-treatment in step (3) includes evaporation, crystallization and centrifugal separation; And / or, the temperature of the evaporation crystallization is 80°C-100°C.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The method for preparing the lithium salt in step (1) comprises: The crude lithium carbonate solution is subjected to causticization reaction to obtain a lithium hydroxide solution and calcium carbonate slag; the lithium hydroxide solution is evaporated and concentrated to obtain a mother liquor and lithium salt.

9. The preparation method according to claim 8, characterized in that: The temperature of the causticizing reaction is 50°C-95°C; And / or, the causticizing reaction time is 1h-5h; And / or, the causticizing reaction is carried out under stirring conditions at a rotation speed of 250 rpm-500 rpm.

10. The preparation method according to claim 8 or 9, characterized in that: During the causticizing reaction, the molar amount of causticizing calcium is 1.05 to 1.3 times the theoretical molar amount required for complete reaction of lithium carbonate; And / or, the Li content in the lithium hydroxide solution is 7 g / L-12 g / L.

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