Process for producing lithium dihydrogen phosphate by using lepidolite alkaline method in short process

Abstract

The invention discloses a technology for producing lithium dihydrogen phosphate through a lepidolite alkaline method short process, and relates to the technical field of lithium carbonate extraction. The method specifically comprises the following steps: mixing lepidolite, a sodium hydroxide solution and lime milk according to an accurate ratio to obtain ore pulp, and reacting at set temperature and pressure under high-speed stirring to obtain a product mixed solution; and carrying out liquid-solid separation and washing on the product mixed solution to obtain a leaching solution, sequentially carrying out impurity removal, extraction and reverse extraction on the leaching solution to obtain a lithium dihydrogen phosphate aqueous solution, carrying out purification through lithium hydroxide to obtain lithium monohydrogen phosphate crystals, and carrying out acidification and evaporative crystallization through phosphoric acid to obtain a lithium dihydrogen phosphate finished product. According to the invention, a high-energy-consumption sintering process is canceled, so that the production energy consumption is reduced, and meanwhile, the carbon emission is reduced; through alkaline high-pressure leaching, metal impurities in the lepidolite ore directly enter a slag phase, so that the metal impurities in the solution are reduced; meanwhile, the technological process is shortened, the efficiency is improved, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of lithium carbonate refining, and more specifically to a process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process. Background Art

[0002] In recent years, with the rapid development of the new energy industry, the demand for lithium dihydrogen phosphate has continued to increase, and the overall production capacity of the industry is on an upward trend.

[0003] At present, the traditional lithium carbonate method and lithium hydroxide monohydrate method for producing lithium dihydrogen phosphate have problems such as complicated process flow, high production cost and excessive pollutants.

[0004] The traditional process requires pretreatment of the raw materials, such as dissolution and filtration of lithium carbonate or lithium hydroxide monohydrate, to remove impurities. At the same time, the product after the reaction also needs to be purified through multiple filtration, washing, drying and other steps. The entire process is relatively complicated, which increases the time and cost of production. On the one hand, the production of lithium carbonate and lithium hydroxide monohydrate itself consumes a lot of energy and raw materials, resulting in high costs; on the other hand, the traditional process has high requirements for the control of reaction conditions, requires the use of special equipment and instruments, and consumes a lot of reagents such as acids and alkalis during the production process, all of which increase production costs.

[0005] Traditional processes will generate a large amount of pollutants such as wastewater, waste gas and waste residue during the production process. For example, the reaction of lithium carbonate and phosphoric acid will produce carbon dioxide gas. If it is discharged directly without treatment, it will pollute the environment. At the same time, the wastewater and waste residue after the reaction may contain unreacted raw materials, impurities and other harmful substances, which require special treatment, otherwise it will cause harm to the soil, water sources, etc. Summary of the invention

[0006] The technical problem to be solved by the present invention is to provide a process for producing lithium dihydrogen phosphate by a short-process method using a lithium mica alkali method in view of the deficiencies of the above-mentioned prior art, aiming to solve the problems of high energy consumption cost, complicated process flow, and excessive pollutants generated by traditional production processes.

[0007] In order to achieve the above object, the main technical scheme adopted by the present invention is: a process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process, comprising the following steps: S1. Ingredients: Grind the lepidolite to a set particle size and mix it with sodium hydroxide solution and lime milk to obtain slurry.

[0008] S2, high pressure leaching: the slurry is reacted under set temperature, pressure and stirring speed conditions to obtain a product mixture.

[0009] S3, post-processing: the product mixed solution is subjected to liquid-solid separation and washing to obtain leaching residue and leaching liquid, and the leaching liquid is treated to obtain the finished lithium dihydrogen phosphate product.

[0010] Furthermore, in S1, the set particle size of the lepidolite is 250 mesh, the mass of the sodium hydroxide solution added is 2 to 4 times the mass of the lepidolite, the mass of the lime milk added is 0.2 to 0.8 times the mass of the lepidolite, and the liquid-to-solid ratio of the slurry is 10 to 14.

[0011] Furthermore, in S2, the temperature is 200-280° C., the pressure is 1.5-6.3 MPa, the stirring speed is 300 rpm, and the reaction time is 1-3 h.

[0012] Furthermore, the leached slag in S3 is calcium-silica slag, which can be directly recovered and used as the main raw material for cement production.

[0013] Furthermore, in S3, the treatment of the leachate specifically comprises the following steps: (1) subjecting the leaching solution to impurity removal, extraction, and stripping in sequence to obtain a lithium dihydrogen phosphate aqueous solution; (2) adding lithium hydroxide to the lithium dihydrogen phosphate aqueous solution to precipitate lithium and purify the slurry, and obtaining an overflow and an underflow after solid-liquid separation, wherein the overflow is returned to the batching unit after evaporation and concentration, and the underflow is washed and filtered to obtain lithium monohydrogen phosphate crystals; (3) The lithium monohydrogen phosphate crystals are acidified with phosphoric acid to obtain a lithium dihydrogen phosphate solution, and the lithium dihydrogen phosphate solution is evaporated and crystallized to obtain a finished lithium dihydrogen phosphate product.

[0014] Furthermore, the impurity removal process is specifically as follows: adding lime milk to the leaching solution, keeping it warm at 90-98° C. for 2-5 hours, separating the aluminum silicon slag after filter pressing and washing to obtain a purified liquid.

[0015] Furthermore, the raffinate obtained by extracting the leaching solution is returned to the batching unit for recycling.

[0016] Furthermore, the mass of the lime milk added is 0.1 to 0.4 times the mass of the lepidolite.

[0017] The present invention has the following beneficial effects and advantages: 1. The present invention uses wet high-pressure leaching of lithium mica to allow metal impurities such as iron, manganese, magnesium, and zinc in the lithium mica ore to directly enter the slag phase, thereby reducing metal impurities in the solution, simplifying the solution purification process, shortening the process, reducing production costs, eliminating the high-energy-consuming sintering process, reducing production energy consumption, and reducing carbon emissions; 2. The present invention adds lime milk during the batching process, which can promote the conversion of sodium aluminosilicate into cancrinite-like substances during the high-pressure leaching process. Cancrinite-like substances have low solubility and are easily separated, thereby reducing impurities in the product; furthermore, cancrinite-like substances can also adsorb impurities and purify the solution; finally, cancrinite-like substances can be reused as cement components.

[0018] 3. The present invention adopts an extraction method to extract lithium, realizes the separation of lithium and sodium in one step, and simultaneously cooperates with phosphoric acid to strip lithium to directly obtain lithium dihydrogen phosphate, shortening the process flow. The generated lithium dihydrogen phosphate is purified by lithium hydroxide to obtain lithium phosphate or lithium monohydrogen phosphate, and finally dissolved by phosphoric acid to obtain lithium dihydrogen phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a process flow chart of a lithium mica alkali method for producing lithium dihydrogen phosphate in a short process. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings.

[0021] Example: Figure 1 The process flow chart of the present invention is a short-process process for producing lithium dihydrogen phosphate by a lithium mica alkali method, such as Figure 1 As shown, the specific steps include: S1. Batching: Mix lepidolite ground to 250 mesh and containing 1.5% lithium oxide, sodium hydroxide solution and lime milk to obtain ore slurry, the batching ratio of sodium hydroxide to lepidolite L / S=3.2, and the mass of lime milk added is 0.5 times the mass of lepidolite; S2, high-pressure leaching: The slurry is reacted at a temperature of 200°C, a pressure of 2.6MPa, and a stirring speed of 300rpm for 2h to obtain a product mixture. This is to control the temperature, the amount of lime milk added, and the leaching residence time during the high-pressure leaching process to control the physical composition of the subsequent leaching residue and minimize the impurities that enter the subsequent leaching solution.

[0022] S3, post-treatment: the product mixture is subjected to liquid-solid separation and washing steps to obtain leaching residue and leaching liquid, wherein the leaching residue can be recycled as the main raw material for cement production; the leaching liquid is first subjected to impurity removal operation, and lime milk is added to the solution in an amount of 0.2 times the mass of lepidolite to deeply remove aluminum, silicon and fluorine elements in the solution. The solution is maintained at 98°C and kept warm for 2 hours. After the reacted slurry is filtered and washed, the residue is separated to obtain a purified solution.

[0023] The concentration of lithium hydroxide in the purified solution is about 5g / l. The purified solution is mixed with an organic phase containing a specific lithium extractant, lithium is extracted into the organic phase, and then washed and impurities are removed, and phosphoric acid is used for back extraction to obtain a lithium dihydrogen phosphate aqueous solution, and the concentration of lithium dihydrogen phosphate reaches 60g / L. The lithium dihydrogen phosphate aqueous solution is further purified by adding lithium hydroxide to obtain lithium monohydrogen phosphate crystals, and then dissolved in phosphoric acid to obtain a lithium dihydrogen phosphate solution, and finally the lithium dihydrogen phosphate finished product is obtained through concentration, crystallization, and refining. The present invention adds lime milk during the batching process, which can promote the conversion of sodium aluminosilicate into cancrystal-like substances during the high-pressure leaching process. Cancrystal-like substances have low solubility and are easily separated, thereby reducing impurities in the product; furthermore, cancrystal-like substances can also adsorb impurities and purify the solution; finally, cancrystal-like substances can be reused as cement components.

[0024] By wet high-pressure leaching of lithium mica, the high-energy sintering process is eliminated, production energy consumption is reduced, and carbon emissions are reduced; by alkaline high-pressure leaching, metal impurities such as iron, manganese, magnesium, and zinc in the lithium mica ore are directly transferred to the slag phase, reducing metal impurities in the solution, simplifying the solution purification process, shortening the process, and reducing production costs; The invention adopts an extraction method to extract lithium, realizes the separation of lithium and sodium in one step, and simultaneously cooperates with phosphoric acid to extract lithium to directly obtain lithium dihydrogen phosphate, thus shortening the process flow.

[0025] The generated lithium dihydrogen phosphate is purified by lithium hydroxide to obtain lithium phosphate or lithium monohydrogen phosphate, and finally dissolved by phosphoric acid to obtain lithium dihydrogen phosphate.

[0026] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A process for producing lithium dihydrogen phosphate by a short-process method using a lepidolite alkaline method, characterized in that: The following steps are involved: S1, batching: grinding the lepidolite to a set particle size, and mixing it with sodium hydroxide solution and lime milk to obtain a slurry; S2, high pressure leaching: react the slurry under set temperature, pressure and stirring speed conditions to obtain a product mixture; S3, post-processing: the product mixed solution is subjected to liquid-solid separation and washing to obtain leaching residue and leaching liquid, and the leaching liquid is treated to obtain the finished lithium dihydrogen phosphate product.

2. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 1, characterized in that: In S1, the set particle size of the lepidolite is 250 mesh, the mass of the sodium hydroxide solution added is 2-4 times the mass of the lepidolite, the mass of the lime milk added is 0.2-0.8 times the mass of the lepidolite, and the liquid-to-solid ratio of the slurry is 10-14.

3. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 1, characterized in that: In S2, the temperature is 200-280°C, the pressure is 1.5-6.3 MPa, the stirring speed is 300 rpm, and the reaction time is 1-3 h.

4. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 1, characterized in that: The leached residue in S3 is calcium-silica slag, which can be directly recovered and used as the main raw material for cement production.

5. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 1, characterized in that: In S3, the treatment of the leachate specifically comprises the following steps: (1) subjecting the leaching solution to impurity removal, extraction, and stripping in sequence to obtain a lithium dihydrogen phosphate aqueous solution; (2) adding lithium hydroxide to the lithium dihydrogen phosphate aqueous solution to precipitate lithium and purify the slurry, and obtaining an overflow and an underflow after solid-liquid separation, wherein the overflow is returned to the batching unit after evaporation and concentration, and the underflow is washed and filtered to obtain lithium monohydrogen phosphate crystals; (3) The lithium monohydrogen phosphate crystals are acidified with phosphoric acid to obtain a lithium dihydrogen phosphate solution, and the lithium dihydrogen phosphate solution is evaporated and crystallized to obtain a finished lithium dihydrogen phosphate product.

6. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 5, characterized in that: The impurity removal process is specifically as follows: adding lime milk to the leaching solution, keeping the temperature at 90-98° C. for 2-5 hours, separating the aluminum silicon slag after filter pressing and washing, and obtaining a purified liquid.

7. A process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 5, characterized in that: The raffinate obtained by extracting the leaching solution is returned to the batching unit for recycling.

8. The process for producing lithium dihydrogen phosphate by a lepidolite alkali method in a short process according to claim 6, characterized in that: The mass of the lime milk added is 0.1 to 0.4 times the mass of the lepidolite.

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