A method for recycling lithium dihydrogen phosphate to treat a lithium-lithiated mother liquor

Abstract

A method for recycling lithium dihydrogen phosphate to treat lithium sinking mother liquor, comprising the following steps: (1) adding a mixed solution of lithium dihydrogen phosphate and lithium sulfate into the lithium sinking mother liquor to obtain lithium phosphate precipitate and low-lithium mother liquor; (2) separating the lithium phosphate precipitate obtained in step (1), then adding the lithium phosphate precipitate into a sulfuric acid solution to react, obtaining a mixed solution of lithium dihydrogen phosphate and lithium sulfate, and simultaneously precipitating lithium sulfate monohydrate crystals; (3) separating, washing and collecting the lithium sulfate monohydrate crystals obtained in step (2); and returning the mixed solution of lithium dihydrogen phosphate and lithium sulfate obtained in step (2) to step (1) for recycling. The method realizes high-content and low-impurity recovery of lithium ions in the lithium sinking mother liquor, consumes an amount of sulfuric acid equivalent to that consumed in the acidification process of the lithium sinking mother liquor, recycles phosphate, only needs to supplement the loss of dissolution, the lithium recovery rate reaches more than 95%, and secondary lithium sinking is not needed, thus simplifying the process and reducing the production cost.

Description

Technical Field

[0001] This invention relates to a method for treating lithium precipitation mother liquor, and more particularly to a method for treating lithium precipitation mother liquor by recycling lithium dihydrogen phosphate. Background Technology

[0002] Currently, there are many methods for treating lithium precipitation mother liquor, such as resin method, extraction method, acidification evaporation method, membrane method, and lithium phosphate method. Among them, the acidification evaporation method converts lithium carbonate in the lithium precipitation mother liquor into soluble lithium salt by adding acid, and then evaporates it to a certain lithium content. In the evaporation liquid, lithium forms a complex salt with sodium, so the lithium content needs to be controlled at a low level. After concentration, secondary lithium precipitation is carried out to recover lithium. Equipment needs to be set up for secondary lithium precipitation, and the quality of lithium carbonate from secondary precipitation is poor. The resin method refers to separating the lithium precipitation mother liquor from impurities through resin ion exchange, which has high production costs. The lithium phosphate method involves adding sodium phosphate to the lithium precipitation mother liquor to obtain lithium phosphate with extremely low solubility. The product is lithium phosphate, but the market for lithium phosphate is small.

[0003] Therefore, it is of great significance to achieve high recovery rate of lithium in the process of recovering lithium from lithium precipitation mother liquor without the need for secondary lithium precipitation and with low production cost. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the above-mentioned defects of the prior art and provide a method for recycling lithium precipitation mother liquor with lithium dihydrogen phosphate, which has a high lithium recovery rate, does not require secondary lithium precipitation, is easy to operate, and has low production cost.

[0005] The technical solution adopted by this invention to solve its technical problem is a method for recycling lithium precipitation mother liquor with lithium dihydrogen phosphate, comprising the following steps:

[0006] (1) Add the mixture of lithium dihydrogen phosphate and lithium sulfate to the lithium precipitation mother liquor to obtain lithium phosphate precipitate and low lithium content mother liquor;

[0007] (2) Separate the lithium phosphate precipitate obtained in step (1), and then add the lithium phosphate precipitate to a sulfuric acid solution to react and obtain a solution of lithium dihydrogen phosphate and lithium sulfate, while lithium sulfate monohydrate crystals precipitate.

[0008] (3) Separate, wash and collect the lithium sulfate monohydrate crystals obtained in step (2); return the solution of lithium dihydrogen phosphate and lithium sulfate obtained in step (2) to step (1) for recycling.

[0009] Furthermore, in step (1), the mass ratio of the lithium precipitation mother liquor to lithium dihydrogen phosphate and lithium sulfate is 100~110:2.0~3.0:1, preferably 106:2.1:1.

[0010] Lithium dihydrogen phosphate in step (1) can be obtained by reacting sodium dihydrogen phosphate, sodium phosphate or phosphoric acid with lithium precipitation mother liquor during initial production and then acidifying it, without the need to purchase lithium dihydrogen phosphate externally.

[0011] Furthermore, the low-lithium mother liquor in step (1) is usually used to evaporate anhydrous sodium sulfate in the ore-based lithium extraction process. Since the lithium phosphate content is low, it has no impact on the product quality. Alternatively, it can be returned to the salt field for concentration and recovery of lithium in the salt lake lithium extraction process.

[0012] Furthermore, in step (2), the concentration of the sulfuric acid solution is 50-70 wt%.

[0013] Furthermore, in step (2), the concentration of the sulfuric acid solution is 60-70 wt%. The concentration of the sulfuric acid solution should ensure the full dissolution of lithium dihydrogen phosphate while minimizing the amount of lithium sulfate dissolved, so that the liquid phase remains acidic. Therefore, a concentration of 60-70% for the sulfuric acid solution is preferable, with an appropriate excess.

[0014] Furthermore, in step (2), the reaction temperature is 70-80℃ and the reaction time is 10-60 minutes, preferably 20-30 minutes.

[0015] Furthermore, in step (2), the lithium phosphate precipitate does not need to be washed and reacts directly with the sulfuric acid solution.

[0016] Furthermore, in step (3), the collected lithium sulfate monohydrate crystals are returned to the previous section for dissolution and reuse; or they are mixed with the leaching liquid after acid burning in the ore-based lithium extraction process, purified and concentrated to remove lithium precipitation; or they are mixed with the lithium-containing liquid before impurity removal in the salt lake lithium extraction process, purified and concentrated to remove lithium precipitation.

[0017] Furthermore, in step (3), the wash water obtained after washing the lithium sulfate monohydrate crystals is used to dilute the sulfuric acid, and the heat of dilution is used to increase the reaction rate, improve the solubility of lithium dihydrogen phosphate, and reduce the solubility of lithium sulfate.

[0018] The solution of lithium dihydrogen phosphate and lithium sulfate mixed in step (3) is recycled to step (1) to recycle phosphate. When recycled to step (1), the main precipitant is lithium dihydrogen phosphate. The lithium sulfate is not separated in order to simplify the production process.

[0019] The principle of this invention is as follows: A mixture of lithium dihydrogen phosphate and lithium sulfate is added to a lithium precipitation mother liquor to obtain lithium phosphate precipitate (the reaction process is shown in reaction formula 1 and reaction formula 2). The lithium phosphate precipitate is separated, and then reacted with sulfuric acid solution to generate a mixture of lithium dihydrogen phosphate and lithium sulfate (the reaction process is shown in reaction formula 3). Since lithium dihydrogen phosphate has a high solubility while lithium sulfate has a low solubility, and the solubility of lithium sulfate decreases with increasing temperature, the difference in solubility between lithium dihydrogen phosphate and lithium sulfate is utilized to control the reaction temperature and concentration of lithium phosphate and sulfuric acid, so that lithium dihydrogen phosphate is fully dissolved in the liquid phase and its solubility is less than its saturation solubility, while lithium sulfate cannot be completely dissolved, precipitating lithium sulfate monohydrate crystals.

[0020] The reaction formulas involved are as follows:

[0021] LiH2PO4 + Li2CO3 → Li3PO4↓ + H2O + CO2↑ (Reaction 1)

[0022] LiH2PO4 + Li2SO4 + Na2CO3 → Li3PO4↓ + H2O + CO2↑ + Na2SO4 (Reaction 2)

[0023] Li3PO4 + H2SO4 + H2O → LiH2PO4 + Li2SO4 (Reaction 3)

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) This invention utilizes the solubility difference between lithium dihydrogen phosphate and lithium sulfate to achieve high content and low impurity recovery of lithium ions in lithium precipitation mother liquor. The amount of sulfuric acid consumed in the process is comparable to that in the acidification process of lithium precipitation mother liquor. Phosphate is recycled and reused. Only the dissolution loss needs to be replenished, and the lithium recovery rate reaches about 90%.

[0026] (2) The present invention does not require secondary lithium precipitation to process lithium precipitation mother liquor. It makes full use of the equipment in the lithium carbonate production process to remove impurities, purify and concentrate lithium precipitation, simplify the process, reduce the number of equipment, reduce raw material costs, and obtain an increased amount of high-quality lithium carbonate with only one lithium precipitation equipment. Detailed Implementation

[0027] The present invention will be further described below with reference to specific embodiments.

[0028] Example 1

[0029] The lithium precipitation mother liquor from the ore method refers to the liquid obtained after calcining, acid calcining, leaching, and impurity removal of spodumene as raw material, followed by the reaction of the concentrated lithium sulfate solution with sodium carbonate to obtain solid lithium carbonate, and the separation of the solid from the liquid.

[0030] This embodiment describes a method for treating lithium precipitation mother liquor using lithium dihydrogen phosphate recycling, comprising the following steps:

[0031] (1) Add 49.6g of a mixture of lithium dihydrogen phosphate and lithium sulfate (23.4g of lithium dihydrogen phosphate and 11g of lithium sulfate) to 1176g of lithium precipitation mother liquor (10g of lithium carbonate). The lithium precipitation mother liquor is at 80°C and no special cooling is required. Sodium carbonate is usually in excess in the lithium precipitation mother liquor, and the system is alkaline, which is conducive to the precipitation of lithium phosphate. The mixture contains a large amount of lithium phosphate and a small amount of lithium sulfate. The main reaction is reaction one, which yields lithium phosphate precipitate and low lithium content mother liquor.

[0032] (2) Separate the lithium phosphate precipitate obtained in step (1). The solid content in the liquid phase of step (1) is low. It needs to be concentrated and then centrifuged to obtain 34.2g of lithium phosphate precipitate and 1191.4g of low lithium mother liquor. Add water quantitatively to the reaction vessel, slowly add 22g of concentrated sulfuric acid, dilute to 60-70% sulfuric acid content, add 34.2g of lithium phosphate solid without washing to the reaction vessel, keep the acid in excess, so that the lithium phosphate reacts fully, converts to lithium dihydrogen phosphate according to the three reaction processes, and completely dissolves it so that its solubility is less than the saturated solubility, so that it will not precipitate. At the same time, lithium sulfate is obtained during the reaction. Due to its low solubility, part of 11g is in the liquid phase and part of 15.9g is precipitated in the form of lithium sulfate monohydrate.

[0033] (3) Separate lithium sulfate monohydrate and return the mother liquor, which is a mixture of lithium dihydrogen phosphate and lithium sulfate, to step (1) for recycling; wash the lithium sulfate monohydrate crystals in the separation equipment, control the amount of washing water, separate again, and use the obtained washing water to dilute concentrated sulfuric acid in step (2);

[0034] (4) The solid lithium sulfate monohydrate obtained in step (3) is mixed with the leaching solution after acid burning in the ore-based lithium extraction process to increase the lithium sulfate content in the liquid phase. After purification and concentration, the lithium is removed from the precipitate. The purification process of the lithium-containing liquid in the ore-based process is fully utilized to meet the composition requirements of primary lithium precipitation.

[0035] According to the test, the lithium recovery rate in the lithium precipitation mother liquor of this embodiment is 88.3% ((lithium in lithium phosphate - lithium in lithium dihydrogen phosphate - lithium in lithium sulfate - lithium in low lithium content mother liquor) ÷ lithium in lithium carbonate = (4.725 - 1.575 - 1.4 - 0.08) ÷ 1.89 = 88.3%)

[0036] Example 2

[0037] The lithium precipitation mother liquor from the salt lake method mainly refers to the liquid obtained after enriching, removing calcium, magnesium, and boron from salt lake brine, concentrating the resulting lithium chloride solution, reacting it with sodium carbonate to obtain solid lithium carbonate, and then separating the solid.

[0038] This embodiment describes a method for treating lithium precipitation mother liquor using lithium dihydrogen phosphate recycling, comprising the following steps:

[0039] (1) Add 26g of lithium dihydrogen phosphate solution (14.5g of lithium dihydrogen phosphate) to 1176g of lithium precipitation mother liquor (10g of lithium carbonate). The lithium precipitation mother liquor is at 80℃ and no special cooling is required. Sodium carbonate is usually in excess in the lithium precipitation mother liquor, and the system is alkaline, which is conducive to the precipitation of lithium phosphate. The mixed solution has a high lithium phosphate content and a low lithium sulfate content. The main reaction formula is reaction one, which yields lithium phosphate precipitate and low lithium content mother liquor.

[0040] (2) Separate the lithium phosphate precipitate obtained in step (1). The solid content in the liquid phase of step (1) is low. It needs to be concentrated and then centrifuged to obtain 20.3g of lithium phosphate precipitate and 1181.5g of low lithium mother liquor. Add water quantitatively to the reaction vessel, slowly add 13.3g of concentrated sulfuric acid, dilute to 60-70% sulfuric acid content, add 20.5g of lithium phosphate solid without washing to the reaction vessel, keep the acid in excess, so that the lithium phosphate reacts fully, converts to lithium dihydrogen phosphate according to the three reaction processes, and completely dissolves it so that its solubility is less than the saturated solubility, so that it will not precipitate. At the same time, lithium sulfate is obtained in the reaction process. Due to its low solubility, part of it (4.5g) is in the liquid phase and part of it (12g) is precipitated in the form of lithium sulfate monohydrate.

[0041] (3) Separate lithium sulfate monohydrate and return the mother liquor, which is a mixture of lithium dihydrogen phosphate and lithium sulfate, to step (1) for recycling; wash the lithium sulfate monohydrate crystals in the separation equipment, control the amount of washing water, separate again, and use the obtained washing water to dilute concentrated sulfuric acid in step (2);

[0042] (4) The solid lithium sulfate monohydrate obtained in step (3) is mixed with the lithium-containing liquid before impurity removal. If nanofiltration is used for impurity removal, sulfate can be removed by nanofiltration. After purification and concentration, lithium is removed to make full use of the purification process of the lithium-containing liquid in the previous process and meet the composition requirements of primary lithium precipitation.

[0043] The lithium recovery rate in the lithium precipitation mother liquor of this embodiment was 92.4% ((lithium in lithium phosphate - lithium in lithium dihydrogen phosphate - lithium in low lithium content mother liquor) ÷ lithium in lithium carbonate = (2.804 - 0.976 - 0.081) ÷ 1.89 = 92.4%)

[0044] Example 3

[0045] Lithium hydroxide production via the ore-based process also involves recovering lithium from the pyrolysis mother liquor. This process involves calcining, acid-cooking, leaching, and removing impurities from spodumene, resulting in a lithium sulfate solution that reacts with sodium hydroxide. After freezing and precipitating sodium sulfate, a mixture of lithium hydroxide and sodium sulfate is obtained. This mixture is then evaporated to obtain solid lithium hydroxide monohydrate, and the remaining liquid is separated from the solid. The high potassium sulfate content in the pyrolysis mother liquor is detrimental to lithium hydroxide production.

[0046] This embodiment describes a method for treating pyrolysis mother liquor using lithium dihydrogen phosphate via a recycling process, comprising the following steps:

[0047] (1) Add 572g of a mixture of lithium dihydrogen phosphate and lithium sulfate (368.6g of lithium dihydrogen phosphate and 91.8g of lithium sulfate) to 1000g of pyrolysis mother liquor (130g of lithium hydroxide). The pyrolysis mother liquor is above 60°C and does not require special cooling.

[0048] LiH₂PO₄ + 2LiOH → Li₃PO₄↓ + 2H₂O (Reaction 4)

[0049] The mother liquor system is alkaline, which is conducive to the precipitation of lithium phosphate. When the reaction becomes neutral, 88.6g of sodium carbonate is added. At this time, the main reaction is reaction two, which yields lithium phosphate precipitate and low lithium content mother liquor.

[0050] (2) Centrifugation was performed to obtain 538.8g of lithium phosphate precipitate and 1033.2g of low-lithium mother liquor. The lithium phosphate was recovered as in Example 1, and lithium sulfate monohydrate was recycled for the production of lithium hydroxide. The low-lithium mother liquor was evaporated to obtain potassium sulfate, which was then hydrolyzed to produce potassium sulfate and sodium sulfate.

[0051] According to the test, the lithium recovery rate in the pyrolysis mother liquor of this embodiment is 99% ((lithium in lithium phosphate - lithium in lithium dihydrogen phosphate - lithium in lithium sulfate - lithium in low lithium content mother liquor) ÷ lithium in lithium hydroxide = (74.3 - 24.8 - 11.8 - 0.071) ÷ 38 = 99%).

Claims

1. A method for recycling a lithium-lithium phosphate mother liquor with lithium dihydrogen phosphate, characterized in that, The method comprises the following steps: (1) adding a mixed solution of lithium dihydrogen phosphate and lithium sulfate into a lithium precipitation mother liquor to obtain lithium phosphate precipitate and a low-lithium mother liquor; the mass ratio of the lithium precipitation mother liquor, lithium dihydrogen phosphate and lithium sulfate is 100-110:2.0-3.0:1; (2) separating the lithium phosphate precipitate obtained in step (1), and then adding the lithium phosphate precipitate into a sulfuric acid solution to react, so as to obtain a mixed solution of lithium dihydrogen phosphate and lithium sulfate, and simultaneously precipitate lithium sulfate monohydrate crystals; the concentration of the sulfuric acid solution is 60-70 wt%; the reaction temperature is 70-80 ℃, and the reaction time is 10-60 minutes; (3) separating, washing and collecting the lithium sulfate monohydrate crystals obtained in step (2); and returning the mixed solution of lithium dihydrogen phosphate and lithium sulfate obtained in step (2) to step (1) for recycling.

2. The method of recycling lithium dihydrogen phosphate to treat a lithium-laden mother liquor according to claim 1, characterized in that, In step (2), the lithium phosphate precipitate does not need to be washed and can be directly reacted with the sulfuric acid solution.

3. The method of recycling lithium dihydrogen phosphate according to claim 1 or 2, characterized in that, In step (3), the collected lithium sulfate monohydrate crystals are returned to the previous stage for dissolution and recycling; or the lithium sulfate monohydrate crystals are mixed with a leaching solution after acid roasting in a lithium extraction process from ores, and then purified, concentrated and subjected to lithium precipitation removal; or the lithium sulfate monohydrate crystals are mixed with a lithium-containing solution before impurity removal in a lithium extraction process from salt lakes, and then purified, concentrated and subjected to lithium precipitation removal.