Method for extracting lithium from high-calcium salt lake brine

Abstract

The invention discloses a method for extracting lithium from high-calcium salt lake brine, which adopts an enhanced salt drying and decalcification technology to greatly reduce the consumption of a subsequent chemical method for removing impurities; calcium salt generated in the enhanced calcium salt removal stage (the Nth stage) is returned to the previous stage for salt drying and decalcification for reverse dissolution, so that the loss of crystalline lithium is avoided; and the calcium crystal salt before the N-1 stage is washed, and washing liquid returns to the system, so that the entrained lithium is effectively recovered, and the comprehensive recovery rate of the lithium is greatly improved. According to the property of the brine solution and the co-precipitation behavior of impurities, the consumption of an impurity removal agent is reduced by utilizing the co-precipitation behavior of calcium and boron in the concentrated brine, and meanwhile, an independent boron removal process can be omitted, and the equipment investment and the operation cost are reduced. The lithium carbonate product is prepared through the procedures of salt concentration in the sun, crystalline salt washing, impurity removal through the chemical precipitation method, lithium precipitation and the like, the method has the advantages of being short in technological process, low in investment cost, high in lithium recovery rate, small in agent consumption, environmentally friendly and the like, the production investment cost of enterprises can be reduced, and the economic benefits of the enterprises are further increased.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, and in particular to a method for extracting lithium from high-calcium salt lake brine. Background Art

[0002] With the rapid development of new energy industry, the demand for lithium batteries has continued to increase dramatically, thus accelerating the development of lithium resources. Compared with hard rock lithium mines, salt lake brine-type lithium mines have the advantages of high resource reserves, greenness, and low cost. With the continuous advancement of brine lithium extraction technology, the production capacity of salt lake-type lithium mines will be further released.

[0003] Salt lake lithium ore accounts for about 60% of the world's lithium resources, and this type of resource in my country accounts for more than 80% of the total reserves. The composition of brines in different regions is different, and the properties are different. Therefore, the extraction of lithium from salt lakes has the characteristics of "one lake, one policy". At present, the main processes for extracting lithium from salt lakes are: salt concentration precipitation method, adsorption method, membrane method, extraction method, and calcination leaching method, but most lithium extraction processes are mainly aimed at the extraction of lithium from salt lake brines with high magnesium-to-lithium ratios. At present, there are relatively few research reports on the extraction of lithium from high-calcium salt lake brines. CN115806301A discloses a method for preparing lithium carbonate from high-calcium deep brine by adsorption, which concentrates high-calcium deep brine with low lithium content (≥50mg / L) into Li + When the content is around 300-600 mg / L, use manganese adsorbent to adsorb-desorb-enrich lithium, adjust to strong alkalinity with sodium hydroxide solution, remove low-content impurity elements such as manganese, magnesium, and iron, and then concentrate the lithium-rich brine to 10-12 g / L, add excess sodium oxalate, adjust the pH to 11.0-11.5 to deeply remove calcium and magnesium, reduce the calcium-to-lithium ratio and magnesium-to-lithium ratio to a certain value, and concentrate to Li + ≥11.0g / L, add saturated sodium carbonate solution in a water bath above 85℃ to precipitate lithium carbonate, and then concentrate the fine washing liquid and tail liquid to Li + ≥11g / L for secondary precipitation to obtain qualified lithium carbonate products. This process has problems such as large consumption of sodium hydroxide, sodium oxalate and other reagents, high dissolution loss of manganese adsorbents, and only 50% comprehensive lithium recovery rate. In addition, when the desorption liquid is a sulfuric acid system, desorption is prone to form calcium sulfate precipitation (gypsum), which affects the subsequent use of the adsorbent.

[0004] CN114014340A discloses a method for removing calcium and enriching lithium from brine in a high calcium-salt ratio salt lake, comprising the following steps: (1) subjecting the lithium-containing brine in a calcium chloride-type salt lake to natural evaporation to precipitate sodium and potassium mixed salts, and then acidifying the brine to remove boron; (2) subjecting the brine treated in step (1) to at least one natural evaporation-freezing calcium precipitation operation to cool the brine, so that calcium chloride crystals are precipitated, and then solid-liquid separation is performed. This process only introduces the process of recovering lithium from brine by drying salt. In the latter stage of drying calcium salt, the viscosity of the old brine gradually increases, and the loss of lithium entrained by the calcium salt increases; furthermore, the lithium concentration of the concentrated brine after drying calcium salt in this technology is controlled within 38g / L to ensure the lithium yield (55%-60%) in the drying calcium stage, but the Ca / Li mass concentration ratio in the concentrated brine is still very high (Ca / Li>3.4), resulting in a large amount of reagent consumption and slag production in the subsequent chemical decalcification process.

[0005] Based on the current problems of lithium extraction from brine with high calcium content, it is necessary to develop a new lithium extraction process with simple process, low investment cost, low reagent consumption and high lithium recovery rate. Summary of the invention

[0006] In view of the deficiencies of the prior art, the present invention aims to provide a method for extracting lithium from high-calcium salt lake brine.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A method for extracting lithium from high-calcium salt lake brine, comprising the following steps:

[0009] Step 1: Pre-concentrate the high-calcium salt lake brine by solarization to remove most of the sodium and potassium salts to obtain a pre-concentrated solution;

[0010] Step 2, subjecting the pre-concentrated liquid in step 1 to N-level solar-salt concentration and decalcification; in each level of solar-salt concentration and decalcification, solar-salt concentration is first performed, and the brine after solar-salt concentration is cooled and crystallized to precipitate calcium crystalline salt, and after solid-liquid separation, the brine continues to be subjected to the next level of solar-salt concentration and decalcification; the calcium crystalline salt obtained in the first N-1 levels is washed, and the washing water obtained after washing is returned to the previous level of solar-salt concentration and decalcification, and the calcium crystalline salt obtained after washing is stored; the calcium crystalline salt produced by the N-level solar-salt concentration and decalcification is returned to the previous level of solar-salt concentration and decalcification, and the lithium-containing concentrated brine produced by the N-level solar-salt concentration and decalcification enters step 3;

[0011] In step 3, after adding alkali to adjust the pH value of the lithium-containing concentrated brine obtained in step 2, react with a calcium precipitation agent, and then perform solid-liquid separation to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake; the calcium-magnesium slag filter cake is washed to obtain a washing liquid, and a high-lithium washing liquid with a Li concentration exceeding a set value is incorporated into the lithium-containing purified liquid to obtain a mixed solution, and a low-lithium washing liquid with a Li concentration not exceeding a set value is returned to step 1 for pre-concentration of salt;

[0012] Step 4: Prepare lithium carbonate from the mixed solution of the high-lithium washing solution and the lithium-containing purification solution in step 3 by sodium carbonate precipitation method, and the lithium precipitation mother liquor after liquid-solid separation is directly returned to step 1 for salt pre-concentration.

[0013] Furthermore, in step 1, the high calcium salt lake brine is chloride brine, wherein Li + The concentration is 200-2000mg / L, Ca 2+ The concentration is 10-85g / L, Na + The concentration is 28-100g / L, K + The concentration is 2-18g / L, the concentration of B is 0.1-3.2g / L, and the concentration of Cl is - The concentration is 80-240g / L, where the mass concentration ratio of Ca / Li is ≥20; Li in the pre-concentrated solution + The concentration is 3-4.5g / L, Ca 2+ The concentration is 180-220 g / L, the B concentration is 1-6.5 g / L, and the mass concentration ratio of Ca / Li is >20.

[0014] Furthermore, in step 2, N is greater than or equal to 4; in order to prevent lithium loss caused by co-crystallization of boron and lithium, concentrated hydrochloric acid is added to the first-level salt concentration and decalcification for deboronization, and the molar ratio of hydrochloric acid to boron in brine is 3-3.5 times.

[0015] Further, in step 2, the cooling crystallization temperature is 0-15°C; in step 2, Li in the brine obtained after the N-1 stage concentration + The concentration is 35-42g / L, Ca 2+ The concentration is 140-170 g / L, the concentration of B is 3-5.5 g / L, and the mass concentration ratio of Ca / Li is 3.5-5; in step 2, the washing water used for washing the calcium crystal salt includes one or more of the pre-concentrated solution, the brine obtained in the first or second stage of the solar salt concentration decalcification, the original brine and the calcium chloride solution, and the specific gravity of the wet weight of the washing water and the calcium crystal salt is m 3 / t is 0.1-0.7; in step 2, the lithium-containing brine produced by the Nth stage concentration has Li + The concentration is 45-50g / L, Ca 2+ The concentration is 110-141 g / L, the B concentration is 5.1-6.0 g / L, and the mass concentration ratio of Ca / Li is 2.0-3.02.

[0016] Furthermore, in step three, the pH value of the lithium-containing concentrated brine is adjusted to 10-11 by adding alkali, and the alkali is one or a combination of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the calcium precipitator is sodium carbonate or sodium sulfate, and the calcium precipitator is prepared into a nearly saturated solution, and the molar ratio of carbonate or sulfate in the calcium precipitator to calcium ion in the lithium-containing concentrated brine is 0.9-1.1; the reaction temperature of the lithium-containing concentrated brine and the calcium precipitator is 30-60°C, the reaction time is 30-120min, and the reaction is carried out under stirring conditions, and the edge linear speed of the stirring blade is 0.3-2.0m / s.

[0017] Further, in step 3, at least one of low salt water and raw brine is used to wash the calcium magnesium slag filter cake; when low salt water is used as washing water to wash the calcium magnesium slag filter cake, the specific gravity of the washing water and the wet weight of the calcium magnesium slag filter cake is m 3 / t is 0.1-0.5; the original brine is used as washing water to wash the calcium magnesium slag filter cake, and the specific gravity of the washing water and the wet weight of the calcium magnesium slag filter cake is m 3 / t is 1-3.

[0018] Furthermore, in step 4, the amount of Na2CO3 added is 0.9-1.1 times the theoretical required mass for complete precipitation of lithium as lithium carbonate, the reaction temperature is 60-90°C, the edge linear speed of the stirring blade is 0.3-2.0 m / s, and the reaction time is 30-120 min.

[0019] Further, in step 4, Li + The concentration of B is 1.0-2.0 g / L, the concentration of B is 0.1-0.9 g / L; the purity of the lithium carbonate product is greater than 90%.

[0020] Furthermore, in steps 2, 3 and 4, the solid-liquid separation method is one or more of belt filtration, plate and frame filter press and centrifugal filtration.

[0021] Furthermore, in step three, the washing solution with a Li concentration greater than 4 g / L is a high-lithium washing solution, and the washing solution with a Li concentration less than or equal to 4 g / L is a low-lithium washing solution.

[0022] The beneficial effects of the present invention are:

[0023] 1) The present invention adopts enhanced solar salt decalcification technology, which can further reduce the concentration ratio of calcium to lithium in concentrated brine and greatly reduce the consumption of subsequent chemical impurity removal agents; the calcium salt (which may contain lithium-containing co-crystallized complex salt) produced in the enhanced decalcification salt stage (Nth stage) is returned to the previous stage solar salt decalcification for anti-dissolution to avoid the loss of crystalline lithium; the calcium crystallized salt before the N-1 stage is washed, and the washing liquid is returned to the system to achieve effective recovery of entrained lithium, thereby greatly improving the comprehensive recovery rate of lithium.

[0024] 2) In the method of the present invention, after adding alkali to the lithium-containing concentrated brine to adjust the pH value, under high alkalinity conditions, the boron in the concentrated brine exists in the form of borate, and further reacts with calcium in the brine to form calcium borate, thereby achieving the purpose of removing boron and calcium. The co-precipitation of the two impurities can reduce the consumption of impurity removal agents, and at the same time can also save the separate boron removal process, reducing equipment investment and operating costs.

[0025] 3) The lithium precipitation mother liquor of the present invention can be co-disposed through salt pans. A lithium extraction processing plant is built in the salt pans, and the lithium precipitation mother liquor is directly returned to the pre-concentration tank. The residual carbonate ions are used to remove calcium from part of the brine, and the sodium chloride in the lithium precipitation mother liquor is precipitated by salting. The lithium in the mother liquor is returned to the system. The recovery process is simple and there is no problem of open-circuit disposal of salt.

[0026] 4) The present invention discloses a new method for extracting lithium from high-calcium salt lake brine, which prepares lithium carbonate products through the processes of solar salt concentration - crystallized salt washing - chemical precipitation to remove impurities - lithium precipitation, etc. It has the characteristics of short process flow, low investment cost, high lithium recovery rate, low reagent consumption and green environmental protection, which can reduce the production investment cost of the enterprise and further increase the economic benefits of the enterprise. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a flow chart of the method of Examples 1-3 of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0029] Example 1

[0030] This embodiment provides a method for extracting lithium from high-calcium salt lake brine, such as Figure 1 As shown, the specific process is:

[0031] Step 1: High calcium salt lake brine (Li + 1g / L, Ca 2+ 40g / L, Na + 73g / L, K + 8.64g / L, Mg 2+ 1.78g / L, B1.6g / L, Cl - 210g / L) for pre-concentration of solar salt to remove sodium and potassium salts, and obtain a pre-concentrated solution with a lithium concentration of 4.3g / L.

[0032] Step 2. The pre-concentrated liquid in step 1 is subjected to 6 levels of solar-salt concentration and decalcification. In each level of solar-salt concentration and decalcification, the brine after the solar-salt concentration is cooled and crystallized at 7°C to precipitate calcium. After centrifugal separation, the obtained brine continues to the next level of solar-salt concentration and decalcification. Among them, 37% hydrochloric acid is added in the 4th level to remove boron, and the molar ratio of the amount of hydrochloric acid added to the boron in the brine is 3.5 times to avoid the formation of colloids and the loss of lithium. After the calcium crystal salts of the first 5 levels are combined, they are washed with the pre-concentrated liquid, and the washing ratio is 0.7 (the washing ratio is the ratio of the volume of washing water to the wet salt (m 3 / t), the washing water (lithium concentration 6.5g / L) is returned to the first stage of salt concentration and decalcification, and the washed calcium salt is frozen and stored. + Concentration 41.3g / L, Ca 2+ The concentration is 143.7g / L, the B concentration is 3.5g / L, and the Ca / Li concentration ratio is about 3.48. After the sixth stage of salt concentration and decalcification, the produced calcium salt returns to the third stage of salt concentration and decalcification, and the produced lithium-containing brine Li + Concentration 50g / L, Ca 2+ Concentration 110g / L, Mg 2+ Concentration 6.6g / L, B concentration 5.5g / L, Ca / Li concentration ratio 2.2.

[0033] Step 3: Add 50% sodium hydroxide solution to the lithium-containing brine obtained by the sixth stage of salt concentration and decalcification to adjust the pH to 10, add a sodium carbonate solution with a mass concentration of 28% (the amount of sodium carbonate is 0.95 times the theoretical amount of calcium precipitation, that is, the molar ratio of sodium carbonate to calcium ions in the lithium-containing brine is 0.95) at 60°C and 1.1m / s stirring, react for 60 minutes, and perform solid-liquid separation by centrifugal filtration to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake; the lithium-containing purified liquid Li + Concentration 29.6g / L, Ca 2+ Concentration 6.1g / L, Mg 2+ The concentration of A is 0.06g / L, and the concentration of B is 1.1g / L. Then, the calcium-magnesium slag filter cake is washed with low brine and original brine respectively. The washing ratio of low brine washing is 0.5, and the lithium concentration of the washed liquid is 4.8g / L. It is added to the lithium-containing purified liquid. After merging, Li + The concentration is 26.2g / L; the washing ratio of the original brine is 1, and the lithium concentration of the washed liquid is 2.2g / L, which is returned to the pre-concentrated salt.

[0034] Step 4: Add the mixed lithium-containing purified liquid to a 28% sodium carbonate solution at 80°C for lithium precipitation, with a stirring blade edge linear speed of 1.0 m / s and a Na2CO3 dosage of 1.1 times the theoretical amount (i.e., Li +The reaction time was 60 min. After the reaction, the mother liquor Li was separated by centrifugation. + The concentration is 1.18g / L, which is returned to the pre-concentrated salt.

[0035] The dry purity of crude lithium carbonate product is 90.4%, and the lithium recovery rate is 68.1%. + After the precipitate (1.18 g / L) was returned to the pre-concentration step, the lithium recovery rate increased to 73.3%.

[0036] Example 2

[0037] This embodiment provides a method for extracting lithium from high-calcium salt lake brine, such as Figure 1 As shown, the specific process is:

[0038] Step 1: High calcium salt lake brine (Li + 0.2g / L, Ca 2+ 10g / L, Na + 93g / L, K + 3.8g / L, Mg 2+ 3.5g / L, B0.52g / L, Cl - 190g / L) is used for pre-concentration of solar salt to remove sodium and potassium salts, and a pre-concentrated solution with a lithium concentration of 4.0g / L is obtained.

[0039] Step 2: The pre-concentrated liquid in step 1 is subjected to 8 levels of solar-salt concentration and decalcification. In each level of solar-salt concentration and decalcification, the brine after solar-salt concentration is cooled and crystallized at 0°C to precipitate calcium. After centrifugal separation, the brine is pumped into the next level of solar-salt concentration and decalcification; wherein, 37% hydrochloric acid is added in the 4th and 6th levels to remove boron, and the molar ratio of hydrochloric acid added to boron in the brine is 3.2 times to avoid the formation of colloids and the loss of lithium. After the first 7 levels of calcium crystal salt are combined, the brine produced by the first level of solar-salt concentration and decalcification is used for washing, and the washing water (lithium concentration 7.8g / L) is returned to the second level of solar-salt concentration and decalcification, and the washed calcium salt is frozen for storage. The brine produced by the 7th level of solar-salt concentration and decalcification Li + Concentration 37g / L, Ca 2+ The concentration is 152g / L, the B concentration is 3.4g / L, and the Ca / Li concentration ratio is about 4.1. After the eighth stage of salt concentration and decalcification, the calcium salt produced returns to the first stage of salt concentration and decalcification, and the lithium-containing brine Li + Concentration 45g / L, Ca 2+ Concentration 136g / L, Mg 2+ The concentration is 5.9 g / L, the B concentration is 5.1 g / L, and the Ca / Li concentration ratio is about 3.02.

[0040] Step 3: Add 50% sodium hydroxide solution to the lithium-containing brine obtained by the eighth-level salt concentration and decalcification to adjust the pH to 11, add a sodium carbonate solution with a mass concentration of 28% under stirring conditions at 30°C and a linear speed of 2m / s, and the molar ratio of carbonate to calcium ions in the brine is 1.0), react for 30 minutes, and then use centrifugal filtration to separate the solid and liquid to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake, wherein the lithium-containing purified liquid Li + Concentration 23.6g / L, Ca 2+ Concentration 147mg / L, Mg 2+ The concentration of A is 5.6 mg / L, and the concentration of B is 1.08 g / L. Subsequently, the calcium-magnesium slag filter cake is washed with low brine and original brine respectively. The washing ratio of low brine washing is 0.1, and the lithium concentration of the washed liquid is 11.8 g / L. It is incorporated into the lithium-containing purified liquid. After merging, Li + The concentration is 23.2 g / L; the washing ratio of the original brine is 3, the lithium concentration of the washed liquid is 0.78 g / L, and it is returned for pre-concentration.

[0041] Step 4: Add the mixed lithium-containing purified liquid into a sodium carbonate solution with a mass concentration of 28% to precipitate lithium at 90°C, with a stirring blade edge linear speed of 1.5 m / s and a Na2CO3 dosage of 0.9 times the theoretical dosage (i.e., Li + The reaction time was 120 min. After the reaction, the mother liquor Li was separated by centrifugation. + The concentration was 2.0 g / L, which was returned to pre-concentration.

[0042] After drying, the crude lithium carbonate product was measured to have a purity of 96.2% and a lithium recovery rate of 64.4%. + After returning to the pre-concentration process (2.0 g / L), the lithium recovery rate increased to 72.6%.

[0043] Example 3

[0044] This embodiment provides a method for extracting lithium from high-calcium salt lake brine, such as Figure 1 As shown, the specific process is:

[0045] Step 1: High calcium salt lake brine (Li + 2g / L, Ca 2+ 85g / L, Na + 28.9g / L, K+18g / L, Mg 2+ 4.2g / L, B3.2g / L, Cl - 240g / L) for pre-concentration of solar salt to remove sodium and potassium salts, and obtain a pre-concentrated solution with a lithium concentration of 4.2g / L;

[0046] Step 2. The pre-concentrated liquid in step 1 is subjected to 4 levels of solar-salt concentration and decalcification. In each level of solar-salt concentration and decalcification, the brine after the solar-salt concentration is cooled and crystallized at 15°C to precipitate calcium. After centrifugal separation, the brine is pumped into the next level of solar-salt concentration and decalcification. In the third level of solar-salt concentration and decalcification, 37% hydrochloric acid is added to remove boron. The molar ratio of hydrochloric acid added to boron in the brine is 3.0 times to avoid the production of colloids and the loss of lithium. After the calcium crystal salts of the first three levels are combined, they are washed with the original brine, and the washing water (lithium concentration 5.6 g / L) is returned to the second level of solar-salt concentration and decalcification, and the calcium salt is frozen for storage. The brine Li produced by the third level of solar-salt concentration and decalcification + Concentration 35g / L, Ca 2+ The concentration is 166g / L, the B concentration is 3.7g / L, and the Ca / Li concentration ratio is about 4.74. After the fourth stage of salt concentration and decalcification, the produced calcium salt returns to the first stage of salt concentration and decalcification, and the produced lithium-containing brine Li + Concentration 48g / L, Ca 2+ Concentration 141g / L, Mg 2+ The concentration is 6.9 g / L, the B concentration is 5.7 g / L, and the Ca / Li concentration ratio is about 2.94.

[0047] Step 3: Add 50% sodium hydroxide solution to the lithium-containing brine obtained by the fourth-stage salt concentration and decalcification to adjust the pH to 11, add a 20% sodium sulfate solution at a stirring rate of 50°C and 0.3m / s, and the molar ratio of sulfate to calcium ions in the lithium-containing brine is 1.0. After reacting for 60 minutes, centrifugal filtration is used for solid-liquid separation to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake, wherein the lithium-containing purified liquid Li + Concentration 18.2g / L, Ca 2+ Concentration 0.63g / L, Mg 2+ The concentration of A is 5.3 mg / L, and the concentration of B is 1.1 g / L. Then, the calcium-magnesium slag filter cake is washed with low brine and original brine respectively. The washing ratio of low brine washing is 0.25, and the concentration of liquid lithium after washing is 5.46 g / L, which is incorporated into the lithium-containing purified liquid. The Li concentration after merging is 17.2 g / L; the washing ratio of original brine washing is 1, and the concentration of liquid lithium after washing is 0.87 g / L, which is returned to pre-concentration.

[0048] Step 4: Add a sodium carbonate solution with a mass concentration of 28% to the mixed lithium-containing purified liquid, and precipitate lithium at 60°C. The edge speed of the stirring blade is 2m / s, and the amount of Na2CO3 is 1.0 times the theoretical amount (i.e., Li + The reaction time was 30 min. After the reaction, the mother liquor Li was separated by centrifugation. + The concentration is 1.53 g / L and is returned to the pre-concentration tank.

[0049] After drying, the crude lithium carbonate product was measured to have a purity of 94.7% and a lithium recovery rate of 64.9%. + After the precipitate (1.53 g / L) was returned to the pre-concentration step, the lithium recovery rate increased to 72.7%.

[0050] Comparative Example

[0051] A comparative implementation was carried out on the traditional solar salt precipitation process of "pre-concentration - concentration and calcium removal - extraction and boron removal - chemical calcium and magnesium removal - precipitation of lithium carbonate".

[0052] Pre-concentration to remove sodium and potassium salt: high calcium lithium brine (Li + 1g / L, Ca 2+ 40g / L, Na + 73g / L, K + 8.64g / L, Mg 2+ 1.78g / L, B 1.6g / L, Cl - 210g / L) is pumped into the pre-concentration tank for pre-concentration of solar salt to remove sodium and potassium, and obtain a pre-concentrated solution with a lithium concentration of 4.3g / L.

[0053] Concentrated decalcified salt: The pre-concentrated liquid is pumped into the concentration tank for 6-stage solar salt concentration and decalcification. In each stage of solar salt concentration and decalcification, the brine after solar salt concentration is cooled and crystallized at 7°C to precipitate calcium, centrifuged, and the produced brine is pumped into the next stage of solar salt concentration and decalcification; 37% hydrochloric acid is added in the 4th stage to remove boron to avoid the formation of colloids; the calcium salt is not washed and stored. The brine produced by the 6th stage solar salt concentration and decalcification has a Li concentration of 40g / L, a Ca concentration of 157g / L, a B concentration of 3.5g / L, and a Ca / Li concentration ratio of about 3.93.

[0054] Extraction and boron removal: The lithium-containing concentrated brine obtained by the 6th level of salt concentration and decalcification is subjected to three-stage cascade extraction with a mono-fatty alcohol extractant at an O / A ratio of 1.5:1 (the diluent is D80 solvent oil and the extractant concentration is 25%). After three-stage extraction, the Li concentration of the boron-extracted residual liquid is 39.87 g / L, the Ca concentration is 156.5 g / L, the B concentration is <0.5 mg / L, and the Ca / Li concentration ratio is about 3.93.

[0055] Calcium and magnesium removal: add 50% sodium hydroxide solution to the boron extraction residual solution to adjust the pH to 10, add 28% sodium carbonate solution (the amount of sodium carbonate is 0.95 times the theoretical amount of calcium in the precipitation brine, that is, the molar ratio of sodium carbonate to calcium ions in the solution is 0.95) at 60°C and 1.1m / s stirring conditions, react for 60 minutes, and then use centrifugal filtration for solid-liquid separation to obtain lithium-containing purified liquid and filter cake, wherein the lithium-containing purified liquid Li + Concentration 19.3g / L, Ca 2+ Concentration 6.91g / L, Mg2+ The concentration is 0.06g / L. Then, the calcium and magnesium slag filter cake is washed with low salt water, and the washing ratio of low salt water washing is 2, and the washing water is returned to the calcium and magnesium removal system.

[0056] Lithium carbonate precipitation: add 28% sodium carbonate solution to the mixed lithium-containing purified liquid and precipitate lithium at 80°C. The amount of Na2CO3 is Li + The amount of Na2CO3 required to completely form Li2CO3 is 1.1 times, the reaction time is 60 minutes, and centrifugal filtration is performed after the reaction. The Li concentration of the lithium precipitated mother liquor is 1.2g / L; after drying, the crude lithium carbonate product is measured to have a purity of 85.3%, and the comprehensive lithium recovery rate is 39.1%.

[0057] The implementation results of Examples 1-3 and Comparative Examples are shown in Table 1.

[0058] Table 1

[0059]

[0060] Through Examples 1-3 and the comparative examples, it can be found that Examples 1-3 use enhanced solar salt decalcification - crystal salt washing - chemical precipitation method for impurity removal (boron synergistic calcium removal in brine) - lithium precipitation and other processes to prepare lithium carbonate products, which have the characteristics of low calcium-lithium ratio in concentrated brine, thereby less reagent consumption, and comprehensive lithium recovery rate and high product purity.

[0061] For those skilled in the art, various corresponding changes and modifications can be made according to the above technical solutions and concepts, and all of these changes and modifications should be included in the protection scope of the claims of the present invention.

Claims

1. A method for extracting lithium from high-calcium salt lake brine, characterized in that: The following steps are involved: Step 1: Pre-concentrate the high-calcium salt lake brine by solarization to remove most of the sodium salt and potassium salt to obtain a pre-concentrated solution; Step 2, subjecting the pre-concentrated liquid in step 1 to N-level solar-salt concentration and decalcification; in each level of solar-salt concentration and decalcification, solar-salt concentration is first performed, and the brine after solar-salt concentration is cooled and crystallized to precipitate calcium crystalline salt, and after solid-liquid separation, the brine continues to be subjected to the next level of solar-salt concentration and decalcification; the calcium crystalline salt obtained in the first N-1 levels is washed, and the washing water obtained after washing is returned to the previous level of solar-salt concentration and decalcification, and the calcium crystalline salt obtained after washing is stored; the calcium crystalline salt produced by the N-level solar-salt concentration and decalcification is returned to the previous level of solar-salt concentration and decalcification, and the lithium-containing concentrated brine produced by the N-level solar-salt concentration and decalcification enters step 3; In step 3, after adding alkali to adjust the pH value of the lithium-containing concentrated brine obtained in step 2, react with a calcium precipitation agent, and then perform solid-liquid separation to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake; the calcium-magnesium slag filter cake is washed to obtain a washing liquid, and a high-lithium washing liquid with a Li concentration exceeding a set value is incorporated into the lithium-containing purified liquid to obtain a mixed solution, and a low-lithium washing liquid with a Li concentration not exceeding a set value is returned to step 1 for pre-concentration of salt; Step 4: Prepare lithium carbonate from the mixed solution of the high-lithium washing solution and the lithium-containing purification solution in step 3 by sodium carbonate precipitation method, and the lithium precipitation mother liquor after liquid-solid separation is directly returned to step 1 for salt pre-concentration.

2. The method according to claim 1, characterized in that In step 1, the high calcium salt lake brine is chloride brine, wherein Li + The concentration is 200-2000mg / L, Ca 2+ The concentration is 10-85g / L, Na + The concentration is 28-100g / L, K + The concentration is 2-18g / L, the concentration of B is 0.1-3.2g / L, and the concentration of Cl is - The concentration is 80-240g / L, where the mass concentration ratio of Ca / Li is ≥20; Li in the pre-concentrated solution + The concentration is 3-4.5g / L, Ca 2+ The concentration is 180-220 g / L, the B concentration is 1-6.5 g / L, and the mass concentration ratio of Ca / Li is >20.

3. The method according to claim 1, characterized in that In step 2, N is greater than or equal to 4; in order to prevent lithium loss caused by co-crystallization of boron and lithium, concentrated hydrochloric acid is added to at least one level of salt concentration and decalcification for deboronization, and the molar ratio of hydrochloric acid to boron in brine is 3-3.5 times.

4. The method according to claim 1, characterized in that: In step 2, the cooling crystallization temperature is 0-15°C; in step 2, the Li + The concentration is 35-42g / L, Ca 2+ The concentration is 140-170 g / L, the concentration of B is 3-5.5 g / L, and the mass concentration ratio of Ca / Li is 3.5-5; in step 2, the washing water used for washing the calcium crystal salt includes one or more of the pre-concentrated solution, the brine obtained in the first or second stage of the solar salt concentration decalcification, the original brine and the calcium chloride solution, and the specific gravity of the wet weight of the washing water and the calcium crystal salt is m 3 / t is 0.1-0.7; in step 2, Li in the lithium-containing brine produced by the Nth stage concentration + The concentration is 45-50g / L, Ca 2+ The concentration is 110-141 g / L, the B concentration is 5.1-6.0 g / L, and the mass concentration ratio of Ca / Li is 2.0-3.

02.

5. The method according to claim 1, characterized in that In step three, the pH value of lithium-containing concentrated brine is adjusted to 10-11 by adding alkali, and the alkali is one or a combination of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the calcium precipitator is sodium carbonate or sodium sulfate, and the calcium precipitator is prepared into a nearly saturated solution, and the molar ratio of carbonate or sulfate in the calcium precipitator to calcium ion in the lithium-containing concentrated brine is 0.9-1.1; the reaction temperature of lithium-containing concentrated brine and the calcium precipitator is 30-60°C, the reaction time is 30-120min, and the reaction is carried out under stirring conditions, and the edge linear speed of the stirring blade is 0.3-2.0m / s.

6. The method according to claim 1, characterized in that In step 3, at least one of low salt water and raw brine is used to wash the calcium magnesium slag filter cake; when low salt water is used as washing water to wash the calcium magnesium slag filter cake, the specific gravity of the washing water and the wet weight of the calcium magnesium slag filter cake is m 3 / t is 0.1-0.5; the original brine is used as washing water to wash the calcium magnesium slag filter cake, and the specific gravity of the washing water and the wet weight of the calcium magnesium slag filter cake is m 3 / t is 1-3.

7. The method according to claim 1, characterized in that In step 4, the amount of Na2CO3 added is 0.9-1.1 times the theoretical required mass for complete precipitation of lithium as lithium carbonate, the reaction temperature is 60-90°C, the edge linear speed of the stirring blade is 0.3-2.0 m / s, and the reaction time is 30-120 min.

8. The method according to claim 1, characterized in that: In step 4, Li in the lithium precipitation mother liquor + The concentration of B is 1.0-2.0 g / L, the concentration of B is 0.1-0.9 g / L; the purity of the lithium carbonate product is greater than 90%.

9. The method according to claim 1, characterized in that: In steps 2, 3 and 4, the solid-liquid separation method is one or more of belt filtration, plate and frame filter press and centrifugal filtration.

10. The method according to claim 1, characterized in that In step 3, the washing solution with a Li concentration greater than 4 g / L is a high-lithium washing solution, and the washing solution with a Li concentration less than or equal to 4 g / L is a low-lithium washing solution.

Images