Method for extracting lithium from high-calcium salt lake brine

Abstract

The application discloses a method for extracting lithium from high-calcium salt lake brine, adopts intensified solar salt decalcification technology, greatly reduces the consumption of subsequent chemical impurity removal reagents, returns calcium salt generated in the intensified decalcification salt stage (Nth stage) to the previous solar salt decalcification stage for reverse dissolution, avoids loss of crystallized lithium, washes calcium crystallized salt before the N-1th stage, returns the washing liquid to the system, realizes effective recovery of lithium carried, and greatly improves the comprehensive lithium recovery rate. According to the properties of the brine solution and the co-precipitation behavior of impurities, the co-precipitation behavior of calcium and boron in concentrated brine is utilized to reduce the consumption of impurity removal reagents, and a separate boron removal process can be omitted, thereby reducing equipment investment and operation cost. The lithium carbonate product is prepared through the processes of solar salt concentration, crystallized salt washing, chemical precipitation impurity removal and lithium precipitation, and has the characteristics of short process flow, low investment cost, high lithium recovery rate, small reagent consumption and green environmental protection, and the like, so that the production investment cost of enterprises can be reduced, and the economic benefits of enterprises can be further increased.

Description

Technical Field

[0001] This invention relates to the field of hydrometallurgical technology, specifically to a method for extracting lithium from high-calcium salt lake brine. Background Technology

[0002] With the rapid development of the new energy industry, the demand for lithium batteries is constantly increasing, thus accelerating the development of lithium resources. Compared with hard rock lithium mines, brine lithium mines in salt lakes have advantages such as high resource reserves, being environmentally friendly, and low cost. Furthermore, with the continuous advancement of brine lithium extraction technology, the production capacity of brine lithium mines will be further released.

[0003] Salt lake lithium deposits account for approximately 60% of global lithium resources, and in my country, this type of resource accounts for over 80% of total reserves. The composition and properties of brine vary across different regions, thus lithium extraction from salt lakes requires a tailored approach for each lake. Currently, the main lithium extraction processes from salt lakes include: solar salt concentration and precipitation, adsorption, membrane methods, extraction, and calcination leaching. However, most of these processes primarily target lithium extraction from high magnesium-to-lithium ratio salt lake brines, with relatively few research reports on lithium extraction from high-calcium salt lake brines. CN115806301A discloses a method for producing lithium carbonate from high-calcium deep brine using adsorption, concentrating high-calcium deep brine with low lithium content (≥50 mg / L) to Li... + When the lithium content is around 300–600 mg / L, a manganese-based adsorbent is used for adsorption-desorption-enrichment. The solution is adjusted to strong alkalinity with sodium hydroxide to remove low levels of impurities such as manganese, magnesium, and iron. The lithium-rich brine is then concentrated to 10–12 g / L, and excess sodium oxalate is added to adjust the pH to 11.0–11.5 to remove calcium and magnesium, reducing the calcium-to-lithium ratio and magnesium-to-lithium ratio to a certain value. Finally, the solution is concentrated to a concentration of Li. + ≥11.0 g / L, lithium carbonate is precipitated by adding a saturated sodium carbonate solution under water bath temperature above 85℃. The washing solution and tailings are then concentrated to Li + A secondary precipitation process is performed at concentrations ≥11 g / L to obtain qualified lithium carbonate product. This process suffers from several drawbacks, including high consumption of reagents such as sodium hydroxide and sodium oxalate, high solubility of manganese-based adsorbents, and an overall lithium recovery rate of only 50%. Furthermore, when the desorption solution is a sulfuric acid system, desorption easily forms calcium sulfate precipitate (gypsum), affecting the subsequent use of the adsorbent.

[0004] CN114014340A discloses a method for calcium removal and lithium enrichment from high-calcium-salt-ratio salt lake brine, comprising the following steps: (1) naturally evaporating calcium chloride-type lithium-containing brine from a salt lake 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, causing calcium chloride crystals to precipitate, and then performing solid-liquid separation. This process only introduces the lithium recovery process of brine salt drying. In the later stage of calcium salt drying, the viscosity of the old brine gradually increases, and the loss of lithium carried by calcium salt increases. Furthermore, the lithium concentration of the concentrated brine after calcium salt drying is controlled within 38 g / L to ensure the lithium yield (55%-60%) in the calcium drying stage. However, 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 calcium removal process.

[0005] Given the current problems in lithium extraction from high-calcium brine, there is a need to develop a new lithium extraction process that is simple, has low investment costs, low reagent consumption, and high lithium recovery rate. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention aims to provide a method for lithium extraction from high-calcium salt lake brine.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for lithium extraction from high-calcium salt lake brine includes the following steps:

[0009] Step 1: The high-calcium salt lake brine is pre-concentrated by evaporation to remove most of the sodium and potassium salts, and then a pre-concentrated solution is obtained.

[0010] Step 2: The pre-concentrated solution from Step 1 undergoes N-stage solar salt concentration and decalcification. In each stage of solar salt concentration and decalcification, solar salt concentration is performed first. After solar salt concentration, the brine is cooled and crystallized to precipitate calcium crystal salt. After solid-liquid separation, the brine continues to the next stage of solar salt concentration and decalcification. The calcium crystal salt obtained from the first N-1 stages is washed, and the wash water is returned to any previous stage of solar salt concentration and decalcification. The calcium crystal salt obtained after washing is stockpiled. The calcium crystal salt produced by the Nth stage of solar salt concentration and decalcification is returned to any previous stage of solar salt concentration and decalcification. The lithium-containing concentrated brine produced by the Nth stage of solar salt concentration and decalcification enters Step 3.

[0011] Step 3: After adjusting the pH value of the lithium-containing concentrated brine obtained in Step 2 with alkali, it reacts with the calcium precipitation agent and then performs solid-liquid separation to obtain lithium-containing purified liquid and calcium-magnesium slag filter cake. The calcium-magnesium slag filter cake is washed to obtain washing liquid. The high-lithium washing liquid with a Li concentration exceeding the set value is added to the lithium-containing purified liquid to obtain a mixed solution, and the low-lithium washing liquid with a Li concentration not exceeding the set value is returned to Step 1 for salt pre-concentration.

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

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

[0014] Furthermore, in step two, 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 primary salt concentration and decalcification process to remove boron, and the molar ratio of hydrochloric acid to boron in the brine is 3-3.5 times.

[0015] Furthermore, in step two, the cooling crystallization temperature is 0-15℃; in step two, the Li in the brine obtained after the N-1th stage concentration... + Concentration of 35-42 g / L, Ca 2+ The concentration is 140-170 g / L, the B concentration is 3-5.5 g / L, and the Ca / Li mass concentration ratio is 3.5-5. In step two, the washing water used to wash the calcium crystal salt includes one or a combination of pre-concentrated solution, brine obtained from the first or second stage of decalcification in salt concentration, raw brine, and calcium chloride solution. The specific gravity m of the washing water and the calcium crystal salt is... 3 / t is 0.1-0.7; in step two, the lithium-containing concentrated brine produced by the Nth stage concentration contains Li + The concentration is 45-50 g / L, Ca 2+ The concentration was 110-141 g / L, the B concentration was 5.1-6.0 g / L, and the Ca / Li mass concentration ratio was 2.0-3.02.

[0016] Further, in step three, the pH value of the lithium-containing concentrated halide is adjusted to 10-11 by adding an alkali, which is one or a combination of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the calcium precipitation agent is sodium carbonate or sodium sulfate, and the calcium precipitation agent is prepared into a near-saturated solution, with the molar ratio of carbonate or sulfate ions in the calcium precipitation agent to calcium ions in the lithium-containing concentrated halide being 0.9-1.1; the reaction temperature of the lithium-containing concentrated halide and the calcium precipitation agent is 30-60℃, the reaction time is 30-120 min, and the reaction is carried out under stirring conditions, with the edge linear velocity of the stirring blade being 0.3-2.0 m / s.

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

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

[0019] Furthermore, in step four, the Li in the lithium precipitation mother liquor... + The concentration of B is 1.0-2.0 g / L, and the concentration of B is 0.1-0.9 g / L; the purity of lithium carbonate products is greater than 90%.

[0020] Furthermore, in steps two, three, and four, the solid-liquid separation method is one or more of belt filtration, plate and frame filtration, 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 this invention are as follows:

[0023] 1) This invention employs enhanced solar salt decalcification technology, which can further reduce the calcium to lithium concentration ratio in concentrated brine and significantly reduce the consumption of subsequent chemical impurity removal agents; the calcium salt (which may contain lithium co-crystallized complex salt) generated in the enhanced decalcification salt stage (Nth stage) is returned to the previous solar salt decalcification stage for reverse dissolution, avoiding the loss of crystalline lithium; the calcium crystalline salt before N-1 stage is washed, and the washing liquid is returned to the system, achieving effective recovery of entrained lithium and significantly improving the overall lithium recovery rate.

[0024] 2) In the method of the present invention, after adjusting the pH value by adding alkali to the lithium-containing concentrated brine, under high alkalinity conditions, boron in the concentrated brine exists in the form of borate ions, 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 can also eliminate the separate boron removal process, thereby reducing equipment investment and operating costs.

[0025] 3) The lithium precipitation mother liquor of this invention can be co-processed in salt fields. A lithium extraction processing plant is built in the salt field, and the lithium precipitation mother liquor is directly returned to the pre-concentration tank. The calcium in the brine is removed by the residual carbonate ions, while the sodium chloride in the lithium precipitation mother liquor is precipitated by sun-drying. 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) This invention discloses a novel method for lithium extraction from high-calcium salt lake brine. The method involves a process of salt concentration by sun-drying, washing with crystallized salt, removing impurities by chemical precipitation, and lithium precipitation to produce lithium carbonate products. This method features a short process flow, low investment cost, high lithium recovery rate, low reagent consumption, and environmental friendliness. It can reduce the production investment cost of enterprises and further increase their economic benefits. Attached Figure Description

[0027] Figure 1 The following are flowcharts of the methods in embodiments 1-3 of the present invention. Detailed Implementation

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

[0029] Example 1

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

[0031] Step 1: High-calcium salt lake brine (Li + 1g / L, Ca 2+ 40g / L, Na + 73g / L, K + 8.64 g / L, Mg 2+ 1.78 g / L, B 1.6 g / L, Cl - The sodium and potassium salts were removed by sun-drying (210 g / L) to obtain a pre-concentrated solution with a lithium concentration of 4.3 g / L.

[0032] Step Two: The pre-concentrated brine from Step One undergoes a 6-stage solar salt concentration and decalcification process. In each stage, the concentrated brine is cooled at 7°C to crystallize calcium, which is then separated by centrifugation. The resulting brine is then further processed in the next stage of solar salt concentration and decalcification. In the fourth stage, 37% hydrochloric acid is added to remove boron. The molar ratio of hydrochloric acid to boron in the brine is 3.5 to avoid the formation of colloidal substances and lithium loss. The calcium crystals from the first five stages are combined and washed with the pre-concentrated brine at a washing ratio of 0.7 (the washing ratio is the volume of washing water relative to the specific gravity of wet salt (m³)). 3 The wash water (lithium concentration 6.5 g / L) is returned to the first stage of solar salt concentration and decalcification, and the washed calcium salt is stored frozen. The Li in the brine produced from the fifth stage of solar salt concentration and decalcification... + Concentration 41.3 g / L, Ca 2+ The concentration of calcium salt was 143.7 g / L, the concentration of boron was 3.5 g / L, and the Ca / Li ratio was approximately 3.48. After the sixth stage of salt concentration and decalcification, the calcium salt produced was returned to the third stage of salt concentration and decalcification, and the resulting lithium-containing concentrated brine was Li. + Concentration 50g / L, Ca 2+ Concentration 110 g / L, Mg 2+ The concentration of B was 6.6 g / L, the concentration of B was 5.5 g / L, and the Ca / Li concentration ratio was 2.2.

[0033] Step 3: Add 50% sodium hydroxide solution to the lithium-containing concentrated brine obtained from the sixth stage of salt concentration and decalcification to adjust the pH to 10. Under stirring conditions of 60℃ and 1.1m / s linear velocity, add a 28% sodium carbonate solution (the amount of sodium carbonate used is 0.95 times the theoretical amount of calcium precipitation, i.e., the molar ratio of sodium carbonate to calcium ions in the lithium-containing concentrated brine is 0.95). After reacting for 60 minutes, use centrifugal filtration to separate the solid and liquid phases to obtain a lithium-containing purified liquid and a calcium-magnesium slag filter cake; the lithium-containing purified liquid Li + Concentration 29.6 g / L, Ca 2+ Concentration 6.1 g / L, Mg 2+ The concentration of B was 0.06 g / L, and the concentration of B was 1.1 g / L. Subsequently, the calcium-magnesium slag filter cake was washed with low-salt water and raw brine, respectively. The washing ratio of the low-salt water was 0.5. The lithium concentration of the washed liquid was 4.8 g / L, which was then added to the lithium-containing purification solution. After merging, the Li... + The concentration was 26.2 g / L; the washing ratio of the original brine was 1, and the lithium concentration of the washed liquid was 2.2 g / L, which was then returned to the pre-concentration and sun-drying process.

[0034] Step 4: Add the mixed lithium-containing purified solution to a 28% sodium carbonate solution and precipitate lithium at 80°C. The linear velocity of the stirring impeller edge is 1.0 m / s, and the amount of Na2CO3 used is 1.1 times the theoretical amount (i.e., Li). +The amount of Na2CO3 required to completely form Li2CO3 was 1.1 times the amount required for complete formation. The reaction time was 60 min. After the reaction, the mixture was centrifuged and filtered to separate the lithium, and the lithium mother liquor was precipitated. + The concentration was 1.18 g / L, and it was returned to the pre-concentration salt production.

[0035] The crude lithium carbonate product has a dry basis purity of 90.4% and a lithium recovery rate of 68.1%. The lithium precipitation mother liquor (Li...) + After returning 1.18 g / L to the pre-concentration process, the lithium recovery rate increased to 73.3%.

[0036] Example 2

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

[0038] Step 1: High-calcium salt lake brine (Li + 0.2g / L, Ca 2+ 10g / L, Na + 93g / L, K + 3.8 g / L, Mg 2+ 3.5g / L, B 0.52g / L, Cl - The sodium and potassium salts were removed by sun-drying (190 g / L) to obtain a pre-concentrated solution with a lithium concentration of 4.0 g / L.

[0039] Step 2: The pre-concentrated brine from Step 1 undergoes an 8-stage solar salt concentration and decalcification process. In each stage, the concentrated brine is cooled at 0°C to crystallize calcium, which is then separated by centrifugation and fed into the next stage. In stages 4 and 6, 37% hydrochloric acid is added to remove boron; the molar ratio of hydrochloric acid to boron in the brine is 3.2 times to avoid the formation of colloidal substances and lithium loss. The calcium crystals from the first 7 stages are combined and washed with the brine produced in the first stage of solar salt concentration and decalcification. The wash water (lithium concentration 7.8 g / L) is returned to the second stage of solar salt concentration and decalcification, and the washed calcium salt is stored frozen. The brine produced in the 7th stage of solar salt concentration and decalcification yields Li... + Concentration 37 g / L, Ca 2+ The concentration was 152 g / L, the B concentration was 3.4 g / L, and the Ca / Li concentration ratio was approximately 4.1. After the 8th stage of salt concentration and decalcification, the produced calcium salt was returned to the 1st stage of salt concentration and decalcification, and the produced lithium-containing concentrated brine was Li. + Concentration 45g / L, Ca 2+ Concentration 136 g / L, Mg 2+ The concentration of B is 5.9 g / L, the concentration of B is 5.1 g / L, and the Ca / Li concentration ratio is approximately 3.02.

[0040] Step 3: Add 50% sodium hydroxide solution to the lithium-containing concentrated brine obtained from the 8th stage of salt concentration and decalcification to adjust the pH to 11. Under the conditions of 30℃ and 2m / s linear speed stirring, add 28% sodium carbonate solution (molar ratio of carbonate to calcium ions in the concentrated brine is 1.0). After reacting for 30 minutes, use centrifugal filtration to separate the solid and liquid phases to obtain lithium-containing purified liquid and calcium-magnesium slag filter cake. The lithium-containing purified liquid contains Li... + Concentration 23.6 g / L, Ca 2+ Concentration 147 mg / L, Mg 2+ The concentration of B was 5.6 mg / L, and the concentration of B was 1.08 g / L. Subsequently, the calcium-magnesium slag filter cake was washed with low-salt water and raw brine, respectively. The washing ratio of the low-salt water was 0.1. The lithium concentration of the washed liquid was 11.8 g / L, which was then added to the lithium-containing purification solution. After merging, the Li... + The concentration was 23.2 g / L; the washing ratio of the original brine was 3, and the lithium concentration of the washed liquid was 0.78 g / L, which was then returned to the pre-concentration.

[0041] Step 4: Add the mixed lithium-containing purified solution to a 28% sodium carbonate solution and precipitate lithium at 90°C. The linear velocity of the stirring impeller edge is 1.5 m / s, and the amount of Na2CO3 used is 0.9 times the theoretical amount (i.e., Li). + The amount of Na2CO3 required to completely form Li2CO3 was 0.9 times the amount required for complete formation. The reaction time was 120 min. After the reaction, the mixture was centrifuged and filtered to separate the lithium, and the lithium mother liquor was precipitated. + The concentration was 2.0 g / L, and it was returned to the pre-concentration stage.

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

[0043] Example 3

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

[0045] Step 1: High-calcium salt lake brine (Li + 2g / L, Ca 2+ 85g / L, Na + 28.9 g / L, K+ 18 g / L, Mg 2+ 4.2 g / L, B 3.2 g / L, Cl - The sodium and potassium salts were removed by sun-drying (240 g / L) to obtain a pre-concentrated solution with a lithium concentration of 4.2 g / L.

[0046] Step 2: The pre-concentrated brine from Step 1 undergoes a four-stage solar salt concentration and decalcification process. In each stage, the concentrated brine is cooled at 15°C to crystallize calcium, which is then separated by centrifugation and fed into the next stage. In the third stage, 37% hydrochloric acid is added to remove boron. The molar ratio of hydrochloric acid to boron in the brine is 3.0 to avoid the formation of colloidal substances and lithium loss. The calcium crystals from the first three stages are combined and washed with the original brine. The wash water (lithium concentration 5.6 g / L) is returned to the second stage of solar salt concentration and decalcification, while the calcium salts are stored frozen. The brine produced from the third stage of solar salt concentration and decalcification yields Li. + Concentration 35g / L, Ca 2+ The concentration was 166 g / L, the B concentration was 3.7 g / L, and the Ca / Li concentration ratio was approximately 4.74. After the fourth stage of solar salt concentration and decalcification, the calcium salt produced was returned to the first stage of solar salt concentration and decalcification, and the resulting lithium-containing concentrated brine (Li) was... + Concentration 48 g / L, Ca 2+ Concentration 141 g / L, Mg 2+ The concentration was 6.9 g / L, the B concentration was 5.7 g / L, and the Ca / Li concentration ratio was approximately 2.94.

[0047] Step 3: Add 50% sodium hydroxide solution to the lithium-containing concentrated brine obtained from the fourth stage of salt concentration and decalcification to adjust the pH to 11. Under stirring conditions of 50℃ and 0.3m / s linear velocity, add 20% sodium sulfate solution (mass concentration). The molar ratio of sulfate to calcium ions in the lithium-containing concentrated 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. The lithium-containing purified liquid contains Li... + Concentration 18.2 g / L, Ca 2+ Concentration 0.63 g / L, Mg 2+ The concentration of B was 5.3 mg / L, and the concentration of B was 1.1 g / L. Subsequently, the calcium-magnesium slag filter cake was washed with low-salt water and raw brine, respectively. The washing ratio of low-salt water washing was 0.25, and the lithium concentration in the washed liquid was 5.46 g / L, which was then added to the lithium-containing purification solution, resulting in a combined Li concentration of 17.2 g / L. The washing ratio of raw brine washing was 1, and the lithium concentration in the washed liquid was 0.87 g / L, which was then returned to the pre-concentration.

[0048] Step 4: Add a 28% sodium carbonate solution to the mixed lithium-containing purified solution, and precipitate lithium at 60°C. The linear velocity of the stirring impeller edge is 2 m / s, and the amount of Na2CO3 used is 1.0 times the theoretical amount (i.e., Li). + The amount of Na2CO3 required to completely form Li2CO3 is 1.0 times the amount required for complete formation. The reaction time is 30 min. After the reaction, centrifugation and filtration are performed to separate the lithium from the mother liquor. + The concentration was 1.53 g / L, and it was returned to the pre-concentration tank.

[0049] After drying, the crude lithium carbonate product was found to have a purity of 94.7%, with a lithium recovery rate of 64.9%. The lithium precipitation mother liquor (Li...) + After returning 1.53 g / L to the pre-concentration process, the lithium recovery rate increased to 72.7%.

[0050] Comparative Example

[0051] A comparative study was conducted on the traditional salt precipitation process of "pre-concentration - concentration to remove calcium - extraction to remove boron - chemical removal of calcium and magnesium - precipitation of lithium carbonate".

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

[0053] Concentration and Decalcification of Salt: The pre-concentrated brine is fed into a concentration tank for six stages of solar salt concentration and decalcification. In each stage, the concentrated brine is cooled at 7°C to crystallize calcium, which is then separated by centrifugation. The resulting brine is fed into the next stage of solar salt concentration and decalcification. In the fourth stage, 37% hydrochloric acid is added to remove boron and prevent the formation of colloidal substances. Calcium salts are not washed and are stored. The brine produced by the sixth stage of solar salt concentration and decalcification has a Li concentration of 40 g / L, a Ca concentration of 157 g / L, a B concentration of 3.5 g / L, and a Ca / Li concentration ratio of approximately 3.93.

[0054] Boron removal by extraction: The lithium-containing concentrated brine obtained from the sixth stage of salt concentration and decalcification was subjected to a three-stage cascade extraction with a single fatty alcohol extractant at an O / A ratio of 1.5:1 (where the diluent was D80 solvent oil and the extractant concentration was 25%). After the three-stage extraction, the concentration of Li in the boron removal residue was 39.87 g / L, the concentration of Ca was 156.5 g / L, the concentration of B was <0.5 mg / L, and the Ca / Li concentration ratio was approximately 3.93.

[0055] Calcium and magnesium removal: The pH of the boron extraction residue was adjusted to 10 by adding 50% sodium hydroxide solution. Under stirring conditions of 60℃ and 1.1 m / s linear velocity, 28% sodium carbonate solution was added (the amount of sodium carbonate used was 0.95 times the theoretical amount of calcium in the precipitated brine, i.e., the molar ratio of sodium carbonate to calcium ions in the solution was 0.95). After reacting for 60 min, solid-liquid separation was performed by centrifugation filtration to obtain a lithium-containing purified solution and a filter cake. The lithium-containing purified solution contained Li... + Concentration 19.3 g / L, Ca 2+ Concentration 6.91 g / L, Mg2+ The concentration was 0.06 g / L. Subsequently, the calcium-magnesium slag filter cake was washed with low-salt water at a washing ratio of 2, and the wash water was returned to the calcium-magnesium removal system.

[0056] Lithium carbonate precipitation: The mixed lithium-containing purified solution is added to a 28% sodium carbonate solution and lithium is precipitated at 80°C. The amount of Na2CO3 used is [missing information - likely a specific concentration]. + The amount of Na2CO3 required to completely form Li2CO3 was 1.1 times that required, and the reaction time was 60 min. After the reaction, centrifugation and filtration were performed to separate the lithium. The concentration of Li in the lithium precipitation mother liquor was 1.2 g / L. After drying, the purity of the crude lithium carbonate product was determined to be 85.3%, and the overall lithium recovery rate was 39.1%.

[0057] The implementation results of Examples 1-3 and the 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 the lithium carbonate products prepared by Examples 1-3 using enhanced sun-drying decalcification, crystallization salt washing, chemical precipitation (boron in brine for calcium removal) and lithium precipitation have the significant advantages of low calcium-to-lithium ratio in concentrated brine, resulting in less reagent consumption, and high comprehensive lithium recovery rate and high product purity.

[0061] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for lithium extraction from high-calcium salt lake brine, characterized in that, Includes the following steps: Step 1: The high-calcium salt lake brine is pre-concentrated by evaporation to remove most of the sodium and potassium salts, and then a pre-concentrated solution is obtained. Step 2: The pre-concentrated solution from Step 1 undergoes N-stage solar salt concentration and decalcification. In each stage of solar salt concentration and decalcification, solar salt concentration is performed first. After solar salt concentration, the brine is cooled and crystallized to precipitate calcium crystals. After solid-liquid separation, the brine continues to the next stage of solar salt concentration and decalcification. The calcium crystals obtained from the first N-1 stages are washed, and the wash water is returned to any previous stage of solar salt concentration and decalcification. The calcium crystals obtained after washing are stockpiled. The calcium crystals produced in the Nth stage of solar salt concentration and decalcification are returned to any previous stage of solar salt concentration and decalcification. The lithium-containing concentrated brine produced in the Nth stage of solar salt concentration and decalcification enters Step 3. The calcium crystals produced in the Nth stage of solar salt concentration and decalcification contain lithium-containing complex salts. 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 remove boron in at least one stage of salt concentration and decalcification, and the molar ratio of hydrochloric acid to boron in brine is 3-3.

5. Step 3: After adjusting the pH of the lithium-containing concentrated brine obtained in Step 2 with alkali, it reacts with the calcium precipitation agent. Simultaneously, boron in the lithium-containing concentrated brine exists as borate ions and reacts with calcium in the lithium-containing concentrated brine to form calcium borate. Then, solid-liquid separation is performed 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. The high-lithium washing liquid with a Li concentration exceeding the set value is added to the lithium-containing purified liquid to obtain a mixed solution, while the low-lithium washing liquid with a Li concentration not exceeding the set value is returned to Step 1 for pre-concentration by sun-drying. The pH of the lithium-containing concentrated brine is adjusted to 10-11 with alkali. The calcium precipitation agent is sodium carbonate or sodium sulfate, prepared as a near-saturated solution. The molar ratio of carbonate or sulfate ions in the calcium precipitation agent to calcium ions in the lithium-containing concentrated brine is 0.9-1.

0. Step 4: Prepare lithium carbonate by using sodium carbonate precipitation method on the mixed solution of high lithium washing solution and lithium-containing purification solution in Step 3. 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 one, the high-calcium salt lake brine is a chloride-type brine, in which Li + Concentration of 200-2000 mg / L, Ca 2+ The concentration is 10-85 g / L, Na + Concentration of 28-100 g / L, K + The concentration of B is 2-18 g / L, the concentration of Cl is 0.1-3.2 g / L, and the concentration of Cl is 0.1-3.2 g / L. - The concentration is 80-240 g / L, where the Ca / Li mass concentration ratio is ≥20; the Li in the pre-concentrated solution + The concentration is 3-4.5 g / L, Ca 2+ The concentration is 180-220 g / L, the B concentration is 1-6.5 g / L, and the Ca / Li mass concentration ratio is >20.

3. The method according to claim 1, characterized in that, In step two, the cooling crystallization temperature is 0-15℃; in step two, the Li in the brine obtained after the N-1th stage concentration... + Concentration of 35-42 g / L, Ca 2+ The concentration is 140-170 g / L, the B concentration is 3-5.5 g / L, and the Ca / Li mass concentration ratio is 3.5-5. In step two, the washing water used to wash the calcium crystal salt includes one or a combination of pre-concentrated solution, brine obtained from the first or second stage of decalcification in salt concentration, raw brine, and calcium chloride solution. The specific gravity m of the washing water and the calcium crystal salt is... 3 / t is 0.1-0.7; in step two, the lithium-containing concentrated brine produced by the Nth stage concentration contains Li + The concentration is 45-50 g / L, Ca 2+ The concentration was 110-141 g / L, the B concentration was 5.1-6.0 g / L, and the Ca / Li mass concentration ratio was 2.0-3.

02.

4. The method according to claim 1, characterized in that, In step three, the alkali is one or a combination of sodium hydroxide, potassium hydroxide, and lithium hydroxide; the reaction temperature of the lithium-containing concentrated halide and the calcium precipitation agent is 30-60℃, the reaction time is 30-120 min, the reaction is carried out under stirring conditions, and the linear velocity of the stirring blade edge is 0.3-2.0 m / s.

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

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

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

8. The method according to claim 1, characterized in that, In steps two, three, and four, the solid-liquid separation method is one or more of belt filtration, plate and frame filtration, and centrifugal filtration.

9. The method according to claim 1, characterized in that, 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.

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