Method for preparing lithium carbonate from carbonate type salt lake sediment lithium ore

Abstract

The invention relates to a method for preparing lithium carbonate from carbonate type salt lake sediment lithium ore, which comprises the following steps: dissolving lithium-containing particles by using fresh water at normal pressure and normal temperature to obtain a dissolved solution and a water-insoluble substance; leaching the water insoluble substance and an ammonium acetate solution at normal pressure and normal temperature, and carrying out solid-liquid separation to obtain a leaching solution I and a leaching residue I; carrying out normal-pressure normal-temperature leaching on the leaching residue I and an acetic acid solution, and carrying out solid-liquid separation to obtain a leaching solution II and a leaching residue II; the dissolving solution, the first leaching solution and the second leaching solution are mixed to obtain a mixed solution, the mixed solution is heated, meanwhile, ammonia water is added for hydrolysis to remove iron and aluminum, solid-liquid separation is conducted, and ferro-aluminum sediment and a first separation solution are obtained; evaporating and concentrating the separated liquid I, removing calcium and magnesium to obtain calcium and magnesium precipitates and separated liquid II, and continuously evaporating and concentrating the separated liquid II to obtain high-temperature lithium-rich liquid; and carrying out heat preservation on the high-temperature lithium-rich liquid, adding alkali to precipitate lithium, washing and drying to obtain a lithium carbonate product. The method realizes effective separation, enrichment and extraction of lithium in the salt lake sediment lithium ore.

Description

Technical Field

[0001] The present invention relates to a method for preparing lithium carbonate from lithium ore in carbonate-type salt lake sediments, and particularly to the extraction of lithium from sedimentary lithium ore, belonging to the technical field of lithium extraction from lithium-containing minerals. Background Art

[0002] With the rapid development of new technologies and new energy vehicles and other industries in China, the demand for lithium and lithium salts has been increasing year by year. This trend poses new requirements for the global lithium resource supply and low-cost lithium extraction methods. Lithium resources in nature are mainly divided into three categories: pegmatite type, brine type, and clay type. Currently, the developed lithium resources are mainly pegmatite type and salt lake type. Most of the lithium extraction methods for solid lithium ore adopt the assistant roasting method and the acid method. The roasting method requires a relatively high temperature, is prone to caking, and the generated Li-K double salt has low solubility, bringing certain difficulties to subsequent separation. When treating lithium minerals by the sulfuric acid method, a large amount of sulfuric acid is consumed, and a large amount of neutralizing agent is also required in the subsequent purification process.

[0003] Most of China's lithium ore is distributed in Qinghai, Tibet, Sichuan, Jiangxi and other places. The lithium resources in salt lakes are mainly stored in salt lake brines, sedimentary debris in the lake area, and salt deposits. Among them, the lithium resources in brines have been widely explored and large-scale development and utilization have been carried out. Recently, lithium resources mainly in the form of adsorption have been found in the bottom sediments of carbonate-type salt lakes. They mainly exist in easily soluble salt minerals, residual pore water, clay and other mineral adsorption, and carbonate minerals. Although their grade is low, they have a large resource volume, a simple extraction process flow, low production energy consumption and cost, and are an important source for future lithium resource extraction.

[0004] Therefore, researching and developing a method for extracting lithium from sedimentary lithium ore in salt lakes has broad application prospects. Summary of the Invention

[0005] The purpose of the present invention is to overcome the deficiencies of the above-mentioned existing technologies and provide a method for preparing lithium carbonate from lithium ore in carbonate-type salt lake sediments. This method realizes the effective separation, enrichment and extraction of lithium in sedimentary lithium ore in salt lakes through the combination of atmospheric pressure direct dissolution, leaching and chemical precipitation, and the lithium recovery rate of the whole process reaches more than 65%.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is: a method for preparing lithium carbonate from lithium ore in carbonate-type salt lake sediments, the method comprising the following steps:

[0007] (1) Crushing the lacustrine sedimentary lithium ore to obtain lithium-containing particles;

[0008] (2) Using fresh water to dissolve the lithium-containing particles in step (1) at normal temperature and atmospheric pressure, standing and separating to obtain a dissolved solution and water-insoluble substances;

[0009] (3) The water-insoluble matter described in step (2) is leached with an ammonium acetate solution at normal pressure and room temperature, and solid-liquid separation is carried out to obtain the first leaching solution and the first leaching residue;

[0010] (4) The first leaching residue obtained in step (3) is leached with an acetic acid solution at normal pressure and room temperature, and solid-liquid separation is carried out to obtain the second leaching solution and the second leaching residue;

[0011] (5) The dissolution solution in step (2), the first leaching solution in step (3), and the second leaching solution in step (4) are mixed to obtain a mixed solution;

[0012] (6) The mixed solution in step (5) is heated and the temperature is raised, and at the same time ammonia water is added to adjust the pH, and iron and aluminum are removed by hydrolysis. Solid-liquid separation is carried out to obtain aluminum-iron precipitate and the first separation solution;

[0013] (7) The first separation solution in step (6) is evaporated and concentrated, then ammonia water is added to adjust the pH, and a precipitant is added to remove calcium and magnesium. Calcium-magnesium precipitate and the second separation solution are obtained. The second separation solution is continuously evaporated and concentrated to obtain a high-temperature lithium-rich solution;

[0014] (8) The high-temperature lithium-rich solution in step (7) is kept warm, alkali is added to precipitate lithium, and washing and drying are carried out to obtain a lithium carbonate product.

[0015] As a preferred embodiment of the method of the present invention, the lithium-containing particles in step (1) are divided into multiple batches and steps (2) to (7) are respectively carried out in different dissolution tanks. The number of batches is not less than 3 batches, and after step (7), the following steps are further included: The calcium-magnesium precipitate in step (7) is leached with fresh water to recover the lithium entrained in the precipitate, and a leaching solution and calcium-magnesium slag are obtained. The leaching solution is mixed with the mixed solution in step (5) of the next batch for the next operation. By leaching the calcium slag and magnesium slag, the lithium entrained therein is recovered, thereby improving the lithium recovery rate.

[0016] As a preferred embodiment of the method of the present invention, in step (1), the crushing particle size is 80 to 200 mesh, and the crushing in step (1) is a fine grinding treatment of the lacustrine sediment lithium ore.

[0017] As a preferred embodiment of the method of the present invention, in the step (2), the solid-liquid ratio of the lithium-containing particles to fresh water is 1:(50-90) kg / L, such as 1:50, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable. The dissolution temperature is 10-40 °C and the time is 6-12 h. Among them, the temperature can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C or 40 °C, etc., and the time can be 6 h, 7 h, 8 h, 10 h, 12 h, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable. The stirring rate is 120-200 rpm.

[0018] As a preferred embodiment of the method of the present invention, in the step (3), the concentration of the ammonium acetate solution is 15%-23.5%, and the solid-liquid ratio of the water-insoluble matter to the ammonium acetate solution is 1:(60-90) kg / L, such as 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable. The leaching temperature is 10-40 °C and the time is 6-12 h. Among them, the temperature can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C or 40 °C, etc., and the time can be 6 h, 7 h, 8 h, 10 h, 12 h, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable. During the leaching process of step (3), 25% ammonia water is added to adjust the pH of the solution to 7.8-8.2, enhancing the ionization of the solution, and the exchangeable cations and the interlayer cations in the low-charge clay structure such as Li + , Na + , K + , etc. are replaced by NH 4+ in the solution.

[0019] It should be noted that the concentration gradient generated at the interface between the lithium-rich powder and the ammonium acetate solution is a key factor affecting the diffusion of lithium ions in the exchange solution, and the diffusion ability directly affects the ion exchange reaction rate and exchange efficiency. The applicant of the present invention found in experiments that when the lithium ion exchange solution is ammonium acetate solution and the concentration is controlled at 15% - 23.5% (i.e., the molar concentration is 2.3 - 4 mol / L), the leaching efficiency of lithium ions is relatively good; in particular, when the concentration of ammonium acetate solution is 20% (i.e., the molar concentration is 3.3 mol / L), the leaching efficiency of lithium ions is the best. As a preferred embodiment of the method of the present invention, in the step (4), the mass concentration of acetic acid solution is 8%, and the solid-liquid ratio of the first leaching residue to the acetic acid solution is 1:(40 - 65) kg / L, such as 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable. The leaching temperature is 10 - 40 °C, and the time is 6 - 12 h. Among them, the temperature can be 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C or 40 °C, etc., and the time can be 6 h, 7 h, 8 h, 10 h, 12 h, etc., but not limited to the listed values, and other unlisted values within the above numerical ranges are equally applicable.

[0020] As a preferred embodiment of the method of the present invention, in the step (5), the pH range of the mixed solution is 2.8 - 4.3, such as 2.8, 3.0, 3.5, 3.7, 3.9 or 4.0, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable. In the dissolution solution, the first leaching solution, and the second leaching solution in the step (5), lithium in the solid mineral enters the solution system, and the lithium recovery rate during the dissolution and leaching process is 91%.

[0021] As a preferred embodiment of the method of the present invention, in the step (6), the heating and temperature rising procedure is: rising the temperature at a rate of 5 - 10 °C / min to 55 °C, then adjusting the temperature rising rate to 0.5 - 1 °C / min, and continuing to rise the temperature to 70 °C; meanwhile, during the period of 55 - 70 °C, adding 25% ammonia water to adjust the pH to 4.9, keeping warm for 10 min, and then adding 25% ammonia water to adjust the pH to 6.8, and keeping warm for 15 min.

[0022] The increase in temperature accelerates the hydrolysis of iron and aluminum ions in the solution, forming iron hydroxide and aluminum hydroxide precipitates. The precipitates also have a purification function for the solution. In addition, the iron hydroxide and aluminum hydroxide precipitates entrain the main calcium and magnesium ions in the solution, reducing the consumption of alkaline reagents in the subsequent calcium and magnesium removal process and lowering the production cost. The applicant found in the experiment that when adding ammonia water in two-step heating to precipitate aluminum and iron ions, the aluminum and iron ions can be fully hydrolyzed completely, and the formed iron hydroxide and aluminum hydroxide precipitates can effectively reduce the calcium and magnesium content in the solution by 13-21%. After the mixed solution is heated to 55 °C, adding ammonia water to adjust the pH can reduce the residence time of ammonia water in the evaporator during the heating process, and reduce the volatilization of ammonia during the heating process.

[0023] As a preferred embodiment of the method of the present invention, in the step (7), adding 25% ammonia water to adjust the pH to 6.8-8.0. Ammonia water, as a crystal promoter, can effectively improve the crystal properties of magnesium hydroxide precipitates and reduce the difficulty of solid-liquid separation. The precipitating agent is any one or a combination of two of sodium sulfate, sodium carbonate, sodium hydroxide, and potassium hydroxide. After adding the precipitating agent, the pH of the solution is 13-14, such as 13.2, 13.5, 13.7, 13.9, 14, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable. The dosage of the precipitating agent is 95%-100% of the theoretical amount required for precipitating calcium and magnesium, and the theoretical amount required for precipitating calcium and magnesium is calculated based on the concentrations of calcium ions and magnesium ions. The calculation method is as follows: Assume the volume of the brine V = 10 L, the calcium concentration C Ca = 0.816 mg / L, and the magnesium concentration C Mg = 0.243 mg / L. Using sodium hydroxide and sodium carbonate to precipitate magnesium and calcium step by step, NaOH: amount of substance = 2×(0.243 / 24.3)×10 = 0.2 mol, mass = 0.2×40.00 = 8.00 g, Na 2 CO 3 : amount of substance = (0.816 / 40.8)×10 = 0.2 mol, mass = 0.2×105.99≈21.20 g.

[0024] As a preferred embodiment of the method of the present invention, in the step (7), the method for calcium and magnesium removal includes mixing the separation liquid I in the step (6) with the precipitating agent, and after reaction, performing solid-liquid separation to obtain calcium and magnesium precipitates and separation liquid II.

[0025] The applicant found in the experiment that using fresh water to wash the calcium residue and magnesium residue in the step (7) can effectively reduce the lithium entrained in the calcium residue and magnesium residue, and the lithium content in the calcium and magnesium residues decreases by 57%.

[0026] As a preferred embodiment of the method of the present invention, in step (8), the heat preservation temperature is 95 °C. Adding alkali to precipitate lithium means adding sodium carbonate for the precipitation reaction. The dosage of sodium carbonate is 110% of the theoretical amount required for lithium precipitation, and the theoretical amount required for lithium precipitation is calculated based on the concentration of lithium ions. The calculation method is as follows: Assume the brine volume V = 10 L, and the lithium ion concentration C Li = 0.694 mg / L, Li + amount of substance = (0.694 / 6.94) × 10 = 1 mol, Na 2 CO 3 amount of substance = 0.5 mol, Na 2 CO 3 mass = 0.5 × 105.99 ≈ 53.00 g, 110% of the theoretical amount = 53 × 1.1 = 58.30 g.

[0027] In one preferred embodiment, the leaching temperature is 20 - 30 °C, and the leaching time is 6 h - 12 h.

[0028] The applicant found in the experiment that when the dissolution temperature is increased from 15 °C to 25 °C, the dissolution of lithium-containing components in the deposited minerals and the leaching rate of lithium increase by 3.8%. The effect of temperature increase is slight. Considering comprehensively, in this scheme, normal-temperature fresh water and ammonium acetate solution are selected to dissolve and leach the deposited minerals.

[0029] Compared with the prior art, the method for extracting lithium from lithium ore in salt lake sediments provided by the present invention has at least one of the following beneficial effects:

[0030] (1) The method of the present invention has no roasting process and does not require the addition of additives, saving raw materials and energy;

[0031] (2) The main mineral structure in the carbonate-type salt lake sediment lithium ore is not damaged, and lithium enters the solution through dissolution and ion exchange; Fresh water, ammonium acetate and acetic acid are used as solvents and leaching solvents, and they also have the advantages of weak acidity, small corrosion to equipment, and small environmental impact.

[0032] (3) The method of the present invention combines direct dissolution, leaching and chemical precipitation under normal pressure, overcomes the deficiencies of high energy consumption, complex process flow and low lithium recovery rate in the existing solid lithium ore process, realizes the effective separation, enrichment and extraction of lithium in salt lake sediment lithium ore, and the lithium recovery rate of the whole process reaches more than 65%. Brief Description of the Drawings

[0033] Figure 1 It is the process flow chart for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore in the present invention.

[0034] Figure 2 It is the X-ray diffraction pattern and analysis result of the salt lake sediment.

[0035] Figure 3 It is the X-ray diffraction pattern of the lithium carbonate product in Example 1.

[0036] Figure 4 It is the physical picture of the lithium carbonate concentrate in Example 1. Specific embodiments

[0037] To better illustrate the purpose, technical solution and advantages of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] Example 1

[0039] A method for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore. The process flow chart of preparing lithium carbonate from carbonate-type salt lake sediment lithium ore in the present invention is as Figure 1 shown, and includes the following steps:

[0040] (1) The lake sediment lithium ore is finely ground, and the pulverization particle size is 100 mesh to obtain lithium-containing particles. The lithium-containing particles are divided into 3 batches and the operations of steps (2) to (7) are carried out in different dissolution tanks respectively; the X-ray diffraction pattern of the salt lake sediment is as Figure 2 shown, and the X-ray diffraction analysis results of the salt lake sediment are shown in Table 1; it can be seen from Table 1 that the main mineral components in the salt lake sediment are quartz, aragonite, halite, hydromagnesite, etc. Combining the occurrence state experimental analysis and chemical multi-element analysis, lithium mainly exists in easily soluble salt minerals, residual pore water, clay and other mineral adsorption and carbonate minerals in the bottom mud;

[0041] Table 1 X-ray diffraction analysis results of salt lake sediment

[0042]

[0043] (2) Weigh 1 kg of lithium-containing particles and add them to a cleaned 100 L reaction kettle, add 80 L of fresh water, stir with a stirrer, the dissolution temperature is 20 °C, the stirring rate is 150 rpm, and after fully dissolving for 12 h; after stopping stirring, let it stand for 6 h to precipitate, and separate the solid and liquid to obtain 0.812 kg of water-insoluble matter and a dissolution solution, and the lithium recovery rate during the dissolution process is 50.82%;

[0044] (3) Add 70 L of 20% mass concentration ammonium acetate solution to the water-insoluble matter, adjust the pH to 8.0 with 25% ammonia water, stir with a stirrer, the leaching temperature is 20 °C, and after fully dissolving for 12 h; after stopping stirring, let it stand for 6 h to precipitate, and separate the solid and liquid to obtain leaching solution 1 and 0.726 kg of leaching residue 1, and the lithium recovery rate during the leaching process is 20.87%;

[0045] (4) Add 42 L of acetic acid solution with a mass concentration of 8% to the first leaching residue, stir with a stirrer, keep the leaching temperature at 20 °C, and after fully dissolving for 12 h; stop stirring and let it stand for 6 h to precipitate, then separate the solid and liquid to obtain the second leaching solution and 0.537 kg of the second leaching residue. The lithium recovery rate during the leaching process is 19.04%;

[0046] (5) Mix the above-mentioned dissolved solution, the first leaching solution and the second leaching solution, and the pH of the mixed solution is 3.0;

[0047] (6) Heat the mixed solution to 55 °C at a heating rate of 10 °C / min, then adjust the heating rate to 0.5 - 1 °C / min and continue heating to 70 °C; meanwhile, during the period of 55 - 70 °C, add 25% ammonia water to adjust the pH to 4.9, keep warm for 10 min, then add 25% ammonia water again to adjust the pH to 6.8, and keep warm for 15 min; perform iron and aluminum removal by hydrolysis, separate the solid and liquid to obtain aluminum and iron precipitate and the first separated solution. The lithium recovery rate during the aluminum and iron removal process is 94.96%;

[0048] (7) Heat and concentrate the first separated solution, then add 25% ammonia water to adjust the pH to 7.0, add precipitants sodium carbonate and sodium hydroxide for calcium and magnesium removal. The dosages of sodium carbonate and sodium hydroxide are 387 g and 165 g respectively. Separate the solid and liquid. The pH of the solution after adding the precipitants is 13 to obtain calcium and magnesium precipitate and the second separated solution. Continue to evaporate and concentrate the second separated solution to obtain a high-temperature lithium-rich solution; the lithium recovery rate during the calcium and magnesium removal process is 89.37%;

[0049] (8) Wash the calcium and magnesium precipitate with fresh water to recover the lithium entrained in the precipitate, obtain the leaching solution and calcium and magnesium residue, and reflux the leaching solution to the mixed solution of the next batch for the next operation;

[0050] (9) Keep the high-temperature lithium-rich solution at 95 °C, add sodium carbonate for lithium precipitation reaction. The dosage of sodium carbonate is 3.85 g. Separate the solid and liquid, wash and dry to obtain lithium carbonate product. The total lithium carbonate recovery rate is 65.45%. The X-ray diffraction pattern of the prepared lithium carbonate product is as Figure 3 shown, and the physical picture of the lithium carbonate concentrate is as Figure 4 shown. It can be seen that the main minerals in the lithium precipitation by sodium carbonate are zabuyelite (Li 2 CO 3 ), natron (Na 2 CO 3 ), thermonatrite (Na 2 CO 3 H 2 O).

[0051] Example 2

[0052] A method for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore, which includes the following steps:

[0053] (1) The lake facies sediment lithium ore is finely ground to a particle size of 200 mesh to obtain lithium-containing particles. The lithium-containing particles are divided into 3 batches and the operations in steps (2) to (7) are carried out in different dissolution tanks respectively;

[0054] (2) Weigh 1 kg of lithium-containing particles and add them to a clean 100 L reactor. Add 50 L of fresh water, stir with a stirrer, the dissolution temperature is 40 °C, the stirring rate is 120 rpm. After fully dissolving for 6 h, stop stirring and let it stand for 6 h to precipitate. Separate the solid and liquid to obtain 0.837 kg of water-insoluble matter and a dissolution solution. The lithium recovery rate during the dissolution process is 50.16%;

[0055] (3) Add 70 L of 20% mass concentration ammonium acetate solution to the water-insoluble matter, adjust the pH to 7.8 with 25% ammonia water, stir with a stirrer, the leaching temperature is 10 °C. After fully dissolving for 6 h, stop stirring and let it stand for 6 h to precipitate. Separate the solid and liquid to obtain leaching solution I and 0.747 kg of leaching residue I. The lithium recovery rate during the leaching process is 20.69%;

[0056] (4) Add 48.5 L of 8% mass concentration acetic acid solution to the leaching residue I, stir with a stirrer, the leaching temperature is 10 °C. After fully dissolving for 6 h, stop stirring and let it stand for 6 h to precipitate. Separate the solid and liquid to obtain leaching solution II and 0.528 kg of leaching residue II. The lithium recovery rate during the leaching process is 19.67%;

[0057] (5) Mix the above dissolution solution, leaching solution I and leaching solution II. The pH of the mixed solution is 2.8;

[0058] (6) Heat the mixed solution at a heating rate of 10 °C / min to 55 °C, then adjust the heating rate to 1 °C / min and continue heating to 70 °C. At the same time, during the period of 55 - 70 °C, add 25% ammonia water to adjust the pH to 4.9, keep warm for 10 min, then add 25% ammonia water to adjust the pH to 6.8, keep warm for 15 min. Carry out iron and aluminum removal by hydrolysis. Separate the solid and liquid to obtain aluminum and iron precipitate and separation solution I. The lithium recovery rate during the aluminum and iron removal process is 94.61%;

[0059] (7) Heat and concentrate the separation solution I, then add 25% ammonia water to adjust the pH to 6.8, add precipitants sodium carbonate and sodium hydroxide for calcium and magnesium removal. The dosages of sodium carbonate and sodium hydroxide are 382 g and 174 g respectively. Separate the solid and liquid. The pH of the solution after adding the precipitants is 14. Obtain calcium and magnesium precipitate and separation solution II. Continue to evaporate and concentrate the separation solution II to obtain a high-temperature lithium-rich solution. The lithium recovery rate during the calcium and magnesium removal process is 88.49%;

[0060] (8) The calcium and magnesium precipitate is leached with fresh water to recover the lithium entrained in the precipitate, obtaining a leaching solution and calcium and magnesium slag. The leaching solution is refluxed to the mixed solution of the next batch for the next operation;

[0061] (9) The high-temperature lithium-rich solution is kept at 95 °C, sodium carbonate is added for lithium precipitation reaction. The amount of sodium carbonate used is 3.74 g. After solid-liquid separation, washing and drying, lithium carbonate product is obtained, and the total lithium carbonate recovery rate is 65.40%.

[0062] Example 3

[0063] A method for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore, which comprises the following steps:

[0064] (1) The lake sediment lithium ore is finely ground, and the pulverization particle size is 80 mesh to obtain lithium-containing particles. The lithium-containing particles are divided into 4 batches and the operations of steps (2) to (7) are carried out in different dissolution tanks respectively;

[0065] (2) Weigh 1 kg of lithium-containing particles and add them to a cleaned 100 L reaction kettle, add 90 L of fresh water, stir with a stirrer, the dissolution temperature is 10 °C, the stirring rate is 200 rpm. After fully dissolving for 8 h, stop stirring and let it stand for 6 h to precipitate. After solid-liquid separation, 0.786 kg of water-insoluble matter and a dissolution solution are obtained. The lithium recovery rate during the dissolution process is 50.94%;

[0066] (3) Add 70 L of 20% mass concentration ammonium acetate solution to the water-insoluble matter, adjust the pH to 8.2 with 25% ammonia water, stir with a stirrer, the leaching temperature is 40 °C. After fully dissolving for 12 h, stop stirring and let it stand for 6 h to precipitate. After solid-liquid separation, leaching solution I and 0.714 kg of leaching residue I are obtained. The lithium recovery rate during the leaching process is 21.07%;

[0067] (4) Add 35 L of 8% mass concentration acetic acid solution to the leaching residue I, stir with a stirrer, the leaching temperature is 40 °C. After fully dissolving for 12 h, stop stirring and let it stand for 6 h to precipitate. After solid-liquid separation, leaching solution II and 0.522 kg of leaching residue II are obtained. The lithium recovery rate during the leaching process is 18.93%;

[0068] (5) Mix the above dissolution solution, leaching solution I and leaching solution II, and the pH of the mixed solution is 4.3;

[0069] After heating the mixed solution at a heating rate of 10 °C / min to 55 °C, adjust the heating rate to 0.5 °C / min and continue heating to 70 °C. Meanwhile, during the period of 55 - 70 °C, add 25% ammonia water to adjust the pH to 4.9, keep it warm for 10 min, then add 25% ammonia water again to adjust the pH to 6.8, and keep it warm for 15 min. Perform iron and aluminum removal by hydrolysis, and carry out solid-liquid separation to obtain aluminum-iron precipitate and separation liquid I. The lithium recovery rate during the aluminum and iron removal process is 93.25%.

[0070] (7) Heat the concentrated separation liquid I, then add 25% ammonia water to adjust the pH to 8.0, add precipitants sodium carbonate and sodium hydroxide for calcium and magnesium removal. The dosages of sodium carbonate and sodium hydroxide are 377 g and 160 g respectively. Carry out solid-liquid separation. The pH of the solution after adding the precipitants is 13 to obtain calcium and magnesium precipitate and separation liquid II. Continue to evaporate and concentrate separation liquid II to obtain high-temperature lithium-rich liquid. The lithium recovery rate during the calcium and magnesium removal process is 89.26%.

[0071] (8) Wash the calcium and magnesium precipitate with fresh water to recover the lithium entrained in the precipitate, obtain the leaching solution and calcium and magnesium slag. The leaching solution is refluxed to the mixed solution of the next batch for the next operation.

[0072] (9) Keep the high-temperature lithium-rich liquid at 95 °C, add sodium carbonate for lithium precipitation reaction. The dosage of sodium carbonate is 3.62 g. Carry out solid-liquid separation, wash and dry to obtain lithium carbonate product. The total lithium carbonate yield is 65.04%.

[0073] Test Examples 1 - 3, Comparative Examples 1 - 2

[0074] In order to investigate the influence of the concentration of ammonium acetate solution on the leaching efficiency of lithium ions, Test Examples 1 - 3 and Comparative Examples 1 - 2 are set. In Test Examples 1 - 3 and Comparative Examples 1 - 2, except for the different concentrations of ammonium acetate solution in step (3), the remaining operation steps and parameters are the same as those in Example 1. The concentrations of ammonium acetate solution and the lithium carbonate yields in Test Examples 1 - 3 and Comparative Examples 1 - 2 are shown in Table 2.

[0075] Table 2

[0076] Concentration of ammonium acetate solution (%) Recovery rate of lithium carbonate (%) Test Example 1 15 66.92 Test Example 2 20 67.14 Test Example 3 23.5 67.04 Comparative Example 1 10 43.20 Comparative Example 2 25 56.77

[0077] As can be seen from Table 2, the lithium carbonate yields of Test Examples 1 - 3 are higher than those of Comparative Examples 1 and 2. That is, when the ammonium acetate concentration is controlled at 15% - 23.5%, the leaching efficiency of lithium ions is the highest, thus resulting in the highest lithium carbonate yield. It shows that the concentration gradient generated at the interface between the lithium-rich powder and the ammonium acetate solution is a key factor affecting the diffusion of lithium ions in the exchange solution, and the diffusion ability directly affects the ion exchange reaction rate and exchange efficiency. The applicant found in the experiment that when the lithium ion exchange solution is ammonium acetate solution and the concentration is controlled at 15% - 23.5%, the leaching efficiency of lithium ions is the best.

[0078] Comparative Example 3 and Comparative Example 4

[0079] In order to investigate the influence of the two-step heating method on the preparation of lithium carbonate, Comparative Example 3 and Comparative Example 4 were set up. Except that the two-step heating method was not used in step (6), the remaining steps and parameters were the same as those in Example 1.

[0080] In Comparative Example 3, in step (6), the temperature was directly increased to 70 °C at a heating rate of 10 °C / min, which increased the dosage of the alkaline reagent in step (8) by 18.5%, and the average calcium and magnesium content in the separated liquid I was 18% higher than that in Example 1.

[0081] In Comparative Example 4, in step (6), the temperature was directly increased to 70 °C at a heating rate of 1 °C / min, which increased the dosage of the alkaline reagent in step (8) by 13.2%, and the average calcium and magnesium content in the separated liquid I was 13% higher than that in Example 1.

[0082] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing lithium carbonate from carbonate salt lake sediment lithium ore, characterized in that: The method comprises the following steps: (1) crushing lake-phase deposited lithium ore to obtain lithium-containing particles; (2) using fresh water to dissolve the lithium-containing particles in step (1) at normal pressure and temperature, and allowing to stand for stratification to obtain a dissolved solution and water-insoluble matter; (3) leaching the water-insoluble matter described in step (2) with an ammonium acetate solution at normal pressure and temperature, and separating the solid from the liquid to obtain a leachate 1 and a leach residue 1; (4) subjecting the leached residue 1 obtained in step (3) to leaching with an acetic acid solution at normal pressure and temperature, and performing solid-liquid separation to obtain a leached solution 2 and a leached residue 2; (5) mixing the dissolving solution in step (2), the leaching solution 1 in step (3) and the leaching solution 2 in step (4) to obtain a mixed solution; (6) heating the mixed solution of step (5) to raise the temperature, adding ammonia water to adjust the pH, performing hydrolysis to remove iron and aluminum, and performing solid-liquid separation to obtain aluminum-iron precipitate and separation liquid 1; (7) evaporating and concentrating the separated liquid 1 in step (6), then adding ammonia water to adjust the pH, adding a precipitant to remove calcium and magnesium, obtaining calcium and magnesium precipitates and a separated liquid 2, and continuing to evaporate and concentrate the separated liquid 2 to obtain a high-temperature lithium-rich solution; (8) The high-temperature lithium-rich solution of step (7) is kept warm, alkali is added to precipitate lithium, and then washed and dried to obtain a lithium carbonate product.

2. The method according to claim 1, characterized in that The lithium-containing particles in step (1) are divided into multiple batches and steps (2) to (7) are performed in different dissolution tanks respectively, with the number of batches being no less than 3 batches, and the following step is also included after step (7): the calcium and magnesium precipitates in step (7) are eluted with fresh water, the lithium entrained in the precipitates is recovered, and the elution liquid and the calcium and magnesium slag are obtained, and the elution liquid is then mixed with the mixed liquid of the next batch of step (5) to perform the next step.

3. The method according to claim 1, characterized in that In the step (1), the crushing particle size is 80 to 200 meshes.

4. The method according to claim 1, characterized in that In the step (2), the solid-liquid ratio of the lithium-containing particles to fresh water is 1:(50-90) kg / L, the dissolution temperature is 10-40° C., the time is 6-12 h, and the stirring rate is 120-200 rpm.

5. The method according to claim 1, characterized in that In the step (3), the mass concentration of the ammonium acetate solution is 15% to 23.5%, the solid-liquid ratio of the water-insoluble matter to the ammonium acetate solution is 1:(60 to 90) kg / L, the leaching temperature is 10 to 40° C., and the leaching time is 6 to 12 hours; during the leaching process of step (3), 25% ammonia water is added to adjust the solution pH to 7.8 to 8.

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6. The method according to claim 1, characterized in that In the step (4), the mass concentration of the acetic acid solution is 8%, the solid-liquid ratio of the leached residue to the acetic acid solution is 1:(40-65) kg / L, the leaching temperature is 10-40° C., and the leaching time is 6-12 hours.

7. The method according to claim 1, characterized in that In the step (5), the pH range of the mixed solution is 2.8 to 4.

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8. The method according to claim 1, characterized in that In the step (6), the heating procedure is as follows: heating to 55°C at a heating rate of 5-10°C / min, then adjusting the heating rate to 0.5-1°C / min, and continuing to heat to 70°C; at the same time, adding 25% ammonia water to adjust the pH to 4.9 at 55-70°C, keeping the temperature for 10 minutes, and then adding 25% ammonia water to adjust the pH to 6.8, and keeping the temperature for 15 minutes.

9. The method according to claim 1, characterized in that In the step (7), 25% ammonia water is added to adjust the pH to 6.8-8.0, the precipitant is any one of sodium sulfate, sodium carbonate, sodium hydroxide, potassium hydroxide or a combination of two thereof, the pH of the solution after the addition of the precipitant is 13-14, and the amount of the precipitant is 95%-100% of the theoretical amount required for precipitation of calcium and magnesium, and the theoretical amount required for precipitation of calcium and magnesium is calculated based on the concentration of calcium ions and magnesium ions.

10. The method according to claim 1, characterized in that In the step (8), the insulation temperature is 95° C., and the addition of alkali to precipitate lithium is to add sodium carbonate to carry out lithium precipitation reaction. The amount of sodium carbonate used is 110% of the theoretical amount required for lithium precipitation. The theoretical amount required for lithium precipitation is calculated based on the concentration of lithium ions.

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