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

Abstract

The present application relates to a kind of carbonate type salt lake deposit lithium ore preparation lithium carbonate method, using fresh water to carry out normal pressure normal temperature dissolution to lithium-containing particles, obtain dissolving solution and water insoluble matter;The water insoluble matter is carried out normal pressure normal temperature leaching with ammonium acetate solution, solid-liquid separation obtains leaching solution one and leaching residue one;Leaching residue one is carried out normal pressure normal temperature leaching with acetic acid solution, solid-liquid separation obtains leaching solution two and leaching residue two;Dissolving solution, leaching solution one and leaching solution two are mixed, obtain mixed solution, hydrolysis iron and aluminium treatment is carried out while adding ammonia water and heating, solid-liquid separation obtains aluminium iron precipitate and separation liquid one;After evaporation concentration of separation liquid one, carry out calcium and magnesium removal treatment, obtain calcium magnesium precipitate and separation liquid two, continue to evaporate concentration of separation liquid two, obtain high-temperature lithium-rich liquid;High-temperature lithium-rich liquid carries out heat preservation, adds alkali and precipitates lithium, and after washing and drying, obtain lithium carbonate product.The present application realizes the effective separation, enrichment and extraction of lithium in salt lake deposit lithium ore.

Description

Technical Field

[0001] This invention relates to a method for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore, and more particularly to the extraction of lithium from sediment lithium ore, belonging to the field of lithium extraction technology from lithium-bearing minerals. Background Technology

[0002] With the rapid development of new technologies and new energy vehicles in my country, the demand for lithium and lithium salts is increasing year by year. This trend poses new requirements for the global lithium resource supply and low-cost lithium extraction methods. Natural lithium resources are mainly divided into three categories: pegmatite, brine, and clay. Currently, the lithium resources that have been developed are mainly pegmatite and brine types. Most lithium extraction methods from solid lithium ore employ auxiliary roasting and acid methods. Roasting requires relatively high temperatures, is prone to agglomeration, and produces Li-K double salts with low solubility, posing challenges for subsequent separation. When using the sulfuric acid process to treat lithium minerals, a large amount of sulfuric acid is consumed, and the subsequent purification process also requires a large amount of neutralizing agent.

[0003] China's lithium mines are mostly distributed in Qinghai, Tibet, Sichuan, and Jiangxi provinces. Salt lake lithium resources are primarily found in salt lake brines, lacustrine sediments, and salt deposits. Lithium resources in brines have been extensively explored and developed on a large scale. Recently, lithium resources, mainly in adsorption form, have been discovered in the bottom sediments of carbonate-type salt lakes. These resources are primarily found in soluble salt minerals, residual pore water, clay, and other mineral adsorption, as well as in carbonate minerals. Although their grade is relatively low, the resource quantity is large, the extraction process is simple, and the production energy consumption and cost are low, making them an important source for future lithium extraction.

[0004] Therefore, developing a method for extracting lithium from lithium deposits in salt lake sediments has broad application prospects. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore. This method achieves effective separation, enrichment and extraction of lithium from salt lake sediment lithium ore by combining direct dissolution, leaching and chemical precipitation under normal pressure, with a lithium recovery rate of over 65% throughout the process.

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

[0007] (1) The lacustrine sedimentary lithium ore was crushed to obtain lithium-containing particles;

[0008] (2) Dissolve the lithium-containing particles from step (1) at room temperature and under normal pressure using fresh water, and let them stand to separate into layers to obtain a solution and water-insoluble matter;

[0009] (3) The water-insoluble matter described in step (2) is leached with ammonium acetate solution at normal pressure and temperature, and solid-liquid separation is performed to obtain leachate one and leach residue one;

[0010] (4) The leachate residue obtained in step (3) is leached with acetic acid solution at normal pressure and temperature, and solid-liquid separation is performed to obtain leachate residue 2 and leachate residue 2.

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

[0012] (6) Heat the mixture from step (5) to increase the temperature, and add ammonia water to adjust the pH. Perform hydrolysis to remove iron and aluminum, and separate the solid and liquid to obtain aluminum-iron precipitate and separation liquid 1.

[0013] (7) Evaporate and concentrate the separation liquid one from step (6), then add ammonia water to adjust the pH, add precipitant to remove calcium and magnesium, and obtain calcium and magnesium precipitate and separation liquid two. Continue to evaporate and concentrate separation liquid two to obtain high temperature lithium-rich liquid.

[0014] (8) The high-temperature lithium-rich liquid from step (7) is kept warm, alkali is added to precipitate lithium, and the liquid is washed and dried to obtain lithium carbonate product.

[0015] In a preferred embodiment of the method described in this invention, the lithium-containing particles in step (1) are divided into multiple batches and subjected to steps (2) to (7) in different dissolving tanks, with a minimum of three batches. After step (7), the following steps are also included: the calcium-magnesium precipitate in step (7) is rinsed with fresh water to recover the lithium entrained in the precipitate, yielding a rinsing solution and calcium-magnesium slag. The rinsing solution is then mixed with the mixture from the next batch of step (5) for the next step. By rinsing the calcium and magnesium slag, the lithium entrained therein is recovered, thereby improving the lithium recovery rate.

[0016] In a preferred embodiment of the method of the present invention, in step (1), the particle size is 80 to 200 mesh, and the crushing in step (1) is to finely grind the lacustrine sedimentary lithium ore.

[0017] In a preferred embodiment of the method described in this invention, in 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; other unlisted values ​​within this range are also applicable. The dissolution temperature is 10~40℃, and the time is 6~12h, wherein the temperature can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, or 40℃, etc., and the time can be 6h, 7h, 8h, 10h, 12h, etc., but not limited to the listed values; other unlisted values ​​within the above ranges are also applicable. The stirring rate is 120~200 rpm.

[0018] In a preferred embodiment of the method described in this invention, in step (3), the concentration of the ammonium acetate solution is 15% to 23.5%, and the solid-liquid ratio of the water-insoluble matter to the ammonium acetate solution is 1:(60 to 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; other unlisted values ​​within this range are also applicable. The leaching temperature is 10 to 40°C, and the time is 6 to 12 hours. 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 hours, 7 hours, 8 hours, 10 hours, 12 hours, etc., but not limited to the listed values; other unlisted values ​​within the above ranges are also applicable. During the leaching process in step (3), 25% ammonia water is added to adjust the pH of the solution to 7.8–8.2, thereby enhancing the ionization of the solution and facilitating the exchange of cations and interlayer cations such as Li in the low-charge clay structure. + Na + K + NH in the solution 4+ replace.

[0019] It should be noted that the concentration gradient generated at the interface between lithium-rich powder and ammonium acetate solution is a key factor affecting the diffusion of lithium ions in the exchange solution, and the diffusion capacity directly affects the ion exchange reaction rate and exchange efficiency. The applicant of this invention found in experiments that when the lithium ion exchange solution is an ammonium acetate solution and the concentration is controlled between 15% and 23.5% (i.e., a molar concentration of 2.3 to 4 mol / L), the lithium ion leaching efficiency is better; in particular, when the concentration of the ammonium acetate solution is 20% (i.e., a molar concentration of 3.3 mol / L), the lithium ion leaching efficiency is optimal. As a preferred embodiment of the method of this invention, in step (4), the mass concentration of the acetic acid solution is 8%, and the solid-liquid ratio of the 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; other unlisted values ​​within this range are also applicable. The leaching temperature is 10–40℃ and the time is 6–12 hours. The temperature can be 10℃, 15℃, 20℃, 25℃, 30℃, 35℃ or 40℃, etc., and the time can be 6 hours, 7 hours, 8 hours, 10 hours or 12 hours, etc., but it is not limited to the listed values. Other unlisted values ​​within the above ranges are also applicable.

[0020] In a preferred embodiment of the method described in this invention, in step (5), the pH range of the mixed solution is 2.8 to 4.3, such as 2.8, 3.0, 3.5, 3.7, 3.9, or 4.0, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. In step (5), the dissolving solution, leaching solution one, and leaching solution two allow lithium from the solid mineral to enter the solution system, and the lithium recovery rate during the dissolution and leaching process is 91%.

[0021] As a preferred embodiment of the method described in this invention, in step (6), the heating procedure is as follows: the temperature is increased to 55°C at a heating rate of 5-10°C / min, and then the heating rate is adjusted to 0.5-1°C / min, and the temperature is continued to increase to 70°C; at the same time, during the period of 55-70°C, 25% ammonia water is added to adjust the pH to 4.9, and the temperature is maintained for 10 min, and then 25% ammonia water is added again to adjust the pH to 6.8, and the temperature is maintained for 15 min.

[0022] The increase in temperature accelerates the hydrolysis of iron and aluminum ions in the solution, forming ferric hydroxide and aluminum hydroxide precipitates. These precipitates also purify the solution. Furthermore, the ferric hydroxide and aluminum hydroxide precipitates entrain the main calcium and magnesium ions in the solution, reducing the consumption of alkaline reagents during subsequent calcium and magnesium removal processes and lowering production costs. The applicant found in experiments that the two-step heating method with the addition of ammonia to precipitate aluminum and iron ions ensures complete hydrolysis of these ions, resulting in ferric hydroxide and aluminum hydroxide precipitates that effectively reduce the calcium and magnesium content in the solution by 13-21%. Adding ammonia to adjust the pH after heating the mixed solution to 55°C reduces the residence time of ammonia in the evaporator during the heating process, thus minimizing ammonia volatilization.

[0023] In a preferred embodiment of the method described in this invention, in step (7), 25% ammonia is added to adjust the pH to 6.8-8.0. Ammonia acts as a crystallization promoter, effectively improving the crystal properties of magnesium hydroxide precipitate and reducing the difficulty of solid-liquid separation. The precipitant is any one or a combination of two of sodium sulfate, sodium carbonate, sodium hydroxide, and potassium hydroxide. After adding the precipitant, the pH of the solution is 13-14, such as 13.2, 13.5, 13.7, 13.9, 14, etc., but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The amount of precipitant used is 95%-100% of the theoretical amount required for calcium and magnesium precipitation. The theoretical amount required for calcium and magnesium precipitation is calculated based on the concentrations of calcium ions and magnesium ions. The calculation method is as follows: Assuming the brine volume V = 10L and the calcium concentration C Ca =0.816 mg / L, magnesium concentration C Mg =0.243mg / L. Magnesium and calcium are precipitated stepwise using sodium hydroxide and sodium carbonate. NaOH: amount of substance = 2×(0.243 / 24.3)×10 = 0.2mol, mass = 0.2×40.00 = 8.00g. Na2CO3: amount of substance = (0.816 / 40.8)×10 = 0.2mol, mass = 0.2×105.99≈21.20g.

[0024] As a preferred embodiment of the method described in this invention, in step (7), the method for removing calcium and magnesium includes mixing the separation liquid one from step (6) with a precipitant, and then separating the solid and liquid to obtain calcium and magnesium precipitate and separation liquid two after the reaction.

[0025] The applicant found in the experiment that rinsing the calcium slag and magnesium slag in step (7) with fresh water can effectively reduce the lithium entrainment in the calcium slag and magnesium slag, and the lithium content in the calcium slag and magnesium slag decreased by 57%.

[0026] In a preferred embodiment of the method described in this invention, in step (8), the heat preservation temperature is 95°C, and the addition of alkali to precipitate lithium is achieved by adding sodium carbonate to carry out the 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 lithium ion concentration. The calculation method is as follows: Assuming the brine volume V = 10L and the lithium ion concentration C... Li =0.694 mg / L, Li + Amount of substance = (0.694 / 6.94) × 10 = 1 mol, Amount of substance of Na2CO3 = 0.5 mol, Mass of Na2CO3 = 0.5 × 105.99 ≈ 53.00 g, 110% of 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 6–12 hours.

[0028] The applicant found in the experiment that increasing the dissolution temperature from 15℃ to 25℃ increased the dissolution of lithium-containing components in the sedimentary minerals and the lithium leaching rate by 3.8%. The effect of the temperature increase was slight. Considering all factors, this scheme uses room temperature fresh water and ammonium acetate solution to dissolve and leach the sedimentary minerals.

[0029] Compared with the prior art, the method for extracting lithium from salt lake sediment lithium deposits 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, thus saving raw materials and energy;

[0031] (2) The main mineral structure of lithium deposits in carbonate-type salt lake sediments is not destroyed, 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 have the advantages of weak acidity, low corrosion to equipment and low environmental impact.

[0032] (3) The method of the present invention overcomes the shortcomings of existing solid lithium ore processes, such as high energy consumption, complex process flow and low lithium recovery rate, by combining direct dissolution, leaching and chemical precipitation under normal pressure. It realizes the effective separation, enrichment and extraction of lithium in salt lake sediment lithium ore, and the lithium recovery rate of the whole process is more than 65%. Attached Figure Description

[0033] Figure 1 This is a process flow diagram for preparing lithium carbonate from carbonate-type salt lake sediment lithium ore in this invention.

[0034] Figure 2 X-ray diffraction patterns and analysis results of salt lake sediments.

[0035] Figure 3 The image shows the X-ray diffraction pattern of the lithium carbonate product in Example 1.

[0036] Figure 4 This is a photograph of the lithium carbonate concentrate from Example 1. Detailed Implementation

[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 diagram of which is shown below. Figure 1 As shown, it includes the following steps:

[0040] (1) The lithium ore in the lacustrine sediments was finely ground to a particle size of 100 mesh to obtain lithium-containing particles. The lithium-containing particles were divided into three batches and subjected to steps (2) to (7) in different dissolution tanks. The X-ray diffraction pattern of the salt lake sediments is shown in the figure. Figure 2 As shown in Table 1, the X-ray diffraction analysis results of the salt lake sediments are as follows. Table 1 shows that the main mineral composition of the salt lake sediments is quartz, aragonite, halite, hydromagnesia, etc. Combined with the experimental analysis of the occurrence state and the chemical multi-element analysis, lithium in the bottom sediment is mainly found in soluble salt minerals, residual pore water, clay and other mineral adsorption and carbonate minerals.

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

[0042]

[0043] (2) Weigh 1 kg of lithium-containing particles and add them to a clean 100 L reactor. Add 80 L of fresh water and stir with a stirrer at a dissolution temperature of 20 °C and a stirring rate of 150 rpm. After dissolving for 12 h, stop stirring and let stand for 6 h to precipitate. Separate the solid and liquid to obtain 0.812 kg of water-insoluble matter and solution. The lithium yield during the dissolution process is 50.82%.

[0044] (3) Add 70L of 20% ammonium acetate solution to the water-insoluble matter, adjust the pH to 8.0 with 25% ammonia water, stir with a stirrer, and leaching at 20℃. After dissolving for 12 hours, stop stirring and let stand for 6 hours to precipitate. Separate the solid and liquid to obtain leachate 1 and 0.726kg leaching residue 1. The lithium recovery rate during the leaching process is 20.87%.

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

[0046] (5) Mix the above-mentioned solution, leachate one and leachate two, and the pH of the mixture is 3.0;

[0047] (6) The mixture was heated to 55°C at a heating rate of 10°C / min, and then the heating rate was adjusted to 0.5-1°C / min. The temperature was then increased to 70°C. At the same time, 25% ammonia was added to adjust the pH to 4.9 during the period of 55-70°C. After holding the temperature for 10 min, 25% ammonia was added again to adjust the pH to 6.8. The temperature was then held for 15 min. The iron and aluminum were removed by hydrolysis. The solid and liquid were separated to obtain aluminum-iron precipitate and separation liquid 1. The lithium recovery rate during the removal of aluminum and iron was 94.96%.

[0048] (7) After heating and concentrating the first separation liquid, 25% ammonia water was added to adjust the pH to 7.0. Sodium carbonate and sodium hydroxide were added as precipitants to remove calcium and magnesium. The amounts of sodium carbonate and sodium hydroxide were 387g and 165g, respectively. Solid-liquid separation was performed. After adding the precipitant, the pH of the solution was 13, and calcium and magnesium precipitate and separation liquid two were obtained. The second separation liquid was further evaporated and concentrated to obtain a high-temperature lithium-rich solution. The lithium yield during the calcium and magnesium removal process was 89.37%.

[0049] (8) The calcium and magnesium precipitate is rinsed with fresh water to recover the lithium entrained in the precipitate, and the rinsing liquid and calcium and magnesium slag are obtained. The rinsing liquid is returned to the next batch of mixed liquid for the next operation.

[0050] (9) The high-temperature lithium-rich solution was kept at 95°C, and sodium carbonate was added to carry out the lithium precipitation reaction. The amount of sodium carbonate used was 3.85 g. After solid-liquid separation, washing and drying, lithium carbonate product was obtained. The total yield of lithium carbonate was 65.45%. The X-ray diffraction pattern of the prepared lithium carbonate product is shown in the figure. Figure 3 As shown in the image, a physical picture of lithium carbonate concentrate is as follows. Figure 4 As shown, the main minerals in the lithium precipitate from sodium carbonate are zabuye stone (Li2CO3), sodium carbonate (Na2CO3), and sodium carbonate (Na2CO3H2O).

[0051] Example 2

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

[0053] (1) The lithium ore in the lacustrine sediments was finely ground to a particle size of 200 mesh to obtain lithium-containing particles. The lithium-containing particles were divided into three batches and carried out in different dissolving tanks in steps (2) to (7).

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

[0055] (3) Add 70L of 20% ammonium acetate solution to the water-insoluble matter, adjust the pH to 7.8 with 25% ammonia water, stir with a stirrer, and leaching at 10℃. After dissolving for 6 hours, stop stirring and let stand for 6 hours to precipitate. Separate the solid and liquid to obtain leachate 1 and 0.747kg leaching residue 1. The lithium recovery rate during the leaching process is 20.69%.

[0056] (4) Add 48.5L of acetic acid solution with a mass concentration of 8% to the leaching residue one, stir with a stirrer, the leaching temperature is 10℃, and after 6 hours of complete dissolution; stop stirring and let stand for 6 hours to precipitate, and separate the solid and liquid to obtain leaching solution two and 0.528kg of leaching residue two. The lithium recovery rate during the leaching process is 19.67%.

[0057] (5) Mix the above-mentioned solution, leachate one and leachate two, and the pH of the mixture is 2.8;

[0058] (6) The mixture was heated to 55°C at a heating rate of 10°C / min, and then the heating rate was adjusted to 1°C / min and the temperature was continued to rise to 70°C. At the same time, during the period of 55-70°C, 25% ammonia was added to adjust the pH to 4.9, and the temperature was kept for 10 min. Then, 25% ammonia was added again to adjust the pH to 6.8 and the temperature was kept for 15 min. The iron and aluminum were removed by hydrolysis, and the solid and liquid were separated to obtain aluminum-iron precipitate and separation liquid 1. The lithium recovery rate during the removal of aluminum and iron was 94.61%.

[0059] (7) After heating and concentrating the first separation liquid, 25% ammonia water was added to adjust the pH to 6.8. Sodium carbonate and sodium hydroxide were added as precipitants to remove calcium and magnesium. The amounts of sodium carbonate and sodium hydroxide were 382g and 174g, respectively. Solid-liquid separation was performed. After adding the precipitant, the pH of the solution was 14, and calcium and magnesium precipitate and separation liquid two were obtained. The second separation liquid was further evaporated and concentrated to obtain a high-temperature lithium-rich solution. The lithium recovery rate during the calcium and magnesium removal process was 88.49%.

[0060] (8) The calcium and magnesium precipitate is rinsed with fresh water to recover the lithium entrained in the precipitate, and the rinsing liquid and calcium and magnesium slag are obtained. The rinsing liquid is returned to the next batch of mixed liquid for the next operation.

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

[0062] Example 3

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

[0064] (1) The lithium ore in the lacustrine sediments was finely ground to a particle size of 80 mesh to obtain lithium-containing particles. The lithium-containing particles were divided into 4 batches and carried out in steps (2) to (7) in different dissolving tanks.

[0065] (2) Weigh 1 kg of lithium-containing particles and add them to a clean 100 L reactor. Add 90 L of fresh water and stir with a stirrer at a dissolution temperature of 10 °C and a stirring rate of 200 rpm. After dissolving for 8 hours, stop stirring and let stand for 6 hours to precipitate. Separate the solid and liquid to obtain 0.786 kg of water-insoluble matter and solution. The lithium yield during the dissolution process is 50.94%.

[0066] (3) Add 70L of 20% ammonium acetate solution to the water-insoluble matter, adjust the pH to 8.2 with 25% ammonia water, stir with a stirrer, and leaching at 40℃. After dissolving for 12 hours, stop stirring and let stand for 6 hours to precipitate. Separate the solid and liquid to obtain leachate 1 and 0.714kg leaching residue 1. The lithium recovery rate during the leaching process is 21.07%.

[0067] (4) Add 35L of acetic acid solution with a mass concentration of 8% to the leaching residue one, stir with a stirrer, the leaching temperature is 40℃, and after fully dissolving for 12h; stop stirring and let stand for 6h to precipitate, separate solid and liquid, and obtain leaching solution two and 0.522kg leaching residue two. The lithium recovery rate during the leaching process is 18.93%.

[0068] (5) Mix the above-mentioned solution, leachate one and leachate two, and the pH of the mixture is 4.3;

[0069] (6) The mixture was heated to 55°C at a heating rate of 10°C / min, and then the heating rate was adjusted to 0.5°C / min and the temperature was continued to rise to 70°C. At the same time, during the period of 55-70°C, 25% ammonia was added to adjust the pH to 4.9, and the temperature was kept for 10 min. Then, 25% ammonia was added again to adjust the pH to 6.8 and the temperature was kept for 15 min. The iron and aluminum were removed by hydrolysis, and the solid and liquid were separated to obtain aluminum-iron precipitate and separation liquid 1. The lithium recovery rate during the removal of aluminum and iron was 93.25%.

[0070] (7) After heating and concentrating the first separation liquid, 25% ammonia water was added to adjust the pH to 8.0. Sodium carbonate and sodium hydroxide were added as precipitants to remove calcium and magnesium. The amounts of sodium carbonate and sodium hydroxide were 377g and 160g, respectively. Solid-liquid separation was performed. After adding the precipitant, the pH of the solution was 13, and calcium and magnesium precipitate and separation liquid two were obtained. The separation liquid two was further evaporated and concentrated to obtain a high-temperature lithium-rich solution. The lithium recovery rate during the calcium and magnesium removal process was 89.26%.

[0071] (8) The calcium and magnesium precipitate is rinsed with fresh water to recover the lithium entrained in the precipitate, and the rinsing liquid and calcium and magnesium slag are obtained. The rinsing liquid is returned to the next batch of mixed liquid for the next operation.

[0072] (9) The high-temperature lithium-rich liquid was kept at 95°C, and sodium carbonate was added to carry out the lithium precipitation reaction. The amount of sodium carbonate used was 3.62g. After solid-liquid separation, washing and drying, lithium carbonate product was obtained. The total yield of lithium carbonate was 65.04%.

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

[0074] To investigate the effect of ammonium acetate solution concentration on lithium ion leaching efficiency, experimental examples 1-3 and comparative examples 1-2 were set up. In experimental examples 1-3 and comparative examples 1-2, except for the concentration of ammonium acetate solution in step (3), the other operating steps and parameters were the same as in example 1. The concentration of ammonium acetate solution and lithium carbonate yield in experimental examples 1-3 and comparative examples 1-2 are shown in Table 2.

[0075] Table 2

[0076] Concentration (%) of ammonium acetate solution Lithium carbonate yield (%) Experimental Example 1 15 66.92 Experimental Example 2 20 67.14 Experimental Example 3 23.5 67.04 Comparative Example 1 10 43.20 Comparative Example 2 25 56.77

[0077] As shown in Table 2, the lithium carbonate yields of Experimental Examples 1-3 were higher than those of Comparative Examples 1 and 2. This indicates that the lithium ion leaching efficiency was highest when the ammonium acetate concentration was controlled between 15% and 23.5%, resulting in the highest lithium carbonate yield. This demonstrates that the concentration gradient 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 diffusion capacity directly affects the ion exchange reaction rate and exchange efficiency. The applicant found in its experiments that the lithium ion leaching efficiency was optimal when the lithium ion exchange solution was an ammonium acetate solution with a concentration controlled between 15% and 23.5%.

[0078] Comparative Example 3 and Comparative Example 4

[0079] To investigate the effect of the two-step heating method on the preparation of lithium carbonate, Comparative Examples 3 and 4 were set up. Except for step (6), the two-step heating method was not used in Comparative Examples 3 and 4. The other steps and parameters were the same as in Example 1.

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

[0081] In Comparative Example 4, step (6) directly heated to 70°C at a heating rate of 1°C / min, which increased the amount of alkaline reagent used in step (8) by 13.2%, and the average calcium and magnesium content in the separation liquid 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 and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention 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-type salt lake sediment lithium ore, characterized in that, The method includes the following steps: (1) The lacustrine sedimentary lithium ore was crushed to obtain lithium-containing particles; (2) Dissolve the lithium-containing particles from step (1) in fresh water at normal pressure and temperature, and let them stand to separate into layers to obtain a solution and water-insoluble matter; (3) The water-insoluble matter described in step (2) is leached with ammonium acetate solution under normal pressure and temperature, and solid-liquid separation is performed to obtain leachate one and leach residue one. The mass concentration of ammonium acetate solution is 15%~23.5%, and the solid-liquid ratio of the water-insoluble matter to ammonium acetate solution is 1:(60~90)kg / L. (4) The leaching residue obtained in step (3) is leached with acetic acid solution at normal pressure and temperature, and solid-liquid separation is performed to obtain leaching solution 2 and leaching residue 2. (5) Mix the dissolving solution in step (2), the first leachate in step (3), and the second leachate in step (4) to obtain a mixed solution; (6) Heat the mixture from step (5) and add ammonia to adjust the pH. Perform hydrolysis to remove iron and aluminum, and separate the solid and liquid to obtain aluminum-iron precipitate and separation liquid 1. The heating procedure is as follows: heat to 55°C at a heating rate of 5~10°C / min, then adjust the heating rate to 0.5~1°C / min and continue to heat to 70°C. (7) Evaporate and concentrate the separation liquid one from step (6), then add ammonia to adjust the pH, add precipitant to remove calcium and magnesium, and obtain calcium and magnesium precipitate and separation liquid two. Continue to evaporate and concentrate separation liquid two to obtain high temperature lithium-rich liquid. (8) The high-temperature lithium-rich liquid from step (7) is kept warm, alkali is added to precipitate lithium, and the liquid is washed and dried to obtain lithium carbonate product.

2. The method as described in claim 1, characterized in that, The lithium-containing particles in step (1) are divided into multiple batches and operated in steps (2) to (7) in different dissolving tanks. The number of batches is not less than 3. After step (7), the following steps are also included: the calcium and magnesium precipitate in step (7) is rinsed with fresh water to recover the lithium entrained in the precipitate, and the rinsing liquid and calcium and magnesium slag are obtained. The rinsing liquid is then mixed with the mixture of the next batch of step (5) for the next operation.

3. The method as described in claim 1, characterized in that, In step (1), the particle size is 80~200 mesh.

4. The method as described in claim 1, characterized in that, In 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℃, the time is 6~12h, and the stirring rate is 120~200rpm.

5. The method as described in claim 1, characterized in that, In step (3), the leaching temperature is 10~40℃ and the time is 6~12h; during the leaching process in step (3), 25% ammonia water is added to adjust the pH of the solution to 7.8~8.

2.

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

7. The method as described in claim 1, characterized in that, In step (5), the pH range of the mixture is 2.8 to 4.

3.

8. The method as described in claim 1, characterized in that, In step (6), at the same time, 25% ammonia water is added to adjust the pH to 4.9 during the period of 55~70℃, and after keeping it warm for 10 min, 25% ammonia water is added again to adjust the pH to 6.8, and after keeping it warm for 15 min.

9. The method as described in claim 1, characterized in that, In step (7), 25% ammonia is added to adjust the pH to 6.8~8.

0. The precipitant is any one or a combination of two of sodium sulfate, sodium carbonate, sodium hydroxide, and potassium hydroxide. After adding the precipitant, the pH of the solution is 13~14. The amount of precipitant used is 95%~100% of the theoretical amount required for calcium and magnesium precipitation. The theoretical amount required for calcium and magnesium precipitation is calculated based on the concentrations of calcium ions and magnesium ions.

10. The method as described in claim 1, characterized in that, In step (8), the heat preservation temperature is 95°C, and the addition of alkali to precipitate lithium is to add sodium carbonate to carry out the 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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