A method for extracting lithium from lepidolite by composite salt roasting-leaching process

Abstract

The application discloses a method for extracting lithium from lepidolite by using composite salt roasting-water leaching process. The method is that lepidolite ore powder and composite salt composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride are mixed for chlorination roasting, and after roasting clinker is water leached, calcium ions are precipitated by using sodium carbonate to obtain calcium-removed purified solution; after pH adjustment, the calcium-removed purified solution is concentrated and crystallized to precipitate sodium chloride and potassium chloride crystals, and then lithium ions are precipitated by adding sodium carbonate into the crystallization mother liquor to obtain lithium carbonate precipitate. The method can realize chlorination conversion of lepidolite into water-soluble chlorides at a lower temperature by using special composite salt, thereby realizing efficient extraction of lithium and obtaining lithium carbonate product, and the composite salt can be regenerated and recycled, so that the cost is low, the method is green and environment-friendly, and the method is beneficial to large-scale production.

Description

Technical Field

[0001] This invention relates to a method for extracting lithium from lepidolite, specifically a method for extracting lithium from lepidolite using a composite salt roasting-water leaching process, belonging to the field of metallurgy. Background Technology

[0002] Lithium extraction from lepidolite mainly includes limestone, sulfuric acid, sulfate roasting, lime pressure boiling, and chlorination roasting methods. Among these, chlorination roasting is further divided into high-temperature roasting and medium-temperature roasting. Roasting is carried out at temperatures below the boiling points of alkali metal chlorides, followed by water leaching to obtain a solution containing alkali metal chlorides. Chlorination roasting has advantages such as high lithium leaching rate, short roasting time, low content of impurities after leaching, and small amount of waste residue. Furthermore, when the chlorinating agent contains calcium chloride, it can solidify fluorine in lepidolite ore into CaF2, reducing the amount of harmful gases to be treated. Chinese patent (publication number CN 101775505 B) discloses a method for extracting lithium from lepidolite ore. This method involves chlorination roasting to volatilize and recover dust including lithium chloride, potassium chloride, sodium chloride, rubidium chloride, and cesium chloride, followed by leaching with sodium carbonate and / or potassium carbonate solutions to obtain lithium carbonate precipitate. This method requires high roasting temperatures, has low lime-sand efficiency, and the subsequent sodium carbonate and potassium carbonate treatments increase the operational steps. Chinese patent (publication number CN 111910088 A) discloses a process for extracting lithium from lepidolite by chlorination roasting. It uses a composite chloride salt composed of sodium chloride, calcium chloride, aluminum chloride, and ferric chloride to chlorinate and roast lepidolite. The chlorination roasting temperature is 750-850℃ and the roasting time is 0.6-3h. The lithium extraction efficiency is high, reaching 98.6%. However, the composite chloride salt is difficult to recycle, resulting in high cost. Furthermore, the roasting process may introduce iron impurities, increasing the workload of subsequent operations. Summary of the Invention

[0003] In view of the shortcomings and defects in the existing technology, the purpose of this invention is to provide a method for extracting lithium from lepidolite using a composite salt roasting-water leaching process. This method uses a special composite salt to achieve the chlorination conversion of lepidolite into water-soluble chloride salt at a lower temperature, thereby achieving efficient lithium extraction and obtaining lithium carbonate products. Moreover, the composite salt can be regenerated and recycled, which is low-cost, environmentally friendly, and conducive to large-scale production.

[0004] To achieve the above-mentioned technical objectives, the present invention provides a method for extracting lithium from lepidolite using a composite salt roasting-water leaching process, the method comprising the following steps: 1) Lithium mica ore powder and a composite salt composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride are mixed and chlorinated and roasted to obtain roasted clinker; 2) The roasted calcined material is soaked in water to obtain an aqueous extract; 3) The aqueous leaching solution is treated with sodium carbonate to precipitate calcium ions, resulting in a calcium-removing purified solution; 4) After adjusting the pH of the calcium removal purification solution, first concentrate and crystallize to precipitate sodium chloride and potassium chloride crystals, then add sodium carbonate to the crystallization mother liquor to precipitate lithium ions, thus obtaining lithium carbonate precipitate.

[0005] The technical solution of this invention employs a composite salt composed of calcium chloride, calcium sulfate, sodium chloride, and potassium chloride in the roasting process of lepidolite. Compared to single chloride salts, the composite salt has a lower melting point, and the molten system formed by calcium chloride-calcium sulfate-sodium chloride-potassium chloride has excellent fluidity, enabling better contact and reaction with the surface of lepidolite ore. This significantly improves the conversion efficiency of lepidolite and is beneficial for increasing lithium extraction efficiency. Some of the chloride salts in the composite salt participate in the lepidolite reaction, while the remaining chloride salts act as fluxes. Furthermore, molten lepidolite ore readily reacts with calcium sulfate in a high-temperature environment, thereby displacing elements such as lithium, potassium, and silicon to form the corresponding sulfates.

[0006] The technical solution of this invention can achieve the regeneration and closed-loop circulation of sodium chloride and potassium chloride in composite salt through concentration and crystallization, which can reduce the cost of lithium recovery. The recycling of residues during the production process also reduces the environmental pressure on enterprises.

[0007] As a preferred embodiment, the composite salt is composed of calcium chloride, calcium sulfate, sodium chloride, and potassium chloride in a mass ratio of 0.8–1:0.8–1:1.8–2:0.8–1. Sodium chloride is the main component, accounting for a relatively high proportion. A portion of the sodium chloride reacts with lepidolite, while the remaining portion acts as a flux. Calcium sulfate reacts with lepidolite at high temperatures, displacing lithium ions and increasing the lithium ion leaching rate. Potassium chloride primarily replaces a portion of the calcium chloride, as calcium chloride is difficult to recycle, while potassium chloride can be regenerated and recycled, thus effectively saving costs. Furthermore, within the preferred proportions, calcium chloride, calcium sulfate, sodium chloride, and potassium chloride can form a molten system with a low melting point and good fluidity, which is beneficial for promoting high-temperature solid-phase reactions.

[0008] As a preferred embodiment, the mass ratio of the composite salt to lepidolite powder is 1:0.8-1.5. A decrease in the mass of the composite salt relative to the lepidolite powder leads to incomplete lepidolite conversion, resulting in a lower lithium leaching rate. However, an excessively high mass of the composite salt relative to the lepidolite powder can cause the composite salt to coat the lepidolite particles during roasting, also reducing the lithium leaching rate. A further preferred mass ratio of the composite salt to lepidolite powder is 1:0.9-1.1.

[0009] As a preferred embodiment, the chlorination roasting conditions are: a temperature of 880–920°C and a time of 35–50 min. If the roasting temperature is too low or the roasting time is too short, the reaction between the composite salt and lepidolite will be incomplete, the lepidolite structure will not be fully destroyed, and lithium will not be fully released, resulting in a lower lithium leaching rate. If the roasting temperature is too high or the roasting time is too long, alkali metal lithium will easily volatilize under high-temperature conditions, causing losses. The temperature is further preferably 880–900°C, and the time is further preferably 40–45 min.

[0010] As a preferred embodiment, the water immersion conditions are: temperature 70–90°C, time 25–35 min, and liquid-to-solid ratio 1–3 mL / g. The temperature is further preferably 80–85°C. The time is further preferably 30–35 min, and the liquid-to-solid ratio (volume-to-mass ratio of water to calcined slag) is further preferably 1.5–2 L:1 kg.

[0011] As a preferred embodiment, during the precipitation of calcium ions, the amount of sodium carbonate used is 105%–110% of the theoretical mass of sodium carbonate required for all calcium ions in the lepidolite ore to be converted into calcium carbonate, and the precipitation time is 2–2.5 hours. Sodium sulfate is not suitable for the precipitation of calcium ions, mainly because the concentration of calcium ions in the aqueous leachate is not high, and calcium sulfate is only slightly soluble in water. If sodium sulfate is used, a large amount of sodium sulfate would be required to remove calcium ions, thus introducing excessive sodium ions. Calcium carbonate has a lower solubility than calcium sulfate, so sodium carbonate precipitation is used to remove calcium from the aqueous leachate, resulting in a purer decalcified solution.

[0012] As a preferred embodiment, the pH is adjusted to 5.5-6.5; the most preferred pH is 6. The solubility of lithium carbonate decreases with increasing temperature. During the heating and concentration process, the system temperature rises. When carbonate ions are present in the system, lithium reacts with carbonate ions to form lithium carbonate, resulting in lithium loss. When the system pH is lowered to around 6, all carbonate ions in the system can be converted to carbonic acid, and then to water and carbon dioxide, which helps reduce lithium loss.

[0013] As a preferred embodiment, during the lithium ion precipitation process, the amount of sodium carbonate used is 105%–120% of the theoretical mass of sodium carbonate required for the complete conversion of lithium ions in lepidolite to lithium carbonate, and the precipitation time is 30–60 minutes. More preferably, the amount of sodium carbonate used is 105%–110% of the theoretical mass of sodium carbonate required for the complete conversion of lithium ions in lepidolite to lithium carbonate.

[0014] The method for extracting lithium from lepidolite using a composite salt roasting-water leaching process provided by this invention includes the following specific steps: (1) The lithium mica ore powder and the composite salt are thoroughly ground and mixed evenly at a mass ratio of 0.8~1.5:1; wherein the composite salt is composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride in a mass ratio of 0.8~1:0.8~1:1.8~2:0.8~1.

[0015] (2) The mineral powder mixed evenly in step (1) is subjected to chlorination roasting at a temperature of 880-920℃ for 35-50 minutes to obtain clinker; (3) The clinker obtained in step (2) is leached with water at a temperature of 70-90℃ for 25-35 min with a liquid-to-solid ratio of 1-3 mL / g, and then filtered to obtain the water leaching solution. (4) Add sodium carbonate to the water leaching solution obtained in step (3). The amount of sodium carbonate used is 105% to 110% of the theoretical mass of sodium carbonate required for all calcium ions in the lithium mica ore to be converted into calcium carbonate. After reacting for 2 to 2.5 hours, stir and filter to obtain filter residue (calcium carbonate) and purified solution (a solution containing lithium, sodium, potassium, etc.).

[0016] (5) Adjust the pH of the purified liquid obtained in step (4) to 5.5~6.5, and use the residual heat in the furnace to heat and concentrate the purified liquid to 1 / 4~1 / 8, concentrate and precipitate sodium chloride and potassium chloride solid particles, filter and separate the solid and liquid to obtain concentrated liquid, which can significantly improve the utilization rate of residual heat of the roasting furnace gas. At the same time, add sodium carbonate and stir for 0.5~1h, and control the mass of sodium carbonate to be greater than 105~120% of the theoretical amount of calcium in lepidolite required to convert to lithium carbonate, filter to obtain lithium carbonate filter residue. Filter and record the volume of filtrate, measure the lithium concentration, calculate the mass and compare it with the initial mass of lithium in the purified liquid to calculate the lithium carbonate synthesis rate, weigh the wet weight of filter cake and record the mass, place it in an oven to dry until there is no free water, and compare the mass of filter cake after drying again with the water content of lithium carbonate.

[0017] Compared with the prior art, the advantages of the technical solution of the present invention are as follows: 1. The technical solution of this invention selects a composite salt composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride, which can lower the melting point of the entire system, increase the utilization rate of salt ore, require a lower temperature during roasting, and consume less energy. At the same time, the molten system formed by calcium chloride-calcium sulfate-sodium chloride-potassium chloride has good fluidity and can better contact and react with the surface layer of lepidolite ore, thereby greatly improving the conversion efficiency of lepidolite and improving the extraction efficiency of lithium.

[0018] 2. The technical solution of this invention allows for water leaching after chlorination roasting, but the aluminum in the lepidolite is not leached out, reducing subsequent impurity removal and greatly reducing the separation and purification steps of lithium carbonate.

[0019] 3. The present invention uses sodium carbonate precipitation to separate the aqueous leaching solution, which avoids the introduction of new impurities and has a low purification load.

[0020] 4. The composite salt selected in this invention is calcium chloride, calcium sulfate, sodium chloride and potassium chloride. After roasting, the amount of residue is small and the lithium leaching rate can reach more than 96%.

[0021] 5. The steps in the technical solution of this invention are well coordinated and coherent. The process of extracting lithium from lepidolite to prepare lithium carbonate is green, environmentally friendly, energy-saving, low in energy consumption, low in cost, and high in extraction rate, and has broad industrial application prospects. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the process flow according to an embodiment of the present invention.

[0024] Figure 2 The lithium leaching rate at different calcination temperatures is shown in Example 4.

[0025] Figure 3 The lithium leaching rate is shown in Example 5 under different calcination times. Detailed Implementation

[0026] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0027] Unless otherwise intended, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0028] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0029] Example 1 (1) Lithium mica ore with a Li2O content of 5.0% (K(Li,Al)4O) 10 (F,OH)2) is mainly composed of oxides of lithium, aluminum, silicon and potassium, which are ground and mixed evenly with calcium chloride, calcium sulfate, sodium chloride and potassium chloride in a mass ratio of 5:1:1:2:1. (2) The material obtained in step (1) is roasted at 900℃ for 40 minutes; (3) The clinker obtained in step (2) is directly soaked in water, filtered to obtain a water leaching solution, the water leaching temperature is controlled at 85℃, the water leaching time is 0.5h, the liquid-solid ratio is 2:1, and the leaching residue is discarded after washing; the lithium leaching rate can reach 96.8%, and the aluminum is almost not leached.

[0030] (4) Add sodium carbonate to the water leaching solution obtained in step (3) and stir to leach for 30 minutes. Control the mass of sodium carbonate to be greater than 110% of the theoretical amount required for the conversion of calcium in lepidolite into calcium carbonate. Filter to obtain a purified solution containing lithium, sodium, potassium and other minerals and calcium carbonate filter residue. Collect the filter residue to obtain calcium carbonate. (5) Adjust the pH of the purified liquid obtained in step (4) to 6, and use the residual heat in the furnace to heat and concentrate 1L of purified liquid to 149ml. Concentrate and precipitate sodium chloride and potassium chloride solid particles, filter to separate solid and liquid, and obtain a concentrated liquid with a lithium concentration of 10.56g / L. At the same time, add sodium carbonate and stir to leach for 1h, and control the mass of sodium carbonate to be greater than 110% of the theoretical amount of lithium in lepidolite required to convert to lithium carbonate. Filter to obtain lithium carbonate filter residue. Record the volume of filtrate and measure the lithium concentration. Calculate the mass and compare it with the initial mass of lithium in the purified liquid to calculate the lithium carbonate synthesis rate. Weigh the wet weight of the filter cake and record the mass. Place it in an oven to dry until there is no free water. After drying again, the mass of the filter cake is compared with the water content of lithium carbonate.

[0031] The lithium recovery rate in this example was determined to be 96.01%.

[0032] Comparative Example 1 The only difference from Example 1 is that step (1) is different, and lepidolite is ground and mixed evenly with calcium chloride, sodium chloride and potassium chloride in a mass ratio of 4:1:2:1; other steps and conditions are the same as in Example 1.

[0033] The lithium recovery rate in this example was measured to be 91.96%. This comparative example shows that the effect is worse when calcium sulfate is not added to the composite salt, indicating that calcium sulfate promotes the destruction of the lepidolite structure and the leaching of lithium ions.

[0034] Comparative Example 2 The only difference from Example 1 is that step (1) is different. Lithium mica ore is ground and mixed evenly with calcium chloride, calcium sulfate and potassium chloride in a mass ratio of 3:1:1:1. Other steps and conditions are the same as in Example 1.

[0035] The lithium recovery rate in this example was measured to be 90.90%. This comparative example shows that the effect is worse when sodium chloride is not added to the composite salt. This may be because the composite salt without sodium chloride does not completely destroy the structure of lepidolite, resulting in a lower lithium ion leaching rate.

[0036] Example 2

[0037] The only difference from Example 1 is that step (1) is different, and lepidolite is ground and mixed evenly with calcium chloride, calcium sulfate and sodium chloride in a mass ratio of 7.5:1:1:2:1.

[0038] The lithium recovery rate in this embodiment was 93.27% at different roasting temperatures. This is mainly because the proportion of the composite salt relative to the lepidolite is relatively low, resulting in incomplete destruction of the lepidolite and incomplete extraction of lithium, thus reducing the lithium leaching rate.

[0039] Example 3

[0040] The only difference from Example 1 is that step (1) is different, and lepidolite is ground and mixed evenly with calcium chloride, calcium sulfate and sodium chloride in a mass ratio of 4:1:1:2:1.

[0041] The lithium recovery rate in this embodiment was 92.07% at different roasting temperatures. This is mainly because the proportion of the composite salt relative to the lepidolite was too high. The molten composite salt would encapsulate the lepidolite, resulting in incomplete reaction of some of the lepidolite and incomplete lithium extraction, thus reducing the lithium leaching rate.

[0042] Example 4

[0043] (1) Lithium mica ore with a Li2O content of 5.0% (K(Li,Al)4O) 10 (F,OH)2) is mainly composed of oxides of lithium, aluminum, silicon and potassium, which are ground and mixed evenly with calcium chloride, calcium sulfate, sodium chloride and potassium chloride in a mass ratio of 5:1:1:2:1. (2) The materials obtained in step (1) are roasted at 840℃, 860℃, 880℃, 900℃ and 920℃ for 45 min respectively; (3) The clinker obtained in step (2) is directly soaked in water, filtered to obtain a water leaching solution, the water leaching temperature is controlled at 85℃, the water leaching time is 0.5h, the liquid-solid ratio is 2:1, and the leaching residue is discarded after washing. (4) Add sodium carbonate to the water leaching solution obtained in step (3) and stir to leach for 2.5 hours. Control the mass of sodium carbonate to be greater than 110% of the theoretical amount required for the conversion of calcium in lepidolite into calcium carbonate. Filter to obtain a purified solution containing lithium, sodium, potassium and other minerals and calcium carbonate filter residue. Collect the filter residue to obtain calcium carbonate. (5) Adjust the pH of the purified liquid obtained in step (4) to 6, and use the residual heat in the furnace to heat and concentrate 1L of purified liquid to 149ml. Concentrate and precipitate sodium chloride and potassium chloride solid particles, filter to separate solid and liquid, and obtain concentrated liquid. At the same time, add sodium carbonate and stir to leach for 1h, and control the mass of sodium carbonate to be greater than 110% of the theoretical amount required for the conversion of lithium in lepidolite to lithium carbonate. Filter to obtain lithium carbonate filter residue. Record the volume of filtrate and measure the lithium concentration. Calculate the mass and compare it with the initial mass of lithium in the purified liquid to calculate the lithium carbonate synthesis rate. Weigh the wet weight of the filter cake and record the mass. Place it in an oven to dry until there is no free water. After drying again, the mass of the filter cake is compared with the water content of lithium carbonate.

[0044] The lithium recovery rates measured in this embodiment at different roasting temperatures were 86.45%, 89.73%, 92.45%, 96.01%, and 93.68%, respectively. It can be seen that within the roasting temperature range of 840℃ to 920℃, increasing the roasting temperature is more conducive to the destruction of the lepidolite structure and improves the lithium recovery rate; however, further increases in temperature also lead to increased lithium volatilization losses.

[0045] Example 5

[0046] (1) Lithium mica with a Li2O content of 5.0% is ground and mixed with calcium chloride, calcium sulfate, sodium chloride and potassium chloride in a mass ratio of 5:1:1:2:1. (2) The material obtained in step (1) is roasted at 900℃ for 30 min, 35 min, 40 min, 45 min and 50 min respectively; (3) The clinker obtained in step (2) is directly soaked in water, filtered to obtain a water leaching solution, the water leaching temperature is controlled at 85℃, the water leaching time is 0.5h, the liquid-solid ratio is 2:1, and the leaching residue is discarded after washing. (4) Add sodium carbonate to the water leaching solution obtained in step (3) and stir to leach for 2.5 hours. Control the mass of sodium carbonate to be greater than 110% of the theoretical amount required for the conversion of calcium in lepidolite into calcium carbonate. Filter to obtain a purified solution containing lithium, sodium, potassium and other minerals and calcium carbonate filter residue. Collect the filter residue to obtain calcium carbonate. (5) Adjust the pH of the purified liquid obtained in step (4) to 6, and use the residual heat in the furnace to heat and concentrate 1L of purified liquid to 149ml. Concentrate and precipitate sodium chloride and potassium chloride solid particles, filter to separate solid and liquid, and obtain concentrated liquid. At the same time, add sodium carbonate and stir to leach for 1h, and control the mass of sodium carbonate to be greater than 110% of the theoretical amount required for the conversion of lithium in lepidolite to lithium carbonate. Filter to obtain lithium carbonate filter residue. Record the volume of filtrate and measure the lithium concentration. Calculate the mass and compare it with the initial mass of lithium in the purified liquid to calculate the lithium carbonate synthesis rate. Weigh the wet weight of the filter cake and record the mass. Place it in an oven to dry until there is no free water. After drying again, the mass of the filter cake is compared with the water content of lithium carbonate.

[0047] The lithium recovery rates in this embodiment were measured to be 87.69%, 93.15%, 95.77%, 94.27%, and 90.93%. It can be seen that at a certain calcination temperature, the longer the calcination time, the more conducive it is to the destruction of the lepidolite structure and the higher the lithium recovery rate. However, with further increases in time, the loss of lithium due to volatilization will also increase.

Claims

1. A method for extracting lithium from lepidolite using a composite salt roasting-water leaching process, characterized in that: Includes the following steps: 1) Lithium mica ore powder and a composite salt composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride are mixed and chlorinated and roasted to obtain roasted clinker; the composite salt is composed of calcium chloride, calcium sulfate, sodium chloride and potassium chloride in a mass ratio of 0.8-1:0.8-1:1.8-2:0.8-1; the chlorination and roasting conditions are: temperature of 880-920℃ and time of 35-50min; 2) The roasted clinker is soaked in water to obtain an aqueous extract; the conditions for soaking are: temperature of 70-90℃, time of 25-35min, and liquid-to-solid ratio of 1-3 mL / g. 3) The aqueous leaching solution is treated with sodium carbonate to precipitate calcium ions, resulting in a calcium-removing purified solution; 4) After adjusting the pH of the calcium removal purification solution to 5.5~6.5, first concentrate and crystallize to precipitate sodium chloride and potassium chloride crystals, then add sodium carbonate to the crystallization mother liquor to precipitate lithium ions, thus obtaining lithium carbonate precipitate.

2. The method for extracting lithium from lepidolite using a composite salt roasting-water leaching process according to claim 1, characterized in that: The mass ratio of the composite salt to lepidolite powder is 1:0.8-1.

5.

3. The method for extracting lithium from lepidolite using a composite salt roasting-water leaching process according to claim 1, characterized in that: In the process of removing calcium ions by precipitation, the amount of sodium carbonate used is 105% to 110% of the theoretical mass of sodium carbonate required for all calcium ions in lepidolite to be converted into calcium carbonate, and the precipitation time is 2 to 2.5 hours.

4. The method for extracting lithium from lepidolite using a composite salt roasting-water leaching process according to claim 1, characterized in that: During the precipitation of lithium ions, the amount of sodium carbonate used is 105% to 120% of the theoretical mass of sodium carbonate required for all lithium ions in the lepidolite ore to be converted into lithium carbonate, and the precipitation time is 0.5 to 1 hour.

Images