Novel lithium, rubidium and cesium co-extraction method for reducing and roasting lepidolite at low temperature by compounding calcium salt with thiosulfate

Abstract

The invention provides a novel lithium, rubidium and cesium co-extraction method for reducing and roasting lepidolite at low temperature by compounding calcium salt with thiosulfate, and belongs to the technical field of extraction of lithium, rubidium and cesium from lepidolite concentrate. Based on the problems of high energy consumption, large slag yield, serious tail gas pollution and the like of a traditional sulfate roasting method, the following changes are made: a roasting aid is changed into a mixture of sodium salt and calcium salt, so that the cost of the roasting aid is reduced by 10-30%; wherein the sodium salt destroys the lattice structure of lepidolite concentrate through a reduction reaction, the leaching rate of lithium, rubidium and cesium is increased by 3%-5%, the calcium salt realizes fluorine fixation through the reaction of calcium ions and fluorine ions, the amount of tailings generated by roasting is reduced by 30%-50%, and tail gas purification is not needed; on the basis of a traditional roasting method, a novel tubular furnace roasting temperature rising procedure is fused, and the roasting heat efficiency is improved by 30% through different reactions in different time zones. In conclusion, the method has high research value and application prospect in improvement of the leaching rate of lithium, rubidium and cesium and treatment of tailings.

Description

Technical Field

[0001] This invention relates to the field of lithium, rubidium, and cesium extraction from lithium ore, specifically to a novel method for the co-extraction of lithium, rubidium, and cesium from lepidolite by low-temperature reduction roasting of calcium salts and thiosulfates. Background Technology

[0002] Lithium is a strategic metal for China, designated as one of the 24 national strategic mineral resources. It is a key material in fields such as new energy vehicles, aerospace, and nuclear industry. In 2024, China's production and sales of new energy vehicles exceeded 12 million units, accounting for over 70% of the global market, and the lithium battery industry became one of the "new three pillars" of exports. Jiangxi Province, as a core cluster of the lithium industry, achieved lithium battery revenue of 235.28 billion yuan in 2022 (accounting for nearly half of the national lithium salt production), forming a complete "lithium ore-recycling" industrial chain. Companies like Ganfeng Lithium lead the global market, with ore-based lithium extraction accounting for over 60%. Promoting technological innovation in the harmless and resource-oriented utilization of lithium ore is a core path to improving total factor productivity and developing the lithium battery industry, and is crucial for ensuring national energy security and industrial competitiveness.

[0003] Existing "high-temperature roasting-wet leaching" processes focus solely on lithium extraction, typically employing large amounts of reagents to efficiently convert lithium-bearing mineral phases. However, this results in high energy consumption, large slag production, and severe tail gas pollution, necessitating a shift from single-phase control of lithium-bearing mineral phases to low-energy synergistic control of multiple mineral phases. This process pioneers a "low-temperature reduction-chlorination synergistic" reaction system, overcoming three major industry pain points in lithium extraction from lepidolite: Firstly, in traditional sulfate roasting processes, Al... 3+ The calcination process of lepidolite significantly inhibits the crystallization process of cesium garnet, making it difficult to improve the leaching efficiency of rubidium and cesium. Secondly, lepidolite is prone to melting at high temperatures and forming an amorphous glass phase, which encapsulates rubidium and cesium, hindering the effective release of the target elements and causing a significant increase in energy consumption. Finally, the fluorine-containing components in lepidolite decompose during the calcination process to produce harmful fluoride gases, which not only pollute the environment and corrode equipment, but also generate a large amount of tailings rich in toxic components, greatly increasing the cost of subsequent treatment. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to provide a new method for the co-extraction of lithium, rubidium, and cesium from lepidolite by low-temperature reduction roasting of calcium salts and thiosulfates.

[0005] The present invention solves the above-mentioned technical problems through the following technical means: This invention provides a method for extracting lithium, rubidium, and cesium from lepidolite concentrate, comprising the following steps: (1) Lithium mica concentrate and roasting aid are mixed, ground evenly, and then roasted under an inert gas atmosphere to obtain mixed clinker; the roasting aid is composed of sodium thiosulfate and calcium chloride; (2) Grind the mixed clinker, soak it in water, and separate the solid and liquid to obtain lithium-rubidium-cesium leachate and leachate residue.

[0006] Preferably, the lepidolite concentrate is granite-type lepidolite concentrate with a lithium content of 1.0~3.0 wt%.

[0007] Preferably, the mass ratio of the lithium mica concentrate to the roasting aid is 5:(1~5).

[0008] Preferably, the calcination aid is composed of sodium thiosulfate and calcium chloride in a mass ratio of (1~5):(5~1).

[0009] Preferably, in step (1), the grinding specifically involves grinding the material until the particle diameter is 100 mesh or less. (Both excessively large and excessively small particle diameters after grinding will affect the calcination efficiency. Excessively large particle diameters cause the calcination reaction interface to be limited to the particle surface, with the core not participating in the reaction. Excessively small particle diameters cause particle agglomeration, forming "pseudo-coarse particles" that reduce the effective reaction area.) Preferably, the inert gas is any one of argon, helium, neon, and krypton. Argon is more preferably preferred. (Argon can maintain a reducing atmosphere, protecting the decomposition products of sodium thiosulfate from reacting with oxygen; argon can control the flow of sulfur, reducing harmful gas emissions; as a dry inert gas, argon can reduce water vapor content, thus preventing high-temperature chloride hydrolysis.) Preferably, the calcination temperature is 650~850℃ and the time is 30~150 min; more preferably, it is 700~800℃ and 60~120 min. (The calcination temperature has a significant impact on the calcination efficiency. Excessively high calcination temperatures increase energy consumption during calcination, and the formation of a glassy phase from aluminosilicates hinders mass transfer. Insufficient calcination temperatures result in incomplete lithium-ion replacement. The calcination time directly affects the calcination efficiency. Excessively long calcination times increase unnecessary energy consumption. Insufficient calcination times lead to reaction interruption during calcination.) Preferably, the calcination heating program is as follows: heating from room temperature to 60°C at a rate of 3 to 5°C / min, and heating from 60°C to 700°C at a rate of 5 to 8°C / min.

[0010] Preferably, in step (2), the grinding time is 20 to 30 minutes.

[0011] Preferably, the conditions for water immersion are: liquid-to-solid ratio of (8~12) mL:1g, temperature of 15~55℃, and time of 30~90min; more preferably, the liquid-to-solid ratio is 10mL:1g, temperature of 25℃, and time of 60min.

[0012] The beneficial effects of this invention are as follows: (1) This invention overcomes the three major bottlenecks of high energy consumption, high pollution, and low rare metal recovery rate of traditional processes by using sodium / calcium salt compound additives in conjunction with low-temperature reduction roasting, providing an efficient, green, and low-cost solution for the resource utilization of lepidolite. The roasting additives used in this invention are cheaper and have a lower roasting temperature than traditional sulfate roasting additives, and have the advantages of low cost and low energy consumption. This invention provides a new direction for existing lithium extraction schemes from lepidolite. In addition to the original roasting method of adding a single sulfate to the roasting additive, this invention mixes sodium and calcium salts and adds them to the roasting additive, making it easier for lithium to be released and converted. This significantly improves the lithium extraction efficiency and reduces the amount of tailings after roasting, by 30% to 50% compared with the traditional sulfate roasting method. (2) The method for co-extraction of lithium, rubidium, and cesium in this invention: Compared with the traditional use of sulfates as roasting aids, sodium thiosulfate decomposes and releases SO2 during roasting, inhibiting Al 3+ Interference with cesium garnet formation; calcium chloride reduces melt viscosity, reduces glass phase formation, and prevents rubidium and cesium from being trapped and difficult to release; sodium salt weakens Li-O bonds, and calcium salt destroys the stable structure of aluminosilicates, resulting in lithium, rubidium, and cesium leaching rates >90%, ultimately achieving efficient co-extraction of the three elements.

[0013] (3) Low lithium extraction roasting temperature and low energy consumption: The low-temperature reduction roasting in this invention reduces the roasting temperature to 700–800℃ (the traditional sulfate method requires >900℃), reducing energy consumption by about 30% and increasing thermal efficiency by 30%. At the same time, low-temperature roasting avoids the glass phase blocking mass transfer at high temperatures, significantly optimizing energy consumption and temperature.

[0014] (4) The amount of lithium slag is greatly reduced after lithium extraction: Calcium chloride combines with fluoride ions released by lepidolite during roasting to generate stable calcium fluoride, thereby achieving in-situ solidification of fluoride and preventing the escape of fluoride gas from the source. At the same time, it reduces the toxic components in the tailings. The solidification reaction further reduces the amount of tailings by 30-50%. Calcium salts reduce the viscosity of the melt and inhibit the formation of the glass phase, making the leaching residue loose and granular, and reducing grinding energy consumption by more than 50%.

[0015] Of course, implementing any product or method of the present invention does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0016] Figure 1 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium under the same conditions between Example 1 and Comparative Examples 1-6. Figure 2 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium under different mineral-salt ratios in Example 2; Figure 3 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium at different calcination temperatures in Example 2; Figure 4This is a comparison chart of the leaching rates of lithium, rubidium, and cesium at different calcination times in Example 2; Figure 5 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium under different water immersion times in Example 2; Figure 6 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium under different sodium to calcium salt mass ratios in Example 2. Figure 7 This is a comparison chart of the leaching rates of lithium, rubidium, and cesium at different water immersion temperatures in Example 2; Figure 8 This is a flowchart of the scale-up test described in Example 3. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art.

[0018] Unless otherwise specified, the test materials and reagents used in the following examples are commercially available or prepared by known methods.

[0019] Unless otherwise specified, all techniques or conditions described in the embodiments can be performed in accordance with the techniques or conditions described in the literature in this field or in the product manual. Unless otherwise specified, the quantitative experiments in the following embodiments are all repeated three times or more, and the results are averaged.

[0020] In the examples, the lepidolite concentrate is granite-type lepidolite concentrate from Yichun, Jiangxi Province, with a lithium content of 1.0~3.0 wt%.

[0021] Example 1: A method for extracting lithium, rubidium, and cesium from lepidolite concentrate, characterized by comprising the following steps: S1. Mix 0.75 g sodium thiosulfate and 2.25 g calcium chloride evenly for 5 min to form a roasting aid. Put the roasting aid and 5 g lepidolite concentrate into an agate mortar and grind for 20 min to mix evenly (grind until the particle diameter is 100 mesh or less) to obtain a uniformly colored mixture. S2. Place the mixture of lepidolite concentrate and roasting aid into an agate mortar and grind it thoroughly for 20 minutes. Then, stir it for 5 minutes to mix it evenly to obtain a uniformly colored mixture for roasting. S3. Place the mixture to be roasted into a tube furnace. Under an argon atmosphere, heat the mixture to 750°C and maintain the temperature for 90 min according to the program of "room temperature ~ 60°C at 5°C / min and 60°C ~ 750°C at 5°C / min" to obtain the roasted mixture. S4. After the tubular furnace cools down, take out the roasted mixture, let it stand and wait for the mixture to cool to room temperature, then grind it for 20 minutes. Then put the ground mixture into a beaker and immerse it in water at a liquid-to-solid ratio of 10 mL: 1 g, a temperature of 25 °C and a time of 60 minutes. The leachate and leach residue are obtained by solid-liquid separation through filtration.

[0022] Comparative Example 1: Unlike Example 1, this experiment was a control experiment. Only lepidolite concentrate was added to the roasting feed, without any roasting aids. The effect of different roasting times on lithium leaching rate was investigated. The remaining steps were the same as in Example 1. The results are as follows: Figure 1 As shown in Figure B, the highest lithium leaching rate is 20%. This is because no roasting aid was added to the roasted material. Although the high temperature damages the structure of the lepidolite concentrate, lithium ions cannot escape from the crystal lattice, resulting in a much lower lithium leaching rate compared to when roasting aids were added.

[0023] Comparative Example 2: Unlike Example 1, this experiment was a control experiment, with only sodium thiosulfate added as a roasting aid. The mass ratio of lithium mica concentrate to sodium thiosulfate was set at 5:3, and the effect of different roasting times on lithium leaching rate was investigated. The remaining steps were the same as in Example 1. The results are as follows: Figure 1 As shown in Figure C, the highest lithium leaching rate after roasting is 75%. When lepidolite concentrate is roasted alone with sodium thiosulfate, sodium thiosulfate decomposes in the low-temperature zone, creating a reducing atmosphere in the roasted material. In the high-temperature zone, sodium thiosulfate reduces iron ions, causing the lepidolite concentrate lattice to break down, resulting in higher lithium ion leaching and a higher lithium leaching rate. However, the lack of calcium salts leads to the escape of fluoride ions, resulting in problems such as equipment corrosion and difficult tailings treatment.

[0024] Comparative Example 3: Unlike Example 1, this experiment was a control experiment, with calcium chloride added as a roasting aid. The mass ratio of lepidolite concentrate to calcium chloride was set at 5:3, and the effect of different roasting times on lithium leaching rate was investigated. The remaining steps were the same as in Example 1. The results are as follows: Figure 1As shown in Figure D, the highest lithium leaching rate after roasting was 40%. Compared with Comparative Example 2, the lithium leaching rate decreased while the fluoride ion emission decreased. This is because when the temperature reaches 600℃ and above, calcium chloride undergoes a hydrolysis reaction to generate hydrogen sulfide gas, which destroys the crystal lattice of lepidolite concentrate. However, the degree of destruction is far less than that of sodium thiosulfate, resulting in fewer lithium ions being precipitated. In contrast, the calcium ions in calcium chloride can effectively fix fluoride ions, reducing their emission and solving the equipment corrosion problem.

[0025] Comparative Example 4: Unlike Example 1, this experiment was a control experiment, with only sodium sulfate added as a roasting aid. The mass ratio of lepidolite concentrate to sodium sulfate was set at 5:3, and the effect of different roasting times on lithium leaching rate was investigated. The remaining steps were the same as in Example 1. The results are as follows: Figure 1 As shown in Figure E, the highest lithium leaching rate after calcination was 15%. This is significantly lower than other comparative examples because pure sodium sulfate is very stable, with a melting point of approximately 884°C and a decomposition temperature exceeding 1600°C. Therefore, at a calcination temperature of 750°C, sodium sulfate itself hardly decomposes and cannot effectively provide highly reactive sodium or sulfate ions to disrupt the lepidolite structure.

[0026] Comparative Example 5: Unlike Example 1, this experiment used a control group, changing the tube furnace roasting atmosphere from argon to air, to investigate the effect of different roasting times on lithium leaching rate. The remaining steps were the same as in Example 1. The results are as follows: Figure 1 As shown in Figure F, the highest lithium leaching rate after roasting was 35%. This is significantly lower than the lithium leaching rate under an argon atmosphere. The reason is that the reduction reaction of sodium thiosulfate in air failed, and it underwent an oxidation reaction to generate sulfur dioxide, which failed to break down the crystal lattice of the lepidolite concentrate, thus preventing lithium ion leaching. Furthermore, the roasting process generates glassy substances, making the tailings even more difficult to handle.

[0027] Comparative Example 6: Unlike Example 1, this experiment used a control group, changing the tube furnace roasting atmosphere from argon to oxygen to observe the effect of different roasting times on lithium leaching rate. The remaining steps were the same as in Example 1. The results are as follows: Figure 1As shown in Figure G, the highest lithium leaching rate after roasting was 20%. Compared to roasting in an argon atmosphere, roasting in an oxygen atmosphere resulted in extremely low lithium extraction efficiency. This is because sodium thiosulfate undergoes a violent oxidation reaction in an oxygen atmosphere, failing to create conditions necessary to break down the lepidolite concentrate lattice. Furthermore, the excessively rapid oxidation reaction prevents calcium ions in calcium chloride from fixing fluoride ions, leading to the production of large amounts of toxic gases and significantly reducing experimental safety. The tailings, on the other hand, form hard, black lumps that are difficult to grind, resulting in incomplete water leaching and a sharp decrease in the lithium leaching rate.

[0028] like Figure 2 The figures show the leaching rates of lithium, rubidium, and cesium in Example 1 and all Comparative Examples 1.

[0029] Example 2: The optimal conditions in Example 1 were verified by performing a gradient optimization of the mineral-to-salt ratio, sodium-to-calcium salt ratio, roasting temperature, roasting time, water immersion temperature, and water immersion time. These conditions were 5:3 mineral-to-salt ratio, 1:3 sodium-to-calcium salt ratio, 750℃ temperature, 90 min roasting time, 25℃ water immersion temperature, and 60 min water immersion time. Specific data are shown in Table 1, and the data analysis is as follows. Figure 2 , Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 7 As shown.

[0030] Table 1

[0031] Example 3: The mass of lepidolite concentrate in Example 1 was increased to 100 kg, and all other materials were scaled up proportionally. The equipment used in the experiment was also upgraded. Finally, the lithium leaching rate was compared with that of Example 1. The specific steps are as follows: 100 kg of lithium mica concentrate was mixed with sodium thiosulfate and calcium chloride at a mass ratio of 5:0.75:2.25, crushed to a particle size of 1-3 mm using a planetary mill, and then processed and granulated using a twin-screw mixer. The resulting roasted granules were placed in a rotary kiln and roasted under the roasting conditions of Example 1. The roasted clinker was then transferred to a metallurgical leaching system, where soluble components were extracted using a water leaching process. Solid-liquid separation was then performed in a leaching tank to ultimately obtain lithium leachate and leaching residue. Figure 8 The steps of this experiment are shown in detail.

[0032] In summary, this invention improves lithium extraction efficiency while reducing energy consumption through the mixed roasting of lepidolite with sodium thiosulfate and calcium chloride, combined with novel equipment applications. Furthermore, by adding sodium and calcium salts to the traditional sulfate roasting method, it further enhances lithium extraction efficiency while ensuring control of air pollution and effective recovery of rare and dispersed metals. The method of this invention is simple to operate and uses readily available materials, showing promising development prospects in the field of tailings treatment.

[0033] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for extracting lithium, rubidium, and cesium from lepidolite concentrate, characterized in that, Includes the following steps: (1) Lithium mica concentrate and roasting aid are mixed, ground evenly, and then roasted under an inert gas atmosphere to obtain mixed clinker; the roasting aid is composed of sodium thiosulfate and calcium chloride; (2) Grind the mixed clinker, soak it in water, and separate the solid and liquid to obtain lithium-rubidium-cesium leachate and leachate residue.

2. The method according to claim 1, characterized in that, The lithium content in the lepidolite concentrate is 1.0~3.0 wt%.

3. The method according to claim 1, characterized in that, The mass ratio of the lithium mica concentrate to the roasting aid is 5:(1~5).

4. The method according to claim 1, characterized in that, The calcination aid is composed of sodium thiosulfate and calcium chloride in a mass ratio of (1~5):(5~1).

5. The method according to claim 1, characterized in that, In step (1), grinding specifically involves grinding the material until the particle diameter is 100 mesh or less; the inert gas is any one of argon, helium, neon, or krypton.

6. The method according to claim 1, characterized in that, The roasting temperature is 650~850℃ and the time is 30~150 min.

7. The method according to claim 6, characterized in that, The roasting temperature is 700~800℃ and the time is 60~120 min.

8. The method according to claim 1, characterized in that, In step (2), the grinding time is 20 to 30 minutes.

9. The method according to claim 1, characterized in that, The conditions for water immersion are: liquid-to-solid ratio of (8~12) mL:1g, temperature of 15~55℃, and time of 30~90min.

10. The method according to claim 9, characterized in that, The conditions for water immersion were: liquid-to-solid ratio of 10 mL: 1 g, temperature of 25 °C, and time of 60 min.

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