Method for extracting lithium and rubidium by low-temperature calcination of composite salt and application thereof

Abstract

This invention provides a method for extracting lithium and rubidium from lithium using a composite salt at low temperature and its application, belonging to the field of valuable metal extraction technology. The method uses spodumene as raw material, adding a composite salt system composed of K₂CO₃, KOH, and Ca(OH)₂, and calcining it at low temperature. This disrupts the spodumene crystal structure, transforming it into an easily leached active phase. The calcined product is then subjected to water leaching, achieving synergistic and efficient leaching of lithium and rubidium. Compared with existing technologies, this invention features a lower calcination temperature and higher lithium and rubidium leaching rates (>90%). Furthermore, the water leaching method is less corrosive and introduces fewer impurities compared to acid leaching systems, facilitating selective leaching of lithium and rubidium and simplifying subsequent separation and purification processes, demonstrating promising industrial application prospects.

Description

Technical Field

[0001] This invention relates to the field of comprehensive utilization of lithium resources and extraction of valuable metals, and particularly to a method for extracting lithium and rubidium by low-temperature roasting of composite salts and its application. Background Technology

[0002] With the rapid development of the new energy industry and energy storage technology, the demand for lithium resources, as a key strategic metal, continues to grow. Spodumene, as an important hard-rock lithium resource, has advantages such as large reserves and relatively stable distribution, making it a crucial raw material for industrial lithium extraction. Furthermore, spodumene often contains rare alkali metal elements such as rubidium, giving it high comprehensive recovery value. Therefore, achieving the synergistic and efficient extraction of lithium and rubidium from spodumene is of great significance.

[0003] In existing technologies, the extraction of lithium and rubidium from spodumene typically employs processes such as the sulfuric acid process or sulfate roasting. These methods usually require phase change roasting at temperatures above 900 °C to disrupt the stable aluminosilicate lattice structure of spodumene, thereby promoting the leaching of lithium and rubidium. However, these processes generally suffer from high roasting temperatures, high energy consumption, demanding equipment requirements, and the potential introduction of acidic wastewater, hindering energy conservation, emission reduction, and green production. To reduce roasting temperatures and improve the extraction efficiency of valuable metals, recent studies have proposed using single-salt or composite salt systems to roast and activate spodumene, promoting the disruption of the mineral structure and improving the leaching behavior of lithium and rubidium. However, existing related technologies still generally suffer from high roasting temperatures, limited reaction efficiency, or unsatisfactory rubidium extraction effects, making it difficult to achieve efficient synergistic recovery of lithium and rubidium.

[0004] Therefore, there is an urgent need to develop a new method that has low calcination temperature, low energy consumption, high salt agent utilization efficiency, and can effectively achieve the co-extraction of lithium and rubidium from spodumene, in order to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] To address the problems of high calcination temperature, high energy consumption, and low synergistic extraction efficiency of lithium and rubidium in existing spodumene extraction processes, this invention provides a method for low-temperature calcination extraction of lithium and rubidium using a composite salt. This method constructs a composite salt system and utilizes its eutectic properties to effectively activate the spodumene crystal structure at a lower calcination temperature, promoting the simultaneous release and conversion of lithium and rubidium, thereby improving the extraction efficiency of lithium and rubidium. Compared with existing technologies, this invention achieves a reduction in calcination temperature and highly efficient synergistic extraction of lithium and rubidium.

[0006] To achieve the above objectives, the present invention provides a method for extracting lithium and rubidium by low-temperature roasting of composite salts, comprising the following steps: S1. Pre-treat the spodumene raw material and sieve it to a particle size of less than 200 mesh to obtain pre-treated spodumene. S2. Mix the pretreated spodumene and the composite salt at a mass ratio of 1:0.5~2.5 to obtain a mixture. The raw materials for preparing the composite salt include KOH, K2CO3 and Ca(OH)2; S3. The mixture is roasted at 368~580°C for 0.5~2.5h to obtain roasted cooked material; S4. The roasted clinker is leached with water, and after solid-liquid separation, a leachate containing lithium and rubidium is obtained.

[0007] This technical solution introduces a Ca(OH)₂-containing composite salt system to achieve efficient conversion of lithium and rubidium in spodumene at low temperatures of 368–580°C. Subsequent water leaching enables the synergistic extraction of lithium and rubidium, resulting in significant energy savings and process advantages. The principle lies in the decomposition of Ca(OH)₂ during calcination to generate highly reactive CaO. CaO reacts with SiO₂ in the spodumene lattice to form stable calcium silicate (CaSiO₃), further disrupting the silicate framework structure and allowing the lithium, which was originally stably present in the lattice, to be extracted. + and Rb + The lithium and rubidium are released and converted into a water-soluble form. This method uses a calcination temperature far lower than traditional processes (>900℃), significantly reducing energy consumption. Furthermore, water leaching replaces acid leaching, avoiding the introduction of corrosive media and impurities, making it environmentally friendly. After water leaching, the leaching rates of both lithium and rubidium exceed 90%, approaching 98% under certain conditions, achieving synergistic and efficient recovery of lithium and rubidium. The process parameters have a wide adjustment range, and the raw material adaptability is strong, demonstrating promising prospects for industrial application.

[0008] According to an embodiment of the present invention, in step S2, the mass ratio of KOH, K2CO3 and Ca(OH)2 is 5.0~10.0:1.0~8.0:0.5~2.5.

[0009] According to an embodiment of the present invention, in step S2, the mass ratio of KOH, K2CO3 and Ca(OH)2 is 8.0~10.0:2.0~8.0:1.0~2.5.

[0010] Under the aforementioned specific ratios, KOH, K₂CO₃, and Ca(OH)₂ work synergistically to efficiently disrupt the spodumene crystal lattice at low temperatures. Specifically: 1. KOH and K₂CO₃ form a eutectic system, ensuring the generation of a sufficient liquid phase at low temperatures of 368–580°C, wetting the mineral and providing a medium for subsequent reactions. 2. This liquid phase encapsulates and promotes the decomposition of Ca(OH)₂, generating highly reactive CaO, significantly reducing the difficulty of its decomposition and reaction. 3. The reactive CaO acts on SiO₂ in the spodumene crystal lattice to generate stable CaSiO₃, thereby disrupting the silicate framework based on the initial activation by the molten salt.

[0011] This invention provides a method for extracting lithium and rubidium from spodumene using low-temperature calcination with a composite salt. The core principle lies in utilizing the eutectic properties of the composite salt system to effectively destroy the crystal structure of spodumene and selectively convert the target valuable metals at a lower temperature. The composite salt system is in a molten state, forming a highly reactive alkaline molten salt medium that disintegrates the stable crystal lattice framework of spodumene. After the crystal lattice is destroyed, the lithium originally bound within the lattice is released... + and associated Rb + The lithium and rubidium compounds are released and undergo ion exchange or binding reactions with the molten salt system, transforming into water-soluble alkaline compounds. When the calcined clinker is treated with water immersion, lithium and rubidium compounds preferentially dissolve into the aqueous phase, while impurity elements such as aluminum and silicon remain in the solid phase as insoluble aluminosilicates or oxides, thus achieving selective separation of lithium, rubidium, and impurity elements.

[0012] According to an embodiment of the present invention, in step S2, the mixing time is 6 to 12 hours.

[0013] According to an embodiment of the present invention, in step S3, the mixture is placed in a muffle furnace and heated to the calcination temperature at a heating rate of 10°C / min for calcination.

[0014] According to an embodiment of the present invention, in step S4, the process conditions for water leaching are as follows: the leaching medium is deionized water, the liquid-to-solid ratio is 1-5:1 mL / g, the leaching temperature is 40-80℃, and the leaching time is 0.5-2.5h.

[0015] According to an embodiment of the present invention, in step S1, the pretreatment step includes drying and grinding.

[0016] According to an embodiment of the present invention, step S4 further includes washing the solid phase obtained from solid-liquid separation with deionized water, and then combining the washing liquid and the leachate and adjusting the volume.

[0017] The present invention also proposes the application of the above-described method in the processing of lithium-containing aluminum silicate minerals.

[0018] According to an embodiment of the present invention, the lithium-containing aluminum silicate mineral includes at least one of spodumene, lepidolite, petalite, nepheline, and lepidolite.

[0019] According to an embodiment of the present invention, when the lithium-containing aluminum silicate mineral is spodumene, the lithium content is 2.18-2.52 wt% and the rubidium content is 0.11-0.25 wt%.

[0020] The present invention has at least the following beneficial effects: (1) The composite salt system used in this invention has a lower eutectic temperature, which allows the roasting reaction to be carried out at a lower temperature, significantly reducing energy consumption. At the same time, it avoids the volatilization and decomposition of residual organic matter in spodumene flotation concentrate under high temperature conditions, and reduces the volatilization loss of alkali metals and equipment corrosion problems. (2) The composite salt can promote the destruction of the spodumene crystal structure during the roasting process, so that lithium and rubidium can be converted into easily leached forms simultaneously, thereby achieving the synergistic and efficient recovery of lithium and rubidium. (3) The present invention can achieve efficient leaching of lithium and rubidium by water immersion. The process is relatively simple, the operating conditions are mild, and the introduction of impurities is minimal. This is conducive to achieving selective leaching of lithium and rubidium relative to impurity elements and simplifies the subsequent separation and purification process of lithium and rubidium.

[0021] (4) The process parameters of the method of the present invention have a wide range of adjustment, good stability and adaptability, and are applicable to spodumene raw materials under different conditions, and have good industrial application prospects. Detailed Implementation

[0022] The following description, in conjunction with embodiments, clearly and completely illustrates the technical solutions of the present invention, enabling those skilled in the art to fully understand the invention. Obviously, the described embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Any equivalent modifications or substitutions made by those skilled in the art to the following embodiments without creative effort are within the protection scope of the present invention.

[0023] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0024] Example 1 This embodiment provides a method for extracting lithium and rubidium by low-temperature roasting of composite salts, specifically as follows: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.32 wt% and the rubidium content is 0.16 wt%. S2. Spodumene and the composite salt system are mixed at a mass ratio of 1:1.5. The composite salt system consists of KOH, K₂CO₃, and Ca(OH)₂, with a mass ratio of 9.0:2.5:1.2. All raw materials are thoroughly mixed for 8 hours to obtain a homogeneous mixture. S3. The mixture is placed in a crucible and placed in a muffle furnace. The temperature is increased to 520°C at a heating rate of 10°C / min. The mixture is then roasted at this temperature for 1 hour. After roasting, the mixture is allowed to cool naturally to room temperature to obtain roasted calcined material. S4. The obtained roasted clinker was ground and then leached with deionized water. The leachate was washed three times during the leaching process. The liquid-solid ratio was controlled at 3:1 mL / g, the leaching temperature was 70 ℃, and the leaching time was 1.5 h. The lithium and rubidium contents in the leachate were then detected, and the results are shown in Table 1.

[0025] Example 2 This embodiment provides a method for extracting lithium and rubidium by low-temperature roasting of composite salts, specifically as follows: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.18 wt% and the rubidium content is 0.11 wt%. S2. The spodumene and the composite salt system are mixed at a mass ratio of 1:0.5, wherein the mass ratio of KOH, K2CO3 and Ca(OH)2 in the composite salt system is 7.5:1.5:0.8, and the mixing time is 10h. S3. Place the mixture in a muffle furnace and heat it to 368 ℃ at a heating rate of 10 ℃ / min. Then, calcine it at this temperature for 2 h and allow it to cool naturally to room temperature after calcineation. S4. After grinding the roasted clinker, deionized water was added for leaching. The liquid-to-solid ratio during leaching was 2:1 mL / g, the leaching temperature was 60 ℃, and the leaching time was 1 h. The lithium and rubidium contents in the leaching solution were then tested, and the results are shown in Table 1.

[0026] Example 3 This embodiment provides a method for extracting lithium and rubidium from spodumene by low-temperature roasting of composite salts, specifically: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.41 wt% and the rubidium content is 0.20 wt%. S2. Lithium spodumene and the composite salt system are mixed at a mass ratio of 1:2.0. The mass ratio of KOH, K2CO3 and Ca(OH)2 in the composite salt system is 9.5:3.0:1.5. The mixing time is 10 h to obtain the mixture. S3. Place the mixture in a muffle furnace and heat it to 450°C at a heating rate of 10°C / min. Calcinate at this temperature for 1 hour and allow it to cool naturally after calcination. S4. After grinding the roasted clinker, deionized water was added for leaching. The liquid-to-solid ratio during leaching was 4:1 mL / g, the leaching temperature was 75 ℃, and the leaching time was 2 h. The lithium and rubidium contents in the leaching solution were then measured, and the results are shown in Table 1.

[0027] Example 4 This embodiment provides a method for extracting lithium and rubidium from spodumene by low-temperature roasting of composite salts, specifically: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.28 wt% and the rubidium content is 0.14 wt%. S2. Lithium spodumene and the composite salt system are mixed at a mass ratio of 1:1.0. The mass ratio of KOH, K2CO3 and Ca(OH)2 in the composite salt system is 8.5:2.2:1.0. The mixing time is 8 h to obtain a mixture. S3. Place the mixture in a muffle furnace and heat it to 580°C at a heating rate of 10°C / min. Calcinate at this temperature for 1 hour. After calcination, allow it to cool naturally to room temperature to obtain the calcined clinker. S4. After grinding the roasted clinker, deionized water was added for leaching. The liquid-to-solid ratio during leaching was 3:1 mL / g, the leaching temperature was 80 ℃, and the leaching time was 2 h. The lithium and rubidium contents in the leaching solution were then detected, and the results are shown in Table 1.

[0028] Example 5 This embodiment provides a method for extracting lithium and rubidium from spodumene by low-temperature calcination of a composite salt, specifically as follows: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.52 wt% and the rubidium content is 0.25 wt%. S2. Lithium spodumene and the composite salt system are mixed at a mass ratio of 1:2.5. The mass ratio of KOH, K2CO3 and Ca(OH)2 in the composite salt system is 10.0:3.5:2.0. The mixing time is 12 h to obtain a mixture. S3. Place the mixture in a muffle furnace and heat it to 420℃ at a rate of 10℃ / min. Calcinate at this temperature for 1 hour, then allow it to cool naturally to room temperature after calcination. The calcined clinker is obtained. S4. After grinding the roasted clinker, deionized water was added for leaching. The liquid-to-solid ratio during leaching was 5:1 mL / g, the leaching temperature was 80 ℃, and the leaching time was 2.5 h. Finally, the lithium and rubidium contents in the leachate were detected. The results are shown in Table 1.

[0029] Example 6 This embodiment provides a method for extracting lithium and rubidium from spodumene by low-temperature roasting of composite salts, specifically: S1. The flotation spodumene concentrate is dried, ground, and sieved to a particle size of less than 200 mesh to obtain pretreated spodumene raw material. Testing shows that the lithium content in the spodumene concentrate is 2.36 wt% and the rubidium content is 0.19 wt%. S2. Spodumene and the composite salt system are mixed at a mass ratio of 1:1.8. The composite salt system consists of KOH, K₂CO₃, and Ca(OH)₂, with a mass ratio of 9.2:2.8:1.3. All raw materials are thoroughly mixed for 9 hours to obtain a homogeneous mixture. S3. The mixture is placed in a crucible and placed in a muffle furnace. The temperature is increased to 500℃ at a heating rate of 10℃ / min. The mixture is then calcined at this temperature for 1 hour. After calcination, it is allowed to cool naturally to room temperature to obtain the calcined clinker. S4. The obtained roasted clinker was ground and then leached with deionized water. During the leaching process, the liquid-to-solid ratio was controlled at 3:1 mL / g, the leaching temperature was 75 ℃, and the leaching time was 2 h. After leaching, the leachate was washed and diluted to a fixed volume. Then, the lithium and rubidium contents in the solution were detected, and the results are shown in Table 1.

[0030] Comparative Example 1 This comparative example provides a method for extracting lithium and rubidium by low-temperature roasting of a composite salt. The steps differ from those in Example 1 in that KOH, K2CO3 and Ca(OH)2 are mixed in a mass ratio of 2.0:1.0:7.0, while the other conditions are the same.

[0031] Under the above conditions, SiO2 in the spodumene lattice cannot be effectively captured to form calcium silicate, resulting in incomplete destruction of the silicate framework, hindering the release of lithium and rubidium, and ultimately significantly reducing the leaching rate.

[0032] Comparative Example 2 This comparative example provides a method for extracting lithium and rubidium by low-temperature roasting of composite salts. The steps differ from those in Example 1 by replacing Ca(OH)2 with CaO, while the other conditions remain the same.

[0033] In this comparative example, finished CaO was used directly. Its surface is already relatively stable, and it exists only as solid particles in the molten salt system, resulting in low reaction efficiency with SiO2 in the spodumene lattice. Furthermore, due to the lack of water vapor released during the decomposition of Ca(OH)2, microchannels conducive to mass transfer could not be formed within the material, leading to reduced damage to the spodumene lattice, hindered release of lithium and rubidium, and a significant decrease in leaching rate.

[0034] Comparative Example 3 This comparative example provides a method for extracting lithium and rubidium by low-temperature roasting of composite salts. The steps differ from those in Example 1 in that Ca(OH)2 is not added, while the other conditions are the same as in Example 1.

[0035] Table 1. Leaching rates of lithium and rubidium in spodumene under different embodiments As shown in Table 1, under the KOH–K2CO3–Ca(OH)2 composite salt low-temperature roasting–water leaching system, high leaching rates of lithium and rubidium were achieved in all embodiments. In most embodiments, the leaching rates of lithium and rubidium exceeded 90%. In Example 2, due to the low amount of composite salt, the reaction between spodumene and the composite salt was insufficient, resulting in relatively low leaching rates of lithium and rubidium, at 80.35% and 77.48%, respectively. As the degree of reaction involving the composite salt increased, the spodumene crystal structure was gradually destroyed, making it easier for lithium and rubidium to be released from the crystal lattice, significantly improving the leaching rate. Example 5 showed the best leaching effect, with leaching rates of lithium and rubidium reaching 97.87% and 96.27%, respectively. The other embodiments also achieved stable and high leaching rates under different combinations of process parameters. Overall, the leaching rate of lithium in each embodiment was generally higher than that of rubidium, indicating that the low-temperature calcination system of the composite salt can effectively promote the activation of the spodumene lattice structure, thereby achieving synergistic and efficient leaching of lithium and rubidium.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Various modifications and variations can be made to the present invention by any person skilled in the art. Any simple equivalent changes and modifications made based on the scope of protection of the present invention and the content of the specification should be included within the scope of protection of the present invention.

Claims

1. A method for extracting lithium and rubidium by low-temperature calcination of a composite salt, characterized by, The method comprises the following steps: S1, pretreating a spodumene raw material, and screening to a particle size less than 200 mesh to obtain a pretreated spodumene; S2, mixing the pretreated spodumene with a composite salt at a mass ratio of 1:0.5-2.5 to obtain a mixture; The preparation raw material of the composite salt comprises KOH, K2CO3 and Ca(OH)2; S3, calcining the mixture at 368-580°C for 0.5-2.5 h to obtain a calcined clinker; S4, water leaching the calcined clinker, and obtaining a leaching solution containing lithium and rubidium after solid-liquid separation.

2. The method of claim 1, wherein the composite salt is low-temperature calcined to extract lithium and rubidium. In step S2, the mass ratio of the KOH, the K2CO3 and the Ca(OH)2 is 5.0-10.0:1.0-8.0:0.5-2.

5.

3. The method of claim 1, wherein the composite salt is selected from the group consisting of lithium chloride, lithium bromide, lithium iodide, rubidium chloride, rubidium bromide, rubidium iodide, and mixtures thereof. In step S2, the mixing time is 6-12 h.

4. The method of claim 1, wherein the composite salt is selected from the group consisting of lithium chloride, lithium bromide, lithium iodide, rubidium chloride, rubidium bromide, rubidium iodide, and mixtures thereof. In step S3, the mixture is placed in a muffle furnace, and heated to the calcination temperature at a heating rate of 10°C / min for calcination.

5. The method of claim 1, wherein the composite salt is selected from the group consisting of lithium chloride, lithium bromide, lithium iodide, rubidium chloride, rubidium bromide, rubidium iodide, and mixtures thereof. In step S4, the process conditions of the water leaching are as follows: the leaching medium is deionized water, the liquid-solid ratio is 1-5:1 mL / g, the leaching temperature is 40-80°C, and the leaching time is 0.5-2.5 h.

6. The method of claim 1, wherein the lithium and rubidium are extracted from spodumene by a complex salt low-temperature calcination, characterized in that, In step S1, the pretreatment step comprises drying and grinding.

7. The method of claim 1, wherein the method is characterized by, In step S4, the solid phase obtained after solid-liquid separation is further washed with deionized water, and the washing liquid is combined with the leaching solution after constant volume.

8. Use of the method according to any one of claims 1-7 in treating lithium-containing aluminosilicate minerals.

9. Use according to claim 8, characterized in that, The lithium-containing aluminosilicate minerals comprise at least one of spodumene, lepidolite, petalite, eucryptite and zinnwaldite.

10. Use according to claim 9, characterized in that, When the lithium-containing aluminosilicate mineral is spodumene, the lithium content is 2.18-2.52 wt%, and the rubidium content is 0.11-0.25 wt%.

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