Method for recovering lithium, rubidium and cesium elements in lepidolite

Abstract

The invention belongs to the field of mineral recovery, and particularly relates to a method for recovering lithium, rubidium and cesium elements in lepidolite, which comprises the following steps: placing a mixed solution dispersed with lepidolite, an inhibitor and an alkali liquor in a closed container, carrying out pressurized alkaline leaching at the temperature of more than 200 DEG C, and then carrying out solid-liquid separation to obtain a leachate; extracting the lithium-rubidium-cesium-rich solution by adopting the organic phase A to obtain lithium extraction raffinate and a lithium-loaded organic phase; the organic phase A comprises a component a # imgabs 0 #, a component b # imgabs 1 # and a hydrophobic diluent; extracting the lithium extraction raffinate by adopting the organic phase B to obtain rubidium and cesium extraction raffinate and a rubidium and cesium loaded organic phase; the organic phase B comprises a component c and a hydrophobic diluent; the component C # imgabs2 # is a compound with a structure as shown in a formula 3. The invention provides a method for recovering valuable elements in lepidolite without roasting, which can effectively and directly recover the valuable elements in the lepidolite and can realize extraction separation selectivity of lithium, rubidium and cesium.

Description

Technical Field

[0001] The invention relates to the technical field of hydrometallurgy, in particular to a method for comprehensively recovering valuable metals from lithium mica ore. Background Art

[0002] Lithium is widely used in batteries, medicine, petrochemicals, rubber industry, nuclear industry, aerospace and other industries. It is known as the energy metal of the 21st century, white oil, and an important element that drives the world forward. Lepidolite is an important lithium resource, and is accompanied by valuable alkali metals such as rubidium and cesium.

[0003] At present, the main method for treating valuable elements in lithium mica is leaching after roasting. For example, the Chinese patent document with publication number CN118724028A discloses a method for preparing lithium carbonate using lithium mica, specifically disclosing a scheme of mixing lithium mica with sulfate and leaching after roasting. This method has a high lithium extraction rate, but a low leaching rate of rubidium and cesium, high energy consumption, and large reagent consumption. Although the sulfuric acid method can achieve simultaneous leaching of lithium, rubidium, and cesium, the amount of waste acid is large, the equipment is severely corroded, the impurity removal is difficult, and the lithium loss is serious.

[0004] For another example, Chinese patent document with publication number CN116103513A discloses a method for extracting lithium from lepidolite by microwave roasting, specifically disclosing a composite of lepidolite ore, charcoal and calcium chloride followed by microwave roasting and subsequent leaching.

[0005] The roasting-leaching process can achieve good extraction results, but the impurity content is large, the difficulty of separating alkali metal elements and the separation selectivity need to be further improved, in addition, there are also shortcomings such as high energy consumption and serious equipment corrosion. Therefore, it is urgent to develop a new lithium mica processing process to achieve clean and efficient recovery of valuable metals in lithium mica. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a method for recovering lithium, rubidium and cesium elements from lepidolite, aiming to provide a method for efficiently and selectively separating lithium, rubidium and cesium without calcination.

[0007] In view of the problems existing in the existing roasting-leaching process, the present invention has previously attempted to provide a direct leaching process for high temperature and high pressure alkali leaching without roasting. However, it has been found in previous studies that the implementation of this idea will consume more alkali components. For this reason, the present inventors have further attempted to adopt a cyclic direct alkali leaching process. However, it was found during the research and development stage that the cyclic direct high pressure alkali leaching process is prone to cause the continuous accumulation of Na and K during the treatment process, which will affect the separation efficiency and selectivity of lithium, rubidium and cesium. In view of this problem, the present invention has provided the following solution after in-depth research:

[0008] A method for recovering lithium, rubidium and cesium elements from lepidolite, comprising the steps of:

[0009] Step (1): Circulating alkali leaching

[0010] Step (1a): Pressure alkali leaching:

[0011] The mixed solution containing lepidolite, inhibitor and alkali solution is placed in a sealed container and subjected to pressurized alkali leaching at a temperature above 200° C., followed by solid-liquid separation to obtain a leachate;

[0012] Step (1b): Removal of impurities

[0013] Adding impurity remover to the leaching solution to remove aluminum, silicon and fluorine to obtain purified solution;

[0014] Step (1c): Loop

[0015] The purified liquid is used as alkaline solution and recycled to step (1a), and circulated to participate in the pressurized alkaline leaching step to obtain a lithium-rich rubidium-cesium leaching solution; wherein the molar amount of sodium hydroxide in the lithium-rich rubidium-cesium leaching solution is 5 to 10 M;

[0016] Step (2): Recovering lithium:

[0017] The lithium-rich rubidium-cesium solution is extracted with an organic phase A to obtain a lithium-extracted residual solution and a lithium-loaded organic phase;

[0018] The organic phase A comprises component a, component b and a hydrophobic diluent;

[0019] The component a is a compound having a structure of formula 1

[0020] The component b is a compound having a structure of formula 2;

[0021]

[0022] R1, R2, and R3 are C4-C8 alkyl groups;

[0023]

[0024] R4 is C1~C 12 The alkyl group;

[0025] Step (3): Recovering rubidium and cesium:

[0026] The organic phase B is used to extract the lithium extraction residual solution to obtain the rubidium-cesium extraction residual solution and the rubidium-cesium-loaded organic phase;

[0027] The organic phase B comprises component C and a hydrophobic diluent; the component C is a compound of formula 3;

[0028]

[0029] R5 is a C1-C6 alkyl group, and R6 is H or a C1-C6 alkyl group;

[0030] The residual solution of rubidium and cesium extraction is reused as alkaline solution to step 1a.

[0031] The present invention provides a method for recovering valuable elements from lepidolite without calcination, which innovatively subjects the lepidolite to the pressurized alkali leaching and cyclic pressurized alkali leaching, and directly extracts lithium and rubidium and cesium under the high-alkali conditions, thereby effectively and directly recovering the valuable elements in the lepidolite, and realizing the extraction and separation selectivity of lithium and rubidium and cesium.

[0032] In the present invention, in step (1a), the inhibitor is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0033] In the present invention, the inhibitor accounts for 10% to 80% of the weight of the lepidolite.

[0034] In the present invention, the alkaline solute in the alkali solution includes at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate.

[0035] In the present invention, the concentration of the alkaline solute in the alkali solution is controlled at 5-10M.

[0036] In the present invention, the temperature of the pressurized alkali leaching stage is 200-280°C;

[0037] Preferably, the time of pressurized alkali leaching is 1 to 8 hours;

[0038] Preferably, the liquid-to-solid ratio in the pressurized alkali leaching stage is 5 / 1 to 50 / 1.

[0039] In the present invention, in step (1b), the impurity remover is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0040] Preferably, the amount of impurity remover added is 5 to 30 g / L;

[0041] Preferably, the temperature in the impurity removal stage is 25°C to 90°C;

[0042] Preferably, the time for removing impurities is 1 to 8 hours.

[0043] Preferably, the lithium concentration in the leaching solution leached in cycles is 1 to 5 g / L.

[0044] In the present invention, the purified liquid is recycled for leaching, so that the recycling of alkali can be achieved. In addition, a leaching solution with high alkalinity (4-8M) can be obtained. The high alkalinity leaching system is directly subjected to subsequent extraction treatment. Compared with the extraction system with a pH of 8-14 commonly used in the industry, the extraction rate and extraction selectivity of lithium, rubidium and cesium elements can be unexpectedly further enhanced.

[0045] In the present invention, in step (2), in the organic phase A, the hydrophobic diluent comprises at least one of sulfonated kerosene, xylene, cyclohexane and diethylbenzene.

[0046] In the present invention, in the organic phase A, the content of component a is 5-30v%, and the volume fraction of component b is 5-30v%.

[0047] In the present invention, in step (2), the concentration of the alkaline component in the aqueous phase of the extraction stage is 4 to 10 M;

[0048] Preferably, O / A in the extraction stage is 5 / 1 to 1 / 10.

[0049] In the present invention, the lithium-carrying organic phase is subjected to a washing treatment and then subjected to a stripping treatment to obtain a lithium-rich stripping solution;

[0050] Preferably, the washing solution is pure water or an acid solution with a concentration of 5 to 20 g / L;

[0051] Preferably, the O / A volume ratio in the washing stage is 5 / 1 to 50 / 1;

[0052] Preferably, the stripping solution is a solution containing at least one acidic solute selected from sulfuric acid, hydrochloric acid and phosphoric acid, and the concentration of the acidic solute is 100 to 900 g / L;

[0053] Preferably, the O / A volume ratio in the stripping stage is 5 / 1 to 50 / 1.

[0054] In the present invention, the compound of formula 3 is preferably a compound of formula 3-1

[0055] Wherein, the R5 is a C3-C5 alkyl group, preferably a tert-butyl group. The R6 is H, methyl or ethyl.

[0056] The present findings indicate that the use of Formula 3, wherein R5 is preferably tert-butyl, can unexpectedly be more suitable for high alkalinity extraction, and contribute to obtaining better rubidium-cesium extraction selectivity.

[0057] In the present invention, in the organic phase B, the concentration of the component c is 0.5 mol / L to 3 mol / L;

[0058] Preferably, in step (3), the O / A volume ratio of the extraction is 5 / 1 to 1 / 5.

[0059] In the present invention, the organic phase carrying rubidium and cesium is washed and then stripped to obtain a rubidium-rich stripping solution;

[0060] Preferably, the washing solution is pure water;

[0061] Preferably, the O / A volume ratio in the washing stage is 5 / 1 to 10 / 1;

[0062] Preferably, the stripping solution is a solution containing at least one acidic solute of sulfuric acid and hydrochloric acid, and the concentration of the acidic solute is 50 to 400 g / L;

[0063] Preferably, the O / A volume ratio in the stripping stage is 2 / 1 to 50 / 1.

[0064] Beneficial effects:

[0065] The present invention adopts a direct circulation pressurized alkaline leaching process to leach the lepidolite, and in view of the problems faced by the process, directly extracts under high alkalinity, and further cooperates with the joint control of the extraction components, so that unexpected synergy can be achieved, and the extraction rate and extraction separation coefficient of lithium, rubidium and cesium elements can be enhanced.

[0066] The method of the present invention realizes the comprehensive and efficient recovery of lithium, rubidium and cesium in lepidolite. The overall process is clean, low-carbon and short in flow. It can not only significantly improve the recovery rate of lithium, rubidium and cesium, but also realize alkali circulation and near-zero discharge of wastewater. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 The process flow chart of Example 1 of the present invention is DETAILED DESCRIPTION

[0068] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0069] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0070] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0071] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology, provide a method for comprehensive recovery of valuable metals from lithium mica, realize the simultaneous and efficient extraction of lithium, rubidium and cesium, improve the utilization efficiency of associated rubidium and cesium resources, realize the recycling of alkali and near-zero discharge of wastewater, and solve the contradiction between the lithium, rubidium and cesium leaching rate and the alkali consumption in the traditional open circuit process.

[0072] A method for comprehensively recovering valuable metals from lepidolite comprises the following steps:

[0073] (1) Pressurized alkaline leaching: adding lepidolite, alkaline solution and inhibitor into a pressurized reactor for leaching to obtain a leachate;

[0074] (2) Removal of aluminum, silicon and fluorine: adding an impurity remover to the leaching solution to remove aluminum, silicon and fluorine to obtain a purified solution;

[0075] (3) Circulating alkaline leaching: After the purified liquid is supplemented with alkali, it is added into a pressure reactor together with lepidolite and an inhibitor for circulating alkaline leaching to obtain a lithium-rich rubidium-cesium leaching solution;

[0076] (4) Recovering lithium: extracting the lithium-rich rubidium-cesium solution to obtain a lithium-extracted residual solution and an organic phase enriched with lithium; washing and stripping the lithium-rich organic phase to obtain a lithium-containing stripping solution;

[0077] (5) Recovering rubidium and cesium: extracting the lithium residual solution again to obtain a rubidium and cesium residual solution and an organic phase enriched with rubidium and cesium; washing and stripping the rubidium and cesium-rich organic phase to obtain a stripping solution containing rubidium and cesium;

[0078] (6) After the alkali is added to the residual solution of rubidium and cesium extraction, it is returned to the alkali pressure cooker.

[0079] In the above method, the preferred step (1) specifically includes the following steps: drying, crushing and grinding the lithium mica to obtain lithium mica powder; adding the lithium mica powder, alkaline solution and inhibitor into a pressure reactor for hydrothermal leaching; the hydrothermal leaching reaction temperature is 200-280° C., the time is 1-8 hours, the liquid-to-solid ratio is 5 / 1-50 / 1, the alkaline solution is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate, and the inhibitor is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0080] The step (2) specifically includes the following steps: adding an impurity remover to the leaching solution to remove aluminum, silicon and fluorine, wherein the impurity remover is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0081] The temperature for removing aluminum, silicon and fluorine is 25° C. to 90° C., and the time is 1 to 8 hours.

[0082] The step (3) specifically comprises the following steps: adding alkali to the purified liquid and adding the lepidolite and inhibitor into a pressure reactor for circulating alkali leaching, wherein the inhibitor is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0083] The circulating alkali leaching temperature is 200-280° C., the time is 1-8 hours, the liquid-to-solid ratio is 5 / 1-50 / 1, and the alkaline solution is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

[0084] The step (4) specifically comprises the following steps: when the lithium-rich rubidium-cesium solution is extracted, the extractant is component a of the structure of formula 1, the modifier is component b of the structure of formula 2, the volume fraction of the extractant is 5% to 30%, the volume fraction of the modifier is 5% to 30%, the diluent is sulfonated kerosene, and the phase ratio O / A is controlled to be 5 / 1 to 1 / 10; pure water or sulfuric acid or hydrochloric acid with a concentration of 5 to 20 g / L is used to enrich the Li + The organic phase is washed with a phase ratio of O / A=5 / 1-50 / 1, and the washed organic phase is stripped with sulfuric acid, hydrochloric acid or phosphoric acid at a concentration of 100-900 g / L, and the phase ratio is controlled to be O / A=5 / 1-50 / 1 to obtain a lithium-rich stripping solution.

[0085] The step (5) specifically comprises the following steps: when extracting the lithium extraction residual solution, using an extractant as a substituted phenol extractant, the concentration of component c of the structure of formula 3 is 0.5 mol / L to 3 mol / L, and the phase ratio O / A is controlled to be 5 / 1 to 1 / 5; using pure water to wash the organic phase enriched with rubidium and cesium, and the phase ratio O / A is controlled to be 5 / 1 to 10 / 1; the washed organic phase is stripped with sulfuric acid or hydrochloric acid with a concentration of 50 to 400 g / L, and the phase ratio O / A is controlled to be 2 / 1 to 50 / 1, to obtain a rubidium-cesium-rich stripping solution.

[0086] The step (6) specifically comprises the following steps: adding alkali to the residual solution of rubidium and cesium extraction, adding the residual solution, lepidolite and an inhibitor into a pressure reactor for circulating alkali leaching, wherein the inhibitor is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide and magnesium sulfate.

[0087] The circulating alkali leaching temperature is 200-280° C., the time is 1-8 hours, the liquid-to-solid ratio is 5 / 1-50 / 1, and the alkaline solution is at least one of sodium hydroxide, sodium carbonate, potassium hydroxide, and potassium carbonate.

[0088] The following are typical cases:

[0089] Example 1 - Leaching

[0090] Example 1-A:

[0091] The lithium mica ore powder (200 mesh) and the alkaline solution are sealed in a pressure-resistant container and leached under pressure at a temperature of 280°C, wherein the added alkaline solution is an aqueous solution of potassium hydroxide and potassium carbonate, wherein the molar ratio of potassium hydroxide to potassium carbonate is 8:2, the concentration of potassium hydroxide is 12M, the liquid-solid ratio is 5:1 ml / g, the amount of inhibitor calcium sulfate added is 25 g / L, the pressure leaching reaction time is 5h, and the solid-liquid separation is performed to obtain lithium, rubidium and cesium leaching solutions, wherein the leaching rates of lithium, rubidium and cesium are 94.56%, 94.88% and 92.32%, respectively.

[0092] Example 1-B:

[0093] Lepidolite powder (200 mesh) and alkaline solution are sealed in a pressure-resistant container and leached under pressure at a temperature of 200° C., wherein the alkaline solution added is an aqueous solution of sodium hydroxide, wherein the concentration of sodium hydroxide is 6M, the liquid-solid ratio is 50:1 ml / g, the amount of inhibitor magnesium hydroxide added is 10 g / L, the pressure leaching reaction time is 8 hours, and the solid-liquid separation is performed to obtain lithium, rubidium and cesium leaching solutions, wherein the leaching rates of lithium, rubidium and cesium are 96.54%, 96.12% and 94.83%, respectively.

[0094] Example 1-C:

[0095] Lepidolite powder (150 mesh) and alkaline solution are sealed in a pressure-resistant container and leached under pressure at a temperature of 260° C., wherein the alkaline solution added is an aqueous solution of potassium hydroxide, wherein the concentration of potassium hydroxide is 7M, the liquid-solid ratio is 25:1 ml / g, the amount of inhibitor calcium hydroxide added is 15 g / L, the pressure leaching reaction time is 5 h, and the solid-liquid separation is performed to obtain lithium, rubidium and cesium leaching solutions, wherein the leaching rates of lithium, rubidium and cesium are 93.34%, 94.78% and 92.22%, respectively.

[0096] Example 1-D:

[0097] The lithium mica ore powder (300 mesh) and the alkaline solution are sealed in a pressure-resistant container and leached under pressure at a temperature of 240°C, wherein the alkaline solution added is sodium hydroxide and sodium carbonate, the molar ratio of which is 5:1, wherein the concentration of sodium hydroxide is 6M, the liquid-solid ratio is 15:1 ml / g, the amount of inhibitor magnesium oxide added is 8 g / L, the pressure leaching reaction time is 3h, and the solid-liquid separation is performed to obtain lithium, rubidium and cesium leaching solutions, wherein the leaching rates of lithium, rubidium and cesium are 92.23%, 93.05% and 91.92%, respectively.

[0098] Example 2

[0099] Step 1: Circulating leaching is carried out based on the conditions of Example 1-A, and the leachate is subjected to impurity removal treatment before circulation, wherein the impurity remover is calcium oxide, the addition amount is 6-8 g / L, and the impurity removal time is 1-2 h. The purified liquid after impurity removal is used as alkaline solution for circulating leaching, and the impurity removal treatment is continued after the last stage of leaching to obtain a lithium rubidium cesium enriched purified liquid, whose Li is 1.41 g / L and NaOH is 7.25 mol / L.

[0100] Step 2: The lithium rubidium cesium enriched purified solution is treated with 0.4M of component a of formula 1a (R1-R3 are all n-octyl in formula 1) + 0.4M of formula 2a (R4 is n-octyl in formula 2) + sulfonated kerosene, and the phase ratio is controlled to be O / A=1 / 1 to obtain a lithium extraction residual solution and a lithium-carrying organic phase;

[0101] The lithium-loaded organic phase is washed with pure water at a ratio of O / A = 5 / 1, and then the washed loaded organic phase is stripped with 200g / L sulfuric acid at a ratio of O / A = 25 / 1 to obtain a lithium stripping solution (lithium extraction solution), wherein the lithium extraction rate is above 99%, and the lithium concentration in the stripping solution is above 20g / L. Separation coefficient β Li / Na , β Li / K , β Li / Rb , β Li / Cs They are 309, 842, 4550 and 4760 respectively, and the separation effect of lithium and other alkali metal ions is good.

[0102] Step 3: The lithium extraction residual solution (Rb 1.21 g / L, Cs 66.58 mg / L, K 11.32 g / L, NaOH 6.75 mol / L) of step 2 is treated with 1 mol / L formula 3a + sulfonated kerosene, with the phase ratio O / A=1 / 1, to extract to obtain an organic phase loaded with rubidium and cesium and a residual solution of rubidium and cesium;

[0103] The organic phase loaded with rubidium and cesium is washed with pure water at an O / A ratio of 5 / 1, and then stripped with 100 g / L sulfuric acid at an O / A ratio of 10 / 1 to obtain a rubidium + cesium stripping solution, in which the (rubidium + cesium) concentration is above 10 g / L. Separation coefficient β (Rb+Cs) / Na , β (Rb+Cs) / K They are 450 and 28 respectively, and the separation effect of rubidium and cesium from sodium and potassium is good.

[0104] Step 4: After the residual solution of rubidium and cesium is supplemented with alkali, an alkaline solution of potassium hydroxide is added at a temperature of 280°C, with a liquid-to-solid ratio of 10:1 and a reaction time of 3h. Magnesium oxide is added, and the leaching rates of lithium, rubidium and cesium are 95.56%, 95.20% and 93.88% respectively.

[0105] Example 3

[0106] Compared with Example 2, the only difference is that the extraction conditions of step 2 are changed, specifically, the concentration of formula 1a in the extraction system is 0.3M, and the concentration of formula 2a is 0.5M; the O. / A ratio in the extraction stage is 2:1;

[0107] In addition, the extraction conditions of step 3 were changed, specifically, the concentration of formula 3a in the extraction system was 0.8 M; the O. / A ratio in the extraction stage was 2:1;

[0108] Other operations and parameters are the same as in Example 1.

[0109] The result is: In step 2, the separation coefficient β Li / Na , β Li / K , β Li / Rb , β Li / Cs They are 321, 881, 4620 and 4670 respectively, and the separation effect of lithium and other alkali metal ions is good.

[0110] In step 3, the separation coefficients β(Rb+Cs) / Na and β(Rb+Cs) / K are 432 and 30 respectively, and the separation effect of rubidium and cesium from sodium and potassium is good.

[0111] Example 4

[0112] Compared with Example 2, the only difference is that in step 3, formula 3b is used The formula 3a is replaced by an equal amount, and the other operations and parameters are the same as those in Example 2.

[0113] The result is: In step 3, the separation coefficient β (Rb+Cs) / Na , β (Rb+Cs) / K They are 305 and 15 respectively.

[0114] Comparative Example 1

[0115] Compared with Example 2, the only difference is that in step 2, the extraction system lacks Formula 2a, and the content of the remaining extraction active ingredients and other operations and parameters are the same as in Example 2.

[0116] The result is: In step 2, the separation coefficient β Li / Na , β Li / K , β Li / Rb , β Li / Cs They are 287, 193, 433 and 308 respectively.

[0117] Comparative Example 2

[0118] Compared with Example 2, the only difference is that in step 2, Formula 1a is missing from the extraction volume, and the content of the remaining extracted active ingredients and other operations and parameters are the same as in Example 2.

[0119] The result is: In step 2, the separation coefficient βLi / Na , β Li / K , β Li / Rb , β Li / Cs They are 7.96, 3.57, 10.70 and 12.66 respectively.

[0120] It can be seen from Example 2 and Comparative Examples 1-2 that under the ultra-high alkalinity, the combined extraction system of the present invention can significantly optimize the extraction effect and selectivity of lithium.

Claims

1. A method for recovering lithium, rubidium and cesium from lepidolite, characterized in that the steps include: Step (1): Circulating alkali leaching Step (1a): Pressure alkali leaching: The mixed solution containing lepidolite, inhibitor and alkali solution is placed in a sealed container and subjected to pressurized alkali leaching at a temperature above 200° C., followed by solid-liquid separation to obtain a leachate; Step (1b): Removal of impurities Adding impurity remover to the leaching solution to remove aluminum, silicon and fluorine to obtain purified solution; Step (1c): Loop The purified liquid is used as alkaline solution and recycled to step (1a), and circulated to participate in the pressurized alkaline leaching step to obtain a lithium-rich rubidium-cesium leaching solution; wherein the molar amount of sodium hydroxide in the lithium-rich rubidium-cesium leaching solution is 4-8M; Step (2): Recovering lithium: The lithium-rich rubidium-cesium solution is extracted with an organic phase A to obtain a lithium-extracted residual solution and a lithium-loaded organic phase; The organic phase A comprises component a, component b and a hydrophobic diluent; The component a is a compound having a structure of formula 1 R1, R2, and R3 are C4-C8 alkyl groups; The component b is a compound having a structure of formula 2; R4 is C1~C 12 The alkyl group; Step (3): Recovering rubidium and cesium: The organic phase B is used to extract the lithium extraction residual solution to obtain the rubidium-cesium extraction residual solution and the rubidium-cesium-loaded organic phase; The organic phase B comprises component C and a hydrophobic diluent; the component C is a compound of formula 3; R5 is a C1-C6 alkyl group, and R6 is H or a C1-C6 alkyl group; The residual solution of rubidium and cesium extraction is reused as alkaline solution to step 1a.

2. The method for recovering lithium, rubidium and cesium elements in lepidolite as claimed in claim 1, characterized in that: In step (1a), the inhibitor is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide, and magnesium sulfate; Preferably, the inhibitor is 10% to 80% by weight of the lepidolite; Preferably, the alkaline solute in the alkali solution includes at least one of sodium hydroxide, sodium carbonate, potassium hydroxide and potassium carbonate; Preferably, the concentration of the alkaline solute in the alkali solution is controlled at 5-10M.

3. The method for recovering lithium, rubidium and cesium elements in lepidolite as claimed in claim 2, characterized in that: The temperature of the pressurized alkali leaching stage is 200-280°C; Preferably, the time of pressurized alkali leaching is 1 to 8 hours; Preferably, the liquid-to-solid ratio in the pressurized alkali leaching stage is 5 / 1 to 50 / 1.

4. The method for recovering lithium, rubidium and cesium elements in lepidolite as claimed in claim 1, characterized in that: In step (1b), the impurity remover is at least one of calcium oxide, calcium hydroxide, calcium sulfate, magnesium oxide, magnesium hydroxide, and magnesium sulfate; Preferably, the amount of impurity remover added is 5 to 30 g / L; Preferably, the temperature in the impurity removal stage is 25°C to 90°C; Preferably, the time for removing impurities is 1 to 8 hours; Preferably, the lithium concentration in the leaching solution leached in cycles is 1 to 5 g / L.

5. The method for recovering lithium, rubidium and cesium elements in lepidolite as claimed in claim 1, characterized in that: In step (2), in the organic phase A, the hydrophobic diluent comprises at least one of sulfonated kerosene, xylene, cyclohexane, and diethylbenzene; Preferably, in the organic phase A, the content of component a is 5-30v%, and the volume fraction of component b is 5-30v%.

6. The method for recovering lithium, rubidium and cesium elements from lepidolite as claimed in claim 1, characterized in that: In step (2), the concentration of the alkaline component in the aqueous phase during the extraction stage is 4 to 8 M; Preferably, O / A in the extraction stage is 5 / 1 to 1 / 10.

7. The method for recovering lithium, rubidium and cesium elements from lepidolite as claimed in claim 1, characterized in that: The lithium-loaded organic phase is subjected to a washing treatment, and then subjected to a stripping treatment to obtain a lithium-rich stripping solution; Preferably, the washing solution is pure water or an acid solution with a concentration of 5 to 20 g / L; Preferably, the O / A volume ratio in the washing stage is 5 / 1 to 50 / 1; Preferably, the stripping solution is a solution containing at least one acidic solute selected from sulfuric acid, hydrochloric acid and phosphoric acid, and the concentration of the acidic solute is 100 to 900 g / L; Preferably, the O / A volume ratio in the stripping stage is 5 / 1 to 50 / 1.

8. The method for recovering lithium, rubidium and cesium from lepidolite as claimed in claim 1, 5, 6 or 7, characterized in that: In the organic phase B, the concentration of the component c is 0.5 mol / L to 3 mol / L; Preferably, in step (3), the O / A volume ratio of the extraction is 5 / 1 to 1 / 5.

9. The method for recovering lithium, rubidium and cesium from lepidolite according to claim 1 or 8, characterized in that: The rubidium-cesium-loaded organic phase is washed and then stripped to obtain a rubidium-cesium-rich stripping solution; Preferably, the washing solution is pure water; Preferably, the O / A volume ratio in the washing stage is 5 / 1 to 10 / 1; Preferably, the stripping solution is a solution containing at least one acidic solute of sulfuric acid and hydrochloric acid, and the concentration of the acidic solute is 50 to 400 g / L; Preferably, the O / A volume ratio in the stripping stage is 2 / 1 to 50 / 1.

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