A method for preparing high-purity cesium salt from two-stage extraction of lithium mica lithium extraction mother liquor

Abstract

The application discloses a method for preparing high-purity cesium salt from two-stage extraction of lithium mica lithium extraction mother liquor, and belongs to the field of rare metal hydrometallurgy. The method breaks through the technical prejudice of "washing section is forbidden to use strong acid" in the prior art, and initiates a two-stage structure: after alkaline extraction, the first stage is controlled washing back-extraction by using pH=1 hydrochloric acid, and the rubidium-cesium ratio in the aqueous phase is actively controlled to about 1:1 by using the selective inversion of t-BAMBP under strong acid conditions; after alkaline extraction of the unloaded blank organic phase obtained by the first stage back-extraction on the obtained aqueous phase, the second stage is sequentially subjected to selective washing by pH=3 hydrochloric acid, pure water washing and CO2 back-extraction, and three synergies are used for deep rubidium removal. The application realizes the series connection and circulation of the extractant between the two stages, and greatly reduces the reagent consumption. The total amount of alkali metal impurities in the obtained cesium salt product can be as low as 0.011%, and the rubidium impurity is as low as 0.008%, which is more than one order of magnitude lower than that of the traditional single-stage hydrochloric acid back-extraction process, and is suitable for industrial production of high-purity cesium carbonate or cesium chloride.

Description

Technical Field

[0001] This invention relates to the fields of rare metal hydrometallurgy and solvent extraction technology, specifically to a method for preparing high-purity cesium salts from lithium mica mother liquor through two-stage extraction-stepwise acid washing-CO2 back-extraction. Background Technology

[0002] Cesium and its compounds have irreplaceable applications in photoelectric conversion, catalysis, medicine, electronic glass, and new energy. The mother liquor produced after lithium extraction from lepidolite ore contains alkali metal ions such as rubidium, cesium, and potassium, making it an important industrial source of cesium. However, the rubidium content in this mother liquor is usually much higher than that of cesium (Rb:Cs mass ratio is approximately 5:1 to 10:1), and rubidium and cesium have extremely similar chemical properties, making separation extremely difficult.

[0003] Currently, the industrial process primarily employs solvent extraction with 4-tert-butyl-2-(α-methylbenzyl)phenol (t-BAMBP) as the extractant for rubidium-cesium separation. A typical process flow involves extraction under alkaline conditions, washing with pure water or a very low concentration of acid to remove co-extracted potassium and some rubidium, followed by back-extraction with hydrochloric acid to obtain a mixed rubidium-cesium solution or cesium salt product. The main drawback of this process is that...

[0004] 1. The washing section is limited by positive selectivity: under alkaline conditions, t-BAMBP has limited effectiveness against Cs. + The extraction ability is far superior to that of Rb. + (Cs) + > Rb + The washing section can only remove weakly extracted potassium and a small amount of rubidium, making it difficult to deeply remove rubidium impurities while maintaining cesium yield;

[0005] 2. The back-extraction section has no additional separation capability: Hydrochloric acid, as a completely dissociable strong acid, performs indiscriminate proton dissociation on cesium and rubidium complexes in the organic phase. The rubidium / cesium ratio in the back-extraction solution is basically the same as the Rb / Cs ratio of the organic phase after the previous washing. The back-extraction section does not contribute any additional separation effect.

[0006] 3. Limited product purity: The total amount of alkali metal impurities in cesium salt products obtained by single-stage extraction-washing-back-extraction process is usually difficult to reduce to below 0.02%, which is difficult to meet the stringent requirements of high-purity application fields.

[0007] The root of the aforementioned shortcomings lies in the fact that existing technologies strictly separate washing and back-extraction into two independent functional stages, adhering to the technical convention of "prohibiting strong acids in the washing stage." This convention stems from a chemical phenomenon generally considered to have a negative effect—under strongly acidic conditions with pH ≤ 1, t-BAMBP undergoes selective reversal, and Cs... +The complexes preferentially dissociate, causing the washing operation to degenerate into uncontrolled back-extraction. Therefore, existing technologies strictly limit the acidity of the washing section to pH ≥ 3 or pure water, and have never attempted to utilize the process method of reversing the selectivity under strong acid conditions to the positive.

[0008] On the other hand, CO2 back-extraction technology has been proven to provide an additional rubidium / cesium separation window in the back-extraction stage through the weak acid slow-release effect. However, due to the difficulty in controlling the Rb / Cs ratio of the organic phase to a sufficiently low level during the initial washing stage, the improvement in cesium salt purity achieved by single CO2 back-extraction is severely limited. Furthermore, in traditional processes, each extraction stage requires independently prepared fresh organic phases, resulting in high extractant consumption and operating costs.

[0009] Therefore, there is an urgent need to develop a new method that can overcome the purity bottleneck of the above-mentioned single-stage process, reduce reagent consumption, and achieve rapid preparation of high-purity cesium salts. Summary of the Invention

[0010] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a process method for achieving efficient separation of rubidium and cesium through a two-stage extraction architecture and intermediate acidity control. This method can rapidly obtain high-purity cesium salts from lithium mica mother liquor, while significantly reducing operating costs through the series circulation of the extractant.

[0011] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0012] A method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite using a two-stage extraction process, characterized by comprising the following steps:

[0013] (1) Extraction-acid washing and back-extraction: The lithium extraction mother liquor from lepidolite is used as raw material liquid 1 and adjusted to alkaline conditions. After mixing with organic phase 1 containing t-BAMBP, multi-stage countercurrent extraction is performed to obtain the first aqueous phase and the first loaded organic phase. The obtained first loaded organic phase is then subjected to controlled washing and back-extraction under strong acid conditions sufficient to induce t-BAMBP selective reversal, releasing the loaded metal ions in the first loaded organic phase into the second aqueous phase and obtaining the deloaded blank organic phase. At this time, the mass ratio of rubidium to cesium in the second aqueous phase is close to 1:1.

[0014] (2) Extraction-step washing-CO2 back-extraction: Using the second aqueous phase as the raw material liquid 2, the raw material liquid 2 is adjusted to alkaline conditions, and the deloaded blank organic phase obtained in step (1) is directly used as the extraction organic phase for multi-stage countercurrent extraction to obtain the third aqueous phase and the second loaded organic phase; the obtained second loaded organic phase is subjected to weak acid selective washing, pure water washing and CO2 back-extraction in sequence to remove residual rubidium ions and acid, and to obtain a high-purity cesium salt solution;

[0015] (3) Cesium salt recovery: Cesium salt products are recovered from the high-purity cesium salt solution.

[0016] Further, the strong acid condition sufficient to trigger the selective reversal of t-BAMBP in step (1) is a hydrochloric acid solution with pH=1, and the controlled washing back-extraction is a three-stage countercurrent operation;

[0017] The weakly acidic selective washing in step (2) is performed by a three-stage countercurrent washing with a hydrochloric acid solution of pH=3, the pure water washing is a three-stage countercurrent washing, and the CO2 back-extraction is a two-stage countercurrent operation.

[0018] Furthermore, after the loaded organic phase in step (1) is washed and back-extracted in three stages with hydrochloric acid at pH=1, the mass ratio of rubidium to cesium in the resulting second aqueous phase is controlled within the range of 0.8:1 to 1.2:1.

[0019] Further, the alkaline condition in step (1) is pH ≥ 13; the alkaline condition in step (2) is pH ≥ 13.

[0020] Furthermore, both organic phase 1 and the unloaded blank organic phase were sulfonated kerosene solutions with a t-BAMBP concentration of 0.8~1.2 mol / L.

[0021] Furthermore, the residual cesium in the organic phase after CO2 back-extraction in step (2) is recovered by auxiliary back-extraction with dilute hydrochloric acid and returned to step (1) as organic phase 1 for recycling, forming a closed loop; the auxiliary back-extraction liquid is not incorporated into the high-purity cesium salt solution, but is treated separately or returned to the extraction section of step (2).

[0022] Further, the cesium salt recovery in step (3) includes evaporating and calcining the cesium carbonate / cesium bicarbonate solution obtained by CO2 back-extraction to obtain high-purity cesium carbonate, or further converting it with hydrochloric acid to obtain high-purity cesium chloride.

[0023] Furthermore, the concentration of dilute hydrochloric acid used in the auxiliary back-extraction process is 0.5 mol / L.

[0024] The high-purity cesium salt prepared according to the method is characterized in that the total content of alkali metal impurities (calculated as metal) in the high-purity cesium salt product is less than 0.02%, and the rubidium impurity content is less than 0.01%.

[0025] In step (1) of the present invention, t-BAMBP under alkaline conditions is first used to target Cs. + The extraction ability is far superior to that of Rb. + (Cs) + > Rb + This characteristic allows Cs in lithium extraction mother liquor from lepidolite to be extracted. + and a small amount of Rb + In the hydrochloric acid washing and back-extraction section at pH=1, under countercurrent operation, t-BAMBP was used to process Cs under strongly acidic conditions. + and Rb+ The selective reversal of Cs loading in the organic phase leads to the reduction of Cs loading in the organic phase. + Preferentially released into the aqueous phase, while Rb + The rubidium-cesium ratio is relatively retained in the organic phase, thereby achieving active control from a high ratio (≥5:1) in the original mother liquor to a ratio close to 1:1. At the same time, this step completely regenerates the loaded organic phase of the first extraction into a blank organic phase, fully restoring its extraction function, which can be directly used for the second extraction operation, realizing the tandem recycling of the extractant.

[0026] In step (2), the hydrochloric acid washing at pH=3 utilizes the partial protonation effect of t-BAMBP at critical acidity to selectively elute residual Rb in the supported organic phase. + And with virtually no loss of Cs + Subsequent pure water washing removes mechanically entrained acid and impurity ions; the final CO2 back-extraction utilizes the weak acid slow-release properties of carbonic acid, further utilizing Cs under weakly acidic conditions. + Complex relative to Rb + The preferential dissociation characteristics of the complex open a "secondary separation window," minimizing rubidium impurities entering the back-extraction solution.

[0027] In this invention, the organic phase extractant system (t-BAMBP-sulfonated kerosene) achieves a series circulation, eliminating the need for additional preparation of a new organic phase. The deloaded blank organic phase obtained after washing and back-extraction at pH=1 in the first stage is directly transferred to the second stage extraction; the organic phase after CO2 back-extraction in the second stage contains residual Cs. + A small amount of dilute hydrochloric acid can be used to assist in back-extraction and recovery, and then the recovered product can be returned to the first extraction stage as organic phase 1 for recycling, forming a complete closed-loop cycle.

[0028] Compared with the prior art, the present invention has the following outstanding advantages:

[0029] (1) Breaking through technical bias and turning disadvantages into advantages: For the first time, the phenomenon of t-BAMBP selective reversal under strong acid conditions of pH=1, which is generally regarded as a process defect, has been transformed into an innovative process segment for actively controlling the rubidium-cesium ratio, filling the gap in existing technology.

[0030] (2) Three-stage synergy for deep rubidium removal: The two-stage extraction architecture is embedded with a triple rubidium repulsion barrier - pH=1 selective reversal and recombination (first stage), pH=3 critical acidity selective scrubbing (second stage), and CO2 weak acid selective release (second stage back-extraction). The three rely on different chemical mechanisms to produce a superimposed separation effect, so that the alkali metal impurity content of the final cesium salt product is reduced by more than one order of magnitude compared with the traditional single-stage hydrochloric acid back-extraction process.

[0031] (3) The extractant is cascaded and recycled, which is economical and environmentally friendly: the deloaded organic phase (organic phase 2) obtained by the first stage acid washing back-extraction is directly used as the organic phase for the second stage extraction. The organic phase is seamlessly connected between the two stages, and there is no need to prepare a new extractant for the second stage. This greatly reduces the total consumption of t-BAMBP and diluent, and reduces operating costs and the amount of organic waste liquid generated.

[0032] (4) The process is fast and efficient: each extraction and washing back-extraction stage is a three-stage countercurrent operation, the total number of stages is controllable, and there is no need for expensive chromatographic separation or repeated recrystallization and other lengthy steps, which is suitable for industrial continuous production.

[0033] (5) Strong adaptability to raw materials: It is especially suitable for the typical raw material characteristics of high rubidium and low cesium in lithium mica mother liquor. It can quickly adjust the rubidium-cesium ratio to the optimal window in the first stage, and then efficiently prepare high-purity cesium salt from this window. Attached Figure Description

[0034] Figure 1 This is a process flow diagram of the method for preparing high-purity cesium salts from lithium mica mother liquor by two-stage extraction, as described in this invention. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the embodiments. Unless otherwise specified, all percentages in the following embodiments are mass percentages.

[0036] The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to the present invention includes the following steps:

[0037] • First stage extraction-acid washing and back-extraction: The lithium extraction mother liquor from lepidolite is adjusted to pH ≥ 13 and subjected to three-stage countercurrent extraction with organic phase 1 containing t-BAMBP; the resulting loaded organic phase is subjected to three-stage countercurrent "washing and back-extraction" with hydrochloric acid solution at pH = 1 to obtain an aqueous phase as feed liquid 2, and at the same time, a deloaded blank organic phase is obtained, which is called organic phase 2; so that the mass ratio of Rb to Cs in feed liquid 2 is close to 1:1;

[0038] • Second stage extraction-step washing-CO2 back-extraction: Adjust the pH of feed solution 2 to ≥13, and directly use the organic phase 2 obtained in step 1 as the organic phase for the second stage extraction for three-stage countercurrent extraction; the resulting loaded organic phase is subjected to the following in sequence: ① three-stage countercurrent washing with hydrochloric acid solution at pH=3, ② three-stage countercurrent washing with pure water, ③ CO2 and water combined back-extraction (second stage) to obtain a high-purity cesium carbonate / cesium bicarbonate mixed solution;

[0039] • Cesium salt recovery: Evaporate and calcine the cesium carbonate / cesium bicarbonate mixed solution obtained in step 2 to obtain high-purity cesium carbonate product, or further convert it with hydrochloric acid to obtain high-purity cesium chloride product.

[0040] Example 1

[0041] The raw material processed in this embodiment is the leachate from a lithium mica ore after lithium extraction, and its main alkali metal composition is as follows: Rb + The concentration was 3.5 g / L, Cs + The concentration is 0.45 g / L, K + The concentration was 12.8 g / L, and the mass ratio of Rb to Cs was approximately 7.8:1. The organic phase of the extractant system was a 1.0 mol / L solution of t-BAMBP in 260# sulfonated kerosene.

[0042] Step 1: First stage extraction - acid washing and back-extraction.

[0043] The leachate from the lithium extraction of the aforementioned lepidolite ore was used as the feed solution, i.e., feed solution 1. First, the pH was adjusted to approximately 13.2 with NaOH, serving as the aqueous phase feed solution for the first stage of extraction. A three-stage countercurrent extraction was then performed using a t-BAMBP 260# sulfonated kerosene solution (referred to as organic phase 1). During this process, the Cs in the leachate... + and Rb + Some of the Rb enters the organic phase through the extraction process. After three-stage extraction, the loaded organic phases are combined and denoted as the first loaded organic phase; most of the Rb... + The phase remaining in the aqueous phase is designated as the first aqueous phase.

[0044] In the simulation experiment of this embodiment, a separatory funnel was used, with a ratio of O / A = 1:1, a mixing time of 5 min, and a settling time for phase separation.

[0045] The first loaded organic phase was subjected to a three-stage countercurrent wash and back-extraction with hydrochloric acid solution at pH 1.0 (operating conditions were the same as extraction, O / A = 1:1). During the back-extraction process, Cs loaded in the first loaded organic phase... + 、Rb + Released into the aqueous phase, the first loaded organic phase becomes a deloaded blank organic phase after back-extraction. After three-stage back-extraction, the aqueous phases obtained from the back-extraction are combined to form the second aqueous phase, which serves as the feed solution 2 in step 2. Analysis revealed that Rb in the second aqueous phase... + The concentration was 1.65 g / L, Cs + The concentration was 1.48 g / L, and the Rb:Cs mass ratio was approximately 1.12:1, which basically achieved the target of adjusting the Rb / Cs ratio from 7.8:1 to approximately 1:1.

[0046] Simultaneously, the pH=1 hydrochloric acid washing and back-extraction process completely deloaded and regenerated the first loaded organic phase, yielding a deloaded blank organic phase. Measurements showed that the t-BAMBP concentration in the deloaded blank organic phase was essentially the same as that in the fresh organic phase, and no detectable degradation in extraction performance occurred.

[0047] Step 2: Second stage extraction - stepwise washing - CO2 back-extraction.

[0048] The feed solution 2 was adjusted to pH ≈ 13.2 with NaOH and used as the aqueous phase feed solution for the second stage extraction. The unloaded blank organic phase obtained in step 1 was directly used as the organic phase for the second stage extraction, and a three-stage countercurrent extraction was performed (operating conditions were the same as the first stage extraction). After the three-stage extraction, the loaded organic phases were combined to obtain the second loaded organic phase; the combined aqueous phases were referred to as the third aqueous phase.

[0049] The second supported organic phase is subjected to the following three steps in sequence:

[0050] (2.1) Three-stage countercurrent washing with hydrochloric acid solution at pH=3: Three-stage countercurrent washing was performed with hydrochloric acid solution at pH=3.0 (O / A=1:1, mixing time 3 min). Analysis showed that this step selectively eluted approximately 75% of the residual Rb in the second loaded organic phase. + Meanwhile, Cs + The loss rate is less than 3%.

[0051] (2.2) Three-stage countercurrent washing with pure water: Three-stage countercurrent washing with deionized water (O / A=1:1) is used to remove mechanically entrained acid and residual impurity ions.

[0052] (2.3) CO2 back-extraction: The second loaded organic phase after water washing was mixed with deionized water at a ratio of O / A = 1:1. CO2 gas was introduced into a sealed container (pressure 0.1 MPa, room temperature), and the mixture was stirred and contacted for 15 min, followed by phase separation. The above CO2 back-extraction operation was repeated once, for a total of two stages. The aqueous phases obtained from the two CO2 back-extractions were combined, i.e., the fourth aqueous phase, to obtain a cesium carbonate / cesium bicarbonate mixed solution. Analysis showed that the Cs in the fourth aqueous phase solution... + The total back-extraction rate was 91.5%, and the Cs in the solution... + The concentration was 1.21 g / L, Rb + The concentration was 0.28 mg / L, which means that the mass ratio of rubidium impurities to cesium was approximately 0.023%.

[0053] The organic phase resulting from the combined CO2 back-extraction is designated as the third organic phase, which contains approximately 8.5% Cs. + A small amount of 0.5 mol / L hydrochloric acid can be used for a supplementary back-extraction recovery. Because the rubidium / cesium ratio of this recovered solution is higher than that of the main back-extraction solution, it is collected separately and not combined with the main product solution. It can be directly returned to the extraction section of step 2 or processed separately. The organic phase after supplementary back-extraction is completely regenerated and can be returned to step 1 as organic phase 1 for recycling, forming a closed-loop cycle.

[0054] Step 3: Cesium salt recovery.

[0055] The cesium carbonate / cesium bicarbonate mixed solution obtained in step 2 was heated and evaporated to dryness, then calcined at 430°C for 2 hours to obtain a high-purity cesium carbonate product. ICP-MS analysis showed that the total alkali metal impurity content (based on metal content) in the product was 0.011%, of which the rubidium impurity content was 0.008%. This indicator is significantly better than that of products obtained by the traditional single-stage hydrochloric acid back-extraction process (typically, the total alkali metal impurity content is 0.02%–0.28%).

[0056] If cesium chloride products are required, cesium carbonate can be dissolved and converted with an equivalent amount of hydrochloric acid, then concentrated and crystallized. The conversion step is carried out in a homogeneous aqueous solution, without introducing additional rubidium impurities.

[0057] Comparative example (traditional single-stage process)

[0058] To demonstrate the technical effectiveness of this invention, a comparative experiment using a traditional single-stage process was conducted using the same leaching solution from lithium extraction from lepidolite: the leaching solution underwent three-stage extraction under alkaline conditions, followed by three-stage washing with pure water, and then two-stage back-extraction with 1.0 mol / L hydrochloric acid. The back-extraction solution was evaporated to obtain cesium chloride product. This process uses only one stage of extractant, without series circulation or intermediate rubidium-cesium ratio control. Measurements showed that the total alkali metal impurities in the cesium chloride product were 0.25%, of which rubidium impurities accounted for 0.19%.

[0059] The ratio of rubidium impurity content in the embodiments of this invention to that in the comparative examples is approximately 1:24 (0.008%:0.19%), meaning the rubidium impurity content is reduced by more than an order of magnitude. Furthermore, in this invention, organic phase 2 is directly derived from the acid washing and regeneration of organic phase 1, eliminating the need for a second, independently prepared fresh organic phase. This reduces the total extractant consumption by approximately 50% compared to the scheme with two independent extraction stages. This fully demonstrates the outstanding technical effectiveness of the method of this invention in deep rubidium removal from cesium salts and in reducing reagent consumption.

[0060] Example 2

[0061] In the lithium extraction leachate from lepidolite treated in this embodiment, Rb + The concentration was 4.2 g / L, Cs + The concentration was 0.52 g / L, K + The concentration was 15.0 g / L, and the mass ratio of Rb to Cs was approximately 8.1:1.

[0062] Step 1: Adjust the pH of the lithium extraction leachate to 13.0 with NaOH. Perform a three-stage countercurrent extraction using organic phase 1 (t-BAMBP concentration 1.0 mol / L, diluent: 260# sulfonated kerosene) at an O / A ratio of 1:1 for 5 min, followed by standing and phase separation. Combine the loaded organic phases (first loaded organic phase). Perform a three-stage countercurrent back-extraction with hydrochloric acid solution at pH 1.0 at an O / A ratio of 1:1 to obtain the second aqueous phase and the deloaded blank organic phase. Analysis showed that the Rb content in the back-extraction aqueous phase (second aqueous phase) was... + The concentration was 1.82 g / L, Cs + The concentration was 1.71 g / L, and the Rb:Cs mass ratio was 1.06:1.

[0063] The aqueous phase obtained from back-extraction (second aqueous phase) is used as the feed liquid 2 in step 2, and the unloaded blank organic phase is directly used for extraction in step 2.

[0064] Step 2: Adjust the pH of feed solution 2 to 13.0 with NaOH, and directly perform three-stage countercurrent extraction with the unloaded blank organic phase, with an O / A ratio of 1:1. After combining the loaded organic phases, a second loaded organic phase is obtained, and the following steps are performed sequentially:

[0065] (2.1) Three-stage countercurrent washing with hydrochloric acid at pH=3.0 (O / A=1:1, mixing time 3 min);

[0066] (2.2) Three-stage countercurrent washing with deionized water (O / A=1:1);

[0067] (2.3) CO2 secondary back-extraction (O / A = 1:1 per stage, CO2 pressure 0.1 MPa, stirring at room temperature for 15 min).

[0068] After combining the two CO2 back-extraction solutions (fourth aqueous phase), Cs was measured. + The concentration was 1.38 g / L, and the mass ratio of rubidium impurities to cesium was 0.025%.

[0069] Step 3: The back-extraction solution was evaporated and calcined at 430℃ for 2 h to obtain high-purity cesium carbonate. ICP-MS analysis showed that the total alkali metal impurities in the product were 0.012%, and the rubidium impurity content was 0.009%.

[0070] Example 3

[0071] In the lithium extraction leachate from lepidolite treated in this embodiment, Rb + The concentration was 5.0 g / L, Cs + The concentration is 0.50 g / L, K +The concentration was 20.0 g / L, and the mass ratio of Rb to Cs was 10:1. The extractant was a 260# sulfonated kerosene solution with a t-BAMBP concentration of 0.8 mol / L.

[0072] Step 1: The lithium extraction leachate was adjusted to pH 13.5 with NaOH and subjected to three-stage countercurrent extraction with organic phase 1 (O / A = 1:1, mixing time 5 min). The loaded organic phases (first loaded organic phase) were combined and back-extracted using three-stage countercurrent washing with hydrochloric acid at pH 1.0 (O / A = 1:1) to obtain the second aqueous phase and the deloaded blank organic phase. Analysis showed that Rb in the second aqueous phase... + The concentration was 1.95 g / L, Cs + The concentration was 1.80 g / L, and the Rb:Cs mass ratio was approximately 1.08:1.

[0073] The aqueous phase obtained from back-extraction (second aqueous phase) is used as the feed liquid 2 in step 2, and the unloaded blank organic phase is directly used for extraction in step 2.

[0074] Step 2: Adjust the pH of feed solution 2 to 13.5 with NaOH, and perform three-stage countercurrent extraction (O / A = 1:1) using the unloaded blank organic phase. After combining the loaded organic phases, a second loaded organic phase is obtained. The loaded organic phases are then subjected to the following processes:

[0075] (2.1) Three-stage countercurrent washing with hydrochloric acid at pH 3.0;

[0076] (2.2) Three-stage countercurrent washing with deionized water;

[0077] (2.3) CO2 secondary back-extraction (conditions as above).

[0078] Combined CO2 back-extraction solutions (fourth aqueous phase), Cs was measured. + The concentration was 1.45 g / L, and the mass ratio of rubidium impurities to cesium was 0.031%.

[0079] Step 3: Evaporate and calcine the back-extraction solution to obtain high-purity cesium carbonate. The total alkali metal impurities in the product are 0.015%, and the rubidium impurity content is 0.011%. This indicates that even with a raw material Rb / Cs ratio as high as 10:1 and the use of a slightly lower concentration of t-BAMBP extractant, the method of this invention can still obtain high-purity cesium salts with extremely low rubidium impurity content.

[0080] Example 4

[0081] This embodiment uses essentially the same leachate (Rb) as in Example 1. + 3.5 g / L, Cs + 0.45 g / L, K +The concentration of the extractant t-BAMBP was 12.8 g / L (Rb:Cs≈7.8:1), and the concentration of the extractant t-BAMBP remained at 1.0 mol / L. The first step was the same as in Example 1, yielding a feed solution 2 with Rb:Cs=1.12:1 and an organic phase 2.

[0082] In step 2, the three-stage hydrochloric acid washing at pH=3 is changed to two stages, the pure water washing remains at three stages, and the CO2 back-extraction is increased from two stages to three stages. That is, the total number of washing / back-extraction stages is: two stages of hydrochloric acid washing at pH=3, three stages of pure water washing, and three stages of CO2 back-extraction.

[0083] After combining the obtained CO2 back-extraction solutions, Cs + The concentration was 1.25 g / L, and the mass ratio of rubidium impurities to cesium was 0.022%. The final cesium carbonate product had a total alkali metal impurity content of 0.010% and a rubidium impurity content of 0.007%. The examples show that by appropriately reducing the number of acid washing stages but increasing the number of CO2 back-extraction stages, excellent cesium salt purity can still be guaranteed, and the process flow has a certain degree of flexibility for adjustment.

[0084] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite using a two-stage extraction process, characterized in that, Includes the following steps: (1) Extraction-acid washing and back-extraction: The lithium extraction mother liquor from lepidolite is used as raw material liquid 1 and adjusted to alkaline conditions. After mixing with organic phase 1 containing t-BAMBP, multi-stage countercurrent extraction is performed to obtain the first aqueous phase and the first loaded organic phase. The obtained first loaded organic phase is then subjected to controlled washing and back-extraction under strong acid conditions sufficient to induce t-BAMBP selective reversal, releasing the loaded metal ions in the first loaded organic phase into the second aqueous phase and obtaining the deloaded blank organic phase. At this time, the mass ratio of rubidium to cesium in the second aqueous phase is close to 1:

1. (2) Extraction-step washing-CO2 back-extraction: Using the second aqueous phase as the raw material liquid 2, the raw material liquid 2 is adjusted to alkaline conditions, and the deloaded blank organic phase obtained in step (1) is directly used as the extraction organic phase for multi-stage countercurrent extraction to obtain the third aqueous phase and the second loaded organic phase; the obtained second loaded organic phase is subjected to weak acid selective washing, pure water washing and CO2 back-extraction in sequence to remove residual rubidium ions and acid, and to obtain a high-purity cesium salt solution; (3) Cesium salt recovery: Cesium salt products are recovered from the high-purity cesium salt solution.

2. The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to claim 1, characterized in that, The strong acid condition sufficient to trigger the selective reversal of t-BAMBP in step (1) is a hydrochloric acid solution with pH=1, and the controlled washing and back-extraction is a three-stage countercurrent operation; The weakly acidic selective washing in step (2) is performed by a three-stage countercurrent washing with a hydrochloric acid solution of pH=3, the pure water washing is a three-stage countercurrent washing, and the CO2 back-extraction is a two-stage countercurrent operation.

3. The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to claim 2, characterized in that, After the loaded organic phase described in step (1) is washed and back-extracted in three stages with hydrochloric acid at pH=1, the mass ratio of rubidium to cesium in the resulting second aqueous phase is controlled within the range of 0.8:1 to 1.2:

1.

4. The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to claim 1, characterized in that, The alkaline condition described in step (1) is pH ≥ 13; the alkaline condition described in step (2) is pH ≥ 13.

5. The method for preparing high-purity cesium salts from lithium-mica mother liquor by two-stage extraction according to claim 1, characterized in that, Both organic phase 1 and the unloaded blank organic phase were sulfonated kerosene solutions with a t-BAMBP concentration of 0.8~1.2 mol / L.

6. The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to claim 1, characterized in that, The residual cesium in the organic phase after CO2 back-extraction in step (2) is recovered by auxiliary back-extraction with dilute hydrochloric acid and returned to step (1) as organic phase 1 for recycling, forming a closed loop; the auxiliary back-extraction liquid is not incorporated into the high-purity cesium salt solution, but is treated separately or returned to the extraction section of step (2).

7. The method for preparing high-purity cesium salts from lithium extraction mother liquor from lepidolite according to claim 1, characterized in that, Step (3) cesium salt recovery includes evaporating and calcining the cesium carbonate / cesium bicarbonate solution obtained by CO2 back-extraction to obtain high-purity cesium carbonate, or further converting it with hydrochloric acid to obtain high-purity cesium chloride.

8. The method according to claim 6, characterized in that, The concentration of dilute hydrochloric acid used in the auxiliary back-extraction process is 0.5 mol / L.

9. The high-purity cesium salt prepared by the method according to any one of claims 1 to 8, characterized in that, The total content of alkali metal impurities (calculated as metals) in the high-purity cesium salt product is less than 0.02%, and the content of rubidium impurities is less than 0.01%.

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