A method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater

Abstract

This application discloses a method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater, relating to the field of liquid waste resource recovery technology in the metallurgical industry. This invention utilizes an integrated process of gradient precipitation-pyrolysis-water leaching-multi-stage crystallization, including rubidium and cesium precipitation, pyrolysis, water leaching, secondary precipitation, crystallization, and recrystallization, to separate and extract the main components such as potassium, sodium, rubidium, and cesium from the washing liquid into products such as potassium chloride, sodium chloride, and mixed rubidium and cesium precipitates. This achieves the reduction, resource recovery, and harmless utilization of multi-metal ion wastewater. This technology enables highly selective enrichment of rubidium and cesium, combines pyrolysis to decompose cyanide ions for harmless treatment, and utilizes the difference in potassium and sodium solubility to achieve efficient separation through multi-stage crystallization. It offers advantages such as high product value, good economic benefits, and ease of industrialization, opening up new avenues for the resource utilization of metal ion wastewater.

Description

Technical Field

[0001] This invention relates to the field of liquid waste resource recycling technology in the metallurgical industry, and in particular to a method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater. Background Technology

[0002] Rubidium and cesium are often dispersed in nature within potassium- and sodium-rich minerals such as lepidolite, potassium feldspar, and carnallite, not forming independent minerals, but often associated with potassium and sodium. During high-temperature (≥1100℃) smelting processes, chlorides and silicates of potassium, sodium, rubidium, and cesium are easily volatilized. As the gas stream rises and cools, it condenses into fine dust particles, which are then captured by bag filters or electrostatic precipitators. Water leaching of the dust can dissolve soluble salts and separate heavy metals, but it also produces a large amount of complex mother liquor. Its main components are high concentrations of KCl and NaCl, and it also contains economically valuable CsCl and RbCl. Direct discharge of this type of mother liquor will severely pollute soil and water bodies, causing salinization and heavy metal toxicity; long-term storage faces high costs and space constraints. Currently, the main treatment methods for recovering steelmaking dust and mother liquor in my country include salt separation and crystallization technology, mother liquor solidification and evaporation crystallization technology, and rare metal extraction technology.

[0003] Salt separation crystallization technology utilizes the difference in salt solubility with temperature to achieve salt separation through evaporation and cooling crystallization. A patented method for the comprehensive utilization of sintering flue gas and desulfurization wastewater from steel plants (CN107673374A) employs a process combining soda ash softening, acidification oxidation, and evaporation crystallization to precipitate NaCl and K₂SO₄ stepwise from a mixture of sintering flue gas washing liquid and desulfurization wastewater. Potassium recovery can reach 89%, and the product can be used as industrial salt or potassium fertilizer raw material. However, this technology faces the problem of fluctuating crystal purity due to organic pollution. Another patent (CN102897837A) utilizes strongly alkaline anions to preferentially adsorb high-valence anionic impurities. The purified solution is then evaporated and crystallized to obtain high-purity (>97%) NaCl and KCl crystals. However, this technology lacks selectivity for monovalent metals such as rubidium and cesium.

[0004] Mother liquor solidification and evaporation crystallization technology: Patent CN219149249U provides a mother liquor treatment system for fly ash washing water salt crystallization. Through technologies such as atomized drying, tail gas heat recovery, and condensate reuse, the volume of the mother liquor is significantly reduced, and the resulting solid salts are stored or further utilized. A co-processing method for high-salt solid waste from the steel industry (such as CN117070756A) mixes sintered ash washing liquid with blast furnace ash washing liquid, and removes heavy metals through ammonia nitrogen concentration adjustment and pH-stage precipitation; the purified liquid enters a multi-effect evaporation system, sequentially precipitating NaCl and KCl crystals, effectively reducing overall water consumption and wastewater treatment costs.

[0005] Rare metal extraction technology: Patent (CN113564370A) discloses a treatment system for complex tin smelting dust. First, strong oxidative leaching with sulfuric acid-potassium permanganate is used to dissolve metals such as cadmium and zinc. Finally, sodium carbonate is added to the washing solution and leaching solution to adjust the pH, obtaining sponge cadmium and crude zinc carbonate as byproducts. Invention patents include a method for preparing cesium sulfate from saline wastewater (CN201811526644.9) and a method and equipment for extracting high-purity cesium sulfate from high-salinity wastewater (CN202010998067.4). These patents employ a "fire-based enrichment and wet extraction multi-stage integrated coupled treatment" technology for steel dust. This technology can treat two types of steel dust—industrial solid waste, blast furnace gas ash (sludge), and electric arc furnace steelmaking ash—in a resource-efficient and harmless manner, comprehensively recovering various valuable metals such as zinc, indium, lead, bismuth, and iron. These processes improve the recovery rate of rare and precious metals.

[0006] In summary, existing technologies for treating potassium and sodium wastewater rich in rubidium and cesium mainly suffer from the following bottlenecks: Due to poor selectivity, existing salt separation crystallization and mother liquor solidification technologies struggle to effectively distinguish K atoms with similar ionic radii. + Na + With higher value Rb + Cs + This results in the loss of rubidium and cesium in the potassium and sodium salt products, leading to low recovery rates. Product purity is also low; due to insufficient selectivity, the resulting potassium and sodium salt products exhibit significant intercontamination, resulting in low purity and value. Furthermore, interference from organic matter causes large fluctuations in the purity of the crystalline products. Most technologies focus on wastewater treatment, failing to achieve efficient enrichment and full-component resource recovery of high-value elements such as rubidium and cesium, thus lacking economic viability.

[0007] Therefore, developing an integrated process that can selectively enrich rubidium and cesium while simultaneously achieving efficient separation and purification of potassium and sodium is key to realizing the high-value resource utilization of this type of wastewater. Summary of the Invention

[0008] This application provides a method for extracting rubidium and cesium from metal ion wastewater and separating potassium and sodium, which solves the problem of low recovery rate in the prior art.

[0009] It achieves highly selective separation of rubidium and cesium ions relative to potassium and sodium ions; combined with pyrolysis process to decompose cyanide ions to achieve harmlessness, it ultimately enriches and recovers rubidium and cesium in a mixed precipitation form with high efficiency, while co-producing high-purity potassium chloride and sodium chloride products, solving the industry problem of poor selectivity and low recovery rate of rubidium and cesium by traditional technology.

[0010] This application provides a method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater, including the following steps: S1: Add zinc salt and potassium ferrocyanide to wastewater rich in Group I metal ions, mix well, stir for 1-2 hours, and then filter to separate the residue A and filtrate A. S2: Calcine filter residue A at 650-750℃ for 1-3 hours, then leach it with water at room temperature for 20-40 minutes, and filter to obtain water-leached residue and filtrate B; S3: Add the rubidium and cesium precipitant to filtrate B, stir for 1-1.5 hours, let stand, filter and separate to obtain a mixed rubidium and cesium precipitate; S4: Evaporate and concentrate filtrate A at 80-100℃ to 30-40% of its volume to precipitate crystals, filter while hot, and separate solid and liquid to obtain hot filtrate C and hot crystals; cool hot filtrate C to room temperature and crystallize for 1-3 hours to obtain cool filtrate and crude potassium chloride. S5: Add the hot crystals to the cooled filtrate at a solid-liquid ratio of 0.1-0.8 kg / L, stir at a temperature greater than 80°C for at least 30 minutes to dissolve the hot crystals of potassium chloride, and then filter while hot to obtain crude sodium chloride and hot filtrate B. S6: After the hot filtrate B is cooled to room temperature and allowed to stand for 0.5-5 hours, it is filtered to obtain filtrate D and crude potassium chloride; S7: Dissolve crude potassium chloride and crude sodium chloride in water at a solid-liquid ratio of 1:2 to 1:5, evaporate 40% to 60% of their volume, and then cool and crystallize for 6 to 12 hours to obtain high-purity potassium chloride and sodium chloride.

[0011] Furthermore, the zinc salt is zinc sulfate heptahydrate or zinc chloride.

[0012] Furthermore, the molar ratio of the zinc salt to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:4-2:5.

[0013] Furthermore, the molar ratio of the potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:4 to 1:2.

[0014] Furthermore, the precipitant is sodium tetraphenylborate, phosphotungstic acid, or silicotungstic acid.

[0015] Furthermore, the molar ratio of the sodium tetraphenylborate to the sum of the molar numbers of rubidium and cesium is 1:4 to 1:3.

[0016] Furthermore, the molar ratio of the phosphotungstic acid to the sum of the molar numbers of rubidium and cesium is 1:3 to 1:5.

[0017] Further, in step S1, zinc salt and potassium ferrocyanide are added to the metal ion wastewater in two batches. The first batch, comprising 40-60% of the total amount, is mixed thoroughly at 5-15°C and heated at 250-400 rpm for 1 hour. Then, the temperature is increased to 50°C, and the remaining zinc salt and potassium ferrocyanide are added. The mixture is stirred at 75-125 rpm for 1-4 hours and filtered to separate the residue A and filtrate A. Further, in step S2, the calcination is a stepped calcination process. First, the temperature is increased to 580-650°C at a rate of 5-10°C per minute and held for 1-2 hours. Then, the temperature is increased to 700-750°C at a rate of 10-20°C per minute and held for 1-2 hours.

[0018] Furthermore, in step S7, preferably, crude potassium chloride and crude sodium chloride are dissolved in water at a solid-liquid ratio of 0.1-0.8 kg / L, evaporated by 40-60% of their volume, and then cooled and crystallized for 6-12 hours to obtain high-purity potassium chloride and sodium chloride.

[0019] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages: By utilizing structural matching to achieve selective precipitation, potassium ferrocyanide and zinc salts are introduced. Taking advantage of the cubic cavity structure of the ferrocyanide ion, whose size is highly matched with the radius of rubidium and cesium ions, insoluble ferrocyanide precipitates are preferentially formed, while potassium and sodium remain in the solution due to size mismatch, thereby achieving highly selective enrichment of rubidium and cesium. The precipitate is decomposed by high-temperature roasting (650-750°C), converting cyanide ions into harmless nitrogen gas, while generating soluble rubidium cesium carbonate, which is then purified by water leaching to obtain a purified solution.

[0020] Secondary precipitation is performed using sodium tetraphenylborate or phosphotungstic acid, taking advantage of their large anions and the low solubility of rubidium and cesium to obtain a high-purity rubidium and cesium mixed precipitate; at the same time, high-purity potassium chloride and sodium chloride are co-produced from the remaining filtrate through temperature-controlled stepwise crystallization, realizing the resource utilization of all components of the wastewater. By adjusting reagent ratios, temperature gradients, and recycling filtrate, selectivity and economy can be further improved, while waste emissions can be reduced. Attached Figure Description

[0021] Figure 1 This is a flowchart of a method for extracting rubidium and cesium from metal ion wastewater and separating potassium and sodium according to the present invention; Figure 2 This is an EDS diagram of rubidium-cesium mixed precipitation in Example 1 of the method for extracting rubidium and cesium from metal ion wastewater and separating potassium and sodium according to the present invention. Figure 3 This is the XRD pattern of cesium phosphotungstenate in Example 3 of the method for extracting rubidium and cesium from metal ion wastewater and separating potassium and sodium according to the present invention. Detailed Implementation

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention; the term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0023] Example 1: In this example, the concentration of KCl in the metal ion wastewater is 162 g / L; NaCl concentration is 232 g / L; CsCl concentration is 31 g / L; RbCl concentration is 15 g / L; in addition, it also contains small amounts of valuable metals such as lithium, molybdenum, rhenium, and cadmium.

[0024] Methods for extracting rubidium and cesium and separating potassium and sodium, such as Figure 1 include: Step 1: Add zinc salt and potassium ferrocyanide to the metal ion wastewater, mix evenly at room temperature, stir for 1 hour, and then filter to separate, obtaining filter residue A and filtrate A; The zinc salt is zinc chloride. The molar ratio of zinc chloride to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 2:5, and the molar ratio of potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:2. Step 2: Calcine the filter residue A at 700℃ for 3 hours, then soak it in water at room temperature with a solid-liquid ratio of 0.2 kg / L for 30 minutes, and filter to obtain water-leached residue and filtrate B; High-temperature roasting decomposes Cs2ZnFe(CN)6 and Rb2ZnFe(CN)6 into rubidium carbonate, cesium carbonate, iron oxide, zinc oxide, nitrogen, etc. After water leaching, the filtrate B mainly consists of rubidium carbonate and cesium carbonate solution. Step 3: Add sodium tetraphenylborate to filtrate B in a molar ratio of 1:3 to the sum of the molar numbers of rubidium and cesium, continue stirring for 1 hour, let stand for 2 hours, filter, and separate the solid and liquid to obtain the filtrate and the rubidium-cesium mixed precipitate; During the stirring process, sodium tetraphenylborate reacts with filtrate B to form precipitates of rubidium tetraphenylborate and cesium tetraphenylborate. After standing, the precipitate particles aggregate to facilitate filtration. The rubidium and cesium mixed precipitate components were determined by atomic absorption spectrometry (AAS) after digestion, as shown in Tables 1 and 2. Table 1. Composition of rubidium-cesium mixed precipitate (wt% as tetraphenylborane) Table 2. Composition of rubidium-cesium mixed precipitate (wt% based on elemental composition) The morphology and micro-area elemental analysis of the precipitate sample were performed using a scanning electron microscope and its accompanying energy dispersive spectroscopy (SEM-EDS). The EDS spectra are shown below. Figure 2As shown, the results are consistent with the elemental trends obtained by AAS, confirming that the precipitate is rich in rubidium and cesium. Energy dispersive spectroscopy (EDS) was used to determine the types and contents of elements in the rubidium-cesium mixed precipitate, as shown in the results. Figure 2 ; Ferrocyanide ion ([Fe(CN)6]) 4- ) is a commonly used coordination compound that can undergo metathesis reactions with many metal salts or ions to produce precipitates or colloids, providing a cubic cavity structure with dimensions similar to Cs. + (Ionic radius approximately 0.165 nm), Rb + (Ionic radius approximately 0.149 nm) Matching degree higher than K + (Approximately 0.133 nm), laying the structural foundation for subsequent selective adsorption. Zn 2+ As a bridging central ion, it can interact with [Fe(CN)6]. 4- Formation of coordinate bonds Zn3[Fe(CN)6]2 2- Thus, it can accommodate the adsorption of Rb + / Cs + Hydrated ions. Therefore, zinc salts are mixed with the mother liquor from steelmaking flue gas washing (metal ion wastewater) to make the solution contain Zn. 2+ .

[0025] During the reaction and precipitation process, the rubidium and cesium ions in the mother liquor from steelmaking flue dust washing mainly react with potassium ferrocyanide and zinc sulfate as follows: 2Cs + +Zn 2+ +Fe(CN)6 4- →Cs2ZnFe(CN)6 2Rb + +Zn 2+ +Fe(CN)6 4- →Rb2ZnFe(CN)6 Filter residue A is a mixture of Cs2ZnFe(CN)6 and Rb2ZnFe(CN)6, and filtrate A is a mixed solution containing potassium chloride and sodium chloride.

[0026] Cesium carbonate (Cs₂CO₃) is an inorganic compound that is highly soluble in water, and its aqueous solution is strongly alkaline. Rubidium carbonate is also strongly alkaline and readily soluble in water. After roasting and cooling, filter residue A is mixed with water at a specific solid-liquid ratio and leached for separation. The resulting water-leached residue is mainly a mixture of ZnO and Fe₂O₃, which can be used as a raw material for iron smelting, with a molar ratio of iron to zinc of 0.2–5. The resulting filtrate B is mainly an alkaline solution containing rubidium and cesium carbonates.

[0027] Potassium ferrocyanide, zinc salt, rubidium, and cesium react to form insoluble ferrocyanide complexes. These complexes have low solubility, while similar complexes of potassium and sodium have high solubility; therefore, rubidium and cesium are selectively precipitated. Filter residue A is roasted, causing the insoluble ferrocyanide complexes to decompose. In air, the decomposition products include rubidium carbonate, cesium carbonate, zinc oxide, iron oxide, and nitrogen. Rubidium carbonate and cesium carbonate are soluble in water, while the metal oxides are insoluble. After water leaching and filtration, filtrate B mainly contains rubidium carbonate and cesium carbonate solution, and may contain small amounts of potassium carbonate and sodium carbonate, but in small quantities.

[0028] Sodium tetraphenylborate reacts with rubidium and cesium ions to form insoluble tetraphenylborate precipitates. Potassium tetraphenylborate is also insoluble, but sodium tetraphenylborate is soluble. Due to the extremely low solubility of tetraphenylborate-cesium and tetraphenylborate-rubidium, rubidium and cesium preferentially precipitate. The high concentrations of rubidium and cesium and the low concentration of potassium in filtrate B further enhance the selectivity.

[0029] Example 2: In this example, the concentration of KCl in the metal ion wastewater is 136 g / L; the concentration of NaCl is 213 g / L; the concentration of CsCl is 43 g / L; and the concentration of RbCl is 18 g / L.

[0030] Methods for extracting rubidium and cesium and separating potassium and sodium include: Step 1: Add zinc salt and potassium ferrocyanide to the metal ion wastewater, mix evenly at room temperature, stir for 2 hours, and then filter to separate, obtaining filter residue A and filtrate A; The zinc salt is zinc sulfate heptahydrate. The molar ratio of zinc sulfate heptahydrate to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:4. The molar ratio of potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is also 1:4. Step 2: Calcine the filter residue A at 750℃ for 2 hours, then soak it in water at room temperature with a solid-liquid ratio of 0.25 kg / L for 40 minutes. Filter to obtain water-leached residue and filtrate B. After water leaching, filtrate B mainly consists of rubidium carbonate and cesium carbonate solution. Step 3: Add sodium tetraphenylborate to filtrate B at a molar ratio of 1:4 (sodium tetraphenylborate to rubidium and cesium), continue stirring for 1.5 hours, let stand for 2 hours, and filter. The solid and liquid are separated to obtain the filtrate and the rubidium and cesium mixed precipitate. During the stirring process, sodium tetraphenylborate reacts with filtrate B to form precipitates of rubidium tetraphenylborate and cesium tetraphenylborate. Step 4: Evaporate 40% of the volume of filtrate A at 100℃ to precipitate crystals, filter while hot, and separate the solid and liquid to obtain hot filtrate C and hot crystals; cool hot filtrate C to room temperature and crystallize for 2 hours, then filter to obtain cool filtrate and crude potassium chloride; Step 5: Add the hot crystallizer to the cooled filtrate at a solid-liquid ratio of 0.33 kg / L, stir at a temperature above 80°C (95°C in this example) for 30 min (stir for at least 30 min to dissolve), and filter while hot to obtain crude sodium chloride and hot filtrate B; Step 6: Cool the hot filtrate B to room temperature and let it stand for no less than 0.5 hours (common standing times include 0.5 hours, 1 hour, 2 hours, 3 hours, 4 hours, and 5 hours). Filter to obtain filtrate D and crude potassium chloride. Filtrate D is returned to the metal ion wastewater in step 1 of the process for recycling. Step 7: Dissolve crude potassium chloride and crude sodium chloride in water at a solid-liquid ratio of 1:3 to obtain a near-saturated or supersaturated solution, then evaporate 50% of the volume and cool for crystallization for 8 hours (cooling time should not be less than 6 hours, generally including 6 hours, 8 hours, 10 hours, and 12 hours). Filter to obtain potassium chloride, sodium chloride, and their respective recrystallization solutions.

[0031] The precipitate samples were digested and then analyzed by atomic absorption spectrometry (AAS). The composition of the rubidium-cesium mixed precipitate is shown in Tables 3 and 4. Table 3. Composition of rubidium-cesium mixed precipitate (wt% as tetraphenylborane) Table 4. Composition of rubidium-cesium mixed precipitate (wt% based on elemental composition) The prepared potassium chloride has a purity of ≥98.7%, which meets the superior grade index of industrial potassium chloride; the sodium chloride has a purity of 99.5%, which meets the superior grade index of industrial sodium chloride. Specific parameters are shown in Table 5 and Table 6. Table 5 Industrial potassium chloride standards and sample parameters Table 6 Standards and Sample Parameters for Industrial Sodium Chloride By adjusting the ratio, not only were impurities potassium and sodium removed from the rubidium-cesium mixed precipitate, but also stepwise crystallization was achieved by exploiting the difference in solubility of KCl and NaCl at different temperatures. Recrystallization was then introduced for further purification, ultimately yielding high-purity KCl and NaCl products. The recycling of filtrate D also reduced waste discharge and raw material consumption. Potassium and sodium are selectively separated based on the differences in solubility of KCl and NaCl with temperature and their supersaturation. The concentration is controlled by the amount of water evaporated. Filtrate A is evaporated and heated to concentrate the solution until it reaches the critical nucleation supersaturation level for NaCl, promoting its preferential precipitation; while KCl remains unsaturated. Thus, NaCl crystallizes out due to supersaturation, while KCl remains stably in the solution. After filtration, the hot crystallizer is a crude salt mainly composed of NaCl, with a small amount of KCl entrained; the hot filtrate C is a solution containing sodium chloride and potassium chloride, where KCl is highly saturated and NaCl is unsaturated. The hot filtrate is cooled to room temperature and allowed to crystallize for a certain period to obtain a cooled filtrate and crude potassium chloride; the cooled filtrate contains residual KCl. + Na + Low-concentration mother liquor.

[0032] Potassium ions have a smaller hydration radius, and their dissolution free energy is more significantly affected by increasing temperature. The solubility of potassium chloride increases with temperature, while the solubility of sodium chloride is basically unaffected by temperature. Therefore, by adding hot crystals, mainly NaCl with a small amount of KCl, to the filtrate preheated to 90-100℃, potassium chloride can be dissolved, thus achieving potassium-sodium separation through solid-liquid separation.

[0033] Filtrate D contains trace amounts of K + Na + Returning to step 1 of the process, the metal ion wastewater is recycled to achieve full recovery of potassium and sodium.

[0034] Crude potassium chloride contains a small amount of sodium chloride. High-purity potassium chloride product can be obtained by recrystallization. Crude sodium chloride contains a small amount of potassium chloride. High-purity sodium chloride product can be obtained by recrystallization. It was found that the solid-liquid ratio of the solutions obtained by dissolving crude potassium chloride and crude sodium chloride in water has no significant effect on subsequent purification. Near-saturated or supersaturated solutions can improve extraction efficiency and have no significant effect on the properties of the product. The solid-liquid ratio of 0.1-0.8 kg / L can meet the requirements. The evaporation volume within the common range (40%-60%) has no significant effect on the subsequent extraction results. By optimizing the precipitant molar ratio in step 1, extremely high selectivity for cesium relative to rubidium precipitation was achieved. The final rubidium-cesium mixed precipitate is essentially a high-purity cesium concentrate with very low rubidium content and complete removal of potassium and sodium.

[0035] This process enriches high-value cesium and produces potassium chloride and sodium chloride that meet industrial premium standards. This significantly enhances the economic and environmental value of the entire process. By adjusting the molar ratio of the potassium ferrocyanide-zinc salt precipitation step, the ratio of rubidium and cesium in the final product can be controlled to meet different extraction requirements. The newly added potassium and sodium separation and purification steps transform the previously treated potassium and sodium-containing wastewater into economically valuable products, making the entire technology more promising for industrial applications.

[0036] Example 3: In this example, the concentration of KCl in the metal ion wastewater is 128 g / L; the concentration of NaCl is 198 g / L; the concentration of CsCl is 52 g / L; and the concentration of RbCl is 14 g / L.

[0037] The specific steps are as follows: Step 1: Add zinc salt and potassium ferrocyanide to the metal ion wastewater, mix evenly at room temperature, stir for 2 hours, and then filter to separate, obtaining filter residue A and filtrate A; The zinc salt is zinc sulfate heptahydrate. The molar ratio of zinc sulfate heptahydrate to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:5, and the molar ratio of potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 3:10. Step 2: Calcine the filter residue A at 650℃ for 2 hours, then soak it in water at room temperature with a solid-liquid ratio of 0.167 kg / L for 20 minutes. Filter to obtain water-leached residue and filtrate B. After water leaching, filtrate B mainly consists of rubidium carbonate and cesium carbonate solution. Step 3: Add phosphotungstic acid to filtrate B at a molar ratio of 1:4 (the sum of the molar numbers of rubidium and cesium), continue stirring for 1 hour, let stand for 1 hour, filter, and separate the solid and liquid to obtain the filtrate and the rubidium-cesium mixed precipitate.

[0038] XRD analysis of the rubidium-cesium mixed precipitate yielded the following results: Figure 3 It can be seen that a phosphorus-containing rubidium-cesium mixed precipitate was obtained, indicating that a reaction was carried out. The composition of the rubidium-cesium mixed precipitate is shown in Tables 7 and 8. Table 7. Composition of rubidium-cesium mixed precipitate (wt% as phosphotungstate) Table 8. Composition of rubidium-cesium mixed precipitate (wt% as elemental) Phosphotungstic acid and its salts can react with cesium and rubidium ions to form cesium phosphotungstate and rubidium phosphotungstate precipitates. The reaction equation is as follows: H3PW 12 O 40 +3Cs ＋ →Cs3PW 12 O 40 ↓+3H + H3PW 12 O 40 +3Rb + →Rb3PW 12 O 40 ↓+3H + Silicotungstic acid and its salts can react with cesium and rubidium ions to form cesium silicotungstate and rubidium silicotungstate precipitates. The reaction equation is as follows: H4SiW 12 O 40 +4Cs ＋ →Cs4SiW 12 O 40 ↓+4H + H4SiW 12 O 40 +4Rb + →Rb4SiW 12 O 40 ↓+4H + Phosphotungstic acid is a heteropolyacid, a giant anionic cluster formed by the central atom (P, Si) and polyacid ligands (tungstate ions) bonded together via oxygen bridges. It possesses a large, negatively charged surface and a defined cavity. It is a large anion with a low charge density; its large size requires bonding with large-radius, low-charge-density cations for a stable crystal lattice. This minimizes lattice energy, resulting in a stable precipitate. For alkali metal ions, the radius order is: Li + < Na + < K + < Rb + < Cs + ;Rb + and Cs + Due to its larger ionic radius and lower hydration energy, it can form salts with extremely low solubility with large heteropolyacid anions; Phosphotungstic acid exhibits extremely high selectivity for cesium and also strong selectivity for rubidium. The resulting cesium / rubidium phosphotungstic acid is an inorganic polymer material with high thermal and chemical stability, making it more stable than tetraphenylborides (organic salts) and less prone to decomposition or oxidation. Compared to sodium tetraphenylboronate, phosphotungstic acid has even stronger selectivity, resulting in products with higher purity.

[0039] The experiment revealed that the lower the amount of phosphotungstic acid used, the lower the yield of rubidium phosphotungstic acid, and the higher the yield of cesium phosphotungstic acid. When the molar ratio of phosphotungstic acid to the sum of the molar numbers of rubidium and cesium was less than 1:4.5, the cesium phosphotungstic acid content in the rubidium-cesium mixed precipitate exceeded that of rubidium phosphotungstic acid. When the molar ratio of phosphotungstic acid to the sum of the molar numbers of rubidium and cesium was 1:5, the cesium phosphotungstic acid content exceeded 64.3 wt%. When the molar ratio of phosphotungstic acid to the sum of the molar numbers of rubidium and cesium was 1:3, the cesium phosphotungstic acid content was less than 16.2 wt%. Meanwhile, the experimental results showed that silicotungstic acid had a similar effect to phosphotungstic acid and could also be used as an alternative.

[0040] Example 4: In this example, the concentration of KCl in the metal ion wastewater is 194 g / L; the concentration of NaCl is 213 g / L; the concentration of CsCl is 27 g / L; and the concentration of RbCl is 13 g / L.

[0041] Methods for extracting rubidium and cesium and separating potassium and sodium include: Step 1: Add zinc salt and potassium ferrocyanide (40-60% of the total amount used, 50% is used in this example) to the metal ion wastewater. Mix evenly at 10℃ (low temperature mixing, commonly 5℃, 10℃, 15℃). Stir for 1 hour at 300 rpm (high speed stirring, commonly 250 rpm, 300 rpm, 350 rpm, 400 rpm). Then raise the temperature to 50℃ (i.e., raise the temperature to 55-65℃), add the remaining zinc salt and potassium ferrocyanide, and stir for 2 hours at 100 rpm (low speed stirring, commonly 75 rpm, 100 rpm, 125 rpm) (the commonly used stirring time is 1-4 hours). Filter and separate to obtain filter residue A and filtrate A. The zinc salt is zinc sulfate heptahydrate. The molar ratio of zinc sulfate heptahydrate to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 2:5, and the molar ratio of potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:2. Step 2: Place filter residue A in a pyrolysis furnace and heat it to 580℃ at 5℃ / min, hold for 2 hours; then heat it to 750℃ at 10℃ / min, hold for 2 hours. The pyrolysis tail gas is treated to meet the standards before being discharged, and then soaked in water at a solid-liquid ratio of 0.2 kg / L for 30 minutes under normal temperature conditions, and filtered to obtain water-leached residue and filtrate B; High-temperature roasting decomposes Cs2ZnFe(CN)6 and Rb2ZnFe(CN)6 into rubidium carbonate, cesium carbonate, iron oxide, zinc oxide, nitrogen, etc. After water leaching, the filtrate B mainly consists of rubidium carbonate and cesium carbonate solution. Step 3: Add sodium tetraphenylborate to filtrate B at a molar ratio of 1:3 to the sum of the molar numbers of rubidium and cesium. Continue stirring for 1 hour, let stand for 2 hours, and then filter. Solid-liquid separation yields filtrate and a mixed rubidium-cesium precipitate. During stirring, sodium tetraphenylborate reacts with filtrate B to form precipitates of rubidium tetraphenylborate and cesium tetraphenylborate. After standing, the precipitate particles aggregate to facilitate filtration. The composition of the mixed rubidium-cesium precipitate is shown in Tables 9 and 10. Table 9. Composition of rubidium-cesium mixed precipitate (wt% as tetraphenylborane) Table 10. Composition of rubidium-cesium mixed precipitate (wt% based on elemental composition) The synergistic effect of temperature-group precipitation (10℃ low-temperature stage and 50℃ high-temperature stage) and stepwise pyrolysis (580℃+750℃) significantly improved the selectivity and purity of rubidium and cesium precipitation. Compared with Example 1, the enrichment effect of cesium was more significant, while potassium and sodium impurities were completely removed.

[0042] Under low-temperature conditions, the precipitation reaction kinetics are slower, but the resulting crystal nuclei are finer and more uniform. The ferrocyanide precipitate formed in this stage has a higher specific surface area and more crystal defects, making it easier to decompose in subsequent pyrolysis. Increasing the temperature accelerates the precipitation reaction rate, which is beneficial for crystal growth and maturation. The precipitate formed in this stage has higher crystallinity, a more complete structure, and better thermal stability. Through precise temperature control and pyrolysis program design, the selectivity of the cubic cavity of ferrocyanide ions for rubidium and cesium ions is fully utilized. The bridging effect of zinc ions forms a more stable coordination structure under optimized temperature conditions, effectively repelling the co-precipitation of potassium and sodium ions. Stepwise pyrolysis ensures the complete decomposition of cyanide ions; the first stage gently decomposes most of the cyanide ions, while the second stage oxidizes the remaining cyanide ions at high temperature, resulting in more thorough tail gas treatment and significantly improved environmental friendliness. The obtained rubidium and cesium mixed precipitate has higher purity, with a cesium content of 20.98%, providing high-quality raw materials for subsequent cesium resource extraction. Simultaneously, potassium and sodium resources in filtrate A are also efficiently separated and purified, achieving resource utilization of all components of the wastewater.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater, characterized in that, Includes the following steps: S1: Add zinc salt and potassium ferrocyanide to wastewater rich in Group I metal ions, mix well, stir for 1-2 hours, and then filter to separate the residue A and filtrate A. S2: Calcine filter residue A at 650-750℃ for 1-3 hours, then leach it with water at room temperature for 20-40 minutes, and filter to obtain water-leached residue and filtrate B; S3: Add the rubidium and cesium precipitant to filtrate B, stir for 1-1.5 hours, let stand, filter and separate to obtain a mixed rubidium and cesium precipitate; S4: Evaporate and concentrate filtrate A at 80-100℃ to 30-40% of its volume to precipitate crystals, filter while hot, and separate solid and liquid to obtain hot filtrate C and hot crystals; cool hot filtrate C to room temperature and crystallize for 1-3 hours to obtain cool filtrate and crude potassium chloride. S5: Add the hot crystallizer to the cooled filtrate at a solid-liquid ratio of 0.1-0.8 kg / L, stir at a temperature greater than 80°C for at least 30 min, and then filter while hot to obtain crude sodium chloride and hot filtrate B. S6: After the hot filtrate B is cooled to room temperature and allowed to stand for 0.5-5 hours, it is filtered to obtain filtrate D and crude potassium chloride; S7: Dissolve crude potassium chloride and crude sodium chloride in water at a solid-liquid ratio of 1:2 to 1:5, evaporate 40% to 60% of their volume, and then cool and crystallize for 6 to 12 hours to obtain high-purity potassium chloride and sodium chloride.

2. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, The zinc salt is zinc sulfate heptahydrate or zinc chloride.

3. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, The molar ratio of the zinc salt to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:4-2:

5.

4. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, The molar ratio of potassium ferrocyanide to the sum of the molar numbers of rubidium and cesium in the metal ion wastewater is 1:4-1:

2.

5. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, The precipitant is sodium tetraphenylborate, phosphotungstic acid, or silicotungstic acid.

6. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 5, characterized in that, The molar ratio of sodium tetraphenylborate to the sum of the molar numbers of rubidium and cesium is 1:4 to 1:

3.

7. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 5, characterized in that, The molar ratio of the phosphotungstic acid to the sum of the molar numbers of rubidium and cesium is 1:3-1:

5.

8. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, In step S1, zinc salt and potassium ferrocyanide are added to the metal ion wastewater in two batches. The first batch contains 40-60% of the total amount and is mixed evenly at 5-15℃. After mixing at 250-400 rpm for 0.5-2 hours, the temperature is raised to 50℃, and the remaining zinc salt and potassium ferrocyanide are added. The mixture is stirred at 75-125 rpm for 1-4 hours and then filtered to separate the residue A and filtrate A.

9. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 8, characterized in that, In step S2, the calcination is a stepped calcination, first raising the temperature to 580-650℃ at a rate of 5-10℃ per minute and holding it for 1-2 hours, then raising the temperature to 700-750℃ at a rate of 10-20℃ per minute and holding it for 1-2 hours.

10. The method for extracting rubidium and cesium and separating potassium and sodium from metal ion wastewater as described in claim 1, characterized in that, In step S7, preferably, crude potassium chloride and crude sodium chloride are dissolved in water at a solid-liquid ratio of 0.1-0.8 kg / L, evaporated by 40-60% of their volume, and then cooled and crystallized for 6-12 hours to obtain high-purity potassium chloride and sodium chloride.

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