A method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum.

Abstract

This invention belongs to the field of hydrometallurgy, specifically relating to a method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum. The steps include: a first carbon fractionation; introducing a carbon dioxide atmosphere into the alkaline solution containing potassium, sodium, and aluminum for the first carbon fractionation treatment, followed by solid-liquid separation to obtain a first potassium-rich solution and a first sodium-aluminum-rich slag; a second carbon fractionation; continuing to perform a stepwise carbon fractionation treatment on the potassium-rich solution using a carbon dioxide atmosphere, wherein, according to the changes in Na and Al concentrations in each carbon fractionation stage, a NaAl regulator is added to control the Na / Al molar ratio in the system to be 1.15~1.35:1; separating, collecting, and combining the solids separated from each carbon fractionation stage to obtain a second sodium-aluminum-rich slag; and combining the second sodium-aluminum-rich slag and the first sodium-aluminum-rich slag to obtain sodium-aluminum slag; the solution separated after the final carbon fractionation stage is a potassium-rich solution with separated sodium and aluminum. This invention can achieve selective separation of potassium, sodium, and aluminum based on precipitation.

Description

Technical Field

[0001] This invention belongs to the field of hydrometallurgy and resource recycling technology, specifically relating to the treatment of alkaline mixed leachate containing potassium, sodium and aluminum. Background Technology

[0002] After extracting potassium from potassium-rich slate, potassium feldspar, nepheline, and other potassium-bearing ores using a high-temperature, high-pressure subtractive hydrothermal process with potassium salts and potassium alkali as additives, the typical composition of the resulting alkaline mixed leachate is: K + Concentration of 20,000~50,000 ppm, Na + Concentration of 5000~10000 ppm, Al element (as Al(OH)4) - (Existing in its original form) The concentration is 5000~10000ppm, and the pH value is approximately 11.0~14.0.

[0003] For alkaline mixed leachates containing potassium, sodium, and aluminum, the conventional separation method is as follows: first, aluminum is recovered from the leachate through carbonation decomposition using CO2, and then potassium carbonate and sodium carbonate in the carbon residue are separated through multiple evaporation and crystallization processes. However, this separation pathway has several problems:

[0004] 1. Carbonation decomposition (carbon fraction) for aluminum recovery is subject to numerous limitations (solution ion concentration, pH value, etc.). This method is unsuitable for solutions with excessively high or low aluminum concentrations. The core principle of preparing gibbsite (Al(OH)3) or pseudoboehmite (AlOOH) via carbonation decomposition lies in using CO2 as a precipitant. By precisely controlling parameters such as pH, temperature, and reaction time, the hydrolysis-precipitation behavior of aluminate ions is regulated in stages, ultimately leading to the formation of the target phase. For gibbsite, the endpoint pH must be precisely controlled between 10.0 and 10.8 (e.g., pH≈10.5), and carbon fractionation should be carried out at 70–90°C. At this temperature, the main reaction is: 2[Al(OH)4]. - +CO2→2Al(OH)3↓+CO3 2- +H₂O, aluminum precipitates efficiently in the form of gibbsite (precipitation rate >90%), but the limiting factor is that the sodium content in the gibbsite product is difficult to control, and the sodium content increases during the precipitation process. +It can be entrained in the form of adsorption or encapsulation, requiring high-temperature crystallization to reduce adsorption, and combined with efficient countercurrent washing to obtain a low-sodium (Na2O<0.05%) product. Meanwhile, excessively rapid carbonization can easily produce fine crystals or colloids, leading to filtration difficulties. For boehmite, a two-step "carbonization-hydrothermal aging" method is required: first, rapid carbonization at higher pH and temperature generates a highly active amorphous Al(OH)3 precursor, followed by hydrothermal aging in a closed reactor at 90~150℃ to promote the transformation of the amorphous phase into crystalline γ-AlOOH. The main limitation of this route is the harshness of the aging conditions; the temperature, time, pH, and stirring intensity must be precisely matched during the process, otherwise a mixed phase of gibbsite and boehmite can easily be obtained. At the same time, the presence of potassium and sodium ions during the aging process may interfere with crystal growth kinetics, resulting in substandard product morphology or pore structure.

[0005] 2. The alkaline leachate after carbonation is a mixed solution of sodium carbonate and potassium carbonate. In industry, evaporation crystallization is commonly used to separate potassium carbonate and sodium carbonate. However, this process involves multiple evaporation steps, is time-consuming and energy-intensive, and has low production efficiency. The initial K / Na ratio of the leachate is low (e.g., in the leachate from a potassium feldspar extracted using KOH-Ca(OH)2 hydrothermal method, the K and Na concentrations are 31000 ppm and 7300 ppm respectively, with K / Na = 4.25). During multi-stage evaporation-cooling crystallization to separate potassium and sodium, the solubility of sodium carbonate (21.5 g / 100 mL) and potassium carbonate (110.0 g / 100 mL) overlaps at 25°C. Even after 3-4 cycles, the K / Na ratio only increases to 15-20, making complete separation of potassium carbonate and sodium carbonate difficult. Potassium carbonate recovery and purity cannot be simultaneously achieved, and the energy consumption for a single evaporation reaches 800-1000 kW·h / t leachate, accounting for over 60% of the total energy consumption of the entire process.

[0006] Existing technologies cannot simultaneously meet the targets of "high aluminum precipitation rate (>95%), high sodium precipitation removal rate (>90%), and low potassium loss rate (<3%)", resulting in problems such as low separation efficiency, complex processes, and high energy consumption. Therefore, there is an urgent need to develop a new method for treating different potassium, sodium, and aluminum alkaline leachates by synergistically regulating the behavior of potassium, sodium, and aluminum. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum, aiming to achieve selective separation of aluminum, potassium, and sodium based on a carbon fractionation-step-sequence series precipitation method.

[0008] A method for separating metal elements from an alkaline solution containing potassium, sodium, and aluminum, comprising the following steps;

[0009] Step 1: First carbon component:

[0010] A carbon dioxide atmosphere is introduced into an alkaline solution containing potassium, sodium, and aluminum to perform the first carbon fractionation treatment, followed by solid-liquid separation to obtain the first potassium-rich solution (also known as the liquid after the first carbon fractionation) and the first sodium-rich aluminum slag.

[0011] Step 2: Second carbon component:

[0012] The potassium-rich solution was further subjected to stepwise carbon separation treatment using a carbon dioxide atmosphere. In each step of the carbon separation treatment system, NaAl regulator was added and the Na / Al molar ratio in the system was controlled to be 1.15~1.35:1.

[0013] Subsequently, the solids separated from each stage of carbon fractionation were separated, collected, and combined to form the second sodium-rich aluminum slag; and the second sodium-rich aluminum slag and the first sodium-rich aluminum slag were combined to obtain sodium-aluminum slag.

[0014] The solution separated after the final stage of carbon fractionation is a potassium-rich solution for separating sodium and aluminum.

[0015] The NaAl regulator is a water-soluble salt that can provide Na and / or Al elements.

[0016] For alkaline solutions containing potassium, sodium, and aluminum, existing metallurgical approaches involve selectively precipitating aluminum to enrich sodium and potassium in the solution, followed by separation of sodium and potassium through evaporation. However, this invention offers a novel approach that precipitates sodium and aluminum together, achieving selective precipitation separation of sodium and potassium. Early research revealed that this novel selective precipitation separation approach needs to overcome the problem of unsatisfactory sodium and potassium precipitation selectivity. To address this issue, this invention innovatively provides a combined treatment scheme involving a pre-treatment of carbon fractionation followed by a stepwise carbon fractionation process with the addition of a NaAl regulator. This achieves process synergy, resolving the issue of low selectivity in sodium and potassium precipitation separation inherent in this novel approach, enabling selective precipitation separation of potassium and sodium / aluminum, thus facilitating the acquisition of high-quality potassium. Furthermore, it allows for selective separation of sodium and aluminum in a simple manner. This invention achieves selective separation of potassium, sodium, and aluminum based on a precipitation process, possessing significant industrial application value.

[0017] In this invention, there are no special requirements for the elemental concentrations of the alkaline solution containing potassium, sodium, and aluminum. For example, as an optional scheme, K + Concentration of 20,000~50,000 ppm, Na + Concentration of 5000~10000 ppm; Al(OH)4 - Concentrations range from 5000 to 10000 ppm; initial pH (pH0) = 11.0 to 14.0. Furthermore, K... + Concentration of 30,000~50,000 ppm, Na +Concentration of 6500~8500ppm; Al(OH)4 - The concentration is 6000~8000ppm; the initial pH value (pH0) is 13.0~13.5.

[0018] In this invention, the alkaline solution containing potassium, sodium, and aluminum is pre-treated by a filtration device with an accuracy of P=0.1~0.5μm for solid-liquid separation before the first carbon fractionation.

[0019] In this invention, the carbon dioxide-containing atmosphere can be pure carbon dioxide or a mixture of carbon dioxide and a diluent gas. Furthermore, the carbon dioxide content in the carbon dioxide-containing atmosphere can be above 50% (v%).

[0020] In this invention, in step 1, the CO2 introduction rate V CO2 =5~8L / min·m 3 Solution.

[0021] The temperature for the first stage of carbon separation is 55~85℃; preferably 60~80℃; and more preferably 75±5℃. Studies have found that at this preferred temperature, it can be combined with other processes to further optimize the selective separation of sodium and potassium.

[0022] The final pH for the first stage of carbon separation is 8.2–9.2, which can be further reduced to 8.5–9; and even further reduced to 8.8–9. At the preferred pH, better separation efficiency and effect of sodium, aluminum, and potassium can be achieved.

[0023] In this invention, once the pH of the carbon system reaches the endpoint pH, aging can be selectively continued as needed. There are no special requirements for the aging time, for example, it can be 10 to 50 minutes; considering the processing efficiency, it can be further 20 to 30 minutes.

[0024] In this invention, the aluminum content in the first potassium-rich solution after the first carbon fraction is preferably controlled below 100 ppm, and more preferably 30 to 60 ppm; in addition, the sodium concentration therein can be 2000 to 4000 ppm.

[0025] In this invention, after the first carbon fractionation, the first potassium-rich solution undergoes a subsequent gradient carbon fractionation treatment, which is expected to further achieve selective precipitation and separation of potassium, sodium, and aluminum.

[0026] In this invention, the Na element in the gradient carbon solution system can be measured, and then, based on the Na content in the solution and the Na / Al requirement of the gradient precipitation of this invention, the NaAl regulator is added to achieve selective removal of Na.

[0027] In this invention, when there is a need to replenish Al during the gradient precipitation process, the NaAl regulator can be potassium aluminate. When there is a need to replenish Na during the gradient precipitation process, the NaAl regulator can be sodium chloride, sodium nitrate, etc.

[0028] In this invention, in step 2, the CO2 introduction rate V in each stage of the carbon fractionation process... CO2 =5~8L / min·m 3 Solution;

[0029] The temperature for each carbon fraction is 55~85℃; preferably 60~80℃; and more preferably 75±5℃. Studies have found that at this preferred temperature, it can be combined with other processes to further optimize the selective separation of sodium and potassium.

[0030] The final pH for each carbon fraction is 8.2–9.2, and can be further set to 8.5–9; even further set to 8.8–9. Optimal pH values ​​contribute to better separation efficiency and effectiveness of sodium, aluminum, and potassium.

[0031] After reaching the endpoint pH during each stage of carbon fractionation, aging treatment can be carried out as needed, for 10-50 minutes; considering processing efficiency, it can be further extended to 20-30 minutes.

[0032] In this invention, in step 2, during each stage of carbon separation, the Na / Al molar ratio of the added NaAl regulator and the solution (referring to the solution to be treated at each stage, such as a potassium-rich solution or the liquid separated after the previous stage of carbon separation) is 1.2~1.3:1. Studies have found that at the preferred Na / Al molar ratio, it can be combined with other processes to further optimize the selective separation effect of sodium and potassium.

[0033] In this invention, in step 2, the carbon fraction is carried out in stages until the sodium content in the potassium-rich solution is less than 150 ppm and the aluminum content is less than 50 ppm.

[0034] In this invention, the graded carbon fractionation includes an N-stage series carbon fractionation process, the steps of which are: first potassium-rich solution and NaAl regulator, and carbon dioxide atmosphere are subjected to first-stage carbon fractionation treatment, followed by solid-liquid separation to obtain solid 1 and solution 1;

[0035] Solution 1 and NaAl regulator were subjected to a second-stage carbon fractionation treatment in a carbon dioxide atmosphere, followed by solid-liquid separation to obtain solid 2 and solution 2.

[0036] ...

[0037] The solution N-1 obtained from the solid-liquid separation of the N-1 stage carbon fractionation process, along with NaAl regulator and a carbon dioxide atmosphere, is subjected to the N-1 stage carbon fractionation process, followed by solid-liquid separation to obtain solid N and solution N.

[0038] The solids from the carbon fractionation (solid 1, solid 2... solid N) are combined to form the second sodium-rich aluminum slag. Solution N is the final potassium-rich solution for separating sodium and aluminum.

[0039] In this invention, in step 2, the number of stages in the graded carbon fraction is 2 or more; preferably 2 to 5 stages. That is, N is an integer greater than or equal to 2, and can further be 2 to 5.

[0040] In this invention, potassium, sodium, and potassium can be separated from the potassium-rich liquid and sodium-aluminum slag using known methods.

[0041] For example, as an alternative, the potassium-rich solution can be crystallized to obtain a potassium product. To further improve the quality of the potassium product, the trace amounts of residual aluminum in the potassium-rich solution can be deeply removed as needed. Deep removal processes are generally known.

[0042] For example, sodium-aluminum slag can be electrolyzed to separate electrolytic aluminum and sodium products.

[0043] Another approach to this invention is to acid treat the sodium aluminum slag to obtain boehmite and sodium solution.

[0044] Beneficial effects

[0045] This invention innovatively provides a novel selective precipitation separation approach that precipitates sodium and aluminum together, allowing for their selective separation from potassium. To better implement this technical approach, the invention pre-treatment of an alkaline solution containing sodium, potassium, and aluminum with a first carbon fractionation, followed by the addition of a NaAl regulator for a stepwise carbon fractionation process. This achieves process synergy, solving the problem of low selectivity in the precipitation separation of sodium, potassium, and aluminum inherent in this novel approach. It enables selective precipitation separation of potassium and sodium / aluminum, facilitating the acquisition of high-quality potassium. Furthermore, it allows for selective separation of sodium and aluminum using a simple method. This invention achieves selective separation of potassium, sodium, and aluminum based on a precipitation process, possessing significant industrial application value.

[0046] Compared with the conventional "carbon fractionation-multi-stage evaporation and crystallization" method, the method used in this invention only requires one concentration and crystallization to obtain high-purity potassium carbonate, avoiding the energy and time consumption of multiple rounds of evaporation and crystallization.

[0047] This invention can be adapted to laboratory reaction vessels, rotary evaporators, industrial multi-effect evaporators, continuous centrifuges, etc., without the need for customized high-pressure or vacuum equipment, and the transition to pilot testing is smooth. The parameters are easy to control during the process, and the continuous operation is highly stable, making it suitable for large-scale production.

[0048] This invention uses CO2 as a precipitant, which has a high utilization rate and realizes carbon fixation and resource utilization. Attached Figure Description

[0049] Figure 1 This is a schematic diagram of the process flow of the present invention;

[0050] Figure 2 The XRD patterns are of the carbon fraction product (labeled as carbon fraction) from step 1 of Example 1 and the product obtained from the step-by-step precipitation in step 2.

[0051] Figure 3 The image shown is a SEM-EDS image of K2CO3 obtained in Example 1, where "K2CO3 crystals" refers to the SEM image; "K", "Na", "Al" and "O" refer to their respective elemental EDS distribution images. Detailed Implementation

[0052] To better understand the present invention, the following embodiments are provided to further illustrate the content of the present invention, but the content of the present invention is not limited to the following embodiments.

[0053] This invention employs a carbonation decomposition method. By adjusting solution parameters and adding an additional aluminum source based on the actual concentration of the leachate, sodium and aluminum are simultaneously recovered from the leachate. After carbonation, only potassium ions remain in the solution, which can be recovered through simple evaporation and crystallization. This avoids the large amount of heat energy consumed by conventional methods that require multiple evaporation and crystallization processes to separate potassium carbonate and sodium carbonate. The use of an external aluminum source for stepwise precipitation control during the carbonation decomposition process not only overcomes the limitations imposed by leachate concentration and pH on product type and properties but also improves sodium and aluminum recovery rates and reduces the difficulty of subsequent potassium and sodium separation. To achieve the above objectives, this invention provides a method for the efficient separation and extraction of aluminum, sodium, and potassium from complex alkaline mixed leachates containing potassium, sodium, and aluminum.

[0054] An optional method of implementation of the present invention includes the following steps:

[0055] Step (1): Leachate pretreatment

[0056] The alkaline mixed leachate is filtered to remove impurities and its pH is adjusted to ensure the stability of subsequent reactions.

[0057] In this invention, there are no special requirements for the concentrations of potassium, sodium, and aluminum in the alkaline mixed leachate to be treated in step (1). For example, K + Concentration C K Within the range of 20,000 to 50,000 ppm, Na + Concentration C Na Al(OH)4 can be found in the range of 5000~10000 ppm. - Concentration C Al It is applicable to leachates with a concentration range of 5000~10000ppm and an initial pH value of pH0=11.0~14.0, as long as the component range or concentration is close to this range.

[0058] In this invention, step (1) uses a filtration device with a precision of P=0.1~0.5μm to perform solid-liquid separation, remove suspended particles such as aluminosilicates or calcium carbonate in the leachate, and avoid particle encapsulation and precipitation that affects the separation effect.

[0059] Step (2): Carbonation decomposition

[0060] In a reactor equipped with a stirrer, online pH monitoring and CO2 metering device, and a bubble disperser, sodium and aluminum are simultaneously recovered through a carbonation reaction, achieving efficient precipitation of aluminum and preliminary removal of sodium.

[0061] In this invention, the reactor volume used in step (2) can be adapted to 0.2L~1m³. 3 It meets the needs of laboratory research and pilot production, with no special parameter restrictions.

[0062] In this invention, step (2) heats the pretreated leachate to T1=75±5℃. This temperature range can ensure the purity of diatomite and avoid prolonged reaction time due to excessively low temperature and the generation of gibbsite impurities due to excessively high temperature.

[0063] In this invention, the stirring speed F1 in step (2) is 200~500 rpm to ensure that CO2 and leachate are in full contact.

[0064] In this invention, step (2) CO2 introduction rate V CO2 =5~8L / min·m 3 leachate;

[0065] In this invention, the endpoint of carbonation decomposition of the leachate in step (2) is pH = 8.2~9.2, and CO2 is stopped after reaching this pH.

[0066] In this invention, preferably, the endpoint pH of carbonation decomposition in step (2) is 8.7~9.0.

[0067] In this invention, after stopping the aeration in step (2), the temperature and stirring are maintained, and the aging time t1 = 30~60 minutes;

[0068] In this invention, preferably, t1 = 45 ± 5 minutes in step (2).

[0069] In this invention, step (2) uses centrifugation or filtration to separate solid and liquid, resulting in leachate A (a potassium-rich solution with Al(OH)4- < 55 ppm) and aluminum slag A (a sodium-rich aluminum slag, whose main components are diatomite and boehmite, with Al2O3 content > 65%).

[0070] Step (3): Gradient multi-stage precipitation

[0071] Based on Na in leachate A +With Al(OH)4 - Add soluble aluminum or sodium salts at specific concentration ratios to perform multi-stage gradient precipitation, minimizing the removal of K. + Under the premise of gradually removing the remaining Na + After adding soluble aluminum or sodium salts, CO2 is introduced into the solution, and the temperature, stirring, and gas introduction parameters are kept consistent with those in step (2).

[0072] In this invention, the concentration C of the soluble aluminum salt solution used in step (3) is... Al =0.4~0.6mol / L. This concentration can ensure the sodium removal efficiency of each precipitation stage, avoiding the need for excessive solution volume due to too low a concentration and excessive aluminum residue due to too high a concentration.

[0073] In this invention, after each stage of precipitation in step (3) is completed, centrifugation or filtration is used for separation.

[0074] In this invention, step (3) involves determining the sodium ion concentration [Na] in the leachate A obtained in step (2). + 1. According to the amount of aluminum added, n [Na+]1 :n [Al3+] Add soluble aluminum salt to the first mother liquor at a ratio of 1.2~1.3:1 (molar ratio of sodium to aluminum). After stirring evenly, introduce CO2 at T2=75±5℃ for a second carbonation precipitation. The reaction time is t2=20~50 minutes. After aluminum ions are completely precipitated, separate the solid and liquid to obtain the second precipitate and the second mother liquor. Repeat the above operation of "measuring the sodium and aluminum ion concentrations in the mother liquor - adding soluble aluminum or sodium salts in proportion - carbonation precipitation - solid-liquid separation". The reaction temperature is 75±5℃ each time, and the reaction time of each subsequent carbonation precipitation is shortened by 5-10 minutes compared with the previous one. Repeat the operation until the sodium and aluminum ion concentrations in the mother liquor are both lower than the specified threshold.

[0075] Preferably, the total number of precipitation steps can be adjusted reasonably as needed. For example, the number of precipitation steps can be determined by controlling the content of Al and Na in the last stage solution. Considering the treatment efficiency, the number of precipitation steps can be 2 to 5.

[0076] In this invention, step (3) combines the precipitates at each stage to obtain aluminum slag B (Al2O3 content > 60%), and finally obtains leachate B (Al(OH)4). - <55ppm).

[0077] Step (4): Remove trace aluminum impurities from leachate B and purify it by potassium carbonate crystallization to obtain a high-purity potassium product.

[0078] In this invention, step (4) involves placing the leachate B in an environment of T3=25±5℃ and letting it stand for t3=1~3 hours;

[0079] In this invention, preferably, t3 = 2 hours in step (4);

[0080] In this invention, step (4) uses a precision P m A microfiltration membrane with a diameter of 0.1~0.2μm was used to filter the solution after it had been left to stand.

[0081] In this invention, step (4) uses evaporation equipment (laboratory rotary evaporator, expanded use multi-effect evaporator) to control the evaporation temperature T4=80±5℃ and the vacuum degree P. V = -0.08 to -0.09 MPa (if evaporating at normal pressure, adjust the temperature to 100±5℃), concentrate the solution to a K2CO3 concentration of C. K2CO3 =45~50wt.%;

[0082] In this invention, step (4) involves cooling the concentrate to T5 = 25~30°C and letting it stand for t4 = 3~4 hours to allow potassium carbonate to fully precipitate.

[0083] In this invention, step (4) involves solid-liquid separation by filtration or centrifugation, washing the crystals with deionized water 1-2 times, and drying them at T6=105℃ to ensure product purity >98% (compliant with GB / T1587-2021 Grade 1 standard).

[0084] Step (5): Process the separated aluminum slag to achieve high-value recovery of aluminum resources.

[0085] In this invention, step (5) involves merging aluminum slag A and aluminum slag B, and removing residual K from the surface by water washing. + Na + Dry at T7 = 105~110℃;

[0086] In this invention, if the Al2O3 content of the aluminum slag after drying is >62% in step (5), it can be used directly as a raw material for electrolytic aluminum, or high-purity boehmite (purity >98%) can be prepared by acid dissolution and recrystallization process. There are no special parameter restrictions, and the utilization path can be selected according to actual needs.

[0087] Example 1

[0088] Raw material: Potassium feldspar hydrothermal extraction potassium leachate, composition: K + 31000ppm, Na + 7000ppm, Al 3+ 6800ppm, pH=13.5; 1L was used for the experiment.

[0089] Step 1: Carbon Separation. Add 1 L of leachate to a 1.5 L reactor. Set the stirring speed to 250 rpm. Heat the leachate to 75 °C under stirring. The CO2 introduction rate is 6 L / min·m. 3The leachate was subjected to real-time pH monitoring. CO2 was bubbled through the leachate until the pH decreased and stabilized at 9.0, then the solution was stirred and aged for 45 minutes. The leachate was then centrifuged to obtain leachate A 0.95 L (K). + 32442ppm, Na + 3664ppm, Al 3+ The potassium loss rate was 0.58%, the sodium precipitation rate was 50.27%, and the aluminum precipitation rate was 99.19%. (58 ppm) and aluminum slag A (19.456 g, Al2O3 content was 65.50%) were added.

[0090] Step 2: Gradient 3-stage precipitation (KAlO2 solution concentration: 0.5 mol / L). The precipitation temperature for each stage was 75℃, and the stirring speed was set to 250 rpm. After adding the KAlO2 solution, the solution was stirred and stabilized for 5 minutes before CO2 was introduced (introduction rate: 6 L / min·m). 3 (Leachate), the results are shown in Table 1.

[0091]

[0092] Note: Aging time refers to the continued treatment time after the endpoint pH is reached.

[0093] After steps (1) and (2), the cumulative precipitation rate of sodium was 98.95%; by combining aluminum slag B (14.407 g, Al2O3 65.30%), approximately 1.2 L (K) of leachate B was obtained. + 25200ppm, Na + 61ppm, Al 3+ 1.5ppm).

[0094] Step 3: Removal of aluminum impurities and evaporation crystallization. After standing for 2 hours, the solution was microfiltered with a precision of 0.1 μm. The filtrate was then rotary evaporated at 80℃ and -0.085 MPa until the K2CO3 concentration was approximately 50 wt.%. Heating was then stopped, and the solution was allowed to cool naturally to room temperature and stand for 3.5 hours to allow the K2CO3 to crystallize fully. The solution was then filtered using a Buchner funnel and washed 1-2 times with cold ultrapure water. The crystals were collected and dried at 105℃ to obtain potassium carbonate crystals (53.41 g, purity 98.5%), with a recovery rate of 97.69%.

[0095] Step 4: Aluminum slag resource utilization. Aluminum slag A and aluminum slag B were combined, washed and dried, and tested to find that the Al2O3 content was 65.42%, which meets the standards for electrolytic aluminum raw materials.

[0096] Example 2

[0097] Compared with Example 1, the difference is that the final pH of carbonization in step 1 is 8.7, the carbonization temperature is 60°C, and the potassium loss rate is 0.43%, the sodium precipitation rate is 49.26%, and the aluminum precipitation rate is 98.38%.

[0098] Example 3

[0099] Compared with Example 1, the reaction parameters for each step were set the same, but the raw material concentration was different. The raw material was a potassium leaching solution obtained by hydrothermal extraction of potassium feldspar in a certain region, with the following composition: K + 45000ppm, Na + 8000ppm, Al 3+ 7500ppm, pH=13.2, take 500 ml for the test.

[0100] Step (1) After carbonization, the leachate A is obtained at 0.475 L (K). + 47120ppm, Na + 3910ppm, Al 3+ 64ppm) and aluminum slag A (10.263g, Al2O3 content 65.55%), in this step the potassium loss rate was 0.55%, the sodium precipitation rate was 51.20%, and the aluminum precipitation rate was 99.23%; after steps (1) and (2), the cumulative sodium precipitation rate was 99.26%; combined with aluminum slag B (7.894g, Al2O3 content 65.35%), about 0.6L (K) of leachate B was obtained. + 37800ppm, Na + 68ppm, Al 3+ 2.0ppm); Step (3) obtained 39.86g of potassium carbonate crystals with a purity of 98.6% and a recovery rate of 98.27%; Step (4) combined aluminum slag A and B, washed and dried, and the Al2O3 content was found to be 66.45%.

[0101] Example 4

[0102] Compared with Example 1, the difference lies in the CO2 introduction rate V in steps (1) and (2). CO2 =7L / min·m 3 The leachate, and in step (2) during the stepwise precipitation, potassium aluminate solution is added to adjust the Na / Al ratio of each precipitate to 1.3:1.

[0103] Step 1: After carbonization, the leachate obtained is 0.95L (K). + 32433ppm, Na + 3384ppm, Al 3+ 47ppm) and aluminum slag A (19.5g, Al2O3 content 65.50%), in this step the potassium loss rate was 0.61%, the sodium precipitation rate was 54.08%, and the aluminum precipitation rate was 99.35%.

[0104] Step 2: Gradient 3-stage precipitation (KAlO2 solution concentration is 0.5 mol / L), and the precipitation data for each stage are shown in Table 2.

[0105]

[0106] After steps (1) and (2), the cumulative precipitation rate of sodium was 98.60%; by combining aluminum slag B (13.2g, Al2O3 content 65.30%), approximately 1.15L (K) of leachate B was obtained. + 26800ppm, Na + 85ppm, Al 3+ 1.5ppm).

[0107] Step 3: After evaporation, concentration and drying, potassium carbonate crystals (58.5g, purity 98.5%) were obtained, with a recovery rate of 97.9%.

[0108] Step 4: Combine aluminum slag A and aluminum slag B, wash with water and dry. After testing, the Al2O3 content is found to be 65.41%.

[0109] Example 5

[0110] Compared with Example 1, the difference is that step (2) involves a two-stage gradient precipitation, and the temperature of steps (1) and (2) is 60°C. The reaction time of step (1) is 50 min, and the reaction time of each precipitation stage in step (2) is also extended accordingly.

[0111] Step 1: After carbonization, the leachate obtained is 0.95L (K). + 32436ppm, Na + 3426ppm, Al 3+ 57ppm) and aluminum slag A (19.45g, Al2O3 content 65.50%), in this step the potassium loss rate was 0.60%, the sodium precipitation rate was 53.50%, and the aluminum precipitation rate was 99.20%.

[0112] Step 2: Gradient two-stage precipitation (KAlO2 solution concentration is 0.5 mol / L), and the precipitation data for each stage are shown in Table 3.

[0113]

[0114] After steps (1) and (2), the cumulative precipitation rate of sodium was 98.91%; by combining aluminum slag B (12.22 g, Al2O3 content 65.30%), approximately 1.265 L (K) of leachate B was obtained. + 28000ppm, Na + 68ppm, Al 3+ 1.5ppm).

[0115] Step 3: After evaporation, concentration and drying, potassium carbonate crystals (60.91g, purity 98.5%) were obtained, with a recovery rate of 97.75%.

[0116] Step 4: Combine aluminum slag A and aluminum slag B, wash and dry them, and test the Al2O3 content to find that it is 65.41%, which meets the standard for electrolytic aluminum raw materials.

[0117] Comparative Example 1 (Conventional carbon fraction – multi-stage evaporation crystallization)

[0118] Compared with Example 1, the difference is that carbon fractionation is performed only in step (1), step (2) does not involve step-by-step precipitation, and the evaporation crystallization in step (3) should be the multi-stage evaporation crystallization separation of potassium and sodium commonly used in industry. The leachate A obtained in step (1) was evaporated and concentrated at 80°C and -0.085 MPa to a K2CO3 concentration of about 50 wt.%, then heating was stopped, cooled to room temperature, and allowed to stand for 3-4 hours before solid-liquid separation was performed to obtain the first batch of potassium carbonate crystals (28.5 g, purity 94.2%). The mother liquor was evaporated and cooled again for crystallization, and this process was repeated 3 times, resulting in a total mass of 47.8 g of potassium carbonate crystals, a total recovery rate of 96.3%, and an average purity of 95.1%. During the evaporation crystallization process, about 14.03% of the sodium was co-precipitated as sodium carbonate. The sodium removal rate was 64.3% (50.27% + 14.03%), the aluminum precipitation rate was 99.19%, and the potassium loss rate was 3.70%.

[0119] Comparative Example 2 (the second carbon fraction is a single-segment carbon fraction)

[0120] Compared with Example 1, the only difference is that step 2 does not involve a step-by-step treatment. That is, the same amount of potassium aluminate and carbon dioxide as in step 2 of Example 1 are mixed with the solution for a single carbon fractionation treatment. All other operations and parameters are the same as in Example 1.

[0121] The results of step 2 were as follows: the precipitation rate of sodium was 32.47%, the precipitation rate of aluminum was 99.50%, and the potassium loss rate was 12.68%; aluminum slag B (17.06 g, Al2O3 content 54.28%) and leachate B (approximately 1.265 L, K) were obtained. + 25870ppm, Na + 918ppm, Al 3+ 18.7 ppm); In steps (1) and (2), the total precipitation rate of sodium was 82.47%, and the total loss rate of potassium was 13.26%.

[0122] Step 3: Obtain potassium carbonate crystals (54.74g, purity 91.5%, doped with sodium carbonate), potassium recovery rate 99.8%.

[0123] Step 4: Combine aluminum slag A and aluminum slag B, wash with water and dry. After testing, the Al2O3 content is found to be 60.30%.

[0124] Comparative Example 3 (No NaAl regulator added during the second carbon fractionation process)

[0125] Compared to Example 1, the only difference is that potassium aluminate was not added in step 2; all other operations and parameters were the same as in Example 1. The results show that selective separation of sodium and potassium is essentially impossible.

[0126] Conclusions and Effects Analysis

[0127] This invention provides an integrated method for the efficient separation and recovery of potassium, sodium, and aluminum from alkaline mixed leachates. By combining carbonation decomposition, gradient precipitation, and evaporation crystallization, it achieves high-purity potassium recovery, deep removal of sodium, and high-value utilization of aluminum. This method boasts significant advantages such as high separation efficiency, low energy consumption, simple operation, and strong adaptability, providing a reliable technical solution for the comprehensive utilization of potassium-containing mineral leachates and demonstrating significant industrial application prospects.

[0128] The above embodiments are merely examples to clearly illustrate the method of the present invention and are not intended to limit the specific implementation methods. Those skilled in the art can make other variations or modifications based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here; therefore, obvious variations or modifications derived therefrom are still within the protection scope of this invention.

Claims

1. A method for separating metal elements from an alkaline solution containing potassium, sodium, and aluminum, characterized in that, The steps include; Step 1: First carbon component: A carbon dioxide atmosphere is introduced into an alkaline solution containing potassium, sodium, and aluminum for the first carbon fractionation treatment, followed by solid-liquid separation to obtain a first potassium-rich solution and a first sodium-rich aluminum slag; in the alkaline solution containing potassium, sodium, and aluminum, K + Concentration of 20,000~50,000 ppm, Na + Concentration of 5000~10000 ppm; Al(OH)4 - Concentration ranges from 5000 to 10000 ppm; initial pH value is pH0 = 11.0 to 14.

0. In step 1, the CO2 injection rate V CO2 =5~8L / min・m 3 Solution; The temperature for the first stage of carbon separation is 55~85℃; The final pH value of the first carbon fraction is 8.2~9.2; Step 2: Second carbon component: The potassium-rich solution was further subjected to stepwise carbon separation treatment using a carbon dioxide atmosphere. In each step of the carbon separation treatment system, NaAl regulator was added and the Na / Al molar ratio in the system was controlled to be 1.15~1.35:

1. Subsequently, the solids separated by carbon fractionation at each stage were separated to form the second sodium-rich aluminum slag; and the second sodium-rich aluminum slag and the first sodium-rich aluminum slag were combined to obtain sodium-aluminum slag. The solution separated after the last stage of carbon fractionation is a potassium-rich solution in which sodium and aluminum have been separated. The NaAl regulator is a water-soluble salt capable of providing Na and / or Al elements; In step 2, the CO2 injection rate V in each stage of the carbon fractionation process CO2 =5~8L / min・m 3 Solution; The temperature for each carbon fraction is 55~85℃; The final pH values ​​for each carbon fraction were 8.2 to 9.

2.

2. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 1, characterized in that, K + Concentration of 30,000~50,000 ppm, Na + Concentration of 6500~8500ppm; Al(OH)4 - Concentration of 6000~8000ppm; initial pH value of pH0=13.0~13.5; The alkaline solution containing potassium, sodium, and aluminum is pre-treated by a filtration device with an accuracy of P=0.1~0.5μm for solid-liquid separation before the first carbon fractionation.

3. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 1, characterized in that, In step 1, the temperature of the first carbon fraction is 60~80℃; The final pH value of the first carbon fraction is 8.5-9.

4. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 1, characterized in that, In step 2, the temperature of each carbon fraction is 60~80℃; The final pH for each carbon fraction is 8.5-9.

5. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 1, characterized in that, In step 2, during each stage of carbon fractionation, the molar ratio of Na / Al in the solution after adding soluble aluminum or sodium salts is 1.2~1.3:

1.

6. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 1, characterized in that, In step 2, carbon fractionation is carried out until the sodium content in the potassium-rich solution is below 150 ppm and the aluminum content is below 50 ppm.

7. The method for separating metal elements in an alkaline solution containing potassium, sodium, and aluminum as described in claim 6, characterized in that, In step 2, the number of stages in the graded carbon fraction is 2 or more.

8. The method for separating metal elements from an alkaline solution containing potassium, sodium, and aluminum as described in any one of claims 1 to 7, characterized in that, The potassium-rich solution is crystallized to obtain potassium products.

9. The method for separating metal elements from an alkaline solution containing potassium, sodium, and aluminum as described in any one of claims 1 to 7, characterized in that, Sodium-aluminum slag is electrolyzed to separate electrolytic aluminum and sodium products.

10. The method for separating metal elements from an alkaline solution containing potassium, sodium, and aluminum as described in any one of claims 1 to 7, characterized in that, Acid treatment of sodium aluminum slag yields boehmite and sodium solution.

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