Method for extracting potassium from potassium-rich slates
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CENT SOUTH UNIV
- Filing Date
- 2026-05-19
- Publication Date
- 2026-06-23
Smart Images
Figure CN122256706A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of hydrometallurgical technology, specifically relating to potassium extraction. Background Technology
[0002] Potassium is one of the three essential elements for crop growth, and potash fertilizer plays a crucial role in stable and high crop yields. 95% of the world's potash is used for potash fertilizer production. Global potassium resources are highly monopolized, with approximately 70% of natural potassium concentrated in the Northern Hemisphere. The world's main potash producers are Canada, Russia, and Belarus. Potash resources are mainly divided into two categories: water-soluble and insoluble potassium resources. Among these, salt lake brines and soluble potassium deposits are the main raw materials for industrial potassium extraction, serving as two important water-soluble potassium resources.
[0003] The Bayan Obo iron ore deposit boasts hundreds of millions of tons of potassium-rich slate reserves. According to relevant geological surveys, the K2O content in this slate ranges from 9% to 14%, meeting the requirements for industrial utilization of potassium-bearing rocks, classifying it as a super-large potassium resource base. Insoluble potassium-bearing minerals mainly exist in the form of silicates or aluminosilicates, such as glauconite, lenticulite, nepheline, mica minerals, and feldspar. Potassium typically exists as ions in the interstitial spaces of these minerals. The basic principle for extracting potassium from insoluble potassium minerals is to utilize various methods to disrupt the mineral structure, releasing potassium ions to form soluble potassium salts. The main methods include high-temperature roasting-water leaching, alkali decomposition, acid decomposition, and sub-molten salt extraction. The development and utilization of potassium extraction technology from insoluble potassium-bearing ores will promote the development of the potash fertilizer industry and greatly alleviate the supply and demand contradiction of potash fertilizer in many countries, including China, with low potash salt reserves.
[0004] High-temperature roasting uses sodium salts (such as sodium carbonate) or calcium salts (such as calcium chloride, calcium sulfate, calcium carbonate, etc.) as additives, mixed with potassium-containing ores and roasted at 800-1300℃. After leaching the roasted product with water, the potassium extraction rate can reach over 80%. However, this method suffers from high energy consumption, large additive usage, and the generation of secondary solid waste. Acid decomposition involves mixing fluorine-containing additives such as fluorite, hexafluorosilicic acid, or ammonium fluoride with H₂SO₄ or HCl to generate the intermediate product HF. HF, at low temperatures (50-100℃), destroys the structure of insoluble potassium-containing ores, achieving a potassium extraction rate of approximately 90%. However, fluorides are expensive, and the formation of HF requires extremely high corrosion resistance and sealing of the reaction equipment. Furthermore, fluorides pose significant potential hazards to human health and the environment.
[0005] The sub-molten salt method involves placing potassium-bearing ore in a high-concentration alkali metal salt (such as NaOH) solution system at a reaction temperature of 160–250 °C. The solid product is then leached with H₂SO₄ or HCl solution to extract potassium, achieving a potassium extraction rate of approximately 90%. This process consumes a large amount of alkali. Although the molten salt can be recycled, soluble impurities from the potassium-bearing minerals inevitably enter the molten salt, reducing the effectiveness of potassium extraction during recycling. The alkaline decomposition method also uses an alkaline solution as a medium, subjecting the potassium-bearing ore to high-temperature and high-pressure decomposition in a closed reaction vessel to dissolve potassium ions. NaOH, CaCl₂, or Ca(OH)₂ are typically used as additives to decompose the potassium-bearing ore, with reaction temperatures ranging from 150–300 °C, achieving a potassium extraction rate of approximately 90%.
[0006] In addition, existing technologies have developed some liquid-phase potassium extraction methods. For example, Chinese patent document CN103937976A discloses a process for the decomposition and desilication of potassium feldspar to obtain soluble potassium. Specifically, it describes a scheme where potassium feldspar powder, a silica precipitation reagent, and a strong alkaline solution are mixed uniformly at a mass ratio of potassium feldspar powder: silica precipitation reagent: strong alkaline solution = 1:0.1~3:0.2~4, followed by a hydrothermal reaction. The core of this process is to decompose the Si-Al-O framework structure of potassium feldspar using a hydrothermal alkaline method and fix silicon using a calcium-based silica precipitation reagent. Although this technology can effectively extract potassium from potassium feldspar, unlike potassium feldspar, potassium-rich slate has a more complex mineral composition. In addition to potassium feldspar, it also contains potassium-bearing minerals such as biotite and illite. The crystal structure and chemical properties of these minerals differ significantly from potassium feldspar, and potassium feldspar often coexists with potassium minerals, making potassium extraction extremely difficult. The optimal hydrothermal conditions for potassium feldspar may not be suitable for the complete decomposition of biotite, requiring higher temperatures or the addition of other additives. Summary of the Invention
[0007] To address the problem of potassium extraction from potassium-rich slate, this invention provides a method for effectively extracting potassium from potassium-rich slate.
[0008] In addition to potassium feldspar (KAlSi3O8), potassium-rich slate also contains biotite (K(Mg,Fe)3AlSi3O8). 10 (OH,F)2), illite (KAl2(Si3Al)O 10 (OH)2), muscovite (KAl2(AlSi3O) 10The minerals present include various potassium-bearing minerals such as (OH)2, and some are also associated with non-potassium minerals such as quartz and kaolinite. This coexistence of multiple minerals results in diverse potassium occurrence states, including both aluminosilicate and layered silicate (illite) structures. During hydrothermal processes, extracting potassium from other non-feldspar potassium-bearing minerals such as biotite requires simultaneously disrupting their octahedral (Mg / Fe-O) and tetrahedral (Si / Al-O) layers, making the reaction pathway more complex. To address this problem, this invention, after in-depth research, provides the following solution:
[0009] A method for extracting potassium from potassium-rich slate includes:
[0010] Step 1: Low-temperature hydrothermal
[0011] Potassium-rich slate was subjected to low-temperature hydrothermal treatment at temperature T1 to obtain leachate A and leachate residue A; in the low-temperature hydrothermal system, the Ca / Si weight ratio was controlled at 2.2~3.0; and the temperature T1 was 120~200℃.
[0012] Step 2: High-temperature hydrothermal treatment
[0013] Leaching residue A and alkali activator are subjected to high-temperature hydrothermal treatment at temperature T2 to obtain leachate B and leaching residue B; wherein, in the high-temperature hydrothermal system, the Ca / Si weight ratio is 2.2~3.0; and the temperature T2 is 1.1~2 times the temperature T1.
[0014] To address the difficulty of potassium extraction from potassium-rich slate, this invention proposes an innovative method: first, subject the raw material to low-temperature hydrothermal treatment to alter its phase and microstructure; then, combine this with a subsequent high-temperature hydrothermal process. The synergistic effect of these two processes effectively disrupts the crystal structure of the potassium-rich slate, thereby significantly improving the extraction efficiency and effectiveness of potassium.
[0015] The potassium-rich slate contains potassium-bearing minerals such as potassium feldspar, biotite, illite, and muscovite.
[0016] In this invention, the potassium-rich slate contains 8-16 wt.% K2O and 0.1-4 wt.% Na2O; further, the K2O content can be 8.5-10 wt.% and the Na2O content can be 2-3 wt.%.
[0017] In this invention, the particle size of potassium-rich slate is controlled between 100 and 300 mesh.
[0018] In this invention, in step 1, the low-temperature hydrothermal process is an N-stage series hydrothermal process, wherein the solvent of the first stage hydrothermal process is water; the solvent of the Nth stage hydrothermal process is the leachate of the N-1th stage hydrothermal process; the Ca / Si weight ratio in the N-stage series hydrothermal process is controlled at 2.2~3.0, and the temperature is T1; after the N-stage series hydrothermal process, the leachate of the Nth stage hydrothermal process is the leachate A, and the leachate residues of the N-stage series hydrothermal process are combined into leachate residue A.
[0019] N is an integer from 2 to 10.
[0020] The present invention demonstrates that the N-stage tandem leaching of potassium-rich slate can effectively alter its phase and microstructure. Furthermore, the compositional characteristics of the tandemly circulating leachate can serve as inducing components, further promoting the physicochemical transformation of the potassium-rich slate, thereby increasing the potassium leaching rate and efficiency. It can also effectively reduce costs and waste generation.
[0021] In this invention, an alkaline activator is added to the first stage hydrothermal solvent system. The alkaline activator is, for example, potassium hydroxide. The concentration of the alkaline activator is below 20 g / L, and considering both effectiveness and cost, it can be further reduced to 1-20 g / L, or even further reduced to 1-5 g / L. Studies have shown that the use of the alkaline activator, in conjunction with the multi-stage leaching process, helps to further pre-extract potassium and activate and modify the residue, thus facilitating the total potassium leaching.
[0022] In this invention, the temperature T1 of each segment in the N-segment series hydrothermal process is 150~195 ℃; it can further be 175~195 ℃.
[0023] In this invention, the heat preservation time for each section is 4 to 10 hours; preferably 5 to 8 hours.
[0024] In this invention, the liquid-to-solid ratio of each segment in the N-segment series hydrothermal process is 10-35 mL / g; more specifically, it can be 15-25 mL / g.
[0025] In step 1 of this invention, the Ca / Si weight ratio is controlled by a calcium-containing additive, which includes one or more of calcium carbonate, calcium oxide, and calcium bicarbonate.
[0026] Preferably, the Ca / Si weight ratio during both low-temperature and high-temperature leaching processes is 2.5 to 2.8. Studies have shown that, under this preferred ratio, combined with the segmented leaching method described in this invention, a better overall K leaching effect can be obtained.
[0027] In this invention, during the high-temperature hydrothermal process, an alkaline activator is added, which can be potassium hydroxide, and the amount added is 50~300 g / L, preferably 80~200 g / L, and further 150~200 g / L.
[0028] In this invention, in step 2, the temperature T2 is 200~300 ℃, preferably 210~280 ℃; more preferably 250~270 ℃;
[0029] Preferably, the heat preservation time at temperature T2 is 5 to 8 hours.
[0030] Beneficial effects
[0031] This invention pre-treats potassium-rich slate with low-temperature hydrothermal treatment, which facilitates the microscopic physicochemical transformation of the potassium-rich slate. This, combined with subsequent high-temperature hydrothermal treatment, helps to effectively construct leaching capillary pathways and improve the leaching efficiency and effect of potassium.
[0032] In this invention, the low-temperature hydrothermal process is carried out in multiple stages in series. This can further improve the physicochemical structure of potassium-rich slate based on the induction effect of the series circulation of the leachate, which helps to further improve the potassium leaching rate and leaching efficiency. In addition, it can also significantly reduce leaching costs and waste generation.
[0033] The process described in this invention uses less reagent and achieves a potassium leaching rate of over 96%, thus reducing the overall energy consumption. The hydrothermal reaction and liquid-solid separation processes involved in this invention are simple to operate, operate at low temperatures, and consume little energy, making them suitable for industrialization. Attached Figure Description
[0034] Figure 1 The XRD patterns of the solid products of Example 1 and Comparative Example 1 are shown below.
[0035] Figure 2 SEM images of the various reaction stages of the potassium-rich slate in Example 1 ((a) Potassium-rich slate ore; (b) Solid product of step 1; (c) Solid product of step 2).
[0036] Figure 3 The images show the XRD patterns of the solid products at each reaction stage in Example 5. Detailed Implementation
[0037] 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.
[0038] To achieve the above objectives, the present invention provides a method for the staged leaching and efficient extraction of potassium from potassium-rich slate.
[0039] An optional solution of the present invention comprises the following main steps:
[0040] (1) Raw material preparation: crush the potassium-rich slate and prepare samples for sieving.
[0041] (2) Preparation for hydrothermal leaching: Mix the calcium-containing additives and potassium-rich slate with the selective addition of alkali activator in a certain proportion, and add them to the water in the corresponding proportion for later use;
[0042] A hydrothermal reaction: The above mixed solution is added to a reaction vessel, and a closed pressurized reaction is carried out at a temperature T1 using the saturated vapor pressure at that temperature for t1 hours.
[0043] (3) After the product of the hydrothermal reaction is cooled to room temperature and pressure, it is taken out and subjected to liquid-solid separation to obtain leachate L1 and solid product S1.
[0044] (4) Two-stage hydrothermal reaction: Calcium-containing additives and potassium-rich slate are added to L1 in the proportion described in step (2). At temperature T1, a closed pressurized reaction is carried out for t1 hours using the saturated vapor pressure at that temperature. After the hydrothermal reaction, the product is cooled to room temperature and pressure and then taken out for liquid-solid separation to obtain leachate L2 and solid product S2.
[0045] (5) Three-stage hydrothermal reaction: Calcium-containing additives and potassium-rich slate are added to L2 in the proportion described in step (2). At temperature T1, a closed pressurized reaction is carried out for t1 hours using the saturated vapor pressure at that temperature. After the hydrothermal reaction, the product is cooled to room temperature and pressure and then taken out for liquid-solid separation to obtain leachate L3 and solid product S3.
[0046] (6) ...
[0047] (7) n-stage hydrothermal reaction: calcium-containing additives and potassium-rich slate are added to Ln-1 in the proportion described in step (2). At temperature T1, a closed pressurized reaction is carried out for t1 hours using the saturated vapor pressure at that temperature. After the hydrothermal reaction, the product is cooled to room temperature and pressure and then taken out for liquid-solid separation to obtain leachate Ln and solid product Sn.
[0048] (8) Mix all the above solid products S1, S2, S3...Sn evenly to obtain Sm, and add calcium-containing additives and alkali activators in proportion to prepare a mixed solution;
[0049] (9) High temperature and high pressure hydrothermal reaction: The mixed solution obtained in step (8) is added to the reactor and a closed pressurized reaction is carried out at temperature T2 using the saturated vapor pressure at that temperature for t2 hours; the product after hydrothermal reaction is cooled to room temperature and pressure and then taken out for liquid-solid separation to obtain leachate L and solid product S.
[0050] (10) Mix the leachate L and leachate Ln to obtain potassium-rich leachate.
[0051] In this invention, there are no special requirements for the content of potassium-rich slate, and there are no special provisions for the potassium and sodium content, for example, the K2O content is 8~16% and the Na2O content is 0.1~4%.
[0052] In this invention, the alkaline activator in steps (2) and (9) is KOH, and the added additives are one or more of calcium carbonate, calcium oxide, and calcium bicarbonate.
[0053] In this invention, step (1) involves crushing potassium-rich slate to 100-300 mesh.
[0054] In this invention, the amount of calcium-containing additive added in step (2) is calculated as the calcium-silicon weight ratio of the molar amount of calcium contained in it to the molar amount of silicon contained in potassium feldspar in potassium-rich slate, ranging from 2.2 to 3.0. The amount of alkali activator added is 0 to 20 g / L. After the calcium-containing additive, alkali activator and potassium-rich slate are mixed evenly, a liquid-solid ratio of 10 to 35 mL / g is added. Further, a corresponding amount of pure water can be added at 15 to 25 mL / g to prepare a mixed solution.
[0055] In this invention, preferably, the calcium-to-silicon ratio of the calcium-containing additive in step (2) is 2.2 to 3.0, and more preferably 2.5 to 2.8;
[0056] In this invention, the reaction temperature T1 of steps (3)-(7) is 150~195 ℃, the pressure reaction time t1 is 4~8 hours, and the process is mechanically stirred at a frequency of 150~400 rpm;
[0057] In this invention, preferably, the reaction temperature of steps (3)-(7) is 170~190 ℃;
[0058] In this invention, preferably, the pressurized reaction time in steps (3)-(7) is 5-8 hours;
[0059] In this invention, the amount of calcium-containing additive added in step (8) is calculated based on the calcium-silicon weight ratio of the molar amount of calcium contained in it to the molar amount of silicon contained in Sm, ranging from 2.2 to 3.0. The amount of alkali activator added is 50 to 300 g / L. After the calcium-containing additive, alkali activator and Sm are mixed evenly, a liquid-solid ratio of 10 to 35 mL / g is added. Further, a corresponding amount of pure water can be added at 15 to 25 mL / g to prepare a mixed solution.
[0060] In this invention, preferably, the calcium-to-silicon ratio of the amount of calcium-containing additive added in step (8) is 2.2 to 3.0, and more preferably 2.5 to 2.8;
[0061] In this invention, preferably, the amount of alkaline activator added in step (8) is 50~300 g / L, more preferably 80~200 g / L, and further preferably 150~200 g / L;
[0062] In this invention, preferably, the reaction temperature T2 in step (9) is 200~300 ℃, the pressurized reaction time t1 is 4~8 hours, and the process is mechanically stirred at a frequency of 150~400 rpm;
[0063] In this invention, preferably, the reaction temperature in step (9) is 250~270 °C;
[0064] In this invention, preferably, the pressurization reaction time in step (9) is 5 to 8 hours;
[0065] In this invention, the potassium-rich leachate obtained in step (10) can be evaporated and crystallized or carbonized to obtain potassium hydroxide or potassium carbonate. The solid obtained in step (9) is mainly composed of dicalcium silicate hydrate, which can be used to prepare cement, silicon fertilizer, adsorbent materials or carbonized materials.
[0066] The main mechanism of this invention lies in the synergistic effect of phase structure destruction and ion exchange mechanisms during hydrothermal processes. The phase structure destruction mechanism mainly utilizes OH groups in the hydrothermal system. - One mechanism involves disrupting the structure of aluminosilicate minerals, causing potassium to dissolve; another mechanism utilizes the smaller radius of the Ca²⁺ ore. 2+ Ions enter the layered structure of aluminosilicate minerals and interact with the larger K ions. + Ion exchange, making K + Ion release. During hydrothermal leaching, structural destruction and Ca / K ion exchange mechanisms occur simultaneously. To achieve ideal potassium leaching efficiency, the key is to match various reaction conditions (such as reaction temperature and time, calcium-silicon weight ratio, KOH concentration, etc.) to achieve a good synergistic effect between the two leaching mechanisms.
[0067] Example 1
[0068] This embodiment uses potassium-rich slate with a K2O content of 9.16% and a Na2O content of 2.56% as raw material. The potassium feldspar phase accounts for 56%, and other potassium-containing phases account for 23%. The potassium-rich slate is crushed to 200 mesh.
[0069] Step 1 (Low-temperature leaching process)
[0070] The potassium-rich slate was divided into two equal parts. The first part of potassium-rich slate and calcium activator (CaO) were mixed with water and subjected to the first stage of hydrothermal leaching (also known as the first stage leaching). Subsequently, solid-liquid separation was performed to obtain the first leachate and the first leaching residue.
[0071] The second portion of potassium-rich slate and calcium activator (CaO) were pulped with the first leachate and then subjected to a second stage of hydrothermal leaching (also known as second stage leaching) to obtain a second leachate and a second leaching residue.
[0072] The first and second leaching residues are combined to form a low-temperature leaching residue;
[0073] In both the first and second hydrothermal leaching systems, the calcium-to-silicon weight ratio was 2.6, the liquid-to-solid ratio was 20 mL / g, the reaction temperature was 180 ℃, the reaction time was 6 hours, and the stirring speed was 250 rpm.
[0074] Based on the potassium content in the second leachate, the potassium leaching rate was 74.78%.
[0075] Step 2:
[0076] The low-temperature leaching residue, KOH, and calcium activator (CaO) were slurried with water, followed by high-temperature hydrothermal treatment to obtain a high-temperature leachate and leaching residue. In the high-temperature hydrothermal stage, the calcium-silicon weight ratio was 2.6, the KOH addition was 100 g / L, the liquid-solid ratio was 20 mL / g, the reaction temperature was 250 ℃, the reaction time was 6 hours, and the stirring speed was 250 rpm. The potassium leaching rate reached 22.12%.
[0077] The total K leaching rate calculated for steps 1 and 2 is 96.9%.
[0078] Example 2
[0079] Compared with Example 1, the difference is that in step 1, KOH is added to the hydrothermal system of the first leaching stage and the second leaching stage, and the amount added is 3.5g / L;
[0080] In step 1, based on the potassium in the second leachate, the potassium leaching rate is 76.22%; the total leaching rate for the entire process is 97.29%.
[0081] Example 3
[0082] Compared with Example 2, the difference is that in step 1, the reaction temperature of the first leaching stage and the second leaching stage is increased to 190 °C;
[0083] In step 1, based on the potassium in the second stage leachate, the potassium leaching rate in step 1 is 76.39%; the total leaching rate for the entire process is 98.15%.
[0084] Example 4
[0085] Compared with Example 2, the difference is that in step 1, the low-temperature leaching only performs the first stage of leaching (the leaching time is extended to 12 hours), followed by the high-temperature leaching stage. The total leaching rate of the entire process is 96.33%.
[0086] Example 5
[0087] Compared with Example 2, the difference is that in step 1, the potassium-rich slate is divided into 7 equal parts and subjected to seven-stage tandem leaching. In the first stage of the tandem leaching process, KOH is added in addition, with an addition amount of 3.5 g / L. The leaching rates of stages 1 to 7 in step 1 and step 2 are shown in Table 1.
[0088] Table 1 Leaching effect of Example 5
[0089]
[0090] The overall leaching rate for the entire process was 98.09%.
[0091] Example 6
[0092] Compared with Example 2, the difference is that in each leaching process of Step 1 and Step 2, the calcium-silicon ratio was adjusted to 2.2 by controlling the amount of calcium activator. The potassium leaching rate in Step 1 was 72.35%, the potassium leaching rate in Step 2 was 21.58%, and the total leaching rate was 93.93%.
[0093] High leaching rates can be achieved in the range of 2.2 to 3.0 for the calcium-silicon ratio. The leaching rate decreases slightly when the ratio is below 2.2, further verifying that 2.5 to 3.0 is the optimal range.
[0094] Example 7
[0095] Compared with Example 2, the difference is that the high-temperature hydrothermal treatment in step 2 uses T2=220℃ (lower than 250℃ in Example 1), and the total potassium leaching rate is 94.94%.
[0096] Example 8
[0097] Compared with Example 2, the difference is that the high-temperature hydrothermal treatment in step 2 uses T2=280℃ (higher than 250℃ in Example 1), and the total potassium leaching rate is 99.36%.
[0098] Within the range of 200~300℃, the leaching rate of T2 increases with increasing temperature, and 250~280℃ is the optimal range that balances leaching rate and energy consumption.
[0099] Example 9
[0100] Compared to Example 2, the difference lies in the liquid-to-solid ratio of 25 mL / g (higher than the 20 mL / g in Example 1) used in steps 1 and 2. The potassium leaching rate in step 1 was 77.13%, and the potassium leaching rate in step 2 was 22.54%; the calculated total potassium leaching rate was 99.67%. A liquid-to-solid ratio of 10–25 mL / g is applicable, with 15–20 mL / g being the optimal range for balancing leaching efficiency and reagent usage.
[0101] Comparative Example 1
[0102] Compared with Example 2, the difference is that the calcium-silicon weight ratio is changed to 1.0 in the first-stage leaching and the second-stage leaching, and the total potassium leaching rate of the entire process is 49%.
[0103] Comparative Example 2
[0104] Compared to Example 1, the difference is that gradient temperature-controlled hydrothermal treatment was not performed; that is, the temperature in step 2 was the same as in step 1. The total potassium leaching rate was only 78.35%, far lower than the 96.9% in Example 1. Low-temperature hydrothermal treatment alone cannot completely destroy the layered mineral structure of biotite, illite, etc.; high-temperature hydrothermal treatment is necessary to achieve efficient potassium leaching.
[0105] Comparative Example 3
[0106] Compared to Example 1, the only difference is that step 1 is omitted; instead, the potassium-rich slate is directly subjected to high-temperature hydrothermal treatment in step 2, with the same parameters as in Example 1 (calcium-silicon weight ratio 2.6, T2 = 250℃, 100 g / L potassium hydroxide, and total reaction time). The potassium leaching rate is 85.62%, lower than the 96.9% in Example 1. Low-temperature multi-stage series hydrothermal treatment can pre-alter the framework phase structure of some potassium-containing minerals in the potassium-rich slate, creating leaching conditions for high-temperature hydrothermal treatment, reducing overall energy consumption, and improving leaching efficiency.
[0107] Comparative Example 4
[0108] Compared to Example 1, the difference lies in that no potassium hydroxide activator is added in step 2 of the high-temperature hydrothermal process, while other parameters remain unchanged. The leaching rate in this stage is 12.45%, and the total leaching rate is 74.78% + 12.45% = 87.23%, which is lower than the 96.9% in Example 1. Potassium hydroxide activator can enhance the decomposition ability of the hydrothermal system at high temperatures on residual sparingly soluble potassium-containing minerals, and is a key additive for achieving high leaching rates.
[0109] Conclusions and Effects Analysis:
[0110] In addition to effectively improving potassium extraction efficiency, this invention also has advantages in terms of cost and waste generation. The following is a comparison of this invention with other inventions.
[0111] 1. Cost Comparison
[0112]
[0113] Note:
[0114] [1] Ma Hongwen, Yang Jing, Wang Yingbin, et al. Preparation of potassium carbonate from non-water-soluble potassium ore: by-product silica-alumina cementitious material [J]. Earth Science - Journal of China University of Geosciences, 2007, 32: 111-118. [2] Bai Lushui, Li Wencheng, Sun Xiping, et al. Formula and process for extracting potassium carbonate and aluminum hydroxide from potassium-rich slate and preparing silicon fertilizer: CN03143378.2 [P]. 2005-04-06. [3] Wang Ying, Guo Juhua, Huang Jinfeng, et al. Decomposition of potassium feldspar ore by NaOH submolten salt method [J]. Journal of Process Engineering, 2014, 14: 280-285. [4] Jiang Wei, Luo Mengjie, Liu Chenglin, et al. Process of low-temperature leaching of potassium feldspar by submolten salt[J]. Journal of East China University of Science and Technology (Natural Science Edition), 2019, 45: 206-215.
[0115] This invention reduces reagent loss through multi-stage series cyclic leaching and reduces energy consumption in the low-temperature stage, resulting in a total cost reduction of 30% to 43% compared to traditional methods.
[0116] 2. Comparison of the output of the three wastes
[0117]
[0118] This invention enables the resource utilization of solid waste, the recycling of wastewater, and the emission of no waste gas. The cost of treating these three types of waste is reduced by more than 60% compared to traditional methods.
[0119] To visually demonstrate the effect of different operations on potassium leaching rate, the XRD patterns of the solid substances obtained after the reaction in Example 1 and Comparative Example 1 were compared. Figure 1 As can be seen, when the calcium-silicon weight ratio of the multi-stage leaching is lower than the range specified in this invention, potassium feldspar is still present in the solid product, resulting in a low potassium leaching rate. In Example 1, both leaching stages were carried out under relatively mild conditions, and the potassium feldspar diffraction peaks disappeared, with most of the potassium dissolved, but some insoluble potassium-containing minerals remained undecomposed. After high-temperature and high-pressure hydrothermal leaching, the reaction product obtained from the entire process consisted of dicalcium silicate hydrate (C2SH) and grossular garnet, with no potassium-containing ore diffraction peaks.
[0120] Figure 2 SEM images of unreacted potassium-rich slate and the solid products from step 1 (low-temperature hydrothermal treatment) and step 2 (high-temperature hydrothermal treatment) in Example 1. In the potassium-rich slate, the distribution patterns of potassium, aluminum, silicon, and oxygen show a highly consistent regional distribution corresponding to potassium feldspar minerals; some potassium elements are closely associated with iron and magnesium elements, which are biotite minerals; there are also some scattered sodium, calcium, and manganese elements, but their contents are relatively low. Some biotite minerals may also contain small amounts of fluorine; the mineral particles are dense and massive. Figure 2 (a)). After the hydrothermal reaction in the low-temperature stage of step 1, cracks appeared on the surface of most minerals, some aluminum ions entered the calcium silicate compound to form grossular garnet, the potassium feldspar structure disintegrated, and the biotite layers separated into thin sheets ( Figure 2 (b)). After the high-temperature hydrothermal reaction in step 2, the potassium-rich slate particles completely disintegrate into loose and structurally regular hydrated dicalcium silicate (C2SH), and grossular grows into regular spheres ( Figure 2 (c) Low-temperature hydrothermal processes can induce lattice defects and interlayer expansion of biotite in potassium-containing minerals, which are more difficult to decompose than potassium feldspar. This weakens the stability of the mineral structure, gradually destroys the dense structure of the mineral, and lays the foundation for complete decomposition in the subsequent high-temperature stage.
[0121] Figure 3 The XRD patterns of the solid products at each reaction stage in Example 5 are shown. The products obtained from the series reactions in the low-temperature stage are consistent. Potassium feldspar can be decomposed in the low-temperature stage. After going through the high-temperature stage, the mica structure is completely destroyed, and potassium is efficiently extracted from the potassium-rich slate.
[0122] 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 extracting potassium from potassium-rich slate, characterized in that, include: Step 1: Low-temperature hydrothermal Potassium-rich slate was subjected to low-temperature hydrothermal treatment at temperature T1 to obtain leachate A and leachate residue A; in the low-temperature hydrothermal system, the Ca / Si weight ratio was controlled at 2.2~3.0; and the temperature T1 was 120~200℃. Step 2: High-temperature hydrothermal treatment Leaching residue A and alkali activator are subjected to high-temperature hydrothermal treatment at temperature T2 to obtain leachate B and leaching residue B; wherein, in the high-temperature hydrothermal system, the Ca / Si weight ratio is 2.2~3.0; and the temperature T2 is 1.1~2 times the temperature T1.
2. The method for extracting potassium from potassium-rich slate as described in claim 1, characterized in that, Potassium-rich slate contains potassium-bearing minerals such as potassium feldspar, biotite, illite, and muscovite; Preferably, the K2O content is 8~16 wt.% and the Na2O content is 0.1~4 wt.%. Preferably, the particle size of the potassium-rich slate is controlled between 100 and 300 mesh.
3. The method for extracting potassium from potassium-rich slate as described in claim 1, characterized in that, In step 1, the low-temperature hydrothermal process is an N-stage series hydrothermal process, wherein the solvent of the first stage hydrothermal process is water; the solvent of the Nth stage hydrothermal process is the leachate of the N-1th stage hydrothermal process; the Ca / Si weight ratio is controlled at 2.2~3.0 and the temperature is T1 in all N-stage series hydrothermal processes; after the N-stage series hydrothermal process, the leachate of the Nth stage hydrothermal process is the leachate A, and the leachate residues of the N-stage series hydrothermal process are combined into leachate residue A. N is an integer from 2 to 10.
4. The method for extracting potassium from potassium-rich slate as described in claim 3, characterized in that, In the first stage of the hydrothermal solvent system, potassium hydroxide is also added, with the concentration of potassium hydroxide being below 20 g / L.
5. The method for extracting potassium from potassium-rich slate as described in claim 3, characterized in that, The temperature T1 of each segment in the N-segment series hydrothermal process is 150~195 ℃; preferably 175~195 ℃.
6. The method for extracting potassium from potassium-rich slate as described in claim 3, characterized in that, The insulation time for each section is 4 to 10 hours; preferably 5 to 8 hours.
7. The method for extracting potassium from potassium-rich slate as described in claim 3, characterized in that, The liquid-to-solid ratio in each segment of the N-segment series hydrothermal process is 10-35 mL / g; it can be further 15-25 mL / g.
8. The method for extracting potassium from potassium-rich slate as described in claim 3, characterized in that, The Ca / Si weight ratio is controlled by a calcium-containing additive, which includes one or more of calcium carbonate, calcium oxide, and calcium bicarbonate.
9. The method for extracting potassium from potassium-rich slate as described in claim 1, characterized in that, During the high-temperature hydrothermal process, potassium hydroxide activator is added at a concentration of 50-300 g / L, preferably 80-200 g / L, and further preferably 150-200 g / L.
10. The method for extracting potassium from potassium-rich slate as described in claim 1, characterized in that, In step 2, the temperature T2 is 200~300℃, preferably 210~280℃; more preferably 250~270℃; Preferably, the heat preservation time at temperature T2 is 5 to 8 hours.