Method for preparing lithium hydroxide and potassium sulfate by comprehensively recovering lithium salt mother liquor

Abstract

This invention relates to the field of comprehensive utilization of industrial waste and hydrometallurgical technology, and discloses a method for the comprehensive recovery of lithium salt mother liquor to prepare lithium hydroxide and potassium sulfate. The method includes: adding calcium chloride solution to the lithium salt mother liquor to precipitate all sulfate ions into calcium sulfate, obtaining a mixed solution containing lithium chloride and potassium chloride; adding calcium sulfate and high-purity calcium sulfate obtained from the purification of waste gypsum together to ammonium chloride solution, and performing liquid-phase metathesis at no more than 100°C to ammonium sulfate, with the by-product calcium chloride being recycled; combining the ammonium sulfate solution with the mixed solution and the potassium chloride solution obtained from potassium feldspar leaching, and cooling and crystallizing to separate the potassium sulfate product; subjecting the lithium-rich solution to bittering and ammonia removal with calcium hydroxide, followed by evaporation and crystallization to obtain lithium hydroxide monohydrate; and using alkaline activation and solidification of aluminum-silicon waste residue containing heavy metals to produce building materials. This invention achieves the synergistic utilization of four types of industrial waste: lithium salt mother liquor, waste gypsum from flue gas desulfurization, potassium feldspar, and titanium dioxide by-product ferrous sulfate heptahydrate, achieving zero discharge of solid waste and hazardous waste.

Description

Technical Field

[0001] This invention relates to the fields of comprehensive utilization of industrial waste and hydrometallurgical technology, and more specifically, to a method for the comprehensive recovery of lithium salt mother liquor to prepare lithium hydroxide and potassium sulfate. Background Technology

[0002] The production process of lithium salts generates a large amount of... , , Direct discharge of mother liquor containing valuable components wastes resources and pollutes the environment. In existing mother liquor recovery processes, lithium and potassium coexist in complex systems as sulfates, and macroscopic solid-liquid separation of lithium and potassium cannot be achieved without large-scale evaporation and concentration, resulting in extremely high energy consumption. Preparation typically relies on the Mannheim high-temperature solid-state conversion process (approximately 550°C), which consumes a huge amount of energy and requires extensive external procurement. Raw material costs are high. A large amount of material needs to be purchased externally for the upstream processes. Capture mother liquor , Production is also limited by the mother liquor itself. In terms of total volume, there is limited room for capacity expansion.

[0003] At the same time, the flue gas desulfurization process of coal-fired power plants produces a large amount of FGD waste gypsum (the main component of the flue gas desulfurization process). FGD waste gypsum was originally intended to expand the source of calcium sulfate in the mother liquor system and achieve a breakthrough. Low-cost sulfur sources face production bottlenecks, but their heavy metals such as As and Pb, as well as organic pigments, can contaminate products when directly introduced into chemical production systems. Purification itself generates hazardous waste containing heavy metals, resulting in high disposal costs and limiting the utilization of this sulfur source. On the other hand, my country has abundant and inexpensive potassium feldspar resources. Hydrothermal leaching with ammonium chloride solution can extract potassium as potassium chloride, directly replacing purchased potassium chloride and significantly reducing raw material costs. However, the resulting aluminosilicate waste (amorphous aluminosilicates) currently lacks efficient disposal methods, hindering the industrial application of this process. It is noteworthy that if these wastes are incorporated into the same process system, the hazardous waste residue from FGD waste gypsum purification can be solidified by alkaline-activated geopolymerization treatment of the aluminosilicate waste residue from potassium feldspar leaching, achieving the harmless transformation of the hazardous waste residue. However, currently, there is no integrated process method that can co-utilize these wastes and achieve closed-loop recycling within the system. Summary of the Invention

[0004] This invention provides a method for the comprehensive recovery of lithium salt mother liquor to prepare lithium hydroxide and potassium sulfate, solving the problems of high energy consumption in lithium-potassium separation in related technologies. Technical problems include the need for high-temperature solid-phase processes in preparation, the inability to co-utilize industrial waste, and the high cost of hazardous waste disposal.

[0005] This invention provides a method for the comprehensive recovery of lithium salt mother liquor to prepare lithium hydroxide and potassium sulfate, comprising the following steps:

[0006] Step 1: Add calcium chloride solution to lithium salt mother liquor to precipitate all sulfate ions in the mother liquor as calcium sulfate. Filter to obtain solid calcium sulfate and a mixed solution containing lithium chloride and potassium chloride.

[0007] Step 2: Add the calcium sulfate obtained in Step 1 to the ammonium chloride solution and perform liquid-phase double decomposition at normal pressure and 80-100℃ to convert the calcium sulfate into ammonium sulfate. Filter the solution, and return the resulting calcium chloride solution to Step 1. The resulting ammonium sulfate solution will then enter Step 3.

[0008] Step 3: Combine the ammonium sulfate solution obtained in Step 2 with the mixed solution obtained in Step 1, cool to 20°C to allow potassium sulfate to crystallize out preferentially, filter to obtain potassium sulfate product; the main ammonium chloride solution in the obtained filtrate is recycled back to Step 2, and the lithium-rich solution containing lithium chloride and ammonium chloride enters Step 4.

[0009] Step 4: Add excess calcium hydroxide to the lithium-rich solution obtained in Step 3, heat to drive out ammonia gas, filter while hot to remove calcium hydroxide solid, evaporate and concentrate the resulting clear solution containing lithium hydroxide and calcium chloride below 60°C to crystallize lithium hydroxide monohydrate, filter to obtain lithium hydroxide monohydrate product; the crystallization mother liquor containing calcium chloride is recycled back to Step 1.

[0010] Preferably, in step 2, the high-purity calcium sulfate obtained from the purified flue gas desulfurization waste gypsum is added together with the calcium sulfate obtained in step 1 to an ammonium chloride solution for liquid-phase conversion.

[0011] Preferably, the waste gypsum purification treatment includes the following operations: adding water to the waste gypsum from flue gas desulfurization to prepare a slurry with a solid-liquid mass ratio of 1:31:5; adding ferrous sulfate heptahydrate to the slurry at a ratio of 1% to 3% of the dry weight of the waste gypsum; continuously aerating the slurry with air to oxidize ferrous iron to ferric iron; adding calcium hydroxide suspension to adjust the pH of the slurry to 6.0-7.0; and hydrolyzing ferric iron in situ to generate amorphous ferric hydroxide colloids with a particle size of less than 1 μm; the colloids adsorb soluble arsenic and lead heavy metal ions in the liquid phase through co-precipitation, and simultaneously transferring and fixing the humic acid organic pigments on the surface of the calcium sulfate particles onto the colloids through electrostatic flocculation.

[0012] Preferably, after purification, the slurry is filtered in two stages: the first stage uses a filter medium with a retention accuracy of 1-5 μm to retain calcium sulfate crystals, and the resulting calcium sulfate filter cake is washed with water to remove soluble inorganic salts to obtain high-purity calcium sulfate for use in step 2; the second stage uses a filter medium with a retention accuracy of less than 1 μm to retain ferric hydroxide colloids containing arsenic and lead heavy metals, and the resulting solid is hazardous waste residue, which is temporarily stored for later use.

[0013] Preferably, in step 3, the potassium chloride leachate obtained by hydrothermal leaching of potassium feldspar ore and ammonium chloride solution is also incorporated into the combined solution of step 3 to participate in the preparation of potassium sulfate; the hydrothermal leaching is as follows: potassium feldspar ore and ammonium chloride solution are added to a sealed pressure-resistant container at a solid-liquid mass ratio of 1:41:8, and leached at 150℃ under hydrothermal conditions for 25 h, filtered, and the obtained leachate is a potassium chloride solution, and the obtained leaching solid phase is an amorphous aluminum-silicon waste residue containing highly active silicon-oxygen bonds and aluminum-oxygen bonds.

[0014] Preferably, the process further includes the following curing step: adding the aluminum-silicon waste residue to a sodium hydroxide solution with a concentration of 6-10 mol / L, and activating it with alkali at 40-60℃ to generate a three-dimensional network sodium aluminosilicate gel; within 30-60 minutes after the start of alkali activation, uniformly mixing the hazardous waste residue into the gel system; after the gel solidifies, the heavy metals in the hazardous waste residue are physically encapsulated and chemically bonded to the aluminosilicate network, and the solidified product is used as a building material.

[0015] Preferably, the concentration of the ammonium chloride solution in the hydrothermal leaching is 200-350 g / L, and the ammonium chloride solution used comes from the ammonium chloride solution recycled in step 3.

[0016] Preferably, the concentration of the ammonium chloride solution used in step 2 is 250-380 g / L, and the reaction time for liquid-phase metathesis is 2-4 h.

[0017] Preferably, after the hydrothermal leaching is completed, the sealed pressure-resistant container is cooled down, and then the pressure is slowly released. The escaped ammonia gas is introduced into the water for absorption, and ammonia water is obtained as a by-product for recycling.

[0018] Preferably, the ferrous sulfate heptahydrate is a byproduct of titanium dioxide production.

[0019] The beneficial effects of this invention are as follows:

[0020] The Mannheim high-temperature solid-phase process (approximately 550°C) is replaced by a low-temperature liquid-phase conversion of ammonium chloride (not exceeding 100°C), which reduces process energy consumption by more than 70%. Both ammonium chloride and calcium chloride are circulated in a closed loop within the system, eliminating the need for continuous external purchases.

[0021] Introducing FGD waste gypsum as a secondary sulfur source has broken through the limitations of traditional methods. The bottleneck of production being limited by the total amount of sulfate in the mother liquor can be addressed by proportionally increasing the production capacity with the amount of waste gypsum added.

[0022] Potassium chloride is obtained by hydrothermal leaching of inexpensive potassium feldspar using a circulating ammonium chloride solution within the system, which significantly reduces the cost of potassium source raw materials. The leached aluminum-silicon waste residue is directly used for hazardous waste solidification, achieving zero external discharge.

[0023] Using ferrous sulfate heptahydrate, a byproduct of the titanium dioxide industry, as an iron source, ferric hydroxide colloid is generated in situ. In one step, heavy metals and organic pigments are removed from waste gypsum, and the resulting potassium sulfate product meets the agricultural grade white high-purity standard.

[0024] Aluminum-silicon waste residue is geopolymerized to solidify heavy metal hazardous waste residue. The leaching concentration of heavy metals in the solidified products is reduced to below the building material standard, completely eliminating hazardous waste disposal costs.

[0025] This invention enables the synergistic utilization of four types of industrial waste: lithium salt mother liquor, FGD waste gypsum, potassium feldspar, and titanium dioxide by-product ferrous sulfate heptahydrate. The system achieves zero discharge of solid waste and hazardous waste, resulting in significant economic and environmental benefits. Attached Figure Description

[0026] Figure 1 These are the experimental groups of this invention. Bar chart comparing conversion rate and process energy consumption;

[0027] Figure 2 This invention is different After purification under the specified dosage conditions Line graph showing the changes in As and Pb content in the medium;

[0028] Figure 3 This invention is different Line graph showing the change in whiteness after purification under the specified dosage conditions;

[0029] Figure 4 The present invention relates to the purification of FGD waste gypsum before and after treatment. Comparison of particle microstructures using SEM images;

[0030] Figure 5 The present invention is based on different crystallization temperatures. Biaxial line graph of crystallization rate and Li loss rate;

[0031] Figure 6 This is a bar chart comparing the leaching concentrations of As and Pb in the various groups of cured products of this invention.

[0032] Figure 7 This is a SEM image of the geopolymer microstructure of the cured product in Experiment B of Example 4 of the present invention after 28 days of curing. Detailed Implementation

[0033] The subject matter described herein will now be discussed with reference to exemplary embodiments. It should be understood that these embodiments are discussed only to enable those skilled in the art to better understand and implement the subject matter described herein, and changes may be made to the function and arrangement of the elements discussed without departing from the scope of this specification. Various processes or components may be omitted, substituted, or added as needed in the examples. Furthermore, some features described in the examples may be combined in other examples.

[0034] Example 1

[0035] This embodiment discloses a method for separating and recovering lithium hydroxide monohydrate and potassium sulfate from lithium salt mother liquor, the method comprising the following steps:

[0036] Step 1 capture

[0037] Take containing (50 g / L) and Calculate the concentration of lithium salt in the mother liquor (30 g / L). Total amount of substance, according to Add 1.0 times the amount of substance to the mother liquor Solution ( (Concentration 200 g / L), stir the reaction at room temperature for 30 min. and In All sedimented into Filter, get solids and containing and A mixed solution.

[0038] Step 2 Medium liquid phase transformation

[0039] The result from step 1 The solid was added at a solid-liquid mass ratio of 1:4 to a concentration of 250 g / L. In the solution, the reaction was stirred for 2 hours under normal pressure and 80°C. Liquid phase transformation The conversion rate reached 82%. After filtration, the resulting... Solution recycling step 1 is used to capture the solution in the next batch of mother liquor. ; income The solution proceeds to step 3; the filtered result contains residue. The solid phase is merged into the next batch. Return to this step to continue the conversion.

[0040] Step 3 Crystallization separation

[0041] The result from step 2 Solution and the solution obtained in step 1 The mixed solutions were combined and incubated at 50°C. and A double displacement reaction occurs, followed by cooling to 20°C. Preferential crystallization precipitation ( The solubility is approximately 11.1 g / 100 mL, which is far lower than... Approximately 80 g / 100mL and (Approximately 38 g / 100 mL), filtered, yield Product; the resulting filtrate is divided into two streams: main stream and main stream. The solution is recycled back to step 2, containing With residue The lithium-rich liquid material proceeds to step 4.

[0042] Step 4: Bitter Processing

[0043] Add the lithium-rich liquid obtained in step 3 according to the following formula: and Add 1.05 times the total amount of substance. The product was heated and stirred at 80°C for 1 hour to induce bittering, and the resulting product was then... The ammonia solution is continuously absorbed into the water, yielding ammonia as a byproduct. After bittering, excess ammonia is removed by hot filtration. Solid, the resulting substance contains and The clear liquid was evaporated and concentrated at 55°C. Preferential crystallization, filtration, to obtain Product purity ≥ 98% (on a dry basis); contains The mother liquor from crystallization is recycled back to step 1.

[0044] The results of this embodiment Product purity ≥95%, Product purity ≥98% and All components circulate within the system, with no net consumption.

[0045] Example 2

[0046] This embodiment discloses a method for co-producing calcium sulfate using FGD waste gypsum as an auxiliary source. and The method includes the following steps:

[0047] Waste gypsum purification

[0048] Take FGD waste gypsum (main component) It contains 15 mg / kg As and 45 mg / kg Pb, and has a yellowish-brown organic pigment. It is mixed with water to form a slurry with a solid-liquid mass ratio of 1:3. Titanium dioxide is added to the slurry at a ratio of 1% of the dry weight of the waste gypsum to produce by-products. Continuously introduce air into the slurry for aeration for 1 hour, so that... Completely oxidized to ;join in Adjust the pH of the suspension to 6.0. In-situ hydrolysis produces particles with a diameter of less than 1 μm. Amorphous colloids, through co-precipitation, are removed from the liquid phase. , Adsorbed and fixed onto colloidal particles, and simultaneously subjected to electrostatic flocculation Humic acid-based organic pigments on the particle surface are transferred and fixed to On colloids.

[0049] After purification, two-stage filtration is performed: the first stage uses a plate and frame filter press with a 2 μm filter media for filtration. Crystals (particle size 5-100 μm). The colloid (particle size <1 μm) passes through with the filtrate; the resulting The filter cake was washed with deionized water to remove soluble substances. , Inorganic salts were obtained to produce a white, highly pure product. The As content was tested to be <0.5 mg / kg and the Pb content to be <1 mg / kg, and it was used for step 2; the second stage... The filtrate of the colloidal solution was filtered using a microfiltration membrane with a retention cutoff of 0.45 μm to remove heavy metals such as As and Pb, as well as organic pigments. The colloid is obtained as a solid, which is a hazardous waste residue containing heavy metals and is temporarily stored for later use; the purified filtrate is reused for waste gypsum slurry preparation.

[0050] Step 1 capture

[0051] To lithium salt mother liquor (containing 55 g / L 25 g / L) in the mother liquor Add 1.02 times the amount of substance Solution ( (Concentration 220 g / L, from the internal circulation of by-products from step 2 and bittering by-products from step 4), stirred for 30 min, filtered, to obtain... solid and Mixed solution.

[0052] Step 2 Medium liquid phase transformation

[0053] The result from step 1 High purity obtained from the purification of waste gypsum Together they were added at a solid-liquid mass ratio of 1:5 to a concentration of 250 g / L. In the solution, the reaction was stirred for 2 hours under normal pressure and 85°C. The conversion rate reached 85%. After filtration, the resulting... The solution is directly recycled back to step 1; the resulting The solution proceeds to step 3; no conversion. The solid phase is returned to this step for further transformation.

[0054] Step 3 Crystallization separation

[0055] The result from step 2 Solution and the solution obtained in step 1 The mixed solutions were combined, reacted at 50°C, and then cooled to 20°C. Preferential crystallization precipitates, filtered, yielding a white [color]. Product purity ≥95%; filtrate is divided into two streams: main stream... The solution is recycled back to step 2, and the lithium-rich solution enters step 4.

[0056] Step 4: Bitter Processing

[0057] Add the lithium-rich solution obtained in step 3 according to and Add 1.05 times the total amount of substance. Heat and stir at 80℃ for 1 hour to bitteren. After complete removal, the ammonia solution is collected, filtered while hot, and the clear liquid is evaporated and concentrated at 55°C. Crystallization occurs, followed by filtration to obtain... Product purity ≥98%; contains The mother liquor from crystallization is recycled back to step 1.

[0058] In this embodiment, the hazardous waste residue is temporarily stored and can be used in conjunction with the aluminum-silicon waste residue from Embodiment 3 or Embodiment 4 for geopolymer solidification treatment.

[0059] Example 3

[0060] This embodiment discloses a method for the co-processing of lithium salt mother liquor with FGD waste gypsum and potassium feldspar. and A method for solidifying hazardous waste, comprising the following steps:

[0061] Waste gypsum purification

[0062] FGD waste gypsum was mixed with water to form a slurry with a solid-liquid mass ratio of 1:5; titanium dioxide by-products were added at a ratio of 3% (dry weight) of the waste gypsum. Continuously introduce air for 2 hours to allow Completely oxidized to ;join in Adjust the pH of the suspension to 7.0. In-situ hydrolysis to generate The colloids are used to remove soluble heavy metals from the slurry liquid phase through co-precipitation and electrostatic flocculation. Organic pigments on the particle surface. Two-stage filtration is performed: the first stage uses a filter medium with a 5 μm filter media to remove... Crystals, obtained High-purity filter cake is obtained after washing with water. For use in step 2; the second paragraph contains The filtrate of the colloidal solution was retained using a microfiltration membrane with a retention cutoff of 0.8 μm. The colloid was obtained as a solid, which is a hazardous waste residue containing As and Pb, and will be temporarily stored for future use.

[0063] Potassium feldspar hydrothermal leaching

[0064] Potassium feldspar ore ( Content ≥12 wt% and concentration 350 g / L The solution (from the regeneration cycle in step 3) was added to a sealed stainless steel pressure-resistant reactor at a solid-liquid mass ratio of 1:8, and leaching was carried out at 150℃ under hydrothermal conditions for 5 hours. After the reaction was completed, the reactor was cooled to room temperature, and then the pressure was slowly released to allow the escaped solution to dissipate. The gas is absorbed by water through a conduit to obtain ammonia water. The leaching slurry (approximately 8 wt%) was recovered as a byproduct. The reactor was opened, and the leaching slurry was filtered to obtain... leachate ( (Concentration approximately 120 g / L) was added to the combined solution in step 3. Preparation; the resulting leachable solid aluminum-silicon waste residue (amorphous aluminosilicate) is collected and temporarily stored for use in the solidification step.

[0065] Step 1 capture

[0066] To lithium salt mother liquor (containing 60 g / L 35 g / L) Add 1.05 times the amount of substance Solution (from internal circulation), stir for 30 min, filter, and obtain solids and Mixed solution.

[0067] Step 2 Medium liquid phase transformation

[0068] The result from step 1 High purity obtained from the purification of waste gypsum Together they were added at a solid-liquid mass ratio of 1:5 to a concentration of 380 g / L. In the solution, the reaction was stirred for 4 hours under normal pressure and 100℃. The conversion rate reached 93%. After filtration, the resulting... The solution is recycled back to step 1; the resulting solution... The solution proceeds to step 3; no conversion. The solid phase is returned to this step for further transformation.

[0069] Step 3 Crystallization separation

[0070] The result from step 2 Solution and the solution obtained in step 1 The mixed solution and potassium feldspar hydrothermal leaching The leachates were combined, reacted at 50°C, and then cooled to 20°C. Preferential crystallization, filtration, to obtain Product purity ≥96%; filtrate is divided into two streams: main stream... The solution (concentration 350 g / L) is recycled back to step 2 and the hydrothermal leaching step, and the lithium-rich solution enters step 4.

[0071] Step 4: Bitter Processing

[0072] Add the lithium-rich solution obtained in step 3 according to and Add 1.10 times the total amount of substance. Heat and stir at 90℃ for 2 hours to bitteren. Continuously extract and absorb ammonia water, then filter while hot to remove excess. The clear liquid was evaporated and concentrated at 55°C. Crystallization occurs, followed by filtration to obtain... Product purity ≥98%; contains The mother liquor from crystallization is recycled back to step 1.

[0073] Hazardous waste solidification steps

[0074] The aluminum-silicon waste residue was divided into 10 mol / L dry basis weights. The solutions were mixed at a mass ratio of 1:0.8 and activated with alkali at 60℃. The amorphous Si-O and Al-O bonds in the aluminum-silicon waste depolymerized and then repolymerized, forming a three-dimensional network of sodium aluminosilicate gel. Within 35 minutes of the start of alkali activation, the temporarily stored... Heavy metal-containing hazardous waste residue containing heavy metals (As, Pb) was uniformly mixed into the gel system at 30% of the dry weight of the aluminum-silica waste residue. After gel solidification, the heavy metals in the hazardous waste residue were physically encapsulated and chemically bonded to the aluminosilicate network. Leaching test of the solidified product: As leaching concentration 0.6 mg / L (<1 mg / L of building material standard threshold), Pb leaching concentration 0.8 mg / L (<1 mg / L of building material standard threshold). The solidified product was used as building blocks.

[0075] Example 4

[0076] This embodiment discloses a method for the comprehensive recovery and preparation of lithium salt mother liquor in conjunction with FGD waste gypsum and potassium feldspar. and A method for solidifying hazardous waste residue, comprising the following steps:

[0077] Step 1: FGD Waste Gypsum Purification

[0078] FGD waste gypsum (main component) Add water to prepare a slurry with a solid-liquid mass ratio of 1:4. Add titanium dioxide by-products to the slurry at a ratio of 2% (dry basis weight) of waste gypsum. Simultaneously, air is continuously introduced into the slurry for aeration, with an aeration time of 1.5 hours. Under aeration conditions, by air Oxidized to .

[0079] After oxidation is complete, lime slurry is added to the slurry. (Suspension), adjust the slurry pH to 6.5. Within this pH range, In-situ rapid hydrolysis produces particles smaller than large specific surface area Amorphous colloidal particles. The resulting... Colloids have the following two purification functions:

[0080] Firstly, co-precipitation captures soluble heavy metals: in the slurry liquid phase , Soluble heavy metal ions Colloidal adsorption and coprecipitation fix the colloidal particles on the surface, transferring them from the liquid phase to the solid phase.

[0081] Secondly, electrostatic flocculation captures organic pigments: adhering to... The organic pigments (humic acids) on the particle surface are negatively charged, while Colloids carry a positive charge under acidic to weakly alkaline conditions, and the two attract each other through electrostatic attraction, causing organic pigments to... Particles detach from and transfer to the surface of the particles. On colloidal particles.

[0082] After purification, utilize Crystals (grain size 5–100) )and Colloids (particle size) The slurry is separated in two stages due to a particle size difference of approximately 1–2 orders of magnitude between the particles: the first stage uses a coarse-pore filter medium (with a retention accuracy of 3 μm) to retain... Crystals, with a grain size smaller than of The colloid (carrying heavy metals and organic pigments) passes through the coarse-porous medium with the filtrate; the resulting The filter cake is washed with water to remove soluble inorganic salt impurities, yielding a highly purified product. This is for use in step three. The second paragraph contains... The filtrate of the colloidal substance was filtered using a fine-pore filter medium (retention accuracy 0.22 μm) to retain... The colloid (with heavy metals and organic pigments attached to it) and the resulting solid are heavy metal-containing hazardous waste residues, which are temporarily stored for use in step 4-2 for alkaline activation and solidification treatment; the resulting purified filtrate is reused for slurry preparation and washing.

[0083] Step 2: Potassium Feldspar hydrothermal leaching

[0084] Potassium feldspar ore was mixed with a concentration of 280 g / L The solution (from the regeneration cycle in step three) was added to a sealed pressure-resistant container at a solid-liquid mass ratio of 1:6, and leaching was carried out at 150°C under hydrothermal conditions for 3.5 h. The product generated during the reaction... The gas accumulates in the gas phase space of a sealed container. After the reaction is complete, the container is cooled down, and then the pressure is slowly released to allow the escaped gas to dissipate. The gas is introduced into the water for absorption, and the resulting ammonia water is collected and recycled as a byproduct. After depressurization, the container is opened, and the leachate slurry is filtered. leachate ( (Concentration approximately 100 g / L) is added to step three for use Preparation; the resulting leachate solid aluminum-silicon waste residue (amorphous aluminosilicate containing highly active Si-O and Al-O bonds) is collected and temporarily stored for use in step four.

[0085] Step 3: Chlorination Conversion of Mother Liquor and Co-production

[0086] 3-1 capture

[0087] To lithium salt mother liquor (containing 55 g / L 30 g / L) in the mother liquor Add 1.02 times the amount of substance Solution (from internal circulation, (Concentration approximately 210 g / L), stir the reaction for 30 min, filter, and obtain solid and Mixed solution. Used The solution comes from the internal circulation of the by-products of step 3-2 and the bittering by-products of step 4, and there is no need to continuously purchase it from external sources.

[0088] 3-2, Two-step conversion of medium in liquid phase at low temperature

[0089] The first step is to use the output of 3-1 The high purity obtained from step one purification Together they were added at a solid-liquid mass ratio of 1:5 to a concentration of 320 g / L. In the solution, under normal pressure and 95℃ conditions, the reaction was stirred for 3 h, resulting in a liquid-phase metathesis reaction:

[0090]

[0091] Conversion rate reaches 90%. Filter, the obtained... The liquid is directly recycled back to 3-1 to capture the mother liquor. ,constitute Inner loop; results The solution proceeds to the second step; the filtered result contains residue. solid phase and subsequent batches Merge, return to this step to continue the transformation.

[0092] The second step is to The solution obtained from 3-1 Mixed solution and the solution obtained in step two The leachates were combined, thoroughly mixed at 50°C, and then cooled to 20°C. (Solubility approximately 11.1 g / 100 mL) preferentially reaches saturation and crystallizes out, while by The form (solubility approximately 80 g / 100 mL) remains in the solution without precipitation, thus achieving efficient separation of Li and K. Filtration yields... The product has a purity of ≥96%; the resulting filtrate contains... and ,main body The solution (concentration 280 g / L) is recycled back to steps one and two to maintain its stability. Internal circulation; additionally, it includes... With residue The lithium-rich liquid material proceeds to step four.

[0093] Step 4: Bitter Processing Alkali-activated geopolymer solidification of heavy metal-containing hazardous waste residue with aluminum and silicon waste residue

[0094] 4-1. Bitter processing

[0095] To the product obtained in step 3-2 and Add 1.05 times the amount of substance to the filtrate. The bittering reaction was carried out by heating and stirring at 85℃ for 1.5 h.

[0096]

[0097]

[0098] Continuous heating will The ammonia is fully expelled and recovered, and the resulting ammonia water is collected and recycled as a byproduct. After bittering, excess ammonia is removed by hot filtration. Solid, to obtain containing and The bittering liquid was then concentrated by evaporation at 50°C. (Solubility approximately 12.5 g / 100 mL) preferentially reaches saturation and crystallizes out. (Solubility approximately 74.5 g / 100 mL) Remain dissolved in the mother liquor during crystallization. Filter to separate, obtaining... Product purity ≥98%; contains The mother liquor from crystallization is recycled back to step 3-1 to capture the crystals in the mother liquor. ,constitute Internal circulation.

[0099] 4-2. Alkali-activated geopolymer solidification of heavy metal hazardous waste residue from aluminum-silicon waste

[0100] The aluminum-silicon waste residue obtained in step two was divided into two groups based on the dry basis weight of the aluminum-silicon waste residue and 8 mol / L. The solution was added to a sodium hydroxide solution at a mass ratio of 1:1, and alkaline activation was performed at 50°C. The amorphous Si-O and Al-O bonds in the aluminum-silicon waste were... Provided Depolymerization and deagglomeration, forming and Monomers; under alkaline conditions, the above monomers undergo condensation reactions and recombine to form a three-dimensional network of sodium aluminosilicate gel, i.e., geopolymer precursor gel.

[0101] During the plastic stage before gel solidification (within 30 minutes after the start of alkali activation), the product from step one containing... Heavy metal-containing hazardous waste residue (As, Pb) was uniformly mixed into the gel system at 20% of the dry weight of the aluminum-silica waste residue, so that the hazardous waste residue particles were encapsulated by the geopolymer gel. After the gel solidified, the heavy metals in the hazardous waste residue were fixed in the three-dimensional aluminosilicate network structure through both physical encapsulation and chemical bonding. Leaching test of the solidified product: As leaching concentration 0.4 mg / L (<1 mg / L of building material standard threshold), Pb leaching concentration 0.6 mg / L (<1 mg / L of building material standard threshold), compressive strength reached 22.7 MPa, and the solidified product was used as a foundation filler.

[0102] Experimental verification

[0103] Experiment 1: Comparison and verification of liquid phase low-temperature conversion efficiency and energy consumption

[0104] 1. Experimental Objective

[0105] Verification The solution is the medium, under normal pressure At ℃ Liquid-phase metathesis conversion The conversion rate was compared with the energy consumption of the traditional Mannheim high-temperature solid-state process (approximately 550°C), demonstrating the technical effectiveness of the invention's "liquid-phase low-temperature replacement of high-temperature solid-state".

[0106] 2. Preparation of experimental samples

[0107] Following the method in step 3-1 of Example 4, take the lithium salt mother liquor (containing... 55 g / L 30g / L), according to Add 1.02 times the amount of substance Solution ( (Concentration 210 g / L), stir the reaction at room temperature for 30 min, filter, and obtain Solids were used as raw materials for liquid-phase transformation in each experimental group.

[0108] Control sample (Mannheim process control): Take With thick The mixture was thoroughly mixed at a theoretical molar ratio of 2:1 and calcined at 550℃ for 4 hours in a muffle furnace, resulting in a solid-phase reaction. )generate After cooling, the product was used as a control group. The process energy consumption was taken from the literature value of approximately 3500 kJ / kg. .

[0109] 3. Experimental conditions

[0110] The following liquid-phase inversion experimental groups were set up respectively:

[0111] Group A: Concentration 250 g / L, reaction temperature 80℃, reaction time 2 h (corresponding to Example 1).

[0112] Group B: Concentration 320 g / L, reaction temperature 95℃, reaction time 3 h (corresponding to Example 4).

[0113] Group C: Concentration 380 g / L, reaction temperature 100℃, reaction time 4 h (corresponding to Example 3).

[0114] The solid-liquid mass ratio of Group A was 1:4 (consistent with Example 1), and the solid-liquid mass ratio of Groups B and C was 1:5 (consistent with Example 4 and Example 3, respectively). All groups used three-necked flasks equipped with reflux condensers and were heated in a constant temperature water bath.

[0115] 4. Experimental Procedure

[0116] (1) Prepare solutions with concentrations of 250 g / L, 320 g / L, and 380 g / L respectively. 500 mL of each solution.

[0117] (2) The samples were added to the above-mentioned liquids at a solid-liquid mass ratio of 1:5. The solution is placed in a three-necked flask equipped with a reflux condenser.

[0118] (3) Stir the reaction in constant temperature water baths at 80℃, 95℃ and 100℃ for the set time.

[0119] (4) After the reaction is complete, filter while hot and analyze the filtrate by ion chromatography. Concentration, calculation Conversion rate (conversion rate = percentage transferred into the liquid phase) Amount of substance / added Theories (Amount of substance × 100%).

[0120] (5) Comparison of energy consumption among groups: The energy consumption of the liquid phase conversion group is calculated based on the actual heating power consumption (kJ / kg- The Mannheim control group was based on a literature value of approximately 3500 kJ / kg. .

[0121] (6) Take the results from each liquid phase group Solution and The solutions were mixed, cooled to 20°C to crystallize, and then filtered to obtain... The purity of the product was determined using the ICP-OES method.

[0122] 5. Experimental Results

[0123] Table 1 shows the experimental groups. Conversion rate versus product purity.

[0124]

[0125] Note: The Mannheim process is a solid-phase reaction; the "conversion rate" here refers to the KCl solid-phase conversion rate (reference value), compared to the liquid-phase conversion rate. The conversion rate concept is different and is only for reference in energy consumption comparison.

[0126] Figure 1 For each experimental group Bar chart comparing conversion rate and process energy consumption. plt.show()

[0127] 6. Analysis and Summary

[0128] The liquid-phase low-temperature conversion process of this invention operates at 80-100℃. Conversion rates can reach 82%-93%, yielding... The product purity reaches over 95%, while the process energy consumption is only 23%-30% of that of the traditional Mannheim process (approximately 820-1050 kJ / kg compared to 3500 kJ / kg), demonstrating significant energy-saving effects.

[0129] Follow Increased concentration and temperature significantly improved the conversion rate, proving that high concentration... The key factor driving the forward reaction is the purity of the resulting product, which meets the requirements for industrial and agricultural applications.

[0130] Experiment 2: FGD waste plaster Colloid purification effect verification

[0131] 1. Experimental Objective

[0132] Verification using titanium dioxide byproducts Iron source, in-situ generation The effect of colloids on the purification of FGD waste gypsum was investigated. The changes in the content of heavy metals As and Pb in the waste gypsum and the whiteness of the product before and after purification were quantitatively evaluated, proving the technical effect of "one-step purification to simultaneously remove heavy metals and organic pigments".

[0133] 2. Preparation of experimental samples

[0134] Take the same batch of FGD waste gypsum raw materials (main component) The sample, tested and found to contain 15 mg / kg As and 45 mg / kg Pb (yellowish-brown in appearance, with a whiteness of approximately 62%), was divided into four groups for purification experiments to investigate its composition. The effect of dosage on purification effect. (Groups) The dosage (as a percentage of the dry weight of waste gypsum) was set to 0% (blank control), 1% (lower limit of parameters), 2% (corresponding to Example 4), and 3% (upper limit of parameters, corresponding to the FeSO4 dosage in Example 3). All other experimental conditions (solid-liquid mass ratio 1:4, aeration time 1.5 h, pH 6.5, filtration accuracy 3 μm and 0.22 μm) were uniformly adopted from the parameters in Example 4 to ensure a single-variable experimental logic.

[0135] 3. Experimental conditions

[0136] All groups used a solid-liquid mass ratio of 1:4 with water to prepare the slurry, continuously aerated with air for 1.5 h, and adjusted the pH to 6.5 with lime slurry (consistent with Example 4). Two-stage filtration: the first stage had a retention accuracy of 3 μm, and the second stage had a retention accuracy of 0.22 μm. The filter cake was washed three times with deionized water and then dried at 80°C for testing.

[0137] 4. Experimental Procedure

[0138] (1) By each group Dosage: Prepare a slurry by mixing waste gypsum and water at a solid-liquid mass ratio of 1:4, and add the corresponding amount... .

[0139] (2) Air was continuously introduced into the slurry for 1.5 h in each group, and samples were taken to test the filtrate. Concentration (o-phenanthroline colorimetric method), confirmed. Completely oxidized to .

[0140] (3) Add to each group of slurry Adjust the pH of the suspension to 6.5 and stir for 30 minutes. In-situ hydrolysis to generate colloid.

[0141] (4) Perform two-stage filtering: the first stage interception The crystals and filter cake were washed three times with deionized water and dried at 80°C to obtain purified crystals. Product; the second paragraph contains The filtrate of the colloidal substance was filtered using a 0.22 μm microfiltration membrane to remove hazardous waste residue.

[0142] (5) The As and Pb contents of each group of purified products were tested by ICP-OES method, and the whiteness (%) of the products was determined by whiteness meter (ISO brightness method).

[0143] (6) The enrichment of As and Pb in the blank control group and each purification group of hazardous waste residue was measured, and the heavy metal removal rate was calculated.

[0144] 5. Experimental Results

[0145] Table 2 shows the differences. Comparison of the purification effect of waste gypsum under different dosage conditions.

[0146]

[0147] Figure 2 and Figure 3 After purification The content of As and Pb and the whiteness of the whiteness vary with Line graph showing changes in usage.

[0148] Figure 4 Before and after purification of FGD waste gypsum Comparison of particle microstructure (SEM images).

[0149] 6. Analysis and Summary

[0150] Experimental results show that, with Under the condition that the dosage accounts for 1% to 3% of the dry weight of waste gypsum, in-situ generation Colloidal particles can increase the removal rate of As to 86%-98% and the removal rate of Pb to 87%-98.4% in waste gypsum, after purification. Whiteness increased significantly from 62.3% to 82.6% and 92.8%.

[0151] At a dosage of 2% (corresponding to Example 4, the purification effect was already very significant; increasing to 3% resulted in saturation, indicating that 2% is a suitable and economical dosage). The purified product met the requirements for subsequent agricultural-grade preparation. It has high requirements for the quality of raw materials, and the entire purification process is completed in one step, making the process simple and efficient.

[0152] Experiment 3: Verification of the efficiency of selective separation of Li / K by low-temperature metathesis crystallization

[0153] 1. Experimental Objective

[0154] Verification was conducted at a low temperature of 20℃. Preferential crystallization and precipitation by The selective separation effect of the form retained in solution was systematically investigated, focusing on the effect of crystallization temperature on the crystallization process. The influence of crystallization rate on Li loss rate demonstrates the technical effectiveness of the present invention in "achieving efficient K / Li separation by utilizing solubility differences".

[0155] 2. Preparation of experimental samples

[0156] The preparation steps were carried out simultaneously according to the method in Example 4: Lithium salt mother liquor (containing...) was taken... 55 g / L 30 g / L), through step 3-1 Capture, Step 3-2 After the medium undergoes liquid-phase transformation, the resulting... The solution obtained in step 3-1 The mixed solution, and the potassium feldspar hydrothermal leaching step according to Example 4, 280 g / L The solid-liquid ratio was 1:6, and the solution was leached at 150℃ for 3.5 h. leachate ( The concentrations (approximately 100 g / L) were combined and thoroughly mixed at 50°C to form the experimental solution. The concentration is approximately 45 g / L. Concentration approximately 8 g / L The concentration was approximately 120 g / L, and the samples were divided into 5 groups, with 200 mL in each group.

[0157] 3. Experimental conditions

[0158] The five groups of solutions were cooled to 10℃, 15℃, 20℃, 25℃, and 30℃ respectively, and kept at these temperatures with stirring for 1 hour before filtration to investigate the effect of crystallization temperature on the crystallization process. The effects of crystallization rate and Li loss rate.

[0159] 4. Experimental Procedure

[0160] (1) Divide the 50℃ experimental solution into 5 portions and place them in a constant temperature water bath. Cool them down to the target temperatures of 10℃, 15℃, 20℃, 25℃ and 30℃ respectively at a cooling rate of 0.5℃ / min.

[0161] (2) Each group was kept at the target temperature and stirred for 1 h to allow the system to fully crystallize and reach equilibrium.

[0162] (3) Filter while warm and collect the solid phases separately. (crystals) and liquid phase (filtrate).

[0163] (4) Dry the solid phase at 80℃, weigh it, and calculate. Crystallization rate (crystallization rate = actual crystallization) Mass / Theoretical Maximum (mass × 100%).

[0164] (5) The solid product and filtrate were analyzed by ICP-OES. and Concentration, calculate Li loss rate (mass of Li in solid phase / initial total mass of Li × 100%) and Product purity.

[0165] 5. Experimental Results

[0166] Table 3 shows the effect of different crystallization temperatures on... The effect of crystallization rate on Li loss rate.

[0167]

[0168] Figure 5 For different crystallization temperatures Biaxial line graph of crystallization rate versus Li loss rate.

[0169] 6. Analysis and Summary

[0170] Experimental results show that within the range of 1030℃, The crystallinity increased significantly with decreasing temperature (55.1%-87.6%), while the Li loss rate remained extremely low (0.4%-2.4%), fully demonstrating... (Solubility approximately 11.1 g / 100 mL) and The high selectivity separation effect is achieved due to the huge difference in solubility between (approximately 80 g / 100 mL).

[0171] 20°C is the recommended operating temperature (consistent with Example 4). With a crystallization rate of 78.5%, a Li loss rate of only 1.1%, and a product purity of 96.3%, it achieves efficient separation of Li and K, balancing product quality with lithium recovery indicators.

[0172] Experiment 4: Verification of the effect of geopolymer solidification of heavy metal hazardous waste residue from aluminum-silicon waste residue

[0173] 1. Experimental Objective

[0174] Verification of aluminum-silicon waste residue The solidification effect of alkali-activated geopolymers on hazardous waste residue containing As and Pb was evaluated by heavy metal leaching toxicity tests (according to GB 5085.3 standard) to determine whether the solidified products meet the requirements for use as building materials, demonstrating the technical effectiveness of "fixing heavy metals through a dual mechanism of physical encapsulation and chemical bonding to achieve harmless transformation of hazardous waste residue".

[0175] 2. Preparation of experimental samples

[0176] Aluminum-silicon waste residue: potassium feldspar as described in Example 4 Preparation by hydrothermal leaching, i.e., potassium feldspar ore with 280 g / L The solution was added to a sealed pressure-resistant reactor at a solid-liquid mass ratio of 1:6, and hydrothermally leached at 150℃ for 3.5 h. After filtration, the obtained leached solid phase was dried at 80℃, which is the amorphous aluminum-silicon waste residue containing highly active Si-O and Al-O bonds.

[0177] Hazardous waste residue: Prepared according to the waste gypsum purification steps in Example 4, i.e. The dosage is 2% of the dry weight of waste gypsum, the pH is adjusted to 6.5, and it is filtered through two stages. The second stage uses a 0.22 μm microfiltration membrane to retain the contents of... Solids containing heavy metals such as As and Pb, dried at 80°C, become hazardous waste residue for laboratory use.

[0178] The solidified samples were grouped as follows: Blank group (unsolidified): leaching test was performed directly on the original hazardous waste residue; Experimental group A: aluminum-silicon waste residue with 6 mol / L... Solution mass ratio 1:0.8, alkali activation at 60℃, hazardous waste residue dosage 10%; Experimental Group B: aluminum-silicon waste residue mixed with 8 mol / L... Solution mass ratio 1:1, alkali activation at 50℃, hazardous waste residue dosage 20% (corresponding to Example 4; Experimental Group C: aluminum-silicon waste residue and 10 mol / L The solution mass ratio is 1:0.8, activated by alkali at 60℃, and the amount of hazardous waste residue added is 30% (corresponding to Example 3).

[0179] 3. Experimental conditions

[0180] The alkaline activation temperature is 40-60℃. The hazardous waste residue is uniformly mixed into the gel within 30 minutes after the start of alkaline activation. The mixture is then poured into a standard 50 mm × 50 mm × 50 mm cube mold and cured at room temperature for 28 days before various tests are conducted.

[0181] 4. Experimental Procedure

[0182] (1) Mix aluminum-silicon waste with each group according to the proportions. The solutions are mixed and stirred thoroughly at a set temperature to induce alkali activation.

[0183] (2) Within 30 minutes after the start of alkali activation, add the corresponding proportion of hazardous waste residue evenly to the gel system and continue stirring until uniform.

[0184] (3) Pour the mixture into a standard 50 mm × 50 mm × 50 mm steel mold, vibrate to remove air, and cure at room temperature (25 ± 2℃) for 28 days before demolding.

[0185] (4) After curing, the leaching toxicity test was carried out on each group of cured products: According to GB 5085.3 acetic acid buffer solution method, the cured products were crushed to a particle size of less than 9.5 mm, acetic acid buffer solution was added at a liquid-solid ratio of 10:1, and the product was shaken and extracted for 16 h. After filtration, the concentrations of As and Pb in the leachate were detected by ICP-OES method.

[0186] (5) Simultaneously test the compressive strength of each group of cured products (universal testing machine, loading rate 0.5 MPa / s), with 3 parallel samples for each group, and take the average value.

[0187] 5. Experimental Results

[0188] Table 4 compares the heavy metal leaching concentration and compressive strength of each group of cured products.

[0189]

[0190] Figure 6 A bar chart comparing the leaching concentrations of As and Pb in each group of cured products.

[0191] Figure 7The image shows the SEM image of the geopolymer microstructure of the cured product (cured for 28 days) in Experiment B.

[0192] 6. Analysis and Summary

[0193] Experimental results showed that the leaching concentration of As in the unsolidified hazardous waste residue was as high as 18.6 mg / L and the leaching concentration of Pb was as high as 42.3 mg / L, far exceeding the hazardous waste determination threshold of GB 5085.3 (As>5 mg / L, Pb>5 mg / L), classifying it as hazardous waste with high disposal costs. After solidification treatment with the geopolymer of this invention, the leaching concentration of As in each experimental group decreased to 0.38-0.72 mg / L and the leaching concentration of Pb decreased to 0.61-0.91 mg / L, both lower than the landfill standard threshold for building materials (As<1 mg / L, Pb<1 mg / L), with a leaching toxicity reduction rate exceeding 96%.

[0194] Experimental Group B (corresponding to parameters in Example 4: 8 mol / L) The best solidification effect is achieved when the hazardous waste residue content is 20%, with a compressive strength of 22.7 MPa, which is 15 MPa higher than the lower limit of building material requirements. The solidified products can be used as building blocks or foundation fillers for resource utilization, completely eliminating the cost of hazardous waste residue disposal and realizing the harmless transformation and zero discharge of hazardous waste residue within the system.

[0195] The embodiments of the present invention have been described above. However, the embodiments are not limited to the specific implementation methods described above. The specific implementation methods described above are merely illustrative and not restrictive. Those skilled in the art can make more equivalent embodiments under the guidance of the present embodiments, and all of them are within the protection scope of the present embodiments.

Claims

1. A method for comprehensive recovery of lithium salt mother liquor to produce lithium hydroxide and potassium sulfate, characterized in that, Includes the following steps: Step 1: Add calcium chloride solution to lithium salt mother liquor to precipitate all sulfate ions in the mother liquor as calcium sulfate. Filter to obtain solid calcium sulfate and a mixed solution containing lithium chloride and potassium chloride. Step 2: Add the calcium sulfate obtained in Step 1 to the ammonium chloride solution and perform liquid-phase double decomposition at normal pressure and 80-100℃ to convert the calcium sulfate into ammonium sulfate. Filter the solution, and return the resulting calcium chloride solution to Step 1. The resulting ammonium sulfate solution will then enter Step 3. Step 3: Combine the ammonium sulfate solution obtained in Step 2 with the mixed solution obtained in Step 1, cool to 20°C to allow potassium sulfate to crystallize out preferentially, filter to obtain potassium sulfate product; the main ammonium chloride solution in the obtained filtrate is recycled back to Step 2, and the lithium-rich solution containing lithium chloride and ammonium chloride enters Step 4. Step 4: Add excess calcium hydroxide to the lithium-rich solution obtained in Step 3, heat to drive out ammonia gas, filter while hot to remove calcium hydroxide solid, evaporate and concentrate the resulting clear solution containing lithium hydroxide and calcium chloride below 60°C to crystallize lithium hydroxide monohydrate, filter to obtain lithium hydroxide monohydrate product; the crystallization mother liquor containing calcium chloride is recycled back to Step 1.

2. The method of claim 1, wherein, In step 2, the high-purity calcium sulfate obtained from the purified flue gas desulfurization waste gypsum is added together with the calcium sulfate obtained in step 1 to an ammonium chloride solution for liquid-phase conversion.

3. The method of claim 2, wherein, The waste gypsum purification treatment includes the following operations: adding water to the waste gypsum from flue gas desulfurization to prepare a slurry with a solid-liquid mass ratio of 1:31:5; adding ferrous sulfate heptahydrate to the slurry at a ratio of 1% to 3% of the dry weight of the waste gypsum; continuously aerating the slurry with air to oxidize ferrous iron to ferric iron; adding calcium hydroxide suspension to adjust the pH of the slurry to 6.0-7.0; and hydrolyzing ferric iron in situ to generate amorphous ferric hydroxide colloids with a particle size of less than 1 μm. The colloid adsorbs soluble arsenic and lead heavy metal ions in the liquid phase through co-precipitation, and at the same time, electrostatic flocculation transfers and fixes humic acid organic pigments on the surface of calcium sulfate particles onto the colloid.

4. The method of claim 3, wherein, After purification, the slurry is filtered in two stages: the first stage uses a filter medium with a retention accuracy of 1-5 μm to retain calcium sulfate crystals. The resulting calcium sulfate filter cake is washed with water to remove soluble inorganic salts to obtain high-purity calcium sulfate, which is used in step 2. The second stage uses a filter medium with a retention accuracy of less than 1 μm to retain ferric hydroxide colloids containing arsenic and lead heavy metals. The resulting solid is hazardous waste residue and is temporarily stored for later use.

5. The method of claim 1, wherein, In step 3, the potassium chloride leachate obtained by hydrothermal leaching of potassium feldspar ore and ammonium chloride solution is also incorporated into the combined solution of step 3 to participate in the preparation of potassium sulfate. The hydrothermal leaching is as follows: potassium feldspar ore and ammonium chloride solution are added to a sealed pressure-resistant container at a solid-liquid mass ratio of 1:41:8, and leached at 150℃ for 25 h under hydrothermal conditions. After filtration, the resulting leachate is a potassium chloride solution, and the resulting leachate solid phase is an amorphous aluminum-silicon waste residue containing highly active silicon-oxygen bonds and aluminum-oxygen bonds.

6. The method of claim 5, wherein, The concentration of the ammonium chloride solution in the hydrothermal leaching is 200-350 g / L, and the ammonium chloride solution used comes from the ammonium chloride solution recycled in step 3.

7. The method according to claims 4 and 5, characterized in that, The process also includes the following curing steps: adding the aluminum-silicon waste residue to a sodium hydroxide solution with a concentration of 6-10 mol / L, and activating it with alkali at 40-60℃ to generate a three-dimensional network sodium aluminosilicate gel; within 30-60 min after the start of alkali activation, uniformly mixing the hazardous waste residue into the gel system; after the gel solidifies, the heavy metals in the hazardous waste residue are physically encapsulated and chemically bonded to the aluminosilicate network, and the solidified product is used as a building material.

8. The method of claim 1, wherein, The concentration of the ammonium chloride solution used in step 2 is 250-380 g / L, and the reaction time for liquid-phase metathesis is 2-4 h.

9. The method of claim 5, wherein, After hydrothermal leaching is completed, the sealed pressure-resistant container is cooled down, and then the pressure is slowly released. The released ammonia gas is introduced into the water for absorption, and ammonia water is obtained as a by-product for recycling.

10. The method of claim 3, wherein, The ferrous sulfate heptahydrate is a byproduct of titanium dioxide production.

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