A stepwise extraction process for potassium-rich multi-component brine

Abstract

This invention provides a stepwise extraction process for potassium-rich multi-component brine. The extraction sequence is as follows: negative pressure desulfurization of brine to produce sodium sulfide; brine alkali adjustment system; adsorption method for strontium extraction to produce strontium carbonate; adsorption method for boron extraction to produce boric acid; lime method reaction to produce magnesium hydroxide and calcium sulfate; stage I evaporation and crystallization to produce sodium chloride; soda ash method to produce calcium carbonate; brine acidification system; adsorption for lithium extraction to produce lithium carbonate; oxidation and blowing of iodine and bromine to produce iodine and bromine; adsorption for cesium extraction to produce cesium nitrate; adsorption for rubidium extraction to produce rubidium nitrate; stage II evaporation and concentration to produce sodium chloride and potassium chloride. The process route of this invention is clear and well-defined, with relaxed production conditions, avoiding interference between elements. It also produces high-quality products, high element yields, low production costs, simple operation, and low labor intensity. The extraction process achieves closed-loop circulation, resulting in zero emissions of waste gas, wastewater, and solid waste, thus achieving green and environmentally friendly production.

Description

Technical Field

[0001] This invention relates to the field of brine chemical technology, specifically to a stepwise extraction process for potassium-rich multi-component brine. Background Technology

[0002] Potassium-rich multi-component brine is a liquid mineral resource, typically rich in elements such as lithium, sodium, potassium, rubidium, cesium, boron, strontium, iodine, bromine, calcium, and magnesium. The common practice in coastal areas and salt lakes both domestically and internationally is to selectively extract high-value-added and easily extractable elements from the brine. Salt lakes, far from downstream industrial areas, are typically used to extract potassium chloride, borax, and lithium chloride due to transportation distance limitations. Coastal areas, influenced by seawater concentration and regional climate, generally extract sodium chloride, potassium chloride, magnesium sulfate, magnesium chloride, and bromine.

[0003] However, existing extraction technologies often result in unextracted elements being discharged as waste liquid into lakes or the sea, leading to the accumulation and disposal of solid waste. This not only wastes resources but also causes environmental pollution. For inland areas, the coastal and salt lake models are not suitable; a more scientific, systematic, and comprehensive extraction process is needed to address the issues of low resource utilization, mediocre product quality, and the discharge of waste gases, wastewater, and solid waste. Summary of the Invention

[0004] In view of the shortcomings and incompleteness of the existing technology, the purpose of this invention is to provide a stepwise extraction process for potassium-rich multi-component brine to solve the problems mentioned in the background technology. This invention is not only simple to operate and has relaxed production conditions, but also produces high-quality products, high element yield, low production cost, high degree of automation, and low labor intensity. It combines environmental protection with product extraction, and the extraction process realizes closed-loop circulation, achieving zero emissions of waste gas, wastewater, and solid waste, thus realizing green and environmentally friendly production.

[0005] To achieve the above objectives, the present invention provides a stepwise extraction process for potassium-rich multi-component brine, comprising the following steps:

[0006] Step 1: Desulfurization of brine under negative pressure to produce sodium sulfide products;

[0007] Step 2: Adjust the alkali content of the brine once;

[0008] Step 3: Strontium extraction using adsorption method to produce strontium carbonate products;

[0009] Step 4: Boron extraction via adsorption to produce boric acid products;

[0010] Step 5: Produce magnesium hydroxide and calcium sulfate products via lime reaction;

[0011] Step Six: Secondary Alkali Adjustment of Brine;

[0012] Step 7: Evaporation and crystallization in stage I to produce sodium chloride product;

[0013] Step 8: Producing calcium carbonate products using the soda ash process;

[0014] Step 9: Lithium extraction using the adsorption method to produce lithium carbonate products;

[0015] Step 10: Oxidation and blowing of iodine and bromine to produce iodine and bromine products;

[0016] Step 11: Extracting cesium from cesium using the adsorption method to produce cesium nitrate;

[0017] Step 12: Rubidium nitrate production by adsorption method;

[0018] Step 13: Stage II evaporation and concentration to produce sodium chloride and potassium chloride products.

[0019] Furthermore, in step one, a negative pressure desulfurization-alkali absorption process is adopted: the mixed acid by-product of the bromine-iodine process is used to adjust the pH of the raw brine to 5-6 and then pumped into the negative pressure degassing tower. Under negative pressure conditions, the hydrogen sulfide gas in the brine is accelerated to escape. The pressure inside the tower is controlled to be -0.01 to -0.05 MPa. After the hydrogen sulfide is removed, the residual concentration of hydrogen sulfide in the brine is ≤10 mg / L. Sodium hypochlorite oxidant is added to the brine after the hydrogen sulfide gas is removed. After passing through a static mixer, it enters the next process. The amount added is 110% to 120% of the residual hydrogen sulfide equivalent. The hydrogen sulfide gas escaping from the brine passes through the absorption tower and is absorbed by a 13% sodium hydroxide solution. When the pH of the absorption solution is <12, the absorption is stopped to obtain the absorption completed solution. The absorption completed solution is replaced and then evaporated, concentrated, dehydrated, and flaked to obtain the alkali sulfide product.

[0020] In step two, the desulfurized brine from the sodium sulfide process in step one is adjusted to pH 8-9 using 10% lime slurry. The brine is then filtered through a precision filter and sent to the strontium extraction process. A small amount of backwash liquid generated by the precision filter is used together with the washing liquid from the magnesium hydroxide and calcium sulfate processes to prepare lime slurry. The precision filter separates solids into a small amount of magnesium hydroxide, suspended solids, and calcium sulfate.

[0021] Furthermore, in step three, strontium is first adsorbed and extracted from the brine, and then strontium carbonate is obtained by reaction and crystallization using soda ash. The specific scheme includes: passing the brine from the first alkali adjustment process through a chelating resin with strong selectivity for strontium at a flow rate of 1~100 BV / h until the strontium concentration in the adsorbed liquid is <5ppm, at which point adsorption is stopped to obtain destrontium brine. The destrontium brine enters the next process, where the concentration of hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2%~10%, and the strontium adsorption resin is desorbed to obtain strontium eluent. The washing flow rate is 1~100 BV / h, and the desorption is stopped when the eluent concentration is below 0.5g / l. The eluent is collected and mixed, filtered through a 5μm security filter to remove suspended impurities, and then evaporated and concentrated to 50~100g / l of strontium. A 40% soda ash solution is added to react and precipitate, followed by dehydration, washing, and drying to obtain the strontium carbonate product.

[0022] Furthermore, in step four, the production process for boric acid includes: passing brine from the strontium carbonate extraction process through a chelating resin with strong boron selectivity at a flow rate of 1-100 BV / h until the boron concentration in the adsorption liquid is <5 ppm, at which point adsorption is stopped to obtain deboronized brine. The deboronized brine enters the subsequent process, where the concentration of hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2%-10%. The boron adsorption resin is eluted with 5% dilute hydrochloric acid to obtain boron eluent, with a washing flow rate of 1-100 BV / h. When the eluent concentration is below 0.5 g / L, the eluent is collected and mixed, filtered through a 5 μm security filter to remove suspended impurities, then heated to 60-90°C, concentrated through a 4-stage membrane evaporation to 50-85 g / L of boron, and then subjected to multi-stage flash cooling crystallization.

[0023] In step five, the specific production plan includes: After boron extraction in the boric acid process, 10% lime slurry is added to the brine in a calcium-magnesium circulating reactor to adjust the pH of the slurry to 11-12. The slurry then enters a continuous circulating reactor for reaction. The feeding rate is controlled to ensure a total aging time of at least 2 hours. The flow rate of magnesium hydroxide-containing slurry overflowing from the top of the circulating reactor and the flow rate of calcium sulfate-containing slurry pumped from the bottom of the circulating reactor are controlled. The magnesium slurry is concentrated through an organic membrane filter. The clear brine produced by the organic membrane filter is pumped into a refined brine buffer tank. The magnesium hydroxide slurry, after being circulated and concentrated by the organic membrane filter, is pumped into the No. 1 intelligent desalting machine to separate solid magnesium hydroxide and brine. The brine is returned to the front end of the organic membrane. The filter cake of the No. 1 intelligent desalting machine is washed with condensate generated from salt evaporation. Magnesium hydroxide is obtained by washing and air drying. The washing water is returned to the lime slurry preparation or pumped to the wastewater pool for well injection mining. The calcium sulfate slurry at the bottom of the calcium-magnesium circulating reactor is pumped into the settling tank for concentration. The clear brine overflowing from the settling tank is pumped into the refined brine buffer tank. The calcium sulfate slurry at the bottom of the settling tank is pumped into the No. 2 intelligent desalting machine to separate the calcium sulfate solid. The filtrate is returned to the settling tank. The filter cake of the No. 2 intelligent desalting machine is washed with the condensate generated by salt evaporation to obtain magnesium-containing calcium sulfate filter cake. The magnesium-containing calcium sulfate filter cake is purified and refined with sulfuric acid, a by-product of the bromine-iodine process, to remove magnesium ion impurities. The purified calcium sulfate slurry is pumped into the No. 3 intelligent desalting machine for filtration, washing, and air drying to obtain high-purity calcium sulfate product. The washing water is sent to the lime slurry preparation area or pumped to the wastewater pool for well injection mining.

[0024] Furthermore, in step six, the brine from the calcium-magnesium process after calcium and magnesium removal is adjusted to pH 8-9 using hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process, resulting in alkaline brine that is then used for evaporation and salt production in stage I.

[0025] Step seven employs a heat pump evaporation process. The specific production plan includes: brine from the secondary alkali adjustment process is preheated by the condensate generated from the first-stage evaporation salt production and then pumped into the evaporator. The first-stage evaporation salt production uses the MVR hot-press evaporation salt production process with low-operating-cost gypsum seeding anti-scaling technology. Sodium chloride crystals are evaporated, concentrated, and crystallized in the range of 80~110℃, while other elements are concentrated and enriched. The salt slurry discharged from the salt foot of the evaporator is washed, dehydrated, dried, and packaged for storage and sale as a product. During the continuous production operation of the evaporation system, the K+ concentration in the discharged salt production mother liquor is controlled to be 40~60g / l to obtain the first-stage salt production mother liquor, which is continuously discharged to the calcium carbonate process after three-stage flash cooling.

[0026] Furthermore, the calcium carbonate production in step eight adopts a chemical precipitation method. The specific production plan includes: calcium sulfate is contained in the evaporation mother liquor from step seven. A 40% concentration of soda ash solution is added to the calcium carbonate reaction tank, and the reaction is stirred. The feeding speed is controlled to ensure that the total aging time is more than 2 hours. The calcium carbonate reaction tank includes three reaction tanks, A, B, and C. The working state is: tank A is used for feeding, tank B is used for reaction and aging, and tank C is used for discharging. The calcium carbonate particles obtained are filtered, dehydrated, washed, desalted, and dried by the No. 4 intelligent desalting machine to obtain calcium carbonate products. The filtrate from the No. 4 intelligent desalting machine is returned to the calcium carbonate settling tank. The clarified upper clear liquid is filtered by a precision filter and then pumped into the lithium extraction process. The lower calcium carbonate slurry is pumped into the No. 4 intelligent desalting machine. The calcium carbonate filter cake from the No. 4 intelligent desalting machine is washed with the condensate generated by salt evaporation. The washing liquid is sent to the lime slurry preparation process or pumped to the wastewater pool for well injection mining.

[0027] Furthermore, step nine involves extracting lithium using adsorption, separating divalent ions via nanofiltration, concentrating lithium ions via reverse osmosis, refining by adsorbing calcium and magnesium using resin, concentrating and evaporating, removing boron by resin adsorption, crystallizing by adding soda ash and maintaining temperature, dehydrating and washing, drying, grinding, and demagnetizing to obtain battery-grade lithium carbonate product. Specifically, this includes acidifying the clear brine after calcium carbonate extraction by adding hydrochloric acid separated from the mixed acid produced in the bromine-iodine process, thus acidifying the pH. =4~6, after acidification, the clear brine is passed through a lithium-ion selective adsorption resin at a flow rate of 1~100 BV / h until the lithium concentration in the post-adsorption liquid is <5ppm, and the adsorption is stopped to obtain delithiated brine. The delithiated brine enters the iodine-bromine process. After the resin adsorption is completed, it is desorbed with RO pure water to obtain lithium chloride solution. When the lithium ion concentration in the effluent is <0.1g / l, the desorption is stopped. The lithium chloride solution is separated into divalent ions by nanofiltration membrane, and then concentrated to a lithium ion concentration of 5g / l by reverse osmosis membrane. Then, trace amounts of calcium and magnesium impurities are adsorbed by special resin, and then evaporated and concentrated to a lithium ion concentration of 22~25g / l by MVR device at 80~85℃. It is then kept at 80℃ for further impurity removal by adsorption of boron. The post-adsorption liquid is reacted and crystallized by adding 40% soda ash solution. The amount of soda ash added is 110% of the reaction equivalent. The addition is slow for 60 minutes, and the mixture is aged for 60 minutes. After filtration and separation, lithium carbonate is washed three times with RO pure water, and then dehydrated, dried by airflow, crushed, demagnetized, and packaged to obtain lithium carbonate products for storage and sale.

[0028] Furthermore, step ten employs an air blowing method. The specific production plan includes: adding a mixed acid from the extraction of iodine and bromine byproducts to the mother liquor of the lithium carbonate process to adjust the pH value to 1-3; then adding chlorine gas to oxidize to a feed liquid potential of 500-800 mV; using an air blowing method to blow out the free iodine from the brine; the blown-out free iodine enters an absorption tower, where it is absorbed by SO2 produced from the combustion of sulfur and the circulating absorption solution in the circulation tank; after absorption, the liquid is further refined to obtain iodine product; and the brine after iodine blowing enters the bromine process.

[0029] The bromine process uses an air blowing method. The specific steps include: adding chlorine gas to the brine after iodine extraction and oxidizing it to a potential of 800~1200mV; then blowing out the free bromine from the brine using an air blowing method. The blown-out free bromine enters an absorption tower, where it is absorbed by SO2 produced from sulfur combustion and the circulating absorption solution in the circulation tank. After absorption, the solution is purified a second time to obtain the bromine product. The brine after bromine blowing then enters the cesium extraction process.

[0030] Furthermore, step eleven uses an adsorption method to extract cesium. The specific production plan includes: adjusting the pH of the brine after the bromine blowing process to 8-9 with a 30% caustic soda solution, and passing it through an HC-Jpgt-Cs adsorbent at a flow rate of 1-50 BV / h to retain the cesium in the bromine extraction mother liquor. The liquid after adsorption is sent to the rubidium extraction process, where a 1%-3% ammonium nitrate solution is passed through an HC-Jpgt-Cs adsorbent at a flow rate of 1-50 BV / h to obtain a cesium eluent. The cesium eluent is then concentrated by membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain the cesium nitrate product.

[0031] Step 12 uses an adsorption method to extract rubidium. The specific production plan includes: passing the mother liquor from the cesium extraction process through an HC-Pmsa-Rb adsorbent at a flow rate of 1~50 BV / h to retain the rubidium in the cesium extraction mother liquor; the liquid after adsorption is sent to the potassium extraction process, where a 1%~3% concentration of ammonium nitrate solution is passed through the HC-Pmsa-Rb adsorbent at a flow rate of 1~50 BV / h to obtain a rubidium eluent; the rubidium eluent is then concentrated by membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain rubidium nitrate product.

[0032] The rubidium extraction mother liquor in step thirteen requires evaporation and concentration to remove sodium chloride. During the sodium precipitation process, potassium ions are greatly enriched, and elements such as calcium, magnesium, and rubidium in the brine are removed, providing a solid foundation for the production of high-quality potassium chloride through cold crystallization. The specific production plan includes: the brine after the rubidium extraction process is preheated by the condensate produced by the second-stage evaporation and salt production and then pumped into the evaporator. Using MVR hot pressing salt technology, partial sodium chloride slurry is obtained by evaporation and crystallization at a temperature of 80~110℃, while potassium ions are concentrated. The sodium chloride slurry discharged from the salt foot is pumped to the first-stage salt production and washing device. The feed continues until the K+ concentration in the mother liquor in the second-stage evaporator reaches 80~120g / l, at which point the mother liquor is discharged. After multi-stage flash cooling to 20~50℃, potassium chloride crystals precipitate, and supersaturation is slowly eliminated to obtain larger-particle potassium chloride product. The potassium chloride slurry is then subjected to sedimentation, washing, filtration, and drying to obtain the potassium chloride product. Part of the potassium chloride washing liquid is returned to the second-stage salt production evaporator, and part is returned to the calcium and magnesium extraction process.

[0033] Furthermore, the production plan for step thirteen also includes: controlling the K+ concentration in the feed material to the second-stage evaporator to be around 50 g / L; pumping the slurry that has been evaporated and crystallized in the second-stage evaporator to the first-stage salt evaporator; stabilizing the potassium chloride solution in the second-stage evaporator to saturation and ensuring that sodium chloride crystals account for more than 10% of the total solids; stopping the pumping of the mixed salt slurry to the first-stage salt evaporator; and when the mixed crystals of potassium chloride and sodium chloride account for 15% to 25% of the total liquid volume, gradually discharging the mixed salts into the multi-stage flash evaporator. As the temperature of the potassium chloride solution decreases, its solubility also decreases, and the potassium chloride crystals mainly grow, causing the solution to slowly eliminate supersaturation, ultimately obtaining larger potassium chloride crystals, thereby directly evaporating to obtain a low-sodium salt product (GB2721-2015 potassium chloride content 10% to 35%).

[0034] The beneficial effects of this invention are:

[0035] This step-by-step extraction process for potassium-rich multi-component brine minimizes the mutual influence between products. It can achieve high-efficiency extraction by using proprietary technology and mature extraction methods. It is not only simple to operate and has flexible production conditions, but also produces high-quality products, high element yield, low production costs, high degree of automation, and low labor intensity.

[0036] This step-by-step extraction process for potassium-rich multi-component brine fully considers environmental factors and comprehensive utilization, combining environmental governance with product extraction. The extraction process achieves a closed-loop cycle, turning hydrogen sulfide waste gas, tail brine, and mixed acids from bromine and iodine byproducts—all traditionally generated by traditional industries—into products or recycling, achieving zero emissions of these three pollutants and realizing green and environmentally friendly production. Simultaneously, it successfully solves the problems of calcium-magnesium separation and desalination, enabling calcium and magnesium to form separate magnesium hydroxide and calcium sulfate products that can be sold as building materials, achieving both economic and environmental benefits.

[0037] This step-by-step extraction process for potassium-rich multi-component brine fully utilizes the advantages of each step, achieving rational use of temperature, pH, and other parameters while minimizing the impact on subsequent processes. It employs a method of gradually increasing the pH value. The adsorption method is highly efficient, avoiding the loss of boron during calcium and magnesium extraction and saving costs.

[0038] This invention separates mixed acids: high-purity hydrochloric acid is used for the desorption and regeneration of adsorption resins, while moderate-purity sulfuric acid is used for the purification and magnesium removal of calcium sulfate products. This solves the problem of waste acid, improves product quality, and saves on production and operating costs.

[0039] This invention avoids the problem of boron precipitation along with calcium during the calcium-magnesium extraction reaction using the lime method, which results in a loss of nearly 40% of boron and substandard calcium products. It also avoids the eutectic phenomenon of rubidium and potassium chloride during the second-stage evaporation concentration-flash cooling potassium precipitation by first extracting boron.

[0040] This invention, by adjusting process pipeline control and parameters, can regulate the production of products (potassium chloride fertilizer and low-sodium salt products) according to market demand. During the production of low-sodium salt products, the particle size of potassium chloride and sodium chloride can be controlled to be close, preventing stratification due to the smaller size of potassium chloride particles during packaging, storage, transportation, and use. This ensures uniform potassium and sodium content in home cooking, improving product quality. Furthermore, the production cost of directly evaporating low-sodium salt is low, half that of mechanically mixing edible potassium chloride and edible sodium chloride in a quantitative manner. On the other hand, in the reprocessing stage, it also avoids the mixing of purchased edible potassium chloride packaging materials into the low-sodium salt products. Attached Figure Description

[0041] Figure 1 This is a partial process flow diagram of a stepwise extraction product from potassium-rich multi-component brine according to the present invention.

[0042] Figure 2 This is another part of the process flow diagram for the stepwise extraction of products from potassium-rich multi-component brine according to the present invention;

[0043] Figure 3 This is a flowchart outlining the process of the present invention. Detailed Implementation

[0044] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0045] Please see Figures 1 to 3 This invention provides the following technical solution: a step-by-step extraction process for potassium-rich multi-component brine. By establishing a reasonable extraction sequence and method, elements with industrial extraction grades are extracted step-by-step and systematically, making it particularly suitable for underground brine with high potassium and sodium content and low calcium and magnesium content. The extraction sequence is as follows: negative pressure desulfurization of brine to produce sodium sulfide; brine alkali adjustment system; adsorption method for strontium extraction to produce strontium carbonate; adsorption method for boron extraction to produce boric acid; lime method reaction to produce magnesium hydroxide and calcium sulfate; stage I evaporation and crystallization to produce sodium chloride; soda ash method to produce calcium carbonate; brine acidification system; adsorption for lithium extraction to produce lithium carbonate; oxidation and blowing of iodine and bromine to produce iodine and bromine; adsorption for cesium extraction to produce cesium nitrate; adsorption for rubidium extraction to produce rubidium nitrate; stage II evaporation and concentration to produce sodium chloride and potassium chloride. Simultaneously, according to market demand, low-sodium salt products can be produced by adjusting the stage II evaporation and concentration ratio.

[0046] The invention fully considers environmental factors and comprehensive utilization, combining environmental governance with product extraction, and achieving a closed-loop extraction process. For example:

[0047] a. In traditional industries, hydrogen sulfide waste gas, tail brine, and mixed acids from bromine and iodine byproducts have all been transformed into products or recycled, achieving zero emissions of the three wastes and realizing green and environmentally friendly production.

[0048] b. Regarding the calcium and magnesium in brine, most companies use methods such as the two-alkali method or the lime-flue gas method to react calcium and magnesium elements to form a solid mixed insoluble substance. Then, the substance is filtered to produce calcium and magnesium slag (mainly a mixture of magnesium hydroxide and calcium sulfate). Since the slag contains a large amount of chloride ions, it needs to be treated by a third party, which results in high environmental costs and seriously affects the company's profits and technological progress.

[0049] This invention successfully solves the problems of calcium and magnesium separation and desalination, and enables calcium and magnesium to form separate magnesium hydroxide and calcium sulfate products, which can be sold as building materials, thus achieving both economic and environmental benefits.

[0050] The process design fully utilizes the advantages between processes, achieving rational use of temperature, pH, and other factors while minimizing the impact on subsequent processes. For example:

[0051] a. The pH value for boron extraction is 8-9, and the pH value for calcium and magnesium extraction is 11-12. A method of gradually increasing the pH value is adopted. The adsorption method is highly efficient, avoiding the loss of boron during calcium and magnesium extraction and saving costs.

[0052] b. During the production of iodine and bromine products in the iodine-bromine process, a mixed acid (sulfuric acid and hydrochloric acid) is produced as a byproduct. Currently, the industry standard is to neutralize this by adding lime before discharging it. This technology separates the mixed acid: the higher-purity hydrochloric acid is used for the analysis and regeneration of the adsorption resin, while the lower-purity sulfuric acid is used for the purification and magnesium removal of calcium sulfate products. This solves the waste acid problem, improves product quality, and saves on production and operating costs.

[0053] The specific steps of this process are as follows in this embodiment:

[0054] 1. Desulfurization of hydrogen sulfide – Production of sodium sulfide products

[0055] 1.1 Product Uses: Sodium sulfide is mainly used in the chemical, papermaking, pharmaceutical, and leather industries. Chemical products made from sodium sulfide include sulfur dyes, lithopone, and zinc sulfide. Sulfur dyes are the largest category of dyes produced in my country, primarily sulfur black and sulfur blue, used for dyeing cotton fibers, and market demand has remained stable.

[0056] 2.2 Process Selection: The process scheme of negative pressure desulfurization-alkali absorption is adopted.

[0057] 2.3 Production Scheme: The mixed acid, a byproduct of the bromine-iodine process, is used to adjust the pH of the raw brine to 5-6 before being pumped into a negative pressure degassing tower. Under negative pressure, hydrogen sulfide gas in the brine is accelerated to escape. The tower pressure is controlled at -0.01 to -0.05 MPa, preferably -0.02 MPa. After hydrogen sulfide removal, the residual hydrogen sulfide concentration in the brine is ≤10 mg / L, preferably ≤7 mg / L. Sodium hypochlorite oxidant is added to the brine after hydrogen sulfide removal, and after passing through a static mixer, it enters the next process. The amount added is 110%–120% of the residual hydrogen sulfide equivalent. The hydrogen sulfide gas escaping from the brine passes through an absorption tower and is absorbed with a 13% sodium hydroxide solution. Absorption is stopped when the pH of the absorbent is <12, obtaining the absorbed solution. The pH is preferably 11–11.5, at which point the absorbent is replaced. The absorbed solution is then evaporated, concentrated, dehydrated, and sheeted to obtain sodium sulfide product.

[0058] 2. First-stage alkali adjustment process for brine

[0059] The desulfurized brine from the previous process (sodium sulfide process) is adjusted to pH 8-9 using 10% lime slurry, preferably pH = 8. The brine is then filtered through a precision filter and sent to the strontium extraction process. The small amount of backwash liquid generated by the precision filter (bag filter or ceramic membrane, etc.) is used together with the washing liquid from the magnesium hydroxide and calcium sulfate processes to prepare lime slurry. The precision filter separates solids into a small amount of magnesium hydroxide, suspended solids, and calcium sulfate.

[0060] 3. Adsorbed Strontium – Production of Strontium Carbonate Products

[0061] 3.1 Product Applications: Mainly used in glass shells, magnetic materials, metal smelting, strontium salt preparation, electronic components, fireworks, etc.

[0062] 3.2 Process Selection: The main methods for producing strontium carbonate include metathesis, coal reduction, strontium pyrolysis, and comprehensive utilization. This scheme adopts the comprehensive utilization method, which involves first extracting strontium from the brine by adsorption, and then using soda ash to react and crystallize the strontium carbonate.

[0063] 3.3 Production Scheme: The brine from the previous process (first-stage alkali adjustment of the brine) is passed through a chelating resin with strong selectivity for strontium at a flow rate of 1~100 BV / h, preferably 100 BV / h, until the strontium concentration in the adsorbed liquid is <5 ppm. Adsorption is then stopped to obtain destrontium brine, which proceeds to the next process. The hydrochloric acid concentration separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2%~10%, preferably 5%, and used to desorb the strontium adsorption resin, obtaining a strontium eluent. The washing flow rate is 1~100 BV / h, preferably 100 BV / h. Desorption is stopped when the eluent concentration falls below 0.5 g / L. The eluent is collected and mixed, filtered through a 5 μm security filter to remove suspended impurities, and then evaporated and concentrated to a strontium concentration of 50~100 g / L, preferably 60 g / L. A 40% soda ash solution is added to react and precipitate the eluent. The eluent is then dehydrated, washed, and dried to obtain the strontium carbonate product.

[0064] 4. Boron adsorption – Production of boric acid products

[0065] 4.1 Product Uses: Boric acid is a multifunctional and important basic inorganic chemical raw material with wide applications in industry, agriculture, national defense, and modern science and technology. In the enamel and ceramics industry, boric acid is used to enhance the gloss and durability of enamel products and is also a component of glazes and pigments. In the pharmaceutical and metallurgical industries, it is used as an additive and co-solvent. In particular, boron steel, with its high hardness and good rollability, has replaced nickel steel. Boric acid has anti-corrosion properties and can be used as a preservative, such as for wood preservation. It is used in metal welding, leather, photography, and in the manufacture of dyes, heat-resistant and fire-retardant fabrics, artificial gemstones, capacitors, and cosmetics. It can also be used as an insecticide and catalyst. In agriculture, it is used as a boron-containing micronutrient fertilizer, which is effective for many crops and can increase the oil content of rapeseed. Various borates can be manufactured from boric acid and are widely used in national defense and other industrial sectors and research institutions.

[0066] 4.2 Process Selection: The main methods for producing boric acid include adsorption, sulfuric acid process (one-step process), hydrochloric acid process, ammonium bicarbonate process, electrolytic electrodialysis process, extraction process, borax acidification and neutralization process (two-step process), nitric acid process, carbonic acid process, and polyborate process. With the promotion and application of new technologies, most boric acid production now adopts adsorption or extraction methods. In particular, the adsorption method has advantages such as low cost, high yield, high product purity, and easy automation, making it suitable for industrial production.

[0067] 4.3 Production Scheme: The brine from the previous process (strontium carbonate process) after strontium extraction is passed through a chelating resin with strong boron selectivity at a flow rate of 1~100 BV / h, preferably 100 BV / h, until the boron concentration in the adsorption liquid is <5 ppm. Adsorption is then stopped to obtain deboronized brine, which proceeds to the next process. The concentration of hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2%~10%, preferably 5%. The boron adsorption resin is eluted with 5% dilute hydrochloric acid to obtain a boron eluent at a washing flow rate of 1~100 BV / h, preferably 100 BV / h. Elumination is stopped when the eluent concentration falls below 0.5 g / L. The eluent is collected and mixed, filtered through a 5 μm security filter to remove suspended impurities, and then heated to 60~90℃, preferably 80℃. The boron content is concentrated to 50-85 g / L (preferably 80 g / L) by four-stage membrane evaporation, followed by multi-stage flash cooling (to slowly eliminate saturation and allow boric acid crystals to grow). The precipitated boric acid crystals are then filtered, washed, dehydrated, and dried to obtain the boric acid product.

[0068] By first extracting boron, the process avoids the near 40% boron loss that occurs during the lime-based calcium-magnesium extraction reaction, where boron precipitates along with calcium, resulting in substandard calcium products. Furthermore, during the first-stage evaporation salt production using the low-cost gypsum seed crystal method, under the set pH conditions, boron combines with calcium to form fine particles that accumulate and float on the evaporator surface, creating vapor resistance. This disrupts the stability and continuity of salt production evaporation, a critical issue in chemical production and absolutely unacceptable. This phenomenon was discovered during our pilot plant operation. Additionally, while the evaporated and crystallized sodium chloride product meets premium-grade standards, its use as raw material in a soda ash plant causes increased foaming in the salt separator, distorted liquid levels, and blocked channels, preventing the soda ash production system from operating continuously and stably.

[0069] 5. Lime process – for the production of magnesium hydroxide and calcium sulfate products

[0070] 5.1 Product Applications:

[0071] 5.1.1 Uses of calcium sulfate:

[0072] ①. Manufacturing cement and building materials: Calcium sulfate is a raw material for manufacturing cement, calcium sulfate hemihydrate, and sulfuric acid. In the construction industry, it is widely used to make various models and building materials, such as gypsum board.

[0073] ②. Agricultural applications: In agriculture, calcium sulfate is used as a fertilizer to reduce soil alkalinity and improve soil properties.

[0074] ③. Paper Industry: Calcium sulfate can be used as a paper coating agent, which not only increases thickness and durability but also makes the paper less prone to tearing. It is also used as a filler, thus reducing the need for other ingredients in papermaking.

[0075] ④. Paints and pigments: Pure white calcium sulfate can be mixed with paint to produce white paint. This type of paint can be used in painting, as well as for interior and exterior applications.

[0076] ⑤. Desiccant: Calcium sulfate can be used as polishing powder, paper filler, and gas desiccant.

[0077] 5.1.2 Uses of magnesium hydroxide:

[0078] ①. Flame retardant: Magnesium hydroxide is an excellent flame retardant for plastics and rubber products. It can be used as a flame retardant or flame retardant filler added to various resins, exhibiting good flame retardant and smoke suppression effects. It releases bound water upon thermal decomposition, absorbing a large amount of latent heat to reduce the surface temperature of the filled synthetic material in a flame. Simultaneously, the magnesium oxide produced during decomposition is a good refractory material, also helping to improve the fire resistance of synthetic materials.

[0079] ②. Environmental Protection: Magnesium hydroxide can be used as a flue gas desulfurizing agent, replacing caustic soda and lime as a neutralizing agent for acidic wastewater. It has advantages such as safety, reliability, non-precipitation, and ease of storage and transportation. In addition to neutralizing acidic solutions, it can also adsorb heavy metal ions, thereby achieving the purpose of heavy metal removal.

[0080] ③. Chemical Materials and Intermediates: Magnesium hydroxide can be used as a chemical material and intermediate, as well as a green and environmentally friendly flame retardant and additive in the polymer industry, including rubber, plastics, fibers, and resins. It exhibits excellent buffering properties, reactivity, adsorption capacity, and thermal decomposition performance.

[0081] 5.2 Process Selection: Currently, most companies use methods such as the two-alkali method or the lime-flue gas method to extract calcium and magnesium from brine. This involves reacting calcium and magnesium elements to form a solid, insoluble mixture, which is then filtered to produce calcium-magnesium slag (mainly a mixture of magnesium hydroxide and calcium sulfate). Because the slag contains a large amount of chloride ions, it requires third-party treatment, resulting in high environmental costs. This process uses the lime method to extract calcium and magnesium ions from brine, employing chemical precipitation to generate magnesium hydroxide and calcium sulfate precipitates. Key features include: firstly, magnesium hydroxide is produced at the top of the circulating reactor, and calcium sulfate at the bottom; secondly, an intelligent desalination machine is introduced to remove salt from the magnesium hydroxide and calcium sulfate, turning waste into a compliant product that can be sold and generate economic benefits.

[0082] 5.3 Production Scheme: After boron extraction in the previous process (boric acid process), the brine is mixed with 10% lime slurry in a calcium-magnesium circulating reactor to adjust the slurry pH to 11-12, preferably 11.5. The slurry then enters a continuous circulating reactor for reaction, with the feeding rate controlled to ensure a total aging time of at least 2 hours. The flow rate of magnesium hydroxide-containing slurry overflowing from the top of the circulating reactor and the flow rate of calcium sulfate-containing slurry pumped from the bottom of the circulating reactor are controlled. The magnesium slurry is concentrated through an organic membrane filter. The clear brine produced by the organic membrane filter is pumped into a refined brine buffer tank. The concentrated magnesium hydroxide slurry from the organic membrane filter is then pumped into the No. 1 intelligent desalination machine to separate solid magnesium hydroxide from the brine. The brine is returned to the front end of the organic membrane filter. The filter cake from the No. 1 intelligent desalination machine is washed and air-dried using the condensate from salt production evaporation to obtain magnesium hydroxide product. The wash water is returned to prepare lime slurry or pumped to a wastewater pond for use in well injection mining.

[0083] The calcium sulfate slurry at the bottom of the calcium-magnesium circulating reactor is pumped into a settling tank for concentration. The clarified brine overflowing from the settling tank is pumped into a refined brine buffer tank. The calcium sulfate slurry at the bottom of the settling tank is pumped into the No. 2 intelligent desalination machine to separate the calcium sulfate solids. The filtrate (i.e., brine) is returned to the settling tank. The filter cake from the No. 2 intelligent desalination machine is washed with the condensate generated from salt production evaporation to obtain a magnesium-containing calcium sulfate filter cake. The magnesium-containing calcium sulfate filter cake is purified and refined with sulfuric acid, a byproduct of the bromine-iodine process, to remove magnesium ion impurities. The purified calcium sulfate slurry is pumped into the No. 3 intelligent desalination machine for filtration, washing, and air drying to obtain a high-purity calcium sulfate product. The wash water is sent to the lime slurry preparation area or pumped to the wastewater pool for use in well injection mining.

[0084] 6. Secondary alkali adjustment of brine

[0085] The brine from the previous process (calcium and magnesium process) after calcium and magnesium removal is adjusted to pH 8-9 using hydrochloric acid separated from the mixed acid byproduct of the bromine and iodine process, with pH 8 being preferred. This alkaline brine is then used for stage I evaporation and salt production.

[0086] 7. Stage I Evaporation Salt Production – Production of Sodium Chloride

[0087] 7.1 Uses of Sodium Chloride: Sodium chloride is an important raw material in the chemical industry. It can be used to produce many chemical products such as metallic sodium, soda ash, and caustic soda, and is known as the "mother of the chemical industry." These products have extremely wide applications, affecting all sectors of the national economy and all aspects of people's lives, including clothing, food, housing, and transportation. The main downstream applications of industrial salt in China include salt used in the production of soda ash and caustic soda, edible salt, and small-scale industrial salt. Among these, salt used in the production of soda ash and caustic soda accounts for a large proportion, approximately 80%.

[0088] 7.2 Process Selection: Sodium chloride production processes include multi-effect vacuum evaporation and heat pump evaporation. Since the project is located in Sichuan, a region rich in hydropower, where the comprehensive price of hydropower is less than 0.6 yuan / kWh, the heat pump evaporation process is adopted.

[0089] 7.3 Production Scheme: The brine from the previous process (secondary alkali adjustment process) is preheated by the condensate generated from the first-stage evaporation salt production and then pumped into the evaporator. The first-stage evaporation salt production adopts the MVR hot-press evaporation salt production process with low operating cost gypsum seeding anti-scaling technology. Sodium chloride crystals are concentrated and crystallized in the range of 80~110℃, preferably 107℃, while other elements are concentrated and enriched. The salt slurry discharged from the salt foot of the evaporator is washed, dehydrated, dried, and packaged for product storage and sale. During continuous production operation of the evaporation system, the K+ concentration in the discharged salt production mother liquor is controlled at 40~60g / l, preferably 50g / l, to obtain the first-stage salt production mother liquor, which is continuously discharged to the calcium carbonate process after three-stage flash cooling.

[0090] 8. Calcium carbonate process

[0091] 8.1 Uses of calcium carbonate products:

[0092] ①. Fillers and Additives: Calcium carbonate is widely used as a filler and additive in industries such as rubber, plastics, coatings, and papermaking. It can increase the volume of products, reduce costs, and improve the processing performance and physical properties of products.

[0093] ②. Chemical raw materials: Calcium carbonate is one of the raw materials for manufacturing products such as optical neodymium glass and coatings.

[0094] ③Agricultural applications: Calcium carbonate can be used to improve acidic soil, adjust soil pH, and improve the crop growth environment.

[0095] 8.2 Process selection: Calcium carbonate production adopts the chemical precipitation method.

[0096] 8.3 Production Plan: The mother liquor from the first stage of salt production (Section I) contains calcium sulfate. A 40% concentration of soda ash solution is added to the calcium carbonate reaction tanks (three tanks, A / B / C, operating in the following mode: tank A for feeding, tank B for reaction and aging, and tank C for discharging, used alternately). The mixture is stirred and the feeding rate is controlled to ensure a total aging time of at least 2 hours. The resulting calcium carbonate particles are filtered, dehydrated, washed, desalted, and dried using the No. 4 intelligent desalting machine to obtain the calcium carbonate product. The filtrate from the No. 4 intelligent desalting machine is returned to the calcium carbonate reaction feed tank. After clarification, the upper clear liquid from the discharge tank is filtered through a precision filter and pumped into the lithium extraction process, while the lower calcium carbonate slurry is pumped into the No. 4 intelligent desalting machine. The calcium carbonate filter cake from the No. 4 intelligent desalting machine is washed with condensate from the salt production evaporation process. The washing liquid is sent to the lime slurry preparation process or pumped to a wastewater pond for use in well injection mining.

[0097] 9. Adsorption Lithium Extraction Process – Production of Lithium Carbonate Products

[0098] 9.1 Process Product Applications: Lithium carbonate products have a variety of industrial applications and can be converted into a variety of other lithium compounds. They are widely used in battery energy storage, atomic energy, aerospace, military industry, refrigeration, welding, lithium alloys, lithium batteries, controlled nuclear fusion reactors, metallurgical continuous casting, medicine and other fields.

[0099] 9.2 Process Selection: There are two main methods for producing lithium carbonate: extraction from lithium-containing ore and extraction from brine. This scheme uses brine extraction. First, lithium is extracted using adsorption, then divalent ions are separated by nanofiltration, lithium ions are concentrated by reverse osmosis, calcium and magnesium are removed by resin adsorption for purification, followed by concentration and evaporation, deboron removal by resin adsorption, crystallization by adding soda ash and maintaining temperature, dehydration and washing, drying, abrasion, and demagnetization to obtain battery-grade lithium carbonate product.

[0100] 9.3 Production Scheme: Hydrochloric acid separated from the mixed acid produced as a byproduct of the bromine-iodine process is added to the clear brine after calcium carbonate extraction for acidification. The acidification pH is 4-6, preferably pH 5. The acidified clear brine is then passed through a lithium-ion selective adsorption resin at a flow rate of 1-100 BV / h, preferably 50 BV / h, until the lithium concentration in the adsorption solution is <5 ppm, at which point adsorption is stopped to obtain delithiated brine. The delithiated brine proceeds to the next process (iodine-bromine process). After resin adsorption is complete, lithium chloride solution is obtained by RO pure water analysis. Analysis is stopped when the lithium ion concentration in the effluent is <0.1 g / L. Lithium chloride solution is prepared by separating divalent ions using nanofiltration membrane, then concentrated to a lithium ion concentration of 5 g / L using reverse osmosis membrane. Trace amounts of calcium and magnesium impurities are then adsorbed using a specialized resin. Following this, the solution is evaporated and concentrated to a lithium ion concentration of 22–25 g / L using an MVR device at 80–85°C. The solution is then held at 80°C for further impurity removal through boron adsorption. The resulting liquid is then reacted with a 40% sodium carbonate solution (110% of the reaction equivalent) for crystallization, with slow addition over 60 minutes. The mixture is then aged for 60 minutes and filtered for separation. Lithium carbonate is washed using RO pure water in a three-stage process, followed by dehydration, airflow drying, pulverization, demagnetization, and packaging to obtain the final lithium carbonate product for storage and sale.

[0101] 10. Iodine blowing process – Production of iodine products

[0102] 10.1 Product Uses: Iodine is a basic raw material for manufacturing inorganic and organic iodides, primarily used in the medical industry to produce various iodine preparations, bactericides, disinfectants, deodorizers, analgesics, and antidotes for radioactive substances. Iodides are also used as drinking water purifiers and swimming pool disinfectants. In agriculture, iodine is a raw material for pesticides and a livestock feed additive. Industrially, iodine is used to manufacture synthetic dyes and other pigments, smoke extinguishers, rapid photosensitive emulsions for photographic materials, and antibacterial agents for cutting oil emulsions. It is also used in the manufacture of single-crystal prisms for electronic instruments and polarizing microscopes for optical instruments. Iodine is one of the essential trace elements for the human body. The total amount of iodine in a healthy adult is 30 mg (20-50 mg), of which 70%-80% is found in the thyroid gland.

[0103] 10.2 Process Selection: Methods for extracting iodine from brine include ion exchange, air blowing, activated carbon extraction, precipitation (silver and copper methods), starch extraction, and organic solvent extraction. The latter methods have been gradually phased out due to their low efficiency, high cost, and complex equipment. Currently, ion exchange and air blowing are the main methods used in industrial production. This scheme adopts the air blowing method.

[0104] 10.3 Production Scheme: The pH value of the mother liquor from the previous process (lithium carbonate process) is adjusted to 1-3 (preferably 2) by adding mixed acid from iodine and bromine extraction. Then, chlorine gas is added to oxidize the solution to a potential of 500-800 mV (preferably 520 mV). Free iodine in the brine is then blown out using an air-blowing method. The blown-out free iodine enters an absorption tower, where it is absorbed by SO2 produced from sulfur combustion and the circulating absorption solution in the circulation tank. The absorbed solution undergoes secondary purification (sublimation cooling method) to obtain iodine product. The brine after iodine removal proceeds to the next process (bromine process).

[0105] 11. Bromine blowing process – Production of bromine products

[0106] 11.1 Product Uses: Bromine has a wide range of uses. Silver bromide is used as a photosensitizer in photography. Lithium bromide refrigeration technology is a recently widely used environmentally friendly air conditioning technology, characterized by the absence of pollution caused by Freon, and its development prospects are promising. Bromine is also a useful element in organic synthesis. In the pharmaceutical industry, many drugs also contain bromine. Bromine is also used in the production of fire extinguishers, such as the "1211" fire extinguisher, which is a bromine-containing polyhalogenated alkane that can extinguish not only ordinary fires but also fires where foam extinguishers are ineffective, such as oil fires. Bromine is also an important raw material for the synthesis of pharmaceuticals and pesticides, such as potassium bromide, sodium bromide, and ammonium bromide. The common mercurochrome is a compound of bromine and mercury. In addition, the production of antibiotics such as penicillin also requires bromine, and bromine is also a raw material for the manufacture of agricultural pesticides.

[0107] 11.2 Process Selection: The following methods are commonly used in the industrial production of bromine.

[0108] ①. Steam distillation method: Preheat the bromine-containing brine, pass chlorine gas into the reaction tower, distill off the bromine with steam, condense and distill to obtain the finished product.

[0109] ②. Air blowing method: The bromine-containing brine is acidified, chlorine gas is introduced, and free bromine is blown out with air in a blowing tower. Then, it is absorbed by an absorbent, desorbed, and purified by distillation.

[0110] ③. Ion exchange method: Acidify low-content brine, oxidize with chlorine, and obtain the brine through ion exchange adsorption, desorption, and distillation.

[0111] 11.3 This scheme adopts the air blowing method.

[0112] Production Scheme: After iodine extraction, the brine is oxidized with chlorine gas to a potential of 800-1200 mV, preferably 980 mV. Free bromine in the brine is then blown out using an air-blowing method. The blown-out free bromine enters an absorption tower, where it is absorbed by SO2 produced from sulfur combustion and the circulating absorption solution in a circulation tank. The absorbed solution undergoes secondary purification (distillation and sulfuric acid drying) to obtain the bromine product. The brine after bromine extraction proceeds to the next process (cesium extraction).

[0113] 12. Adsorption and cesium extraction process

[0114] 12.1 Uses of Cesium Nitrate: Preparation of other cesium salts; Detection of radioactive substances in environmental control analysis; Oxidizing agent, etc.

[0115] 12.2 Process Selection: When using brine as raw material, the process routes for extracting cesium include precipitation, extraction, and adsorption. This scheme employs the adsorption method for cesium extraction.

[0116] 12.3 Production Scheme: The brine from the previous process (bromine blowing process) is adjusted to pH 8-9 using a 30% caustic soda solution, preferably pH 9. It is then passed through an HC-Jpgt-Cs adsorbent at a flow rate of 1-50 BV / h, preferably 10 BV / h, to retain cesium in the bromine extraction mother liquor. The resulting solution is then transported to the next process (rubidium extraction process). A 1%-3% ammonium nitrate solution is passed through the HC-Jpgt-Cs adsorbent at a flow rate of 1-50 BV / h, preferably 10 BV / h, to obtain a cesium eluent. This eluent is then concentrated via membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain the cesium nitrate product.

[0117] 13 Adsorption and Rubidium Extraction Process

[0118] 13.1 Uses of rubidium nitrate products: Primarily used in magnetohydrodynamic (MHD) power generation and the production of other rubidium salt raw materials. It also serves as a catalyst in organic synthesis and a chelating agent, playing a crucial role in specialty ceramics, aerospace, and military industries. The success of MHD power generation alone would cause the application of rubidium salts to surge to tens of thousands of tons.

[0119] 13.2 Process Selection: Using brine as raw material, the process routes for extracting rubidium include precipitation, extraction, and adsorption. This scheme employs the adsorption method for rubidium extraction.

[0120] 13.3 Production Scheme: The mother liquor from the previous process (cesium extraction process) is passed through an HC-Pmsa-Rb adsorbent at a flow rate of 1~50 BV / h, preferably 10 BV / h, to retain rubidium in the cesium extraction mother liquor. The solution after adsorption is then transported to the next process (potassium extraction process). A 1%~3% ammonium nitrate solution is passed through the HC-Pmsa-Rb adsorbent at a flow rate of 1~50 BV / h, preferably 10 BV / h, to obtain a rubidium eluent. The rubidium eluent is then concentrated through a membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain the rubidium nitrate product.

[0121] By extracting rubidium as described above, the eutectic phenomenon between rubidium and potassium chloride during the second-stage evaporation concentration-flash cooling potassium precipitation is avoided. This process results in a rubidium loss of nearly 40%, and the potassium chloride product can only be sold as agricultural potassium, not for producing high-quality edible potassium chloride products or low-sodium salt products.

[0122] The technical system for the stepwise extraction of potassium-rich multi-component brine products must ensure the continuous and stable operation of the system, taking into account product quality, element recovery rate, and interference between elements.

[0123] 14. Stage II: Evaporation for salt production and cooling crystallization for potassium chloride or low-sodium salt products.

[0124] 14.1 Uses of Potassium Chloride: Potassium chloride is an important potassium product, accounting for over 90% of potassium production. It is mainly used in the inorganic industry as a basic raw material for manufacturing various potassium salts, such as potassium hydroxide, potassium carbonate, potassium sulfate, potassium nitrate, potassium chlorate, and potassium dichromate. In the pharmaceutical industry, it is used as a diuretic and a drug to prevent potassium deficiency. In the dye industry, it is used to produce potassium salts and reactive dyes. In agriculture, it is a potassium fertilizer. Its fertilizer effect is rapid; direct application to farmland can raise the moisture content of the lower soil layers, providing drought resistance. However, it is not suitable for saline-alkali soils or for crops such as tobacco, sweet potatoes, and sugar beets. Potassium chloride has a similar taste to sodium chloride and is also used as an additive in low-sodium salts or mineral water. In addition, it is used to manufacture flash suppressants for gun muzzles or cannon muzzles, heat treatment agents for steel, and in photography. It also has applications in medicine, scientific research, and food processing.

[0125] 14.2 Uses of low-sodium salt products: Potassium chloride can partially replace sodium chloride in table salt to reduce the likelihood of high blood pressure.

[0126] 14.3 Process Selection: The commonly used method for potassium chloride extraction is evaporation and concentration followed by cold crystallization. Salt production and potassium production are often combined to simultaneously obtain sodium chloride and potassium chloride products. This process produces high-purity products with no pollutant emissions. In this scheme, the rubidium extraction mother liquor needs to be evaporated and concentrated to remove sodium chloride. During the sodium precipitation process, potassium ions are greatly enriched, while elements such as calcium, magnesium, and rubidium in the brine are removed, providing a solid foundation for the cold crystallization of potassium to produce high-quality potassium chloride.

[0127] ① Production Scheme 1: The brine from the previous process (rubidium extraction process) is preheated by the condensate produced during the second-stage evaporation and salt production, then pumped into the evaporator. Using MVR hot pressing salt technology, evaporation and crystallization are carried out within the range of 80-110℃, preferably 107℃, to obtain a partial sodium chloride slurry, while simultaneously concentrating potassium ions. The sodium chloride slurry discharged from the salt residue is pumped to the first-stage salt production and washing unit. This system is a continuous feed system. When the K+ concentration in the mother liquor in the second-stage evaporator reaches 80-120 g / L, preferably 120 g / L, the mother liquor is discharged. After multi-stage flash cooling to 20-50℃, preferably 40℃, potassium chloride crystals precipitate. The purpose of multi-stage flash cooling is to slowly eliminate supersaturation, thereby obtaining larger potassium chloride particles, which facilitates filtration and washing, resulting in a high-quality potassium chloride product. The potassium chloride slurry undergoes sedimentation, washing, filtration, and drying to obtain the potassium chloride product. Part of the potassium chloride washing liquid is returned to the second-stage salt production evaporator, and part is returned to the calcium and magnesium extraction process.

[0128] ②. Production Plan Two: Control the K+ concentration in the feed to the Stage II evaporator to approximately 50 g / L. The slurry that crystallizes first in the Stage II evaporator is pumped to the Stage I salt evaporator (potassium chloride crystals will also dissolve in the low-potassium brine; potassium chloride dissolves very quickly at high temperatures, ensuring the purity of the sodium chloride product). Pumping the mixed salt slurry to the Stage I evaporator stops when the potassium chloride crystals in the Stage II evaporator are stable and the sodium chloride crystals account for more than 10% of the total solids. The mixed salt, with sodium chloride and potassium chloride crystals accounting for more than 15% to 25% of the total solids, is then pumped step-by-step into the multi-stage flash evaporator. As the temperature of the potassium chloride solution decreases, its solubility also decreases, causing potassium chloride to crystallize or grow, slowly eliminating supersaturation and obtaining larger potassium chloride crystals (crystalline sodium chloride crystals). This results in potassium chloride crystals accounting for approximately 20% of the solids, meeting the standard of 10% to 35% potassium chloride content in low-sodium salt products (GB2721-2015 Edible Salt Standard).

[0129] The above-described method for producing low-sodium salt ensures that the particle size of potassium chloride and sodium chloride is similar, preventing stratification caused by the smaller potassium chloride particles during packaging, storage, transportation, and use. This avoids uneven potassium-sodium content in home cooking, resulting in a bitter taste and reduced quality of life due to excessive potassium chloride. Direct evaporation for low-sodium salt production is also cost-effective, requiring only half the amount of mechanical mixing of edible potassium chloride and sodium chloride. Furthermore, it prevents the contamination of purchased edible potassium chloride packaging materials with the low-sodium salt product during the subsequent production process.

[0130] The foregoing has shown and described the basic principles and main features of the present invention and its advantages. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0131] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A stepwise extraction process for potassium-rich multi-component brine, characterized in that, Includes the following steps: Step 1: Using negative pressure desulfurization-alkali absorption process, sodium sulfide products are produced by desulfurization of brine under negative pressure; this includes the step of adjusting the pH of the raw brine to 5~6 using the mixed acid byproduct of the bromine-iodine process. Step 2: First-time alkali adjustment of brine. In this process, the desulfurized brine from the sodium sulfide process in Step 1 is adjusted to pH 8-9 using 10% lime slurry. Step 3: Strontium carbonate is produced by adsorption method. First, strontium element is adsorbed and extracted from brine, and then strontium carbonate is obtained by reaction and crystallization using soda ash. Step 4: Boron extraction by adsorption to produce boric acid products. The brine after strontium extraction from the strontium carbonate process is passed through a chelating resin with strong selectivity for boron at a flow rate of 1~100 BV / h until the boron concentration in the brine after adsorption is <5ppm, at which point adsorption is stopped to obtain deboronized brine. Step 5: The lime process is used to produce magnesium hydroxide and calcium sulfate products. After the boron is extracted in the boric acid process, 10% lime slurry is added to the calcium-magnesium circulating reactor to adjust the pH of the slurry to 11-12. Step 6: Secondary alkali adjustment of brine. The brine from the calcium-magnesium process after calcium and magnesium removal is adjusted to pH 8-9 using hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process. The resulting alkali-adjusted brine is then used for stage I evaporation and salt production. Step 7: Using a heat pump evaporation process, sodium chloride is produced by evaporation and crystallization in stage I; the salt is produced by evaporation using gypsum seed crystals. Step 8: Producing calcium carbonate using the soda ash method. Calcium sulfate from the mother liquor of the first stage of evaporation in Step 7 is added to a calcium carbonate reaction tank with a 40% concentration of soda ash solution, and the mixture is stirred to react. Step 9: Lithium carbonate production by adsorption method. Lithium element is extracted by adsorption, followed by nanofiltration to separate divalent ions, reverse osmosis to concentrate lithium ions, resin adsorption for calcium and magnesium impurity removal and purification, concentration and evaporation, resin adsorption for boron removal, addition of soda ash for heat preservation and crystallization, dehydration and washing, drying, abrasion, and demagnetization to obtain battery-grade lithium carbonate product. This includes the step of adding hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process to the clear brine after calcium carbonate extraction for acidification, with the acidification pH being 4-6. Step 10: Oxidation and blowing of iodine and bromine to produce iodine and bromine products. This process uses the air blowing method. Mixed acid from the extraction of iodine and bromine byproducts is added to the mother liquor of the lithium carbonate process to adjust the pH value to 1~3. Then, chlorine gas is added once to oxidize the liquid to 500~800mv and the free iodine in the brine is blown out using the air blowing method. Then, chlorine gas is added a second time to oxidize the liquid to 800~1200mv and the free bromine in the brine is blown out using the air blowing method. Step 11: Cesium nitrate production by adsorption method. The brine after the bromine blowing process is adjusted to pH 8-9 with 30% caustic soda solution and passed through HC-Jpgt-Cs adsorbent at a flow rate of 1-50 BV / h to retain the cesium element in the bromine extraction mother liquor. The liquid after adsorption is sent to the rubidium extraction process. Step 12: Rubidium nitrate production by adsorption method. The mother liquor from the cesium extraction process is passed through HC-Pmsa-Rb adsorbent at a flow rate of 1~50 BV / h to retain the rubidium element present in the cesium extraction mother liquor. The liquid after adsorption is sent to the potassium extraction process. Step Thirteen: In the second stage of evaporation and concentration to produce sodium chloride and potassium chloride products, the rubidium mother liquor needs to be evaporated and concentrated to remove sodium chloride. During the sodium precipitation process, potassium ions are greatly enriched, and at the same time, calcium, magnesium and rubidium elements in the brine have been removed, providing a solid foundation for the production of high-quality potassium chloride by cold precipitation and crystallization of potassium.

2. The stepwise extraction process for potassium-rich multi-component brine according to claim 1, characterized in that, The process for producing sodium sulfide in step one includes: adjusting the pH of the raw brine to 5-6 using mixed acid, a byproduct of the bromine-iodine process, and then pumping it into a negative pressure degassing tower. Under negative pressure, hydrogen sulfide gas in the brine is accelerated to escape. The pressure inside the tower is controlled to be -0.01 to -0.05 MPa. After hydrogen sulfide removal, the residual concentration of hydrogen sulfide in the brine is ≤10 mg / L. Sodium hypochlorite oxidant is added to the brine after hydrogen sulfide gas removal. After passing through a static mixer, it enters the next process. The amount added is 110% to 120% of the residual hydrogen sulfide equivalent. The hydrogen sulfide gas escaping from the brine passes through an absorption tower and is absorbed by a 13% sodium hydroxide solution. When the pH of the absorption liquid is <12, the absorption is stopped to obtain the absorption liquid. The absorption liquid is replaced, and the absorption liquid is evaporated, concentrated, dehydrated, and flaked to obtain sodium sulfide product. In step two, the brine is filtered through a precision filter and then sent to the strontium extraction process. The small amount of backwash liquid generated by the precision filter is used together with the washing liquid from the magnesium hydroxide and calcium sulfate processes to prepare lime slurry. The precision filter separates solid substances into a small amount of magnesium hydroxide, suspended solids, and calcium sulfate.

3. The stepwise extraction process for potassium-rich multi-component brine according to claim 2, characterized in that: The process for producing strontium carbonate in step three includes: passing brine from the primary alkali adjustment process through a chelating resin with strong selectivity for strontium at a flow rate of 1-100 BV / h until the strontium concentration in the adsorbed liquid is <5 ppm, at which point adsorption is stopped to obtain destrontium brine. The destrontium brine enters the next process, where the concentration of hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2%-10%, and the strontium adsorption resin is desorbed to obtain strontium eluent. The washing flow rate is 1-100 BV / h, and the desorption is stopped when the eluent concentration is below 0.5 g / L. The eluent is collected and mixed, filtered through a 5 μm security filter to remove suspended impurities, and then evaporated and concentrated to 50-100 g / L of strontium. A 40% soda ash solution is added to react and precipitate the eluent, followed by dehydration, washing, and drying to obtain the strontium carbonate product.

4. The stepwise extraction process for potassium-rich multi-component brine according to claim 3, characterized in that: The process for producing boric acid in step four includes: the deboronized brine enters the subsequent process, the concentration of hydrochloric acid separated from the mixed acid byproduct of the bromine-iodine process is adjusted to 2% to 10%, the boron adsorption resin is eluted with 5% dilute hydrochloric acid to obtain boron elution solution, the washing flow rate is 1 to 100 BV / h, the elution is stopped when the elution solution is below 0.5 g / L, the elution solution is collected and mixed, and suspended impurities are filtered out through a 5 μm security filter. Then it is heated to 60 to 90°C, concentrated to 50 to 85 g / L of boron element through a 4-stage membrane evaporation, and then subjected to multi-stage flash cooling crystallization to obtain high-quality boric acid product in granular form. The process for producing magnesium hydroxide and calcium sulfate in step five includes: adjusting the slurry pH to 11-12; the slurry entering a continuous circulating reactor for reaction; controlling the feeding rate to ensure a total aging time of at least 2 hours; controlling the flow rate of magnesium hydroxide-containing slurry overflowing from the top of the circulating reactor and the flow rate of calcium sulfate-containing slurry pumped from the bottom of the circulating reactor; concentrating the magnesium slurry through an organic membrane filter; pumping the clear brine produced by the organic membrane filter into a refined brine buffer tank; circulating and concentrating the magnesium hydroxide slurry through the organic membrane filter and pumping it into the No. 1 intelligent desalination machine to separate solid magnesium hydroxide and brine; returning the brine to the front end of the organic membrane filter; and washing and air-drying the filter cake from the No. 1 intelligent desalination machine with the condensate generated from salt production evaporation to obtain magnesium hydroxide. Magnesium products are processed by washing water, which is then returned to the lime slurry preparation process or pumped to a wastewater pond for use in well injection mining. Calcium sulfate slurry from the bottom of the calcium-magnesium circulating reactor is pumped into a settling tank for concentration. The clarified brine overflowing from the settling tank is pumped into a refined brine buffer tank. The calcium sulfate slurry from the bottom of the settling tank is pumped into the No. 2 intelligent desalting machine to separate solid calcium sulfate. The brine is returned to the settling tank. The filter cake from the No. 2 intelligent desalting machine is washed with condensate from salt evaporation to obtain a magnesium-containing calcium sulfate filter cake. This magnesium-containing calcium sulfate filter cake is purified and refined using sulfuric acid, a byproduct of the bromine-iodine process, to remove magnesium ion impurities. The purified calcium sulfate slurry is pumped into the No. 3 intelligent desalting machine for filtration, washing, and air drying to obtain a high-purity calcium sulfate product. The washing water is sent to the lime slurry preparation area or pumped to a wastewater pond for use in well injection mining.

5. The stepwise extraction process for potassium-rich multi-component brine according to claim 4, characterized in that: The process for preparing sodium chloride in step seven includes: brine from the secondary alkali adjustment process is preheated by the condensate generated during stage I evaporation and salt production, and then pumped into the evaporator. Stage I evaporation and salt production employs a low-cost MVR hot-press evaporation process using gypsum seeding for scale prevention. Sodium chloride crystals are evaporated, concentrated, and crystallized at 80-110°C, while other elements are simultaneously concentrated and enriched. The salt slurry discharged from the evaporator's salt foot is washed, dehydrated, dried, and packaged for storage and sale. During continuous operation of the evaporation system, the K+ content in the discharged mother liquor is controlled. + When the concentration is 40-60 g / L, the first stage of salt production mother liquor is obtained, which is continuously discharged to the calcium carbonate process after three-stage flash evaporation and cooling.

6. The stepwise extraction process for potassium-rich multi-component brine according to claim 5, characterized in that, The calcium carbonate production in step eight adopts a chemical precipitation method to produce calcium carbonate products. The feeding rate is controlled to ensure that the total aging time is more than 2 hours. The calcium carbonate reaction tank includes three reaction tanks, A, B, and C. The working state is: tank A feeds, tank B reacts and ages, and tank C discharges, which are used alternately. The obtained calcium carbonate particles are filtered, dehydrated, washed, desalted, and dried by the No. 4 intelligent desalting machine to obtain calcium carbonate products. The filtrate from the No. 4 intelligent desalting machine is clarified in a settling tank. The upper clear liquid is filtered through a precision filter and then pumped into the lithium extraction process. The lower calcium carbonate slurry is pumped into the No. 4 intelligent desalting machine. The calcium carbonate filter cake from the No. 4 intelligent desalting machine is washed with the condensate generated by salt evaporation. The washing liquid is sent to the lime slurry preparation process or pumped to the wastewater pool for well injection mining.

7. The stepwise extraction process for potassium-rich multi-component brine according to claim 1, characterized in that: The process of step nine includes: adding a mixed acid, a byproduct of the bromine-iodine process, to the clear brine after calcium carbonate extraction for acidification, thereby acidifying the pH. =4~6, after acidification, the clear brine is passed through a lithium-ion selective adsorption resin at a flow rate of 1~100 BV / h until the lithium concentration in the post-adsorption liquid is <5ppm, and the adsorption is stopped to obtain delithiated brine. The delithiated brine enters the iodine-bromine process. After the resin adsorption is completed, it is desorbed with RO pure water to obtain lithium chloride solution. When the lithium ion concentration in the effluent is <0.1g / l, the desorption is stopped. The lithium chloride solution is separated into divalent ions by nanofiltration membrane, and then concentrated to a lithium ion concentration of 5g / l by reverse osmosis membrane. Then, trace amounts of calcium and magnesium impurities are adsorbed by special resin, and then evaporated and concentrated to a lithium ion concentration of 22~25g / l by MVR device at 80~85℃. It is then kept at 80℃ for further impurity removal by adsorption of boron. The post-adsorption liquid is reacted and crystallized by adding 40% soda ash solution. The amount of soda ash added is 110% of the reaction equivalent. The addition is slow for 60 minutes, and the mixture is aged for 60 minutes. After filtration and separation, lithium carbonate is washed three times with RO pure water, and then dehydrated, dried by airflow, crushed, demagnetized, and packaged to obtain lithium carbonate products for storage and sale.

8. The stepwise extraction process for potassium-rich multi-component brine according to claim 1, characterized in that, The process of producing iodine and bromine products by blowing iodine and bromine in step 10 includes: the blown free iodine enters the absorption tower, and absorbs the free iodine in the absorption tower with SO2 produced by burning sulfur and the circulating absorption solution in the circulating tank. After absorption, the liquid is purified twice to obtain iodine products. The brine after blowing off the iodine enters the bromine process. The bromine process uses an air blowing method. The specific steps include: adding chlorine gas to the brine after iodine extraction and oxidizing it to a potential of 800~1200mV; then blowing out the free bromine from the brine using an air blowing method. The blown-out free bromine enters an absorption tower, where it is absorbed by SO2 produced from sulfur combustion and the circulating absorption solution in the circulation tank. After absorption, the solution is purified a second time to obtain the bromine product. The brine after bromine blowing then enters the cesium extraction process.

9. The stepwise extraction process for potassium-rich multi-component brine according to claim 8, characterized in that, The process for preparing cesium nitrate product in step eleven includes: passing a 1% to 3% concentration ammonium nitrate solution through an HC-Jpgt-Cs adsorbent at a flow rate of 1 to 50 BV / h to obtain a cesium eluent; the cesium eluent is then concentrated by membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain the cesium nitrate product. The process for preparing rubidium to produce rubidium nitrate in step twelve includes: passing a 1% to 3% concentration ammonium nitrate solution through an HC-Pmsa-Rb adsorbent at a flow rate of 1 to 50 BV / h to obtain a rubidium eluent; the rubidium eluent is then concentrated by membrane, purified, evaporated and crystallized, washed, filtered, and dried to obtain the rubidium nitrate product. The specific production plan for step thirteen includes: the brine after the rubidium extraction process is preheated by the condensate produced in stage II evaporation and salt production, and then pumped into the evaporator. Using MVR hot pressing salt technology, partial sodium chloride slurry is obtained through evaporation and crystallization at 80-110℃, while simultaneously concentrating potassium ions. The sodium chloride slurry discharged from the salt foot is pumped to the stage I salt production and washing unit, and continuously fed into the stage II evaporator to further concentrate potassium ions in the mother liquor. + When the concentration is 80-120 g / L, the mother liquor is discharged. After multi-stage flash evaporation and cooling to 20-50℃, potassium chloride crystals precipitate out, and supersaturation is slowly eliminated to obtain potassium chloride products with larger particles. The potassium chloride slurry is then subjected to sedimentation, washing, filtration, and drying to obtain the potassium chloride product. Part of the potassium chloride washing liquid is returned to the second-stage salt evaporator, and part is returned to the calcium and magnesium extraction process.

10. The stepwise extraction process for potassium-rich multi-component brine according to claim 9, characterized in that, The process for preparing sodium chloride and potassium chloride products in step thirteen includes: controlling the potassium content in the feed material to the stage II evaporator. + With a concentration of approximately 50 g / L, the slurry from the second-stage evaporator is first evaporated and then pumped to the first-stage salt evaporator. This continues until the potassium chloride solution in the second-stage evaporator is nearly saturated and no longer crystallizes, and sodium chloride crystals account for 10%–25% of the total solids. Then, the mixed salt slurry pump is started to pump the sodium chloride slurry to the first-stage evaporator. The saturated potassium chloride solution is then discharged step by step into the multi-stage flash evaporator. As the temperature of the potassium chloride solution decreases, its solubility also decreases, causing potassium chloride to crystallize or grow crystals. This slowly eliminates the supersaturation of the solution, ultimately yielding larger potassium chloride crystals.

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