A resourceful treatment method of ammonium chloride crystallization mother liquor dry salt

Abstract

The present application relates to a kind of resourceful treatment method of ammonium chloride crystallization mother liquor dry salt, belong to the waste residue processing technical field of ion type rare earth hydrometallurgy field.The present application uses adsorption technology and chemical precipitation method, step by step separates pollutants from waste residue, produces calcium sulfate, calcium carbonate, the crystalline precipitate of ammonium magnesium phosphate, carries out solid-liquid separation, and then converts evaporation salt into high-purity ammonium chloride solution.The present application is suitable for the treatment of ammonium chloride crystallization mother liquor dry salt with different proportions of various components, according to the solubility product constant of sulfide precipitation, calcium sulfate, calcium carbonate, ammonium magnesium phosphate is very small, step-by-step precipitation method is used to separate impurity elements in salt, strictly control process parameters, realize the transformation of ammonium chloride crystallization mother liquor dry salt to high-purity ammonium chloride solution, the existing precipitation and adsorption material in step is easy to solid-liquid separation, process technology is simple, easy to operate control, chemical reagent consumption is less, and salt treatment cost is low.

Description

Technical Field

[0001] This invention relates to the field of waste residue treatment technology in ion-type rare earth hydrometallurgical processes, specifically to a resource-based treatment method for drying and processing mixed salts from ammonium chloride crystallization mother liquor. Background Technology

[0002] In the hydrometallurgical process of ionic rare earth ores in southern China, ammonium salts (such as ammonium chloride) are commonly used as leaching agents, resulting in a large amount of highly concentrated acidic wastewater containing ammonium chloride. To achieve "zero discharge" of the wastewater and recover valuable components, two main industrial technical routes have been developed: one is to recover ammonia water through an "ammonia stripping" process, with the remaining wastewater being evaporated to produce calcium chloride as a byproduct; the other is to directly evaporate and crystallize the wastewater without ammonia stripping, producing industrial ammonium chloride as a byproduct.

[0003] In the direct evaporation crystallization process for producing ammonium chloride, a large amount of mother liquor is generated to maintain system water balance and control impurity concentration. Currently, the industry practice is to return most of the mother liquor to the upstream process for recycling. However, this recycling model leads to the continuous enrichment and accumulation of calcium ions, magnesium ions, heavy metal ions, and organic pollutants in the mother liquor. When the impurity concentration exceeds a certain threshold, it will cause a series of serious problems: First, the coexistence of impurity ions will seriously affect the purity and crystal form of ammonium chloride crystals, resulting in a yellowish product color, decreased purity, and difficulty in meeting the standards for industrial or agricultural products, significantly reducing the economic value of the product. Second, calcium and magnesium ions easily form hard scale layers such as calcium sulfate and calcium carbonate in the evaporator, severely reducing heat transfer efficiency, increasing energy consumption, and requiring frequent shutdowns for cleaning, shortening the service life of the equipment; at the same time, chloride ions and certain heavy metal ions will exacerbate the corrosion of core equipment such as the evaporator. Third, excessively high impurity concentrations will change the physicochemical properties of the solution, such as increasing the boiling point and viscosity, leading to instability in the evaporation crystallization process, difficulty in operation control, and affecting continuous production.

[0004] To address the aforementioned issue of cyclic accumulation, the current practice is to discharge a portion of the crystallization mother liquor from the main process. This discharged mother liquor is typically dried to form solid "dried mixed salts." These dried mixed salts still contain 35%–45% ammonium chloride, possessing significant resource recovery value. However, due to the presence of large amounts of impurities such as calcium, magnesium, heavy metals, and organic matter, directly recycling them into the evaporation crystallization process would reintroduce contaminants into the system, failing to fundamentally solve the problem.

[0005] Therefore, this portion of miscellaneous salts is often managed as solid waste, facing the dilemma of stockpiling or outsourcing disposal. This not only occupies land resources and poses potential environmental risks, but also wastes the ammonium and chlorine resources it contains, while imposing a continuous economic burden on production enterprises.

[0006] In existing technologies, there is a lack of mature processes that are both economical and efficient for the resource recovery of complex mixed inorganic salts. Simple recrystallization methods are insufficient to effectively separate multiple impurities; while end-of-pipe disposal methods such as incineration and landfill completely abandon resource recovery, failing to meet the requirements of a circular economy and clean production. Therefore, developing a treatment method that can accurately separate various impurities and achieve efficient recovery of ammonium chloride and complete resource recovery of mixed salts has become a significant technical challenge in this field. This invention is proposed based on this practical need. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a simple, low-cost, and highly resource-efficient method for the resource-based treatment of waste salts from the drying of ammonium chloride crystallization mother liquor. This method can accurately and efficiently separate impurities such as organic matter, calcium, magnesium, and heavy metals from waste salts through stepwise precipitation and adsorption technology, ultimately converting waste waste salts into a high-purity ammonium chloride solution that can be directly reused, thereby realizing the resource-based recycling of waste and solving the industry problem of impurity accumulation in the system.

[0008] To address the aforementioned technical problems, this invention provides a method for the resource-based treatment of impurities from the dried mother liquor of ammonium chloride crystallization, comprising the following steps: S1. Dissolving: First, mix the dried miscellaneous salt with water at a ratio of 1:2 g / mL, and stir for 60 min to 120 min to dissolve it and obtain the solution. S2, Acidity Adjustment: Adjust the pH of the feed solution to 3.5-4.5 using pH Adjuster I; S3. Adsorption: Based on the turbidity and total organic carbon concentration of the feed liquid, add 1% to 3% of the feed liquid volume of adsorbent to the reaction tank and stir. Then, perform solid-liquid separation and transfer the obtained filtrate I to the subsequent treatment process. S4. Breakpoint calcium removal: Based on the calcium ion concentration in filtrate I, add soluble calcium precipitant I to filtrate I, react in a reaction tank, let stand, and then perform solid-liquid separation to obtain filtrate II and filter residue II. After drying, filter residue II is calcium sulfate with a purity of over 90%, which can be used in building materials. S5. Alkalinity adjustment: Adjust the pH of filtrate II to 7.0–8.0 using pH adjuster II; S6. Deep weight removal: Based on the concentration of heavy metal ions in filtrate II, add a soluble weight removal precipitant to filtrate II, react in a reaction tank and let it stand, then perform solid-liquid separation to obtain filtrate III. S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, an oxidant is added to filtrate III, and after reaction in a reaction tank, desulfurized filtrate III is obtained. S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add soluble calcium precipitant II to desulfurization filtrate III, react in the reaction tank and let it stand, then perform solid-liquid separation to obtain filtrate IV. S9. Deep magnesium removal: Based on the magnesium ion concentration in filtrate IV, a soluble magnesium precipitant is added to filtrate IV, reacted in a reaction tank and allowed to stand, followed by solid-liquid separation to obtain filtrate V and filter residue V. Filter residue V is magnesium ammonium phosphate crystals with a purity greater than 80%, which can be used for fertilizer. Filtrate V is high-purity ammonium chloride mother liquor, which is transferred to subsequent processing.

[0009] In some embodiments of the present invention, in step S2, pH adjuster I is H2SO4.

[0010] In some embodiments of the present invention, in step S3, the adsorbent is powdered biochar.

[0011] As some embodiments of the present invention, in step S3, the mixture is stirred in the reaction tank for 4 to 12 hours.

[0012] In some embodiments of the present invention, in step S4, the soluble calcium precipitant I is (NH4)2SO4, and the main reaction in this step is as follows: Ca 2+ +SO4 2- +2H₂O=CaSO₄·2H₂O↓ As some embodiments of the present invention, in step S4, soluble calcium precipitant I is added to filtrate I at a molar ratio of sulfate ions to calcium ions of 0.5 to 0.6.

[0013] As some embodiments of the present invention, in step S4, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

[0014] As some embodiments of the present invention, in step S5, pH adjuster II is NH3·H2O.

[0015] In some embodiments of the present invention, in step S6, the soluble heavy precipitant is Na2S, and the main reaction in this step is as follows: M 2+ +S 2- =MS↓ (M represents Zn, Pb, Cu, Cr, Cd) As some embodiments of the present invention, in step S6, a soluble heavy metal precipitant I is added to filtrate II according to the concentration of heavy metal ions in filtrate II at a molar ratio of sulfide ions to heavy metal ions of 0.9 to 1.1.

[0016] As some embodiments of the present invention, in step S6, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

[0017] In some embodiments of the present invention, in step S7, the oxidant is H2O2, and the main reaction in this step is as follows: S 2- +4H₂O₂=SO₄ 2- +4H2O As some embodiments of the present invention, in step S7, an oxidant is added to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 4.0 to 4.2; As some embodiments of the present invention, in step S7, the reaction is carried out in the reaction tank for 15 min to 30 min.

[0018] In some embodiments of the present invention, in step S8, the soluble calcium precipitant II is NH4HCO3, and the main reaction in this step is as follows: HCO3 - +OH - =CO3 2- +H2O Ca 2+ +CO3 2- =CaCO3↓ As some embodiments of the present invention, in step S8, soluble calcium precipitant II is added to the desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 1.8 to 2.2.

[0019] As some embodiments of the present invention, in step S8, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

[0020] In some embodiments of the present invention, in step S9, the soluble magnesium precipitant is (NH4)2HPO4, and the main reaction in this step is as follows: Mg 2+ +HPO4 2- +NH3·H2O=MgNH4PO4↓+H2O As some embodiments of the present invention, in step S9, a soluble magnesium precipitant is added at a molar ratio of phosphate to magnesium ions of 0.9 to 1.0.

[0021] As some embodiments of the present invention, in step S9, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

[0022] In some embodiments of the present invention, the adsorbent, soluble calcium precipitant I, soluble de-gravity precipitant, soluble calcium precipitant II, and soluble magnesium precipitant are added by means of adding dry powder.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention is applicable to the treatment of mixed salts from the dried ammonium chloride crystallization mother liquor with different compositions and proportions. Based on the small solubility product constants of sulfide precipitates, calcium sulfate, calcium carbonate, and magnesium ammonium phosphate, a stepwise precipitation method is used to gradually separate impurity elements in the mixed salts. By strictly controlling the process parameters, the mixed salts from the dried ammonium chloride crystallization mother liquor are transformed into a high-purity ammonium chloride solution. The precipitates and adsorbents present in the steps are easy to separate into solid and liquid components. The process technology is simple, easy to operate and control, consumes less chemical reagents, and has low cost for mixed salt treatment.

[0024] 1. High resource utilization and closed-loop recycling: The core objective of this invention is to transform dried miscellaneous salts rich in ammonium chloride (35%–45%) from solid waste into a resource-recoverable product. Through this method, the final product is high-purity ammonium chloride mother liquor, which can be directly returned to the main evaporation and crystallization process as raw material. This not only recovers valuable ammonium salts and chloride ions but also fundamentally solves the problem of impurity accumulation in the system, achieving a closed-loop recycling of waste within the process system, thus combining environmental and economic benefits.

[0025] 2. Precise and efficient impurity separation with significant purification effect: This invention is based on the principle that substances such as sulfides, calcium sulfate, calcium carbonate, and magnesium ammonium phosphate have extremely small solubility product constants, and adopts a "stepwise precipitation" technical route. By precisely controlling the pH and reaction sequence, targeted separation of different impurities such as calcium, magnesium, heavy metals, and organic matter is achieved. In the examples, the maximum removal rate of calcium ions is 99.98%, the maximum removal rate of magnesium ions is 99.998%, the maximum removal rate of zinc ions is 99.985%, the maximum removal rate of lead ions is 100%, and the maximum removal rate of COD is 80.75%. The relatively low COD removal rate of this invention is because the organic matter in the dried mixed salts is mainly in the form of soluble organic matter. Adsorption can remove most of it, but not completely. Moreover, the COD removal rate is highly correlated with the amount of activated carbon added. When the amount of activated carbon added is 3% of the liquid volume, the residual COD in the solution can be reduced to 458 mg / L. Furthermore, the advantage of this invention is that even if COD removal is incomplete, it has less interference with the subsequent precipitation removal of other impurity ions, and the process indicators are stable.

[0026] 3. The process is simple, stable, and easy to operate and control: The entire process mainly consists of conventional steps such as dissolution, pH adjustment, chemical dosing and reaction, and solid-liquid separation. The process route is rationally designed and logically clear. The reaction conditions (such as pH range, reaction and settling time) and chemical dosing coefficients for each step have clear and optimized parameter ranges, making it easy to achieve precise control and stable operation in industrial production. The technical requirements for operators are relatively low.

[0027] 4. Low processing cost and optimized reagent selection: The reagents selected in this invention, such as ammonium sulfate, ammonium bicarbonate, diammonium hydrogen phosphate, and biochar, are all common, inexpensive, and readily available industrial raw materials. More importantly, the selected precipitants are all ammonium salts, which remove impurity ions while avoiding the introduction of new cation impurities such as sodium and potassium, preventing secondary pollution and ensuring the purity of the final product, ammonium chloride solution. Simultaneously, by optimizing the reagent dosage, the consumption of chemical reagents is minimized while ensuring precipitation effect, thereby effectively reducing the processing cost of impurity salts.

[0028] 5. Excellent solid-liquid separation performance, with potential value in byproducts: The calcium sulfate, calcium carbonate, magnesium ammonium phosphate, and heavy metal sulfides generated during the process are all well-crystallized and dense precipitates with fast settling speeds and excellent filtration performance, easily achieving thorough mud-water separation using conventional solid-liquid separation equipment (such as filter presses). The resulting precipitates, such as calcium sulfate (gypsum), calcium carbonate, and magnesium ammonium phosphate (struvite, a slow-release fertilizer), also have certain resource utilization potential, providing possibilities for further reducing treatment costs and even creating additional revenue. Attached Figure Description

[0029] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the process flow of an embodiment of the present invention. Detailed Implementation

[0031] To make the technical means, creative features, objectives and effects of this invention easier to understand, the technical solutions in the specific embodiments of this invention are described clearly and completely below to further illustrate this invention. Obviously, the specific embodiments described are only a part of the embodiments of this invention, and not all of them.

[0032] Example 1: This embodiment employs a resource-based treatment method for dried mixed salts from an ion-adsorption rare earth ore hydrometallurgical plant, utilizing the dried mixed salts from the mother liquor of high-concentration ammonium chloride crystallization wastewater. The dried mixed salts are produced by drying a portion of the high-concentration mother liquor after the high-concentration ammonium chloride acidic wastewater in the plant has undergone evaporation and crystallization to produce ammonium chloride as a byproduct. By mass percentage, the dried mixed salts contain 4.3% calcium, 5.1% magnesium, 37.6% chlorine, 21.1% ammonium, 0.5% zinc, 0.03% lead, and 0.3% organic matter (as COD). Figure 1 As shown, the resource recovery method for this dried mixed salt includes the following steps: S1. Dissolving: Take 50g of ammonium chloride crystallization mother liquor to dry the mixed salts, add 100mL of tap water and stir for 60min to obtain the liquid. S2. Acidity adjustment: While stirring, add dilute sulfuric acid (pH adjuster I) dropwise to the solution to adjust the pH value to 4.0; S3, Adsorption: Add 1% activated carbon (adsorbent) by volume of the liquid and stir for 4 hours; then separate the liquid after reaction to obtain filtrate I and filter residue I. S4. Breakpoint Calcium Removal: Based on the calcium ion concentration in filtrate I, (NH4)2SO4 (soluble calcium precipitant I) was added to filtrate I at a sulfate ion to calcium ion molar ratio of 0.6. The mixture was stirred for 60 min, allowed to stand for 60 min, and then solid-liquid separation was performed to obtain filtrate II and calcium sulfate. In this embodiment, the obtained calcium sulfate was also tested using the IPS-OES method. The lead and zinc contents were both less than 0.001%, and the calcium mass content was 25.14%. The gravimetric method was used to test the sulfate mass content, which was 57.95%, and the calcium sulfate dihydrate mass content was 103.82% (the calcium sulfate content exceeded 100%, which is within the test error range, indicating that the calcium sulfate dihydrate is of high purity).

[0033] S5. Alkalinity adjustment: While stirring, add ammonia (pH adjuster II) to filtrate II to adjust the pH value to 7.5; S6. Deep heavy removal: Based on the concentration of heavy metal ions in filtrate II, add Na2S·9H2O (soluble heavy removal precipitant I) to filtrate II at a molar ratio of sulfide ions to heavy metal ions of 1.0. Stir the reaction in the reaction tank for 60 min, let it stand for 60 min, and then perform solid-liquid separation to obtain filtrate III and sulfide precipitate. S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, add H2O2 (oxidant) to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 4.0. After reacting in the reaction tank for 30 minutes, desulfurized filtrate III is obtained. S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add NH4HCO3 (soluble calcium precipitant II) to desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 2.0. Stir and react in the reaction tank for 60 min, let stand for 60 min, and then perform solid-liquid separation to obtain filtrate IV and calcium carbonate. S9. Deep Magnesium Removal: Based on the magnesium ion concentration in filtrate IV, (NH4)2HPO4 (soluble magnesium precipitant) was added at a phosphate to magnesium ion molar ratio of 1.0. The mixture was stirred in the reaction tank for 60 min, allowed to stand for 60 min, and the supernatant was analyzed. As shown in Table 1, the calcium concentration was 4.48 mg / L, the magnesium concentration was 0.51 mg / L, the COD concentration was 458 mg / L, the zinc concentration was 1.3 mg / L, and the lead concentration was 0 mg / L. That is, the calcium removal rate was 99.98%, the magnesium removal rate was 99.998%, the COD removal rate was 78.42%, the zinc removal rate was 99.94%, and the lead removal rate was 100.00%. Subsequently, solid-liquid separation was performed, and the obtained filtrate V was high-purity ammonium chloride mother liquor, which was transferred to subsequent processes. Filter residue V was magnesium ammonium phosphate.

[0034] The formula for calculating the removal rate is as follows: Removal rate = In the formula: C 1 indicates the concentration before treatment. V 1 represents the volume before processing. C 2 indicates the concentration after treatment. V 2 indicates the volume after processing.

[0035] Example 2: This embodiment employs a resource-based treatment method for dried mixed salts from an ion-adsorption rare earth ore hydrometallurgical plant, utilizing the dried mixed salts from the mother liquor of ammonium chloride crystallization. The dried mixed salts are produced by drying a portion of the high-concentration mother liquor from the high-concentration ammonium chloride acidic wastewater after evaporation and crystallization to produce ammonium chloride as a byproduct. By mass percentage, the dried mixed salts contain 5.3% calcium, 4.1% magnesium, 35.6% chlorine, 25.1% ammonium, 0.4% zinc, 0.02% lead, and 0.2% organic matter (as COD). Figure 1 As shown, the resource recovery method for this dried mixed salt includes the following steps: S1. Dissolving: Take 50g of ammonium chloride crystallization mother liquor to dry the mixed salts, add 100mL of tap water and stir for 120min to obtain the liquid. S2. Acidity adjustment: While stirring, add dilute sulfuric acid (pH adjuster I) dropwise to the solution to adjust the pH value to 4.5; S3, Adsorption: Add 1% activated carbon (adsorbent) by volume of the liquid and stir for 6 hours; then separate the liquid after reaction to obtain filtrate I and filter residue I. S4. Breakpoint calcium removal: Based on the calcium ion concentration in filtrate I, add (NH4)2SO4 (soluble calcium precipitant I) to filtrate I at a molar ratio of sulfate ions to calcium ions of 0.5, stir for 50 min, let stand for 60 min, and then perform solid-liquid separation to obtain calcium sulfate filtrate II. S5. Alkalinity adjustment: While stirring, add ammonia (pH adjuster II) to filtrate II to adjust the pH value to 7.5; S6. Deep heavy removal: Based on the concentration of heavy metal ions in filtrate II, add Na2S·9H2O (soluble heavy removal precipitant I) to filtrate II at a molar ratio of sulfide ions to heavy metal ions of 1.0. Stir the reaction in the reaction tank for 50 min, let it stand for 60 min, and then perform solid-liquid separation to obtain filtrate III and sulfide precipitate. S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, add H2O2 (oxidant) to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 4.2. After reacting in the reaction tank for 30 minutes, desulfurized filtrate III is obtained. S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add NH4HCO3 (soluble calcium precipitant II) to desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 1.8. Stir the reaction in the reaction tank for 50 minutes, let it stand for 60 minutes, and then perform solid-liquid separation to obtain filtrate IV and calcium carbonate. S9. Deep Magnesium Removal: Based on the magnesium ion concentration in filtrate IV, (NH4)2HPO4 (soluble magnesium precipitant) was added at a phosphate to magnesium ion molar ratio of 1.1. The mixture was stirred in the reaction tank for 50 min, allowed to stand for 60 min, and the supernatant was analyzed. As shown in Table 1, the calcium concentration was 16.26 mg / L, the magnesium concentration was 0.99 mg / L, the COD concentration was 1550 mg / L, the zinc concentration was 1.63 mg / L, and the lead concentration was 0.05 mg / L. That is, the calcium removal rate was 99.85%, the magnesium removal rate was 99.99%, the COD removal rate was 27.5%, the zinc removal rate was 99.985%, and the lead removal rate was 99.9%. Subsequently, solid-liquid separation was performed, and the obtained filtrate V was the high-purity ammonium chloride mother liquor, which was transferred to subsequent processes. The filter residue V was magnesium ammonium phosphate. In this embodiment, to illustrate that the removal of organic matter has little impact on subsequent precipitation steps, a small amount of adsorbent was added. This demonstrates that even if the COD removal rate is not high enough, the removal rate of metal ions in the subsequent process remains high, further indicating the stability of the process.

[0036] Example 3: This embodiment employs a resource-based treatment method for dried mixed salts from an ion-adsorption rare earth ore hydrometallurgical plant, utilizing the dried mixed salts from the mother liquor of high-concentration ammonium chloride crystallization. The dried mixed salts are produced by drying a portion of the high-concentration mother liquor from the high-concentration ammonium chloride acidic wastewater after evaporation and crystallization to produce ammonium chloride as a byproduct. By mass percentage, the dried mixed salts contain 9.3% calcium, 2.1% magnesium, 30.1% chlorine, 15.7% ammonium, 0.3% zinc, 0.03% lead, and 0.4% organic matter (as COD). Figure 1 As shown, the resource recovery method for this dried mixed salt includes the following steps: S1. Dissolving: Take 50g of ammonium chloride crystallization mother liquor to dry the mixed salts, add 100mL of tap water and stir for 120min to obtain the liquid. S2. Acidity adjustment: While stirring, add dilute sulfuric acid (pH adjuster I) dropwise to the solution to adjust the pH value to 3.5; S3, Adsorption: Add 3% (by volume) of activated carbon (adsorbent) to the liquid and stir for 4 hours; then separate the reacted liquid into filtrate I and filter residue I. S4. Breakpoint calcium removal: Based on the calcium ion concentration in filtrate I, add (NH4)2SO4 (soluble calcium precipitant I) to filtrate I at a molar ratio of sulfate ions to calcium ions of 0.6, stir for 45 min, let stand for 50 min, and then perform solid-liquid separation to obtain filtrate II and calcium sulfate. S5. Alkalinity adjustment: While stirring, add ammonia (pH adjuster II) to filtrate II to adjust the pH value to 7.2; S6. Deep heavy removal: Based on the concentration of heavy metal ions in filtrate II, add Na2S·9H2O (soluble heavy removal precipitant I) to filtrate II at a molar ratio of sulfide ions to heavy metal ions of 1.0. Stir the reaction in the reaction tank for 50 min, let it stand for 60 min, and then perform solid-liquid separation to obtain filtrate III and sulfide precipitate. S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, add H2O2 (oxidant) to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 3.9. After reacting in the reaction tank for 30 minutes, desulfurized filtrate III is obtained. S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add NH4HCO3 (soluble calcium precipitant II) to desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 1.9. Stir the reaction in the reaction tank for 60 minutes, let it stand for 50 minutes, and then perform solid-liquid separation to obtain filtrate IV and calcium carbonate. S9. Deep Magnesium Removal: Based on the magnesium ion concentration in filtrate IV, (NH4)2HPO4 (soluble magnesium precipitant) was added at a phosphate to magnesium ion molar ratio of 1.0. The mixture was stirred in the reaction tank for 50 min, allowed to stand for 60 min, and the supernatant was analyzed. As shown in Table 1, the calcium concentration was 2.13 mg / L, the magnesium concentration was 11.51 mg / L, the COD concentration was 477 mg / L, the zinc concentration was 0.5 mg / L, and the lead concentration was 0.05 mg / L. That is, the calcium removal rate was 99.99%, the magnesium removal rate was 99.89%, the COD removal rate was 76.15%, the zinc removal rate was 99.96%, and the lead removal rate was 99.96%. Subsequently, solid-liquid separation was performed, and the obtained filtrate V was the high-purity ammonium chloride mother liquor, which was transferred to subsequent processes. The filter residue V was magnesium ammonium phosphate.

[0037] Example 4: This embodiment employs a resource-based treatment method for dried mixed salts from an ion-adsorption rare earth ore hydrometallurgical plant, utilizing the dried mixed salts from the mother liquor of ammonium chloride crystallization. The dried mixed salts are produced by drying a portion of the high-concentration mother liquor from the high-concentration ammonium chloride acidic wastewater after evaporation and crystallization to produce ammonium chloride as a byproduct. By mass percentage, the dried mixed salts contain 7.47% calcium, 3.16% magnesium, 34.1% chlorine, 15.7% ammonium, 0.21% zinc, 0.01% lead, and 0.48% organic matter (as COD). Figure 1 As shown, the resource recovery method for this dried mixed salt includes the following steps: S1. Dissolving: Take 50g of ammonium chloride crystallization mother liquor to dry the mixed salts, add 100mL of tap water and stir for 80min to obtain the liquid. S2. Acidity adjustment: While stirring, add dilute sulfuric acid (pH adjuster I) dropwise to the solution to adjust the pH value to 4.2; S3, Adsorption: Add 3% (by volume) of activated carbon (adsorbent) to the liquid and stir for 4 hours; then separate the reacted liquid into filtrate I and filter residue I. S4. Breakpoint calcium removal: Based on the calcium ion concentration in filtrate I, add (NH4)2SO4 (soluble calcium precipitant I) to filtrate I at a molar ratio of sulfate ions to calcium ions of 0.55, stir for 60 min, let stand for 50 min, and then perform solid-liquid separation to obtain filtrate II and calcium sulfate. S5. Alkalinity adjustment: While stirring, add ammonia (pH adjuster II) to filtrate II to adjust the pH value to 7.4; S6. Deep heavy removal: Based on the concentration of heavy metal ions in filtrate II, add Na2S·9H2O (soluble heavy removal precipitant I) to filtrate II at a molar ratio of sulfide ions to heavy metal ions of 1.1. Stir the reaction in the reaction tank for 60 min, let it stand for 50 min, and then perform solid-liquid separation to obtain filtrate III and sulfide precipitate. S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, add H2O2 (oxidant) to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 4.1. After reacting in the reaction tank for 30 minutes, desulfurized filtrate III is obtained. S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add NH4HCO3 (soluble calcium precipitant II) to desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 1.8. Stir and react in the reaction tank for 50 minutes, let stand for 50 minutes, and then perform solid-liquid separation to obtain filtrate IV and calcium carbonate. S9. Deep Magnesium Removal: Based on the magnesium ion concentration in filtrate IV, (NH4)2HPO4 (soluble magnesium precipitant) was added at a phosphate to magnesium ion molar ratio of 1.1. The mixture was stirred in the reaction tank for 60 min, allowed to stand for 50 min, and the supernatant was analyzed. As shown in Table 1, the calcium concentration was 52.66 mg / L, the magnesium concentration was 1.46 mg / L, the COD concentration was 462 mg / L, the zinc concentration was 0.24 mg / L, and the lead concentration was 0.01 mg / L. That is, the calcium removal rate was 99.86%, the magnesium removal rate was 99.99%, the COD removal rate was 80.75%, the zinc removal rate was 99.98%, and the lead removal rate was 99.98%. Subsequently, solid-liquid separation was performed, and the obtained filtrate V was high-purity ammonium chloride mother liquor, which was transferred to subsequent processes. Filter residue V was magnesium ammonium phosphate.

[0038] Table 1. Detection results of the content of each substance Based on the results of the various embodiments in Table 1, it is shown that the present invention can effectively remove calcium, magnesium, zinc, and lead ions from dried mixed salts. In the above embodiments, the maximum removal rate of calcium ions was 99.98%, the maximum removal rate of magnesium ions was 99.998%, the maximum removal rate of zinc ions was 99.985%, the maximum removal rate of lead ions was 100%, and the maximum removal rate of COD was 80.75%. The relatively low COD removal rate of the present invention is because the organic matter in the dried mixed salts mainly exists in the form of soluble organic matter. Adsorption can remove most of it, but not completely. Furthermore, the COD removal rate is highly correlated with the amount of activated carbon added. When the amount of activated carbon added is 3% of the liquid volume, the residual COD in the solution can be reduced to 458 mg / L. The advantage of the present invention is that even if COD removal is incomplete, it has minimal interference with subsequent precipitation removal of other impurity ions, and the process indicators remain stable.

[0039] The main technical features, basic principles, and related advantages of the present invention have been described above. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the concept or basic characteristics of the invention. Therefore, the above-described embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

[0040] Furthermore, it should be understood that although this specification describes various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard 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 method for the resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization, characterized in that, Includes the following steps: S1. Dissolving: First, mix the dried miscellaneous salt with water at a ratio of 1:2 g / mL, and stir for 60 min to 120 min to dissolve it and obtain the solution. S2, Acidity Adjustment: Adjust the pH of the feed solution to 3.5–4.5 using pH Adjuster I; S3. Adsorption: Based on the turbidity and total organic carbon concentration of the feed liquid, add 1% to 3% of the feed liquid volume of adsorbent to the reaction tank and stir. Then, perform solid-liquid separation and transfer the obtained filtrate I to the subsequent treatment process. S4. Breakpoint calcium removal: Based on the calcium ion concentration in filtrate I, add soluble calcium precipitant I to filtrate I, react in the reaction tank, let stand, and then perform solid-liquid separation to obtain filtrate II and filter residue II. Soluble calcium precipitant I is (NH4)2SO4; Add soluble calcium precipitant I to filtrate I at a molar ratio of sulfate ions to calcium ions of 0.5 to 0.6; After drying, filter residue II is calcium sulfate with a purity of over 90%, which is used in building materials; S5. Alkalinity adjustment: Adjust the pH of filtrate II to 7.0–8.0 using pH adjuster II; S6. Deep weight removal: Based on the concentration of heavy metal ions in filtrate II, add soluble weight removal precipitant I to filtrate II, react in the reaction tank and let it stand, then perform solid-liquid separation to obtain filtrate III; The soluble heavy precipitation remover is Na2S; Based on the concentration of heavy metal ions in filtrate II, add soluble heavy metal precipitant I to filtrate II at a molar ratio of sulfide ions to heavy metal ions of 0.9 to 1.

1. React in the reaction tank for 30-60 minutes, then let stand for 45-60 minutes; S7. Oxidative desulfurization: Based on the sulfur ion concentration in filtrate III, an oxidant is added to filtrate III, and after reaction in a reaction tank, desulfurized filtrate III is obtained. The oxidizing agent is H2O2; An oxidant is added to filtrate III at a molar ratio of oxidant molecules to sulfur ions of 4.0 to 4.

2. React in the reaction tank for 15 to 30 minutes; S8. Deep calcium removal: Based on the calcium ion concentration in desulfurization filtrate III, add soluble calcium precipitant II (NH4HCO3) to desulfurization filtrate III. React in the reaction tank and let stand, then perform solid-liquid separation to obtain filtrate IV and calcium carbonate. S9. Deep magnesium removal: Based on the magnesium ion concentration in filtrate IV, add soluble magnesium precipitant to filtrate IV, react in the reaction tank and let it stand, then perform solid-liquid separation to obtain filtrate V and filter residue V. Filtrate V is a high-purity ammonium chloride mother liquor, which is transferred to subsequent process treatment. The soluble magnesium precipitant is (NH4)2HPO4; Add a soluble magnesium precipitant at a molar ratio of phosphate to magnesium ions of 0.9–1.

0. Filter residue V is magnesium ammonium phosphate crystals with a purity greater than 80%, used in fertilizers.

2. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S2, pH adjuster I is H2SO4.

3. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S3, the adsorbent is powdered activated carbon; Stir in the reaction tank for 4 to 12 hours.

4. The method for resource utilization of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S4, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

5. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S5, pH adjuster II is NH3·H2O.

6. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S8, soluble calcium precipitant II is added to the desulfurization filtrate III at a molar ratio of bicarbonate ions to calcium ions of 1.8 to 2.

2. React in the reaction tank for 30 to 60 minutes, then let it stand for 45 to 60 minutes.

7. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, In step S9, the reaction is carried out in the reaction tank for 30 min to 60 min, and then left to stand for 45 min to 60 min.

8. The method for resource-based treatment of miscellaneous salts from the dried mother liquor of ammonium chloride crystallization according to claim 1, characterized in that, The adsorbent, soluble calcium precipitant I, soluble de-gravity precipitant, soluble calcium precipitant II, and soluble magnesium precipitant are added by adding dry powder.

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