CN115304105B - A method for hydrothermal solidification of arsenic-rich crystals - Google Patents

Abstract

A method for hydrothermally curing arsenic-rich crystals. The invention discloses a method for recycling arsenic ferric salt and sodium sulfate crystals from arsenic-enriched crystal water after being thermally solidified into scorodite crystals and arsenic-immobilized liquid, and relates to the field of non-toxicity and harmless arsenic-containing byproducts in nonferrous metal smelting. The invention provides a method for synthesizing a sodium arsenate crystal produced in the resource utilization of antimony smelting arsenic alkali slag into a complete flaky scorodite crystal by adding a solid ferric iron source into a high-temperature hydrothermal kettle, wherein the arsenic concentration in toxic leaching (TCLP) is lower than a specified value of national standard (GB 5085.3-2007) by 5mg/L, the method is suitable for safe storage, and the problems of acid accumulation of a solution and innocuity of arsenic in the arsenic alkali slag in the synthesis process are solved. And respectively recovering arsenic iron salt and sodium sulfate crystals from the arsenic-fixing solution through neutralization precipitation and evaporative crystallization, so as to realize deep removal of arsenic iron from the solution and closed-circuit treatment. The invention has the advantages of simple operation, high stability of scorodite crystals, no arsenic-containing wastewater discharge, environmental protection and the like.

Description

A method for hydrothermal solidification of arsenic-rich crystals

Technical field

The present invention relates to the field of non-toxic and harmless treatment of arsenic-containing by-products in non-ferrous metal smelting, particularly a method for utilizing hydrothermal solidification of antimony to smelt sodium arsenate crystals for resource utilization of arsenic-alkali slag.

Background technique

Arsenic mainly exists in the form of sodium arsenate and sodium arsenite in the arsenic-alkali residue of antimony smelting, with its content ranging from 5 to 20%. In the resource utilization of arsenic-alkali residue, arsenic is enriched in the leachate, and sodium arsenate crystals are produced through concentrated crystallization or fractional crystallization. Since only a small amount of arsenic can be used in the chemical and semiconductor fields and the product market is small, large amounts of sodium arsenate crystals can only be piled up for a long time. Highly toxic sodium arsenate is easily soluble in water and may be penetrated by rainwater during long-term storage, causing serious arsenic pollution and placing great environmental pressure on the clean utilization of arsenic-containing by-products of non-ferrous metal smelting.

Scorodite (FeAsO ₄ ·2H ₂ O) is a highly crystalline iron arsenate, mainly in the form of bipyramids, columns, clusters or grapes, etc., with a single crystal particle size of 0.1 to 0.5 mm. It is a granular aggregate of 3 to 5 mm with a density of 3.10g/cm ³ and its colors are mainly light green, light yellow, white, etc. The crystal parameters of octahedral scorodite are It is an orthorhombic crystal system with Z=8 and its space group is Pcab. The standard enthalpy of formation of scorodite is -1508.9kJ/mol, the standard entropy is 188.0J·mol ^-1 ·K ^-1 , the Gibbs free energy is -1284.8kJ/mol, and the solubility product is only (log K _sp = -26.4) One thousandth of amorphous iron arsenate (log K _sp = -23.0). Scorodite in the natural environment is the weathering product of arsenopyrite minerals and can exist stably in nature. It mainly exists as FeAsO ₄ ·2H ₂ O in acidic media and forms FeAsO ₄ ·2H ₂ O in alkaline environments. @FeOOH core-shell stable structure. Scorodite has the advantages of stable crystal structure, high arsenic content (32.5%), small slag content, easy filtering, non-toxicity and low storage cost.

Among the currently published patents, patent CN 109809494 A discloses an arsenic fixation method for preparing scorodite by stabilizing arsenic-alkali residue. The antimony is recovered through oxidative leaching, and then CO ₂ is introduced for dealkalization to produce sodium arsenate. Add acid to the solution to adjust the pH = 1.0 to 2.5. Add a mixed solution of ferrous salt and H ₂ O ₂ and then heat to react to synthesize bipyramidal octahedral scorodite crystals, as shown in chemical reaction formula (1). This method can effectively solidify arsenic in arsenic-alkali residue into non-toxic scorodite crystals, but the pH at the end of the reaction drops significantly, forming a cumulative effect of acid, resulting in poor arsenic fixation effect. This method is only suitable for synthesizing scorodite from solutions with arsenic concentration lower than 20g/L, which increases the burden of post-arsenic solidification liquid treatment.

2Fe ²⁺ +2H ₃ AsO ₄ +H ₂ O ₂ +2H ₂ O＝2FeAsO ₄ ·2H ₂ O+4H ⁺ (1)

Contents of the invention

In order to solve the environmental hazards caused by acid accumulation in the synthesis of scorodite from sodium arsenate crystals in arsenic-alkali residues, poor arsenic fixation effect and discharge of arsenic fixation liquid. The first object of the present invention is to provide a solid ferric salt that can efficiently synthesize scorodite crystals in a hydrothermal reaction, achieve solidification of sodium arsenate crystals, and be suitable for long-term safe storage. This method has good arsenic fixation effect, is suitable for high arsenic solutions, has small pH changes of the solution before and after synthesis, and has no H ⁺ accumulation.

The second object of the present invention is to use the neutralization and precipitation method to deeply remove arsenic and iron ions in the liquid after solid arsenic, and the obtained arsenic and iron salts are used for hydrothermal synthesis of scorodite. The neutralization precipitation method has the advantages of thorough removal of arsenic and iron salts and reuse of arsenic and iron salts.

The third object of the present invention is to use evaporation crystallization method to recover the sodium salt in the liquid after neutralization and precipitation, so as to realize zero discharge treatment of the solution. This method has the advantages of high sodium salt crystallization rate and stable sodium salt product composition.

In order to achieve the above object, the present invention provides the following technical solution: add sodium arsenate crystals to distilled water, slowly add sulfuric acid dropwise to adjust the pH, then transfer to a hydrothermal kettle and add a solid ferric iron source, and at a higher temperature Keep warm and stir evenly to precipitate and crystallize the iron arsenic. After filtering, washing and drying the precipitate, stable flaky scorodite can be obtained. The neutralization precipitation method is used to add sodium hydroxide to the post-arsenic solidification solution to adjust the pH of the solution. The reaction forms a precipitate of arsenic iron salt. The precipitate is filtered, washed, dried and finely ground for use in synthesizing scorodite. The neutralized liquid is continuously evaporated at high temperature and then cooled and crystallized at low temperature to precipitate the sodium sulfate crystal product to achieve the goal of zero discharge of the solution. The essence of the present invention is to utilize the principle that high-valent arsenic and iron ions are easy to co-precipitate into scorodite crystals with low solubility and non-toxicity in high-temperature solutions to achieve non-toxic and harmless arsenic in sodium arsenate. The principle of hydrolyzing and precipitating arsenic and iron ions into iron arsenate and iron hydroxide with small solubility products is then used to complete the efficient removal of residual arsenic and iron in the liquid after arsenic solidification. Finally, the characteristic that sodium sulfate can crystallize and precipitate in a supersaturated solution is used to realize the evaporation and crystallization of the neutralized liquid to recover the sodium salt.

In order to achieve the above objects, the present invention provides the following technical solutions:

(1)Scorodite crystal synthesis

Scorodite crystals are obtained by first dissolving sodium arsenate crystals into a high-arsenic acidic solution, and then adding a solid ferric iron source to the solution for high-temperature hydrothermal crystallization. Take 100g of sodium arsenate crystals, add distilled water according to the liquid-to-solid ratio of (2~30):1, and then add sulfuric acid to adjust the solution pH=1~ according to the mass ratio of sulfuric acid to sodium arsenate crystals of 1:(1.5~5). 4. Add the solution into the hydrothermal kettle, add solid ferric salt according to the molar ratio of iron to arsenic (1 to 4): 1, adjust the rotation speed to 200 to 600 rpm, and raise the temperature to 100 to 180°C, and keep it warm for 4 ~12 hours, after the reaction is completed, cool to room temperature, and use vacuum filtration to separate liquid and solid. Add the solid arsenic precipitate and distilled water at a mass ratio of 1: (10 to 15), add distilled water to wash and filter, and dry at 60 to 85°C for 5 to 8 hours to obtain scorodite crystals. The toxic leaching performance of the synthesized scorodite crystals meets the requirements of Chinese national standards (GB5085.3-2007). The chemical reactions that may occur during the above process are:

2Na ₃ AsO ₄ ·12H ₂ O+3H ₂ SO ₄ =3Na ₂ SO ₄ +2H ₃ AsO ₄ +24H ₂ O (2)

Fe(OH) ₃ +3H ⁺ =Fe ³⁺ +3H ₂ O (3)

Fe ₂ O ₃ +6H ⁺ =2Fe ³⁺ +3H ₂ O (4)

FeAsO ₄ +nH ⁺ =Fe ³⁺ +H _n AsO ₄ ^(3-n)- (n＝0,1,2,3) (5)

Fe ³⁺ +H _n AsO ₄ ^(3-n)- +2H ₂ O＝FeAsO ₄ ·2H ₂ O+nH ⁺ (n＝0,1,2,3) (6)

(2) Neutralization and precipitation of arsenic and iron

The neutralization precipitation method is used to add alkali solution to the arsenic solidification solution produced by the above-mentioned synthesis of scorodite, adjust the pH of the solution, and form iron arsenate and iron hydroxide precipitates to achieve the goal of arsenic and iron removal. Measure the arsenic solidification solution, add 1 to 8 mol/L alkali solution dropwise, adjust the initial pH of the solution to 4 to 8, and react at room temperature for 1 to 3 hours. After the reaction is completed, vacuum filtrate, add distilled water to the precipitate and distilled water at a mass ratio of 1:(5-10), wash and filter, dry at 50-80°C for 3-6 hours, and then the dried arsenic iron salt is fully finely ground and sieved. Afterwards, the iron salt is returned as the synthesized scorodite crystal, and the neutralized and precipitated liquid is used for sodium salt recovery. The chemical reactions that may occur in the above process are:

Fe ³⁺ +3OH ^- =Fe(OH) ₃ (7)

Fe ³⁺ +H _n AsO ₄ ^(3-n)- =FeAsO ₄ +nH ⁺ (n＝0,1,2,3) (8)

Fe(OH) ₃ +H _n AsO ₄ ^(3-n)- +(3-n)H ⁺ =FeAsO ₄ +3H ₂ O (n＝0,1,2,3) (9)

H ⁺ +OH ^- =H ₂ O (10)

(3) Evaporation and crystallization to recover sodium salt

The neutralized and precipitated liquid is evaporated at high temperature and then cooled and crystallized at low temperature. The crystallized product is sodium sulfate crystal product. Add the above-mentioned neutralized and precipitated liquid into the evaporation crystallizer, continuously concentrate it at 120-160°C for 4-10 hours until the specific gravity of the material liquid is 2-6g/cm ³ , and then cool and crystallize it at 5-10°C for 5-12 hours. hour, vacuum filtration, and drying the white crystals at 60 to 80°C to obtain the sodium sulfate crystal product. Achieve the goal of zero discharge of solution during the solidification of sodium arsenate crystals. The chemical reactions that occur during the recovery of sodium sulfate are:

2Na ⁺ +SO ₄ ^2- =Na ₂ SO _4(crystal) (11)

The arsenic-rich crystal used in the present invention is sodium arsenate crystal produced during the resource utilization of arsenic-alkali slag in antimony smelting, and its physical phase is Na ₃ AsO ₄ ·xH ₂ O (x=10,12), where The main chemical components (wt%) are Na14~26, As15~25, Sb 0.2~0.5, the remaining impurities are Ca, Cd, B≤0.10, and the crystal water is 45~58.

In the present invention, the solid ferric salt is one or more of Fe(OH) ₃ , Fe ₂ O ₃ , rust, and arsenic iron salt recovered by neutralization and precipitation.

The sulfuric acid used in the present invention is an analytically pure reagent, and its content is greater than 98%. The alkali solution is obtained by dissolving one or more of analytically pure sodium hydroxide, potassium hydroxide, and sodium carbonate into water.

Toxicity leaching test (TCLP), in accordance with the operating specifications of "Solid Waste Leaching Toxicity Leaching Method—Nitric Acid Sulfuric Acid Method HJ/T299-2007", the synthesized scorodite crystal material was added to pH=3.15~3.25 according to the liquid-to-solid ratio of 10:1. In a mixed aqueous solution of nitric acid and sulfuric acid, shake horizontally for 16 to 20 hours. After standing, the supernatant is filtered with a 0.8 μm filter membrane. The arsenic concentration of the toxic leachate is measured by ICP-AES. According to the requirements of the "Hazardous Waste Identification Standard - Identification of Leaching Toxicity" (GB5085.3-2007), when the arsenic concentration in the measured toxic leachate is less than 5 mg/L, the synthesized scorodite crystals can be considered non-toxic and harmless materials. Safe long term storage.

Compared with the traditional method of solidifying arsenic-rich products from arsenic-alkali residue into scorodite crystals, the present invention has the following advantages: (1) The dissolution of the solid ferric salt consumes the H ⁺ released during the synthesis of scorodite, eliminating the need for The accumulation of acid maintains the acid balance and stability of the solution. (2) The pH of the solution changes little before and after the reaction, which improves the arsenic fixation effect and the arsenic fixation rate is greater than 99.5%. (3) The synthesized scorodite crystals have a flaky structure and are fully developed. The arsenic concentration in TCLP is far less than 5 mg/L. The crystal structure is stable and suitable for long-term safe storage. (4) The removal rate of iron and arsenic in the neutralization precipitation is high (≥99.9%). The arsenic iron salt can be used as a solid iron salt to synthesize scorodite to realize the utilization of residual arsenic and iron. (5) The sodium sulfate product obtained by evaporation and crystallization has low arsenic and iron content (<0.01%) and is suitable as a raw material for the synthesis of other chemicals. (6) In the entire arsenic-rich crystal solidification technology process, the post-arsenic solidification liquid, post-neutralization precipitation liquid and crystallization mother liquor are not discharged, which eliminates the environmental pollution caused by traditional arsenic-containing wastewater discharge.

Description of the drawings

Figure 1 is a process technology flow chart of the present invention;

Figure 2 is the XRD pattern of the scorodite crystal synthesized by the present invention;

Figure 3 is an SEM image of the scorodite crystal synthesized by the present invention;

Figure 4 is the XRD pattern of the neutralized and precipitated arsenic iron salt of the present invention;

Figure 5 is an XRD pattern of the sodium sulfate crystal recovered in the present invention.

Specific implementation methods

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

Example 1:

Weigh 100g of sodium arsenate crystals, add them to 3000 mL of distilled water at a liquid-to-solid ratio of 30:1, and add sulfuric acid dropwise to adjust the pH of the solution to 2.0 according to a mass ratio of sulfuric acid to sodium arsenate crystals of 1:2.5 to make arsenic acid After the sodium is completely dissolved, an acidic solution containing 5g/L arsenic is obtained. Add the solution to the hydrothermal kettle, add ferric oxide solid iron salt according to the iron to arsenic molar ratio of 2:1, start stirring to 300 rpm, and raise the temperature to 130°C, keep the reaction for 10 hours, after the reaction is completed Cool to room temperature and use vacuum filtration to separate liquid and solid. Add the arsenic-solidified precipitate and distilled water to the distilled water at a mass ratio of 1:10, wash and filter, and dry at 65°C for 8 hours to obtain scorodite crystals with an arsenic-solidifying rate of 99.60%. The pH of the solution after arsenic solidification is 2.02, which is basically close to the initial pH, achieving acid balance and stabilization in the solution. Add 5 mol/L sodium hydroxide solution dropwise to the post-arsenic solidification solution to adjust the initial pH of the solution = 4, and react at room temperature for 1 hour. After the reaction is completed, vacuum filtration is carried out. The precipitate and distilled water are added to the distilled water at a mass ratio of 1:5, washed and filtered. After drying at 80°C for 6 hours, the produced arsenic iron salt is fully finely ground and sieved as the raw material for synthesizing scorodite crystals. Iron source. Add the neutralized and precipitated liquid into the evaporation crystallizer, continuously concentrate it at 120°C for 6 hours until the specific gravity of the material liquid is 5g/cm ³ , then cool and crystallize it at 5°C for 10 hours, vacuum filtrate, and remove the white crystals at 60 After drying at ~80°C, the sodium sulfate crystal product can be obtained.

Example 2:

Weigh 100g of sodium arsenate crystals, add them to 282 mL of distilled water at a liquid-to-solid ratio of 2.82:1, and slowly add sulfuric acid dropwise to adjust the pH of the solution to 2 at a mass ratio of sulfuric acid to sodium arsenate crystals of 1:2.92 to make the arsenic The sodium acid is completely dissolved to obtain an acidic solution containing 50g/L arsenic. Add the solution to the hydrothermal kettle, add solid ferric salt (based on the mass ratio of recovered arsenic iron salt and ferric hydroxide 2:1) according to the iron to arsenic molar ratio of 1.5:1, and adjust the stirring to 300 rpm/ minutes, and raise the temperature to 120°C, and keep the reaction for 8 hours. After the reaction is completed, it is cooled to room temperature, and vacuum filtration is performed to separate the liquid and solid. Add the arsenic-solidified precipitate and distilled water to the distilled water at a mass ratio of 1:10, wash and filter, and dry at 85°C for 8 hours to obtain scorodite crystals with an arsenic-solidifying rate of 99.80%. The pH of the solution after arsenic solidification is 2.05, which is basically close to the initial pH, achieving acid balance and stabilization in the solution. Add 8mol/L sodium hydroxide solution dropwise to the arsenic solidification solution until the initial pH=6.0, and react at room temperature for 2 hours. After the reaction is completed, the precipitate and distilled water are washed and filtered by adding distilled water at a mass ratio of 1:6. After drying at 80°C for 6 hours, the produced arsenic iron salt is fully finely ground and sieved, and returned as synthetic scorodite crystals. of iron salt. Add the neutralized and precipitated liquid into the evaporation crystallizer, continuously concentrate it at 140°C for 6 hours until the specific gravity of the material liquid is 3g/cm ³ , then cool and crystallize it at 5°C for 8 hours, vacuum filtrate, and the white crystals are collected at 60 After drying at ℃, the sodium sulfate crystal product is obtained.

Example 3:

Weigh 100g of sodium arsenate crystals, add to 200 mL of distilled water at a liquid-to-solid ratio of 2:1, add sulfuric acid at a mass ratio of sulfuric acid to sodium arsenate crystals of 1:2.18 to adjust the pH of the solution = 1, so that sodium arsenate Dissolve completely to obtain an acidic solution containing 70g/L arsenic. Add the solution to the hydrothermal kettle, add iron hydroxide according to the iron to arsenic molar ratio of 1.8:1, adjust the rotation speed to 400 rpm, and raise the temperature to 150°C, keep the reaction for 12 hours, and cool to room temperature after the reaction is completed. Vacuum filtration is used to separate liquid and solid. Add the arsenic-solidified precipitate and distilled water at a mass ratio of 1:15, add distilled water for washing, filter, and dry at 80°C for 6 hours to obtain scorodite crystals with an arsenic-solidifying rate of 99.5%. The pH of the solution after arsenic solidification is 1.04, which is basically close to the initial pH, achieving acid balance and stabilization in the solution. Add 4 mol/L alkaline solution dropwise to the post-arsenic solidification solution to adjust the initial pH of the solution = 7.0, and react at room temperature for 3 hours. After the reaction is completed, vacuum filtrate, add distilled water to the precipitate and distilled water at a mass ratio of 1:5, wash and filter, and dry at 80°C for 4 hours. The produced arsenic iron salt is fully finely ground and sieved, and then returned as synthetic scorodite crystals. of iron salt. Add the neutralized and precipitated liquid to the evaporation crystallizer, continuously concentrate it at 120°C for 4 hours until the specific gravity of the material liquid is 2.5g/cm ³ , then cool and crystallize at 8°C for 7 hours, vacuum filtrate, and white crystallize. After drying the material at 80°C, the sodium sulfate crystal product can be obtained.

The scorodite crystals synthesized above were leached for toxicity leaching experiments in accordance with the "Solid Waste Leaching Toxicity Leaching Method - Nitric Acid Sulfuric Acid Method HJ/T299-2007" operating specifications. The toxicity leachate was measured by ICP-AES, and the arsenic concentrations were all lower than 5mg/L. It is a non-toxic and harmless arsenic-fixing material, suitable for safe storage.

Figure 1 is a technical flow chart of the present invention. This technology consists of three key processes: hydrothermal solidification, neutralization precipitation and evaporation crystallization. Arsenic-rich crystals are converted into scorodite crystals, arsenic iron salts and sodium sulfate crystals respectively. Among them, scorodite is a non-toxic material and is suitable for safe storage; the arsenic iron salt is returned to hydrothermal solidification to synthesize scorodite to realize iron and arsenic circulation; the post-arsenic liquid, post-neutralization liquid and crystallization mother liquor produced in the process are processed in a closed circuit. These three processes are closely linked and together constitute a non-toxic and harmless technology for arsenic-rich crystallization in the resource utilization of arsenic-alkali slag.

Figure 2 shows that the scorodite crystal synthesized by hydrothermal solidification is a FeAsO ₄ ·2H ₂ O phase with sharp diffraction peaks, corresponding to (1 1 1), (2 0 0), (2 1 2), (1 31), and (3 2 0) crystal planes, indicating that the synthesized scorodite crystal has good crystallinity. Figure 3 shows that the synthesized scorodite has a flaky structure with a particle size of 5-10 μm. These flaky structures are closely arranged and the crystals are fully developed.

Figure 4 shows that the arsenic iron salt recovered by neutralization precipitation is an amorphous phase. In the XRD pattern, there are only weak diffraction angles in three wide ranges of 2θ=10~20°, 25~40° and 50~65°. The crystallization peak has a low matching degree with the standard spectra of FeAsO ₄ and Fe(OH) ₃ , indicating that the arsenic iron salt produced by the neutralization precipitation method has an amorphous structure. Figure 5 shows that the sodium sulfate crystal obtained after evaporation and crystallization has a single phase composition, sharp diffraction peaks, and a high degree of matching with the Na ₂ SO ₄ standard PDF card, indicating that the sodium sulfate crystal has good crystallinity.

In summary, the hydrothermal solidification method proposed in the present invention can convert arsenic-rich crystals used in the resource utilization of arsenic-alkali residue into non-toxic and harmless flaky scorodite crystal arsenic-fixing materials. Solid ferric salt can neutralize the hydrogen ions released during synthesis to achieve acid balance and stabilization of the solution. There is no arsenic-containing solid waste and wastewater discharge, achieving safe treatment of arsenic in arsenic-alkali residue and environmental protection.

Claims (3)

1. A method for hydrothermal solidification of arsenic-rich crystals, characterized by comprising: (1)Scorodite crystal synthesis: Arsenic-rich crystals are added dropwise to the aqueous solution to adjust the pH of the solution. After adding a solid ferric iron source, the arsenic-rich crystal is subjected to a hydrothermal solidification reaction under high-temperature stirring in a hydrothermal kettle to obtain flaky scorodite crystals; First, weigh 100g of arsenic-rich crystals and add it to distilled water according to a liquid-to-solid ratio of (2 to 30): 1. Add sulfuric acid dropwise to adjust the pH according to a mass ratio of sulfuric acid and sodium arsenate crystals of 1: (1.5 to 5). =1～4; Secondly, add the solution into the hydrothermal kettle, add the solid ferric iron source according to the molar ratio of iron to arsenic (1 to 4): 1, control the stirring rate to 200 to 500 rpm, and raise the temperature to 100 to 160°C , keep warm for 4 to 12 hours; Finally, after the reaction is completed, the slurry is cooled to room temperature, and vacuum filtration is used to separate the liquid and solid. The solid arsenic precipitate and distilled water are washed with distilled water at a mass ratio of 1: (10 to 15), filtered, and dried at 60 to 85°C. After drying for 5 to 8 hours, scorodite crystals can be obtained; The solid ferric iron source is one or more of Fe(OH) ₃ , Fe ₂ O ₃ , rust and recovered arsenic iron salts; (2) Neutralization and precipitation: Add alkali solution to the arsenic fixation solution to adjust the pH, so that the arsenic and iron in the solution coprecipitate into arsenic and iron salts, and the generated arsenic and iron salts are used for hydrothermal synthesis of scorodite crystals; The alkali concentration used for neutralization and precipitation is 1 to 8 mol/L, adjust to the initial pH of the solution = 4 to 8, and react at room temperature for 1 to 3 hours; (3) Evaporation crystallization: After neutralization and precipitation, the liquid is evaporated at high temperature and crystallized by low-temperature cooling to obtain sodium sulfate crystals to realize the recovery of sodium salt in the solution; For evaporative crystallization, first continuously concentrate at 120-160°C for 4-10 hours until the specific gravity of the material liquid is 2-6g/cm ³ , and then cool and crystallize at 5-10°C for 5-12 hours. 2. The method for hydrothermal solidification of arsenic-rich crystals according to claim 1, characterized in that the arsenic-rich crystals are sodium arsenate crystals produced in the resource utilization of antimony smelting arsenic-alkali slag, and their physical phase is Na ₃ AsO ₄ ·10H ₂ O and/or Na ₃ AsO ₄ ·12H ₂ O, the main chemical components in weight percentage are: Na14～26%, As 15～25%, Sb 0.2～0.5%, the remaining impurities are Ca, Cd and B are less than 0.10%, and crystal water is 45 to 58%. 3. The method for hydrothermal solidification of arsenic-rich crystals according to claim 1, characterized in that the scorodite crystal synthesized by hydrothermal solidification has a single phase and a microscopic morphology of flakes with a particle size of 5 to 10 μm. Structure, good stability, non-toxic and harmless arsenic-fixing material, suitable for long-term safe storage.