A process for the recovery of valuable metals and the production of metallic arsenic from arsenic-containing spent acid

Abstract

The application discloses a method for recovering valuable metals and preparing metallic arsenic from arsenic-containing waste acid. The method comprises the following steps: adding active arsenic sulfide reagent into the arsenic-containing waste acid to perform a displacement reaction, so as to obtain metal sulfide precipitate and arsenic-rich purified liquid; and adding iron powder and an antioxidant into the arsenic-rich purified liquid to perform a reduction reaction, so as to obtain elemental arsenic and ferrous solution. The method realizes the recovery of valuable metal elements and arsenic in the waste acid, and simultaneously realizes the wet preparation of metallic arsenic at normal temperature and pressure. The method has the advantages of simple process, easy control, low cost, high quality of obtained metallic arsenic and the like, and is favorable for the popularization and application of industrialization.

Description

Technical Field

[0001] This invention relates to a method for treating arsenic-containing waste acid, and particularly to a method for recovering valuable metals and preparing metallic arsenic from arsenic-containing waste acid, belonging to the field of arsenic-containing waste acid treatment technology. Background Technology

[0002] In recent years, with economic development and the further improvement of people's living standards, various industrial production activities have been accelerating. Common industrial production processes include mineral smelting and processing, chemical industry, machinery manufacturing, pharmaceuticals, electronics, and pigments. These industrial processes discharge large amounts of wastewater containing heavy metal ions, i.e., heavy metal wastewater. Arsenic exists in nature in association with or associated with non-ferrous metal ores. Influenced by human mining and metallurgical activities (especially in the copper, lead, zinc, and gold metallurgical industries), arsenic, after mining and beneficiation, enters non-ferrous smelters along with the concentrate for smelting. It continuously migrates and accumulates in the environment. Especially in the smelting of non-ferrous metals such as copper, lead, and zinc, large amounts of arsenic-containing flue gas are generated, containing large amounts of SO2 and harmful metal ions. Most smelters have acid production systems to recover flue gas dust and produce acid from SO2 flue gas. Before acid production, flue gas purification is required, which generates large amounts of highly acidic wastewater containing heavy metals, referred to as waste acid. Waste acid is large in volume and complex in composition, containing metal ions such as arsenic, copper, lead, zinc, cadmium, and bismuth. These arsenic-containing waste acids not only contain arsenic but also a large amount of valuable metals that need to be recovered, such as copper. Improper disposal of these waste acids will result in a huge waste of resources. Therefore, recycling waste acids generated during non-ferrous metal smelting can not only improve resource utilization efficiency and the environment but also promote sustainable economic and social development.

[0003] However, the current utilization rate of secondary resources is not high, mainly because it is difficult to separate valuable elements from arsenic in these arsenic-containing waste acids. To recover and utilize valuable metal elements in these copper-based solid wastes, the first problem to solve is how to achieve efficient separation of arsenic from valuable metal elements. Currently, most enterprises do not use effective methods for this. The treatment of waste acid directly employs neutralization precipitation, which not only fails to recover valuable metal elements but also generates large amounts of gypsum slag, increasing the difficulty of waste disposal and treatment. Traditional sulfide precipitation methods not only easily generate highly toxic hydrogen sulfide gas but also produce heavily contaminated products that are difficult to utilize; moreover, most of the arsenic obtained is separated as hazardous waste arsenic sulfide slag, increasing the processing burden. Chinese patent (CN114921662A) discloses a method for reducing and removing arsenic from acidic arsenic-containing solutions and preparing metallic arsenic. However, it does not consider the influence of other impurity ions in the solution, and the introduction of transition metal ions as activators will severely reduce the quality of the subsequent metallic arsenic. Moreover, the processing conditions are demanding, requiring high temperature and pressure, making the operation difficult and costly. Chinese patent (CN111003864B) discloses an ultrasonic-enhanced method for removing arsenic from waste acid. Although it introduces an enhancement method, the use of copper sulfate to promote the displacement reaction results in cuprous arsenide (Cu3As) as the final arsenic product, failing to achieve the resource utilization of arsenic. Therefore, there is an urgent need for a method that can efficiently separate valuable metals from arsenic in arsenic-containing waste acid and obtain high-quality metallic arsenic in one step. Summary of the Invention

[0004] To overcome the shortcomings of traditional methods for treating arsenic-containing waste acid, the present invention aims to provide a method for recovering valuable metals and preparing metallic arsenic from arsenic-containing waste acid. This method combines the idea of ​​recovering valuable metals by displacement with enhanced iron reduction of arsenic, thereby simultaneously recovering valuable metal elements and arsenic and obtaining high-value-added elemental arsenic products. The method is simple to operate, low in cost, and conducive to industrial application.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a method for recovering valuable metals from arsenic-containing waste acid and preparing elemental arsenic, the method comprising the following steps:

[0006] 1) Add active arsenic sulfide reagent to arsenic-containing waste acid to carry out a displacement reaction, and obtain metal sulfide precipitate and arsenic-rich purified liquid;

[0007] 2) Add iron powder and antioxidant to the arsenic-rich purification solution to carry out a reduction reaction and obtain a solution of elemental arsenic and ferrous iron.

[0008] The arsenic-containing waste acid of this invention mainly comes from smelting plant waste acid, or arsenic-containing leachate, as well as arsenic-containing acidic waste liquid produced by other industries such as metal smelting, electronic manufacturing, and pesticide production. Its main components include metallic elements such as arsenic (As), copper (Cu), zinc (Zn), and cadmium (Cd), as well as non-metallic elements such as chlorine (Cl) and fluorine (F).

[0009] As a preferred embodiment, the active arsenic sulfide reagent is a suspension obtained by reacting an arsenic-rich purification solution with a sulfiding agent. The active arsenic sulfide reagent of this invention utilizes a sulfiding agent and arsenic in an arsenic-rich purification solution to obtain a suspension containing active arsenic sulfide through a sulfidation precipitation reaction. The resulting active arsenic sulfide is a highly active, amorphous, nano-sized colloidal arsenic sulfide. Preferred sulfiding agents are common sulfide salts, such as sodium sulfide, sodium hydrosulfide, ferrous sulfide, and other soluble or insoluble sulfiding agents. Ferrous sulfide is a preferred sulfiding agent. According to the solubility product theory between sulfides, the solubility product of arsenic sulfide is greater than that of copper sulfide, meaning that arsenic sulfide can gradually dissolve in a copper-containing solution and transform into a more stable copper sulfide precipitate, thereby achieving the recovery and purification of heavy metals such as copper from arsenic-containing waste acid. However, traditional arsenic sulfide slag has low solubility, resulting in poor reactivity and insufficient conversion efficiency during the sulfidation precipitation of heavy metal ions such as copper ions. The highly active, amorphous, nano-sized arsenic sulfide slag synthesized in this invention can promote efficient replacement and conversion of copper ions in an acidic environment, thus overcoming the barrier of low reactivity of traditional arsenic sulfide slag. Furthermore, it can improve the grade of the produced copper sulfide slag while reducing the amount of arsenic sulfide slag used. In addition, using highly active arsenic sulfide for copper removal does not introduce other new impurity elements, and it can increase the arsenic concentration in the solution, providing favorable conditions for the subsequent reduction of arsenic-rich solutions to prepare elemental arsenic. It is also worth noting that the active arsenic sulfide has relatively low reactivity compared to general water-soluble sulfiding agents, avoiding the release of highly toxic H2S gas during use in acidic solutions.

[0010] As a further preferred embodiment, the active arsenic sulfide agent is prepared by the following method: an arsenic-rich purification solution is mixed with ferrous sulfide particles, and the mixture is reacted at 25℃~45℃ for 20~40 min. The particle size of the ferrous sulfide particles is 38~74 μm. The arsenic concentration in the arsenic-rich purification solution is 1~10 g / L. The amount of ferrous sulfide particles used is 1.5~2.5 times the theoretical molar amount of ferrous sulfide particles required for the conversion of arsenic in the arsenic-rich purification solution into arsenic sulfide.

[0011] As a preferred embodiment, the amount of the active arsenic sulfide agent added to the arsenic-containing waste acid is measured to be 1.5 to 5 times the molar amount of arsenic sulfide component in the active arsenic sulfide agent compared to the molar amount of heavy metal ions in the arsenic-containing waste acid. More preferably, the amount of the active arsenic sulfide agent added to the arsenic-containing waste acid is measured to be 1.5 to 2 times the molar amount of arsenic sulfide component in the active arsenic sulfide agent compared to the molar amount of heavy metal ions in the arsenic-containing waste acid.

[0012] As a preferred embodiment, the conditions for the displacement reaction are: temperature 80–90°C and time 1–2 hours. The displacement reaction between active arsenic sulfide and copper ions is endothermic; therefore, higher temperatures are more conducive to the reaction. Under these preferred displacement reaction conditions, efficient displacement of copper and other heavy metal ions from arsenic-containing waste acid by the active arsenic sulfide reagent can be achieved.

[0013] As a preferred embodiment, the amount of iron powder added is 2 to 5 times the molar amount of arsenic in the arsenic-rich purification solution. This invention uses iron powder as a reducing agent. Under appropriate reaction conditions, the iron powder can undergo a reduction reaction with arsenic compounds, reducing high-valence arsenic ions to atomic-state metallic arsenic (As), while the iron powder itself is oxidized.

[0014] As a preferred embodiment, the amount of antioxidant added is 0.5-2% of the molar amount in the arsenic-rich purification solution. The antioxidant used in this invention is primarily to prevent the generated metallic arsenic from being re-oxidized into arsenic compounds, thus maintaining the purity and stability of the metallic arsenic. The addition of the antioxidant can effectively inhibit the oxidation reaction and slow down the oxidation rate of metallic arsenic.

[0015] As a preferred embodiment, the antioxidant comprises ascorbic acid and / or disodium ethylenediaminetetraacetate. More preferably, the antioxidant is composed of ascorbic acid and disodium ethylenediaminetetraacetate in a mass ratio of (10-20):1. This invention uses a combination of ascorbic acid and EDTA as an antioxidant, which exhibits a significant synergistic effect in antioxidant activity. Ascorbic acid, as a strong reducing agent, can donate electrons to neutralize free radicals and reduce oxidation reactions. EDTA, on the other hand, has the ability to chelate metal ions, reducing the catalytic oxidation effect of metal ions. Therefore, by using ascorbic acid and EDTA in combination, the antioxidant capacity can be enhanced, and the effects of free radical scavenging and antioxidant reactions can be improved. The antioxidant effect of using ascorbic acid or EDTA alone is significantly worse than that of using them in combination.

[0016] As a preferred embodiment, the iron powder has a purity greater than 99% and a particle size of 38–150 μm. The finer the iron powder particles, the larger their surface area. This increases the contact area for the reduction reaction, which is beneficial to the reaction rate between reactants. Therefore, finer iron powder can increase the reduction rate of metallic arsenic. However, fine iron powder particles are prone to agglomeration and accumulation. Agglomeration and accumulation lead to prolonged diffusion paths of reactants between particles, thereby reducing reaction efficiency. Before use, the iron powder is preferably pretreated with dilute acid to remove surface oxides and improve its reactivity. For example, it can be added to a dilute sulfuric acid solution and stirred thoroughly, then washed with deionized water until the rinsing water is neutral, followed by vacuum drying and storage for later use.

[0017] As a preferred embodiment, the reduction reaction is carried out under the following conditions: a protective atmosphere, a temperature of 25°C to 65°C, and a time of 0.5 to 1 hour. The protective atmosphere may be, for example, an inert atmosphere or nitrogen. The inert gas may be argon, etc., and the purity of the nitrogen or inert gas may be not less than 99.999%, with a gas flow rate of 0.3 to 0.8 L / min.

[0018] As a preferred embodiment, the reduction reaction is carried out under ultrasonic or microwave assistance. Applying external field enhancement methods such as ultrasound or microwaves can effectively improve reaction efficiency, and this method solves the passivation problem of iron powder during the reaction process. When iron powder comes into contact with moisture, oxidation and hydrolysis reactions may occur on the iron surface. This leads to the formation of substances such as iron oxide and iron hydroxide, further increasing the passivation layer on the surface. Simultaneously, as metallic arsenic is continuously reduced from the solution, it coats the unreacted iron powder surface, exacerbating passivation and reducing the reduction capacity and reaction efficiency of the iron powder. To solve the passivation problem, external field enhancement methods can be employed. Ultrasonic vibration can generate intense physical effects, such as cavitation, micro-eddies, and vortex shearing, which can effectively remove the passivation layer on the metal surface and restore the reduction capacity of metallic iron. Microwave heating can rapidly heat the iron powder, increasing its temperature and activating the reduction-active sites on the surface. High temperatures can destroy the passivation layer, remove oxides and other inactive substances, and restore the reduction capacity of the iron powder. In addition, microwave heating can promote collisions and diffusion between reactant molecules, accelerate the reaction rate, and improve reaction efficiency.

[0019] As a preferred embodiment, the ultrasound conditions are: frequency of 10-30kHz and output power of 100-300W.

[0020] As a preferred embodiment, the microwave conditions are: frequency of 2000-3000MHz and output power of 400-800W.

[0021] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0022] 1) The technical solution of this invention adopts the approach of "replacing and recovering valuable metals + strengthening iron reduction of arsenic" for arsenic-containing waste acid, which simultaneously realizes the recovery of valuable metal elements and arsenic, and obtains high-value-added elemental arsenic products.

[0023] 2) In the technical solution of this invention, the arsenic-containing waste acid is converted and impurities are removed by a highly active arsenic sulfide reagent. Compared with traditional sulfiding agents such as sodium sulfide, the purification depth is higher, the product has better crystal form, larger crystal particle size, faster sedimentation speed, higher separation efficiency, and high reactivity. After precipitation and conversion, high-grade copper sulfide slag can be obtained. The high purification depth creates the prerequisite for obtaining a high-purity high-arsenic solution.

[0024] 3) The present invention effectively solves the passivation problem of iron powder during the reaction process by introducing external field strengthening methods such as ultrasound or microwave, and achieves the purpose of improving the replacement and reduction efficiency of iron powder without introducing impurity ions such as activators. The resulting metallic arsenic is of high quality and can be used as a raw material for further production of high-purity arsenic.

[0025] 4) The operation process of the technical solution of the present invention is simple and low-cost. It achieves high-precision separation of valuable metal elements and arsenic and stable preparation of metallic arsenic. Furthermore, the entire process is reduced in volume and solidified, which is low-cost and easy to operate, thus facilitating industrial application. Attached Figure Description

[0026] Figure 1 The flowchart illustrates a process for recovering valuable metals from arsenic-containing waste acid and preparing metallic arsenic, as provided by the present invention.

[0027] Figure 2 To obtain the XRD pattern of metallic arsenic. Detailed Implementation

[0028] The following examples are intended to further illustrate the present invention, but not to limit the scope of protection of the claims of the present invention.

[0029] The following examples illustrate the preparation method of the active arsenic sulfide reagent: Ferrous sulfide particles with a particle size distribution ranging from 38 to 74 μm are added to an arsenic-rich solution. The arsenic concentration in the arsenic-rich solution is 5 g / L. The amount of ferrous sulfide particles used is twice the theoretical molar amount required for the conversion of arsenic element into arsenic sulfide. The reaction temperature is 30°C, and the reaction time is 0.5 h. After obtaining the suspension, it is allowed to stand for a period of time, and the supernatant is poured off. The underflow is the desired highly active arsenic sulfide reagent.

[0030] Example 1

[0031] The main components (g / L) of the waste acid produced by a domestic enterprise in copper concentrate smelting are: As 5.3%, Cu 2.3%, Bi 0.2%, and H2SO4 1O3. 100 mL of the waste acid was reacted by adding highly active arsenic sulfide reagent directly to the waste acid without drying for copper displacement precipitation. The amount added was 1.5 times the theoretically calculated amount for copper removal. The conversion temperature was 85℃, and the conversion time was 1 hour. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper grade exceeding 38%. Subsequently, pretreated metallic iron powder was added to the high-arsenic solution (7.01 g / L), at twice the theoretical molar amount (1.06 g). The reaction temperature was 25℃, and 1% antioxidant (ascorbic acid and ethylenediaminetetraacetic acid in a 10:1 ratio) was added. The argon gas flow rate was 0.5 L / min, the ultrasonic output power was 300 W, and the reaction time was 1 hour. After the reaction was completed, a solution of metallic arsenic and ferrous iron was obtained. The arsenic content in the metallic arsenic was found to be over 99.6%, and the arsenic content in the filtrate was less than 0.1 ppm, thus obtaining high-quality metallic arsenic.

[0032] Example 2

[0033] A domestic company's acid leaching solution for copper concentrate contains the following main components (g / L): As 9.8, Cu 20.5, Bi 0.3, H2SO4 70. 100 mL of the acid leaching solution was reacted by adding highly active arsenic sulfide reagent directly to the solution without drying for copper displacement precipitation. The amount added was twice the theoretically calculated amount for copper removal. The conversion temperature was 90℃, and the conversion time was 1 hour. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper grade exceeding 37%. Subsequently, pretreated metallic iron powder (3 times the theoretical molar amount, 5.74 g) was added to the high-arsenic solution (25.3 g / L). The reaction temperature was 40℃, and 2% antioxidant (ascorbic acid and ethylenediaminetetraacetic acid in a 20:1 ratio) was added. The nitrogen gas flow rate was 0.8 L / min; the ultrasonic output power was 500 W, and the reaction time was 0.5 hours. After the reaction, a solution of metallic arsenic and ferrous iron was obtained. Testing showed that the arsenic content in the metallic arsenic exceeded 99.8%, while the arsenic content in the filtrate was below 0.1 ppm. High-quality metallic arsenic was thus obtained.

[0034] Example 3

[0035] The smelting waste acid produced by a domestic enterprise in copper concentrate smelting has the following main components (g / L): As 2.7, Cu 2.5, Bi 0.2, H2SO4 160. 100 mL of the waste acid solution was reacted by adding highly active arsenic sulfide reagent directly to the acid leaching solution without drying to displace and precipitate copper. The amount added was 1.5 times the theoretically calculated amount for copper removal. The conversion temperature was 80℃, and the conversion time was 2 hours. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper grade exceeding 40%. Subsequently, pretreated metallic iron powder was added to the high-arsenic solution (4.5 g / L), at a rate 5 times the theoretical molar amount (1.7 g). The reaction temperature was 65℃, and 0.5% antioxidant (ascorbic acid and ethylenediaminetetraacetic acid in a 20:1 ratio) was added. Nitrogen gas was introduced at a rate of 0.3 L / min; the microwave output power was 800 W, and the reaction time was 1 hour. After the reaction, a solution of metallic arsenic and ferrous iron was obtained. Testing showed that the arsenic content in the metallic arsenic exceeded 99.5%, while the arsenic content in the filtrate was below 0.1 ppm. High-quality metallic arsenic was thus obtained.

[0036] Comparative Example 1

[0037] The main components (g / L) of the waste acid produced by a domestic enterprise in copper concentrate smelting are: As 5.3, Cu 2.3, Bi 0.2, H2SO4 103. 100 mL of the waste acid was reacted, and sodium sulfide was directly used for the first stage of impurity removal and copper precipitation. The amount added was 1.5 times the theoretical calculation amount for copper removal. The conversion temperature was 85℃, and the conversion time was 1 hour. The copper ion removal rate in the solution was 75%, and the copper sulfide product had a copper grade of only 23%. Then, pretreated metallic iron powder (Cu: 0.57 g / L, As: 4.3 g / L) was added to the copper-arsenic mixture after copper precipitation. The amount added was twice the theoretical molar amount (1.06 g). The reaction temperature was 25℃, and 1% antioxidant (ascorbic acid and ethylenediaminetetraacetic acid in a 10:1 ratio) was added. The argon gas flow rate was 0.5 L / min; the ultrasonic output power was 300 W, and the reaction time was 1 hour. After the reaction, a solution of metallic arsenic and ferrous iron was obtained. Testing showed that the arsenic content in the metallic arsenic was 63%, and the arsenic content in the filtrate was below 1 ppm. The product phase was cuprous arsenide (Cu3As), and a qualified metallic arsenic product was not obtained.

[0038] Comparative Example 2

[0039] A domestic company's acid leaching solution for copper concentrate contains the following main components (g / L): As 9.8, Cu 20.5, Bi 0.3, H2SO4 70. 100 mL of the acid leaching solution was reacted by adding a highly active arsenic sulfide reagent directly to the solution without drying for copper displacement precipitation. The amount added was twice the theoretically calculated amount for copper removal. The conversion temperature was 90℃, and the conversion time was 1 hour. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper grade exceeding 37%. Subsequently, pretreated metallic iron powder (3 times the theoretical molar amount, 5.74 g) was added to the high-arsenic solution (25.3 g / L). The reaction temperature was 40℃, and 2% antioxidant (ascorbic acid and ethylenediaminetetraacetic acid in a 20:1 ratio) was added. Nitrogen gas was introduced at a rate of 0.8 L / min. No external enhancement methods such as ultrasound or microwave were used, and the reaction time was 0.5 hours. After the reaction, a solution of metallic arsenic and ferrous iron was obtained. Testing revealed that the arsenic content in the metallic arsenic was only 43%, and the arsenic content in the filtrate was 5.5 g / L. The product phase was a mixture of iron and arsenic. The passivation by the iron powder prevented further reduction of arsenic, therefore a qualified metallic arsenic product was not obtained.

[0040] Comparative Example 3

[0041] A domestic enterprise's copper concentrate smelting waste acid, mainly composed of (g / L): As 2.7, Cu 2.5, Bi 0.2, H2SO4 160. 100 mL of the waste acid solution was reacted by adding highly active arsenic sulfide reagent directly to the acid leaching solution without drying, at a rate 1.5 times the theoretically calculated amount for copper removal. The conversion temperature was 80℃, and the conversion time was 2 hours. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper content exceeding 40%. Subsequently, pretreated metallic iron powder (5 times the theoretical molar amount, 1.7 g) was added to the high-arsenic solution (4.5 g / L). The reaction temperature was 65℃, no antioxidant was added, nitrogen gas was introduced at a rate of 0.3 L / min, microwave output power was 800 W, and the reaction time was 1 hour. After the reaction was completed, a solution of metallic arsenic and ferrous iron was obtained. The arsenic content in the metallic arsenic was only slightly over 90.3%, and the arsenic content in the filtrate was less than 15 ppm. Phase analysis showed that arsenic trioxide phase appeared in the product, indicating that the degree of oxidation of metallic arsenic increased during the reduction process.

[0042] Comparative Example 4

[0043] The smelting waste acid produced by a domestic enterprise in copper concentrate smelting has the following main components (g / L): As 2.7, Cu 2.5, Bi 0.2, H2SO4 160. 100 mL of the waste acid solution was reacted. Highly active arsenic sulfide solid, prepared by sodium hydrosulfide in a high-arsenic solution, was added directly to the acid leaching solution without drying for copper displacement precipitation. The amount added was 1.5 times the theoretically calculated amount for copper removal. The conversion temperature was 80℃, and the conversion time was 2 hours. The copper ion removal rate in the solution exceeded 99%, and the copper sulfide product had a copper grade exceeding 40%. Subsequently, pretreated metallic iron powder was added to the high-arsenic solution (4.5 g / L), at an amount 5 times the theoretical molar amount (1.7 g). The reaction temperature was 65℃, and 0.5% antioxidant (ethylenediaminetetraacetic acid) was added. The microwave output power was 800 W, and the reaction time was 1 hour. After the reaction was completed, a solution of metallic arsenic and ferrous iron was obtained. The arsenic content in the metallic arsenic was 93.2%, and the arsenic content in the filtrate was less than 10 ppm. Phase analysis showed that arsenic trioxide was present in the product, indicating that the metallic arsenic was oxidized during the reduction process.

Claims

1. A method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid, characterized in that: Includes the following steps: 1) Add an active arsenic sulfide reagent to arsenic-containing waste acid and carry out a displacement reaction to obtain metal sulfide precipitate and arsenic-rich purification liquid; the active arsenic sulfide reagent is prepared by the following method: mix the arsenic-rich purification liquid with ferrous sulfide particles and react at a temperature of 25℃~45℃ for 20~40min. 2) Add iron powder and antioxidant to the arsenic-rich purification solution to carry out a reduction reaction and obtain a solution of elemental arsenic and ferrous iron. The antioxidant is composed of ascorbic acid and disodium EDTA in a mass ratio of (10-20):

1. The reduction reaction is carried out under the assistance of ultrasound or microwave.

2. The method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to claim 1, characterized in that: The amount of the active arsenic sulfide agent added to the arsenic-containing waste acid is measured to be 1.5 to 5 times the molar amount of heavy metal ions in the arsenic-containing waste acid.

3. A method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to any one of claims 1 to 2, characterized in that: The conditions for the displacement reaction are: temperature of 80-90℃ and time of 1-2 hours.

4. The method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to claim 1, characterized in that: The amount of iron powder added is 2 to 5 times the molar amount of arsenic in the arsenic-rich purification solution; The amount of antioxidant added is 0.5% to 2% of the molar amount of arsenic in the arsenic-rich purification solution; The iron powder has a purity greater than 99% and a particle size of 38–150 μm.

5. A method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to claim 1 or 4, characterized in that: The reduction reaction is carried out under a protective atmosphere at a temperature of 25℃ to 65℃ for a time of 0.5 to 1 hour.

6. The method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to claim 1, characterized in that: The conditions for the ultrasound are: frequency of 10-30kHz and output power of 100-300W.

7. The method for recovering valuable metals and preparing elemental arsenic from arsenic-containing waste acid according to claim 1, characterized in that: The microwave conditions are: frequency of 2000-3000MHz and output power of 400-800W.

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