A method for high-efficiency arsenic removal and zinc-cadmium separation and recovery from arsenic-containing waste acid

Abstract

This invention provides a method for efficiently removing arsenic and separating and recovering zinc and cadmium from arsenic-containing waste acid, comprising the following steps: filtering the arsenic-containing waste acid solution to remove suspended solids and particulate impurities, and then performing diffusion dialysis to allow H₂ to form a solution. + The arsenic is separated from metal ions to obtain recovered acid and residual acid containing metal ions. The residual acid is added to an autoclave along with an iron salt coagulant, and oxygen or air is simultaneously introduced to carry out a high-pressure oxidation precipitation reaction. After the reaction, liquid-solid separation is performed to obtain arsenic-containing precipitate and arsenic-precipitated liquid. The arsenic-precipitated liquid is added to carbide slag water for neutralization treatment to obtain gypsum slag and neutralized liquid. Zinc powder is added to the neutralized liquid for displacement, and after liquid-solid separation, sponge cadmium and zinc sulfate solution are obtained. This invention uses high-pressure oxidation precipitation of arsenic, which has a better arsenic precipitation effect. The arsenic content in the precipitated liquid is extremely low and a stable arsenic-containing precipitate is formed, which can be safely stored for a long time. At the same time, zinc and cadmium are recovered, realizing the high value of zinc and cadmium elements, and no wastewater is generated in the whole process.

Description

Technical Field

[0001] This invention relates to the field of secondary resource recycling technology, specifically to a method for efficiently removing arsenic from arsenic-containing waste acid and separating and recovering zinc and cadmium. Background Technology

[0002] Arsenic is a highly toxic chemical element and is not essential for the human body. In non-ferrous metallurgical processes, arsenic mainly exists in waste acids in the forms of As(III) and As(V). As(III) is far more toxic than As(V), and arsenite is dozens of times more toxic than arsenate and is a recognized carcinogen. Therefore, the national standard GB8978-1996 for integrated wastewater discharge clearly stipulates that the mass concentration of arsenic discharged should be ≤0.5 mg / L.

[0003] In recent years, the rapid development of non-ferrous metallurgical technology in my country has led to a continuous increase in non-ferrous metallurgical output, resulting in a large amount of arsenic-containing wastewater annually. Arsenic-containing wastewater from smelting enterprises typically exhibits three high characteristics: high acidity, high arsenic concentration, and high concentration of valuable metal elements. Treating arsenic-containing waste acid is a major challenge in environmental governance, thus holding significant importance. Currently, relatively systematic treatment methods exist. Among them, chemical methods are simple, easy to implement, and suitable for treating large quantities of high-concentration arsenic-containing wastewater, thus enjoying widespread industrial application.

[0004] Currently, the traditional treatment processes for arsenic-containing waste acid from smelting enterprises include: (1) Neutralization method: Alkaline substances are directly added to the arsenic-containing waste acid for acid-base neutralization. Chinese patents CN106396200A and CN103435188A use lime milk as a neutralizing agent to adjust the pH to neutral or weakly alkaline, and arsenic precipitates in the form of calcium arsenate or calcium arsenite. However, this method not only generates a large amount of solid waste, but also cannot make the wastewater meet the discharge standards. The solubility of calcium arsenite is much greater than that of calcium arsenate, with a solubility of 0.9 g / L. (2) Sulfide precipitation method: The sulfide arsenate method can effectively remove arsenate and produce less precipitation, but the H2S produced in the process is highly toxic and seriously endangers the environment and personal safety. (3) Iron salt precipitation method: This method uses iron salts (such as ferric chloride, ferrous sulfate, polyferric sulfate, etc.) as arsenic precipitation agents. Ferric chloride solution has a better arsenic precipitation effect, but it is highly corrosive and requires high equipment corrosion resistance. Chinese patents CN113620464A and CN110745988A use ferrous sulfate as an arsenic precipitant, controlling a certain iron-arsenic ratio to form ferric arsenate precipitate. This method is limited by the solubility product, requiring the consumption of large amounts of alkali and iron salts to achieve the required removal rate of trivalent arsenic. Furthermore, the ferric arsenate formed under normal pressure is amorphous and has poor long-term stability, failing to meet the needs of practical applications. Summary of the Invention

[0005] To address the aforementioned problems, this invention provides a method for efficiently removing arsenic from arsenic-containing waste acid and separating and recovering zinc and cadmium. The design concept is as follows: after the arsenic-containing waste acid solution undergoes diffusion dialysis to reduce acidity, it is subjected to a high-pressure oxidation precipitation process to completely precipitate the arsenic in the form of arsenic-containing slag, thus achieving arsenic desulfurization. The precipitated liquid is then neutralized with carbide slag water, resulting in gypsum slag containing less than 0.1% heavy metals, meeting the standards for grade II gypsum. Zinc powder is used to displace the neutralized liquid to obtain sponge cadmium and liquid zinc sulfate. This invention is particularly suitable for waste acid containing arsenic, high acidity, and high-value metals, solving problems such as poor arsenic removal efficiency using conventional methods and the inability of wastewater to meet discharge standards after arsenic removal. It achieves efficient arsenic removal from waste acid and high-value recovery of zinc and cadmium.

[0006] The present invention adopts the following technical solution:

[0007] A method for efficiently removing arsenic and separating and recovering zinc and cadmium from arsenic-containing waste acid includes the following steps:

[0008] Step 1: Pretreatment: The arsenic-containing waste acid solution is filtered through coarse filtration and fine filtration to remove suspended solids and particulate impurities, and the filtrate is obtained, which meets the requirements for diffusion dialysis feed liquid.

[0009] Step 2: Diffusion Dialysis for Acid Reduction: The filtrate obtained in Step 1 is fed by gravity into a diffusion dialysis system for diffusion dialysis. The influent flow rate and acid influent flow rate are adjusted, and the concentration difference is used as the driving force to reduce H₂O. + The acid is separated from the metal ions to obtain recovered acid and residual acid containing metal ions.

[0010] Step 3: High-pressure oxidation precipitation of arsenic: The residual acid obtained in step 2 is added to the high-pressure reactor, and iron salt coagulant is added to control the iron / arsenic molar ratio. At the same time, oxygen or air is introduced to carry out the arsenic precipitation reaction. After the reaction is completed, liquid-solid separation is performed to obtain stinky onion stone and arsenic-precipitated liquid.

[0011] Step 4: Neutralization: The arsenic-precipitated liquid obtained in Step 3 is added to the carbide slag water for neutralization treatment. The final pH is controlled at 5-6. After liquid-solid separation, gypsum slag and neutralized liquid are obtained.

[0012] Step 5: Zinc powder replacement: Add zinc powder to the neutralized liquid obtained in step 4 for replacement. After liquid-solid separation, sponge cadmium and zinc sulfate solution are obtained.

[0013] Furthermore, the iron salt coagulant is ferrous sulfate or polyferric sulfate.

[0014] Furthermore, the residual acid obtained in step 2 has a pH of 0 to 1.

[0015] Furthermore, the acidity of the recovered acid obtained in step 2 is greater than 105 g / L and the concentrations of Zn, Cd, and As are less than 2 g / L.

[0016] Furthermore, in step 3, the molar ratio of iron in the iron salt coagulant to arsenic in the residual acid is (1-2):1, that is, the amount of iron salt coagulant added is controlled to ensure that the molar ratio of iron / arsenic in the reaction system is (1-2):1.

[0017] Furthermore, in step 3, the flow rate of oxygen or air introduced is 0.5–2 L / min.

[0018] Furthermore, in step 3, the reaction temperature for the arsenic precipitation reaction is 120–160°C, and the reaction time is 4–6 h.

[0019] Furthermore, in step 3, the pressure of the autoclave is 0.6–1.0 MPa.

[0020] The technical principles employed in this invention are as follows:

[0021] 1. Diffusion Dialysis: The polymer backbone of anion exchange membranes contains positively charged fixed groups. Driven by a concentration gradient, anions in the acid compartment can migrate through the membrane while cations are blocked. Simultaneously, based on the electroneutrality requirement, positively charged ions may also be entrained. Due to H+... + The hydration radius of H is relatively small, and the charge is relatively low; while the hydration ion radius of metal salts is larger, and they are also highly valent, therefore H + It will pass through the membrane first.

[0022] 2. The core of this invention is the "high-pressure oxidation precipitation of arsenic" process. Research indicates that increasing the reaction temperature is beneficial for the extraction of As and the synthesis of well-formed arsenic trioxide. Air or oxygen is used as the oxidant to precipitate Fe... 2+ And As 3+ Oxidized to Fe 3 + And As 5+ In the pH range of 0 to 1, Fe 3+ And As 5+ The reaction forms a stable crystalline precipitate of styraxite (FeAsO4•2H2O). The specific reaction equation is shown below:

[0023] H3AsO3 + O2 = H3AsO5

[0024] Fe2(SO4)3+7H2O+As2O5= 2FeAsO4·2H2O+3H2SO4

[0025] Compared with the prior art, the present invention has the following technical effects:

[0026] 1. This invention uses diffusion dialysis to reduce acidity, which can reduce the amount of neutralizing agent consumed in the traditional neutralization process and avoid the production of neutralization residue.

[0027] 2. This invention uses high-pressure oxidation to precipitate arsenic, which has a better arsenic precipitation effect compared with the traditional iron salt method. The concentration of As in the precipitated solution is ≤0.5mg / L. The high-pressure oxidation process generates a stable crystalline arsenic precipitate (FeAsO4•2H2O), which can be safely stored for a long time.

[0028] 3. The gypsum residue produced by the neutralization treatment of arsenic precipitation solution of this invention contains ≤0.1% arsenic, ≤0.1% zinc, and ≤0.05% cadmium, which meets the first-grade standard of "Gypsum by-product of heavy non-ferrous metal smelting".

[0029] 4. This invention fully considers the "three highs" characteristics of arsenic-containing wastewater: high acidity, high arsenic concentration, and high concentration of valuable metal elements. It uses oxygen or air oxidation, resulting in extremely low arsenic content in the treated solution. At the same time, all valuable metal elements are recovered and reused, achieving efficient arsenic removal from high-acid wastewater and high-value utilization of zinc and cadmium elements. No wastewater is generated throughout the process, which is in line with the concept of green metallurgy. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the membrane stack structure of a diffusion dialysis system;

[0031] Figure 2 This is a schematic diagram of ion migration in a diffusion dialysis system;

[0032] Figure 3 This is a process flow diagram of a method for efficiently removing arsenic from arsenic-containing waste acid and separating and recovering zinc and cadmium according to the present invention. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0034] like Figure 3 As shown, this invention provides a method for efficiently removing arsenic and separating and recovering zinc and cadmium from arsenic-containing waste acid. The high-arsenic waste acid solution is pretreated to remove suspended solids and particulate impurities, then subjected to diffusion dialysis to reduce the acid content, yielding residual acid containing metal ions and recovered acid. An iron salt coagulant is added to the residual acid as an arsenic precipitant, while oxygen or air is simultaneously introduced into a high-pressure autoclave to remove Fe... 2+ Oxidized to Fe 3+ As 3+ Oxidation to As 5+ At a temperature of 120–160℃, relatively stable arsenic-containing osmanthus stone and arsenic-precipitated liquid are generated. The arsenic-precipitated liquid is then neutralized with carbide slag water to obtain gypsum slag and a neutralized liquid. Cadmium is recovered from the neutralized liquid by replacing it with zinc powder, yielding zinc sulfate liquid and sponge cadmium. This invention is a fully wet treatment process, where arsenic can be stably stored in the form of osmanthus stone, achieving efficient arsenic removal from waste acid and high-value recovery of zinc and cadmium.

[0035] Example 1

[0036] The main components of the arsenic-containing waste acid solution used in this embodiment are: 187 g / L H2SO4, 18 g / L As, 15 g / L Cd, and 18 g / L Zn.

[0037] Pretreatment: The arsenic-containing waste acid solution is passed through a bag filter system with a pore size of 5μm and a security filter system with a pore size of 1μm to remove suspended solids and particulate impurities. Finally, it is passed through a 0.1μm uniform pore membrane filter to make the arsenic-containing waste acid solution meet the quality and technical requirements for entering the diffusion dialysis unit.

[0038] Diffusion dialysis for acid reduction: The treated filtrate is fed by gravity into the diffusion dialysis system, with the acid inlet flow rate adjusted to 220 L / h and the water inlet flow rate adjusted to 250 L / h. Utilizing the concentration difference as the driving force, recovered acid and residual acid containing metal ions are obtained. The residual acid has a pH of 0.1, an arsenic rejection rate R≥90%, a zinc and cadmium rejection rate R≥97%, and the acidity of the recovered acid is greater than 105 g / L, while the concentrations of Zn, Cd, and As are all less than 2 g / L.

[0039] like Figure 1 and Figure 2 As shown, the pretreated filtrate (i.e., waste acid) is introduced into the bottom of the acid chamber (i.e., chamber A), and tap water is introduced into the top of the water chamber (i.e., chamber B). The concentration difference between the solutions in the acid and water chambers is used as the driving force to make H... + The acid is separated from the metal ions, and residual acid containing metal ions is obtained at the top of the water chamber, while recovered acid is obtained at the bottom of the water chamber. The acidity of the recovered acid is greater than 105 g / L and the concentrations of Zn, Cd, and As are less than 2 g / L.

[0040] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution produced by the above method, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. At the same time, ferrous sulfate is added to the reactor. The iron / arsenic molar ratio in the reaction system is controlled to be 1.5:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. The pressure inside the high-pressure reactor is 0.8 MPa, and the reaction temperature is 140℃. After precipitation for 5 h, the solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.12 ppm of As.

[0041] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.08 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0042] Example 2

[0043] High-pressure oxidation precipitation of arsenic: Take 500 ml of the residual acid solution produced by the diffusion dialysis deacidification step in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Polyferric sulfate is added to the reactor at the same time. The iron / arsenic molar ratio in the reaction system is controlled to be 1.5:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. The pressure inside the high-pressure reactor is 0.8 MPa, and the reaction temperature is 140 °C. After precipitation for 5 h, the solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.13 ppm of As.

[0044] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.05 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0045] Comparative Example 1

[0046] Arsenic precipitation by oxidation under normal pressure: Take 500 ml of the residual acid solution produced by the diffusion dialysis deacidification step in Example 1. The residual acid contains 16.5 g / L of arsenic. Add it to the autoclave and ferrous sulfate at the same time. Control the iron / arsenic molar ratio in the reaction system to be 1.5:1. During the reaction, continuously introduce compressed air at 1 L / min for oxidation. After precipitation at 90 °C under normal pressure for 5 h, filter the solution. Wash and dry the precipitate to obtain arsenic-iron slag precipitate. The precipitate solution contains 3.6 g / L of As.

[0047] Toxicity leaching: The obtained arsenic iron slag precipitate was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The solubility of As in the arsenic iron slag precipitate was 100 mg / L. The arsenic iron slag could not exist stably, and when the pH exceeded 2.2, ferric arsenate was easily decomposed into goethite.

[0048] Comparative Example 2

[0049] High-pressure oxidation precipitation of arsenic: Take 500 ml of the residual acid solution produced by the diffusion dialysis deacidification step in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Polyferric sulfate is added to the reactor at the same time. The iron / arsenic molar ratio in the reaction system is controlled to be 1.5:1. After precipitation at 90°C under normal pressure for 5 hours, the solution is filtered, and the precipitate is washed and dried to obtain arsenic-iron slag precipitate. The precipitate solution contains 4.9 g / L of As.

[0050] Toxicity leaching: The obtained arsenic iron slag precipitate was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The solubility of As in ferric arsenate was 240 mg / L. The arsenic iron slag could not exist stably, and when the pH exceeded 2.2, ferric arsenate was easily decomposed into goethite.

[0051] Comparative Examples 1 and 2 show that under normal pressure conditions, regardless of Fe... 3+ Or Fe 2+ Neither of them easily forms the stinky onion stone crystal form.

[0052] The residual acid obtained from diffusion dialysis in Example 1 is used in Examples 3 to 11 below.

[0053] Example 3

[0054] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. At the same time, ferrous sulfate is added to the reactor. The molar ratio of iron to arsenic in the reaction system is controlled to be 1:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. After precipitation for 5 h at a pressure of 1.0 MPa and a reaction temperature of 140 °C, the solution is filtered. The precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.09 ppm of As.

[0055] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.02 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0056] Example 4

[0057] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. At the same time, ferrous sulfate is added to the reactor. The molar ratio of iron to arsenic in the reaction system is controlled to be 2:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. The pressure in the high-pressure reactor is 0.6 MPa, and the reaction temperature is 140 °C for precipitation for 5 h. The solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.05 ppm of As.

[0058] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.05 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0059] Example 5

[0060] High-pressure oxidation precipitation of arsenic: Take 500 ml of the residual acid solution obtained from diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Simultaneously add ferrous sulfate to the reactor and control the iron / arsenic molar ratio in the reaction system to be 1.5:1. During the reaction, continuously introduce compressed air at 2 L / min for oxidation. The pressure inside the high-pressure reactor is 1.0 MPa, and the reaction temperature is 140℃ for precipitation for 5 h. Filter the solution, wash and dry the precipitate to obtain arsenic precipitate. The precipitate solution contains 0.03 ppm of As.

[0061] Toxicity leaching: The obtained styrofoam was subjected to toxicity leaching according to GB5085.3-2007 (Standard for Identification of Solid Waste - Leaching Toxicity Identification). The arsenic leaching concentration was 0.04 mg / L, which is less than the limit of 5 mg / L for the mass concentration of hazardous components in the leachate, and it can be safely and stably stored.

[0062] Example 6

[0063] High-pressure oxidation precipitation of arsenic: Take 500 ml of the residual acid solution obtained from diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Simultaneously add ferrous sulfate to the reactor and control the iron / arsenic molar ratio in the reaction system to be 1.5:1. During the reaction, continuously introduce compressed air at 0.5 L / min for oxidation. The pressure inside the high-pressure reactor is 0.6 MPa, and the reaction temperature is 140 °C for precipitation for 5 h. Filter the solution, and wash and dry the precipitate to obtain arsenic precipitate. The precipitate solution contains 0.19 ppm of As.

[0064] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.11 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0065] Example 7

[0066] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. At the same time, ferrous sulfate is added to the reactor. The iron / arsenic molar ratio in the reaction system is controlled to be 1.5:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. The pressure in the high-pressure reactor is 0.8 MPa, and the reaction temperature is 120 °C for precipitation for 5 h. The solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.13 ppm of As.

[0067] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.19 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0068] Example 8

[0069] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Simultaneously add ferrous sulfate to the reactor and control the iron / arsenic molar ratio in the reaction system to be 1.5:1. During the reaction, continuously introduce compressed air at 1 L / min for oxidation. The pressure in the high-pressure reactor is 0.8 MPa, and the reaction temperature is 160℃ for precipitation for 5 h. The solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.04 ppm of As.

[0070] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.05 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0071] Example 9

[0072] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. Simultaneously add ferrous sulfate to the reactor and control the iron / arsenic molar ratio in the reaction system to be 1.5:1. During the reaction, continuously introduce compressed air at 1 L / min for oxidation. The pressure in the high-pressure reactor is 0.8 MPa, and the reaction temperature is 140 °C for precipitation for 4 h. The solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.05 ppm of As.

[0073] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Identification Standard for Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.05 mg / L, which is less than the mass concentration limit of 5 mg / L for hazardous components in the leachate, and it can be safely and stably stored.

[0074] Example 10

[0075] Arsenic precipitation by high-pressure oxidation: Take 500 ml of the residual acid solution obtained by diffusion dialysis in Example 1, which contains 16.5 g / L of arsenic, and add it to a high-pressure reactor. At the same time, ferrous sulfate is added to the reactor. The iron / arsenic molar ratio in the reaction system is controlled to be 1.5:1. During the reaction, compressed air is continuously introduced at a rate of 1 L / min for oxidation. The pressure in the high-pressure reactor is 0.8 MPa, and the reaction temperature is 140 °C for precipitation for 6 h. The solution is filtered, and the precipitate is washed and dried to obtain arsenic precipitate. The precipitate solution contains 0.03 ppm of As.

[0076] Toxicity leaching: The obtained scorched onion stone was subjected to toxicity leaching according to GB5085.3-2007 (Standard for Identification of Solid Waste - Leaching Toxicity Identification). The leaching concentration of arsenic was 0.03 mg / L, which is less than the limit of 5 mg / L for the mass concentration of hazardous components in the leachate, and it can be safely and stably stored.

[0077] Example 11

[0078] Neutralization of the arsenic-precipitated liquid: Calcium carbide slag water was gradually added to the arsenic-precipitated liquid obtained in Example 1 for neutralization to remove excess acid. The pH endpoint was controlled at 6. After filtration and washing, gypsum slag and the neutralized liquid were obtained. The gypsum slag contained 80.55% CaSO4•2H2O, 0.079% As, 0.059% Zn, and 0.023% Cd. It meets the first-grade standard of "Gypsum by-product of heavy non-ferrous metal smelting" and can be sold as a by-product.

[0079] Zinc powder replacement: Add zinc powder to the neutralized solution obtained in the above steps. The amount of zinc powder is 1.2 times the molecular weight of cadmium. The replacement temperature is 60℃ and the replacement time is 1h. Zinc sulfate solution and sponge cadmium are obtained. The zinc sulfate solution contains Cd < 1mg / L and the cadmium recovery rate is ≥ 98%.

[0080] The embodiments described above are merely preferred embodiments of the present invention and are only used to explain the present invention. They are not intended to limit the scope of the present invention. For those skilled in the art, other implementation methods can be easily made by substitution or modification based on the technical content disclosed in this specification. Therefore, all changes and improvements made to the principles and process conditions of the present invention should be included within the scope of the patent application of the present invention.

Claims

1. A method for efficiently removing arsenic from arsenic-containing waste acid and separating and recovering zinc and cadmium, characterized in that, Includes the following steps: Step 1: Pretreatment: The arsenic-containing waste acid solution is filtered to remove suspended solids and particulate impurities, yielding the filtrate; Step 2: Diffusion Dialysis to Reduce Acidity: The filtrate obtained in Step 1 is subjected to diffusion dialysis to reduce H₂. + The acid is separated from the metal ions to obtain recovered acid and residual acid containing metal ions; Step 3: High-pressure oxidation precipitation of arsenic: The residual acid obtained in Step 2 is added to a high-pressure reactor, along with an iron salt coagulant. Oxygen or air is introduced simultaneously to carry out the arsenic precipitation reaction. After the reaction is completed, liquid-solid separation is performed to obtain arsenic-precipitated stone and the arsenic-precipitated liquid. An iron salt coagulant is added to make the molar ratio of iron to arsenic in the reaction system (1-2):

1. The reaction temperature of the arsenic precipitation reaction is 120-140℃, and the reaction time is 4-6 hours. The pressure of the high-pressure reactor is 0.6-1.0 MPa. Step 4: Neutralization: The arsenic-precipitated liquid obtained in Step 3 is added to the carbide slag water for neutralization treatment. The final pH is controlled at 5-6. After liquid-solid separation, gypsum slag and neutralized liquid are obtained. Step 5: Zinc powder replacement: Add zinc powder to the neutralized liquid obtained in step 4 for replacement. After liquid-solid separation, sponge cadmium and zinc sulfate solution are obtained.

2. The method for efficient removal of arsenic and separation and recovery of zinc and cadmium from arsenic-containing waste acid according to claim 1, characterized in that, The iron salt coagulant is ferrous sulfate or polyferric sulfate.

3. The method for efficient removal of arsenic and separation and recovery of zinc and cadmium from arsenic-containing waste acid according to claim 1, characterized in that, The residual acid obtained in step 2 has a pH of 0 to 1.

4. The method for efficient removal of arsenic and separation and recovery of zinc and cadmium from arsenic-containing waste acid according to claim 1, characterized in that, The acidity of the recovered acid obtained in step 2 is greater than 105 g / L and the concentrations of Zn, Cd, and As are less than 2 g / L.

5. The method for efficient removal of arsenic and separation and recovery of zinc and cadmium from arsenic-containing waste acid according to claim 1, characterized in that, In step 3, the flow rate of oxygen or air introduced is 0.5 to 2 L / min.

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