Comprehensive utilization of arsenic-containing pyroacid

Arsenic is highly toxic; abroad, the cement solidification technique is generally used – cement is employed to solidify arsenic, which is then buried or put to other use. You can look up relevant literature on this! :victory:

Advances in Treatment Technologies for Arsenic-Containing Waste Residues Wang Dan, Zhu Yinnian (Guilin University of Technology) Abstract With the development of industry, arsenic pollution has become a global environmental issue. Therefore, in recent years, countries around the world have placed increasing emphasis on addressing arsenic pollution. This article provides a brief overview of the research progress on arsenic-containing waste over the past few years, both domestically and internationally. Keywords: arsenic-containing waste residues; treatment methods; stabilization; solidification. Arsenic is one of the common pollutants and is quite toxic to the human body ； Arsenic is also a toxin that causes cumulative poisoning, and in recent years it has been found to be a carcinogen as well. Arsenic pollution in the environment is primarily caused by industrial waste streams, including arsenic-containing dust, wastewater, exhaust gases, and waste residues generated during processes such as the mining, roasting, and smelting of arsenic-containing metal ores, as well as in industries like chemicals, coking, thermal power generation, papermaking, and leather production. Among these, the metallurgical and chemical industries emit the largest amounts of arsenic, making them the main sources of environmental pollution. During the production process in the metallurgical industry, approximately 30% of arsenic ends up in wastewater and waste gases; therefore, the final treatment of arsenic-containing waste residues resulting from the removal of arsenic from wastewater has always been an important research topic for metallurgical and environmental protection professionals. This article provides a brief introduction to the treatment technologies for arsenic-containing waste residues at home and abroad in recent years. I. Stabilization techniques The stabilization process is a method that uses additives to modify the engineering properties of waste (such as permeability, compressibility, and strength), thereby turning the waste into an immobile solid. This process converts harmful pollutants into substances with low solubility, low toxicity, and low mobility, thereby reducing the hazards of waste. Both domestically and internationally, chemical methods are commonly used to stabilize toxic arsenic residues and sludge, that is, through chemical reactions to form relatively insoluble metal arsenates and arsenites that are more stable under natural conditions, including common compounds such as calcium arsenite, calcium arsenate, and iron arsenate. Since soluble arsenic can form such compounds with many metal ions, this property is utilized in precipitation methods, where salts and sulfides of calcium, iron, magnesium, aluminum, etc., are used as precipitants; filtration then allows the removal of arsenic from the liquid phase. Based on this, when dealing with arsenic-containing waste residues and sludge, pretreatment is required: arsenic is leached out using hot water or solutions of acids and bases, and then the leachate is stabilized. In recent years, the commonly used methods at home and abroad have been calcium salt and iron salt precipitation methods. (1) Calcium salt precipitation method: The calcium salt precipitation method has low treatment costs and a simple process, and it is currently a commonly used stabilization method. Kim Cheol-nam and others used the calcium salt precipitation method when dealing with antimony-arsenic-alkali slag; the reaction equations for this process are as follows: 4Ca2+ + 2AsO43- + 2OH- = Ca3(AsO4)2•Ca(OH)2, and 4CaOH+ + 2AsO43- = Ca3(AsO4)2•Ca(OH)2. The process flow involves hot water leaching of the antimony-arsenic-alkali slag, followed by arsenic precipitation using calcium oxide. In this experiment, hot water leaching was used to ensure that over 96% of the antimony ended up in the leach residue, while over 97% of the arsenic went into the leachate, thus achieving effective separation of arsenic and antimony. Subsequently, lime milk was employed to precipitate arsenic from the leachate; when the calcium-arsenic equivalent ratio exceeded 1.85 and the temperature was 85°C, the arsenic precipitation rate reached over 95%. After the arsenic precipitation test, calcium arsenide slag with a high arsenic content was obtained. In his research on arsenic removal techniques for arsenic-containing waste residues, Li Minghua also employed the calcium salt precipitation method for treating such residues, and the treatment results were identical to those obtained by Kim Cheol-nam. Wang Rongyan also employed the calcium salt precipitation method to deal with the large amount of phosphorus-arsenic slag generated during the production of ammonium tungstate and tungsten oxide from black tungsten concentrate. The process he tried involved autoclaving phosphorus-arsenic slag under alkaline conditions, causing magnesium tungstate in the phosphate slag to react with sodium hydroxide to form magnesium hydroxide. Magnesium hydroxide then reacted with sodium arsenate in the solution to produce sodium arsenate. The reaction equations are as follows: MgWO4 + 2NaOH = Na2WO4 + Mg(OH)2↓; 3Mg(OH)2(s) + 2Na3AsO4(aq) = Mg3(AsO4)2(s) + 6NaOH(aq). Experiments showed that these reactions must take place under highly alkaline conditions. Under high-alkaline conditions, Mg3(AsO4)2 partially dissolves back into Na3AsO4, and Na3AsO4 reacts with Ca(OH)2, which is the product of the decomposition of wolframite in the concentrate, under alkaline leaching conditions, to form less soluble compounds such as calcium arsenate and NaCaAsO4. This solidifies the contaminant arsenic in the tungsten slag, thereby converting the harmful phosphorus-arsenic slag into harmless tungsten slag. Vandacasteel et al. successfully treated arsenic-containing fly ash. Test analysis indicates that its success lies in the formation of Ca3(AsO4)2 within the cured product; it was also found that pre-oxidizing the waste can reduce the amount of arsenic leached from the stabilized product by an order of magnitude. Additionally, in recent years a new method has been developed abroad—mineral precipitation. This method involves adding H3PO4 and CaO to arsenic-containing leachates at a pH of 12 to produce the stable Ca10(AsxPyO4)6(OH)2 precipitate. The drawback of the calcium salt precipitation method is that calcium salts have high solubility; therefore, a significantly high concentration of calcium is required to reduce the arsenic concentration to lower levels. This results in the need for large amounts of flocculants, as well as an increase in the amount of residue left after treatment. (II) Iron salt precipitation method: The use of iron salts to remove arsenic is also a common method; ferric chloride is often used as a flocculant and added to water bodies. Under high pH conditions, this method not only produces ferric arsenate but also generates a large amount of ferric hydroxide colloids. The arsenate ions in the solution can also undergo adsorption and coprecipitation with ferric hydroxide, thereby achieving a high arsenic removal rate. Fang Zhaoheng and others used a NaOH solution along with nitric acid to carry out catalytic oxidative leaching of highly arsenic-resistant gold ores, causing the arsenic in the leachate to combine with the trivalent iron ions present there, thereby forming stable ferric arsenate. Studies have found that the final pH for neutralization and precipitation using NaOH should be between 5 and 7, as at higher pH levels, some of the iron arsenate precipitate converts into iron hydroxide or goethite, thereby releasing arsenate ions and increasing the arsenic content in the solution. Sun Fengqin and others used the iron salt precipitation method to process the arsenic-, cobalt-, and nickel-containing concentrate obtained from the flotation of cyanide slag. In the experiment, they first used bacteria to leach arsenic-containing cobalt-nickel concentrates, and then oxidized the arsenic-containing minerals through bacterial oxidation. The reaction equations are as follows: FeAs2 + 2O2 + H2SO4 + 2H2O → FeSO4 + 3H3AsO3; CoAs2 + 2O2 + H2SO4 + 2H2O → CoSO4 + 2H3AsO3; 2FeAs2 + 13/2O2 + Fe2(SO4)3 + 2H2O → 4FeAsO4 + 3H2SO4; CoSO4 + 2Fe2(SO4)3 + 2H2O → CoSO4 + 2FeAsO4 + 2H2SO4. As can be seen from these reactions, bacterial leaching continuously produces ferric sulfate and sulfuric acid, while the arsenic, which is harmful to the environment, is precipitated in the form of ferrous arsenate (FeAsO4). JU-YONG KIM et al. employed As(III) and Fe(III) adsorption coprecipitation to treat arsenic slag generated from Korean metal mines, and the vast majority of arsenic combined with iron to form stable iron-containing precipitates. Q. Wang et al. pointed out that the solidification of arsenic occurs through the adsorption coprecipitation of As(V) and Fe(III) to form arsenic-containing goethite, as well as the formation of chalcanthite precipitate from As(III) and Fe(II). Since the arsenic-containing goethite precipitate formed by co-precipitation of arsenic and iron is quite stable, this method is currently the most widely used approach for fixing arsenic in the world. P. M. Swash et al. demonstrated through column immersion experiments that the stability of skutterudite precipitates is at least on par with that of arsenic-bearing goethite precipitates with a Fe/As ratio greater than 3, and it is better than the stability of arsenium-fixing compounds currently used in the metallurgical industry. Therefore, skutterudite precipitates are an excellent arsenium-fixing compound, and using skutterudite precipitates to fix arsenium represents a developing trend in the treatment of arsenic-containing materials. II. Solidification technology: Solidification technology is a method of harmless treatment that uses physical and chemical means to fix or enclose hazardous solid waste within an inert solid matrix, thereby granting it chemical stability or sealing properties. Curing techniques can be classified by curing agents into coating curing, self-curing, and melting curing (glass curing). Coating curing can further be divided into cement curing, lime curing, plastic material curing, organic polymer curing, and ceramic curing, depending on the coating material used. Currently, the commonly used stabilization methods for treating arsenic-containing waste residues and sludge at home and abroad are cement solidification, organic polymer solidification, plastic material solidification, and melting solidification. (1) Cement and organic polymer curing: Cement curing is a treatment method in which cement is used as a curing agent to solidify hazardous waste. During curing, the cement reacts with the moisture in the waste or with additional water to form a gel, which encapsulates the harmful particles in the waste, and it gradually hardens into a cement-based solid. Cement solidification is one of the main methods used internationally to deal with toxic and hazardous waste, and the U.S. Environmental Protection Agency also considers cement solidification to be the best technology for treating hazardous waste. The curing of organic polymers involves fully mixing the monomers of a certain organic polymer with waste materials in a specially designed container, adding a catalyst and stirring everything together to facilitate polymerization and curing. Zhao Meng and others used cement solidification when dealing with arsenic-containing sludge; after forming the solidified balls, leaching tests were conducted on these balls. Seven days after the solidified balls had hardened, they were immersed in a leaching agent (tap water) for 7 days, after which the arsenic concentration in the leachate was measured. The results showed that the arsenic leaching concentration was far below the requirement of 1.5 mg/L specified in GB5085.1-1996, the Standard for Identifying Hazardous Wastes – Leaching Toxicity Test, and this concentration further decreased as the proportion of cement increased. The Golder Association in Australia also used cement solidification for arsenic-containing roasted ore waste, and leaching experiments were conducted subsequently, yielding results identical to those of Zhao Meng. Currently, there is another method abroad for the solidification of volcanic ash cement, which involves using a solidifying material composed mainly of silicoaluminates – namely volcanic ash – to treat arsenic-containing waste. Studies have shown that treating arsenic-containing sludge with a mixture of volcanic ash and lime results in a product that still has a soil-like appearance; however, leaching tests confirm that this stabilization process significantly reduces the leaching rate of arsenic. Tri T. Hoang conducted experiments on the solidification of arsenic-containing mixed waste using calcium thioaluminate (CSA) cement, magnesium phosphate (MP) cement, polyester resin (OPE) for solidification, and epoxy vinyl ester resin (EVE) for solidification. In the experiments, the cured products were also tested using the TCLP and SPLC methods. The results showed that, except for MP curing, CSA, OPE, and EVE all provided good curing stability; as for the durability and hardness of the cured products, those cured with OPE and EVE were superior, indicating that OPE and EVE curing methods hold great promise. The arsenic sulfide precipitate obtained by a Japanese smelting plant from treating arsenic-containing wastewater using the sulfidation precipitation method was piled up on-site after being solidified through organic polymerization. Cement curing is widely used in industry due to its simple curing process, low costs for equipment and operation, as well as the good strength, heat resistance, and durability of the cured products. However, cement curing also has certain disadvantages: the leaching rate of cement-cured materials is high, requiring coating treatment ； The volume expansion of cementitious solids is relatively high ； Some wastes require pretreatment and the addition of additives, which increases the treatment costs]. The advantage of organic polymer curing is that it can be carried out at room temperature ； A very small amount of catalyst is added, resulting in a final product of smaller volume compared to other curing methods; it can handle both dry slag and wet slurry. The downside is that it is not safe enough; sometimes the strongly acidic catalysts used can cause heavy metals to leach out during the polymerization process, and corrosion-resistant equipment is required ； The cured material has poor aging resistance ； Moreover, the cured material is loose and must be placed in containers for disposal, which increases the disposal costs. (II) Curing of plastic materials: The curing of plastic materials can be divided into thermosetting plastic curing and thermoplastic curing, depending on the properties of the materials used; thermoplastic curing is the more common method. The curing of thermoplastic materials involves mixing molten thermoplastic substances (asphalt, paraffin, polyethylene, polypropylene, etc.) with hazardous waste at high temperatures in order to stabilize it. Currently, the most commonly used thermoplastic curing technique at home and abroad is the asphalt curing technique. Asphalt curing involves using asphalt-based materials as curing agents, which are mixed uniformly with waste at an appropriate temperature to initiate a saponification reaction. This reaction causes the harmful substances to be trapped within the asphalt, forming a solid mass that thus becomes stable. Asphalt is a hydrophobic substance; a fully cured asphalt mass possesses excellent waterproof properties, as well as good adhesion and chemical stability. It also shows high resistance to most acids and bases, which is why cured asphalt has good stability. Q. Wang et al. used asphalt curing for the stabilization of arsenic-containing slag, and he also proposed that freezing treatment could be applied to arsenic-containing waste slag. The advantage of curing thermoplastic materials is that the leaching rate of the cured product is lower than that of other curing methods, and the compatibilization ratio is small ； Curing provides good barrier properties to the solution and strong resistance to microbial erosion. Its drawback is that the cured substrate is flammable, so the product requires appropriate packaging ； Thermoplastic materials are expensive, require complex handling, and have high equipment costs. (III) Melting solidification: The melting solidification technique is also known as the glass solidification technique. This method involves mixing the waste to be treated with fine glassy materials such as glass shards and glass powder; after mixing and granulation, it is melted at high temperatures to form a glass-solidified product. The dense crystalline structure of the glass ensures the permanent stability of this solidified product. L.G. Twidwell and others carried out glass solidification of arsenic-containing residues, and demonstrated through experiments that it enables their long-term stable storage. The advantage of glass curing is that the resulting glassy material possesses higher durability, better impermeability, and greater resistance to acid corrosion compared to cement-cured products. Since the components of the waste become part of the glass, the leaching rate of the glass-cured product is very low, and the amount by which the waste is incorporated into the glass is not significant. The disadvantage of this method is its complex process, high requirements for equipment materials, and high treatment costs. In addition, in recent years, both domestically and internationally, another method for treating arsenic-containing waste has been pyrological solidification – which involves high-temperature calcination of arsenic-containing residues such as calcium arsenide residues and iron arsenide residues. Experimental results show that the higher the calcination temperature, the lower the solubility of the arsenic slag after calcination. In recent years, several copper smelters in Chile have adopted thermal solidification methods for treating arsenic-calcium slag, achieving good results. Liu Zheng and others have achieved good results by using high-temperature thermal treatment for the solidification of arsenic-containing waste generated during the pyrometallurgical enrichment of high-arsenic cobalt ores. For arsenic-containing waste residues and sludge that have been cured and stabilized, their final disposal must also be considered, in order to isolate these solid wastes from the biosphere as much as possible. Key references: Zhao Youcai. Hazardous Waste Treatment Technologies. Chemical Industry Press, 2003. Fang Zhaoheng, Shi Wei, Han Baoling, et al. Neutralization and arsenic removal process from high-arsenic solutions. Chemical Engineering & Metallurgy, 2000, 21(4): 359–362. Wang Qiankun and Demopoulos GP, ICHM’98 Proceedings of the Third International Conference on Hydrometallurgy, Kunming, China, Nov. 3–5, 1998

Our organization is also researching new technologies in this area, but progress so far has been limited. Solid slag is ultimately a problem

Since it is a difficult issue to address, the traditional arsenic-fixation method merely converts the form of arsenic from liquid to solid. It’s not a solution after all. I hope everyone will pay active attention to this post. If any student is interested, they can add me on QQ: 543659370

If it is only curing, all the methods mentioned above are feasible. But turning it into a product still requires some effort. The simplest method is to produce arsenic; there are many ways to do this, depending on the owner’s requirements and environmental considerations, as well as the investment needed.

Preliminary Study on the Interference Principle of Sulfite and Its Elimination in the Determination of Arsenic in Wastewater from the Sulfuric Acid Industry by Zheng Weixing (Longyou County Environmental Monitoring Station, Longyou, Zhejiang 324400) Abstract: To gain a better understanding of the interference caused by sulfite in the determination of arsenic in wastewater discharged from the sulfuric acid industry, this paper analyzes the production processes in this industry. To address the issue of sulfite interference during the determination of arsenic in such wastewater, comparative experiments were conducted using both the sulfuric acid-nitric acid digestion method and the potassium permanganate digestion method. The results show that when sulfite interference is present alone, it can be simply treated using the potassium permanganate oxidation method, which yields acceptable accuracy and is a straightforward process. Keywords: Sulfuric acid industry; Arsenic; Sulfite; Interference and elimination. The influence of inferior sulfur and acid radicals on the determination of arsenic in industrial wastewater from the sulfuric acid industry and methods for eliminating this influence. Zheng Weing. (Environmental Monitoring Station of Longyou County, Longyou, Zhejiang 324400) Abstract: Based on an analysis of sulfuric acid production technologies, this study examined the interference caused by inferior sulfur and acid radicals on the determination of arsenic in industrial wastewater, and proposed methods for eliminating such interference. Keywords: Sulfuric acid industry; Arsenic; Inferior sulfur and acid radicals; Interference and elimination. In the “Standard Work Manual for Water Environment Analysis Methods” compiled by the Science, Technology and Standards Department of the Environmental Protection Bureau, the silver diethyldithiocarbamate spectrophotometric method is used for determining total arsenic in water quality; the document mentions that elements such as antimony, lead, and sulfides can cause interference in the determination of arsenic. In daily work, when collecting sulfuric acid industrial wastewater for direct analysis of its arsenic content, it sometimes happens that the lead acetate cotton turns black very quickly, rendering the sample unusable; other times, this phenomenon does not occur. To this end, the sulfuric acid production process was combined to conduct further research on the aforementioned situations, and a preliminary exploration was carried out on the principles of interference and their elimination. 1 Source of the problem: Arsenic determination was carried out on the wastewater from the sulfuric acid production plant directly; when lead acetate caused the cotton to turn black, a qualitative analysis for sulfides was performed on the original sample ； 50 mL of the mixed water sample was taken and placed in a 150 mL conical flask. 1+1 sulfuric acid and several glass beads were added, after which filter paper was immediately placed over the mouth of the flask and secured with an rubber band. A drop of 10% lead acetate solution was dropped in the center of the filter paper. The flask was then heated to boiling on an electric hot plate; once it had cooled, the filter paper was removed and the spot facing the liquid surface was inspected – no color change was observed. Therefore, it is preliminarily determined that the sulfide content in the water sample is at least very low, insufficient to cause all of the lead acetate-treated cotton to turn black and become ineffective. When testing arsenic in the wastewater from the sulfuric acid plant, there are times when there is no interference from sulfides, and other times there is such interference. How can this abnormal situation occur? 2 Problem Analysis 2.1 Analysis of the production process in the sulfuric acid industry: Ferrous sulfate → roasting in a bubbling furnace → electrostatic dust removal → purification → electrostatic mist removal → drying → absorption. 2.2 Generation and hazards of arsenic in the sulfuric acid industry production: The flue gas produced after roasting ferrous sulfide in a bubbling furnace contains mainly SO2, N2, O2, as well as mineral dust, arsenic trioxide, fluorides, selenium dioxide, sulfur trioxide, and oxides of non-ferrous metals. Arsenic exists in furnace gas in the form of arsenic trioxide. Arsenic trioxide is the most harmful toxin to barium catalysts in sulfuric acid production ； It also affects the quality of the final acid, limiting its industrial applications ； As a Class I pollutant, arsenic poses severe hazards to both humans and the environment. 2.3 Removal of arsenic from flue gas in the sulfuric acid production process: The flue gas generated during the roasting of pyrite often contains high levels of arsenic. In China, the traditional process is commonly used: the flue gas is washed and purified to further remove any remaining slag, as well as impurities such as arsenic trioxide and chlorides. According to literature, after the furnace gas is washed and purified and its temperature drops below 50 °C, the arsenic trioxide contained in it is present in trace amounts, at about 0.016 mg/Nm3. 2.4 Sources of wastewater in the sulfuric acid production process Based on an analysis of the sulfuric acid production process, the harmful wastewater generated during this process mainly arises from the purification stage. According to an investigation of the purification unit at the sulfuric acid production plant of Longyou Feiyan Chemical Co., Ltd., the process is as follows: Water → Flue gas → Venturi tube → Foam tower → Condenser → Electrostatic precipitator → Drying tower. Dilute acid, dilute acid, polluted acid, polluted acid. In the purification stage, most of the impurities such as arsenic trioxide are removed; however, due to the use of a closed-loop dilute acid washing system, these impurities gradually accumulate in the wastewater and sludge. As the furnace gas undergoes successive stages of washing and acid treatment with a gradual decrease in temperature, the solubility of sulfur trioxide and sulfur dioxide in the wastewater increases, resulting in a gradual increase in the concentration of the dilute acid. To prevent mineral dust sludge from accumulating in the acid and causing equipment wear and blockages, a certain amount of this dilute acid must be discharged regularly. This waste acid contains various impurities such as sulfuric acid, sulfurous acid, and arsenic trioxide. 2.5 Principle of arsenic determination and interference mechanisms in sulfuric acid industry wastewater. Currently, the standard method for determining arsenic is the silver diethyldithiocarbamate colorimetric method. The principle behind this method is as follows: in an acidic solution, pentavalent arsenic is reduced to trivalent arsenic through the action of potassium iodide and stannous chloride; subsequently, the trivalent arsenic is reduced to arsine by zinc and nascent hydrogen produced during sulfuric acid production. HsAsO4 + 2KI + H2SO4 → HsAsO3 + I2 + K2SO4 + H2O
HsAsO4 + 3Zn + 3H2SO4 → AsH3 + 3ZnSO4 + 3H2O
The hydrogen arsenide produced is absorbed by a diethyl dithiocarbamate-triacetamidine-chloroform solution and reduced to form red colloidal silver: AsH3 + 6Ag → 6Ag+ + 3HDCC + AsS. If the sample contains substances that are easily reduced, the highly reducing nature of atomic hydrogen will cause these substances to be reduced, thereby affecting the accurate determination of arsenic. In sulfuric acid industrial wastewater, factors such as excessively low flue gas temperature or low temperature of the dilute acid lead to an increased solubility of sulfur dioxide in the wastewater, thereby raising the concentration of sulfurous acid. As a result, during testing, sulfite ions are easily reduced to S2- (SO2-3+6→S2-+3H2O), causing interference. Based on the above preliminary analysis, when the sulfide content in sulfuric acid industrial wastewater is not high but the sulfite concentration reaches a certain level, it can also cause lead acetate cotton to turn black or even become ineffective, thereby interfering with sample testing. Furthermore, since sampling at the pollution source is done instantaneously, and sometimes the wastewater from the purification unit is kept in a closed loop and not discharged during sampling, there is no interference when measuring arsenic ； And if cyclic dilute acid emissions occur, interference from sulfite ions may arise. 3 Experimental Section Reagents: 1% Na2SO3 ； For the rest, refer to the reagents specified in GB7458-87 of the \"Standards for Methods of Water Environment Analysis\". Experiment 1: Interference of sulfite in arsenic determination. Experimental method: To a series of blank samples, 0.5, 1.0, 1.5, 2.0, 5.0, and 10 mL of 1% Na2SO3 solution were added respectively, and the reaction was carried out following the same steps as those used for arsenic determination; the results are shown in Table 1. Table 1 Results of the sulfite interference experiment: Amount of 1% Na2SO3 solution in mL – 0, 0.5, 1, 2, 5, 10. Changes in lead acetate cotton: No change, partially blackened, mostly blackened, almost completely blackened, completely blackened, completely blackened. Experiment 2: Determination of samples containing sulfites using sulfuric acid-nitric acid digestion. (1) Pretreatment: Take 50 mL of the water sample to which 1 mL of Na2SO3 has been added, place it in a hydrogen arsenide generation flask, add a few glass beads, then add 4 mL of concentrated sulfuric acid and 5 mL of concentrated nitric acid. Boil the mixture on an electric hot plate inside a fume hood until large amounts of white sulfur trioxide smoke are produced and the solution becomes clear. After cooling, carefully add water to bring the volume to 25 mL, then heat again until large amounts of smoke are emitted to remove all remaining nitric acid. Once cooled again, add water to reach a volume of 50 mL for later use. (2) Determination: In the hydrogen arsenide generation bottle, add 4 mL of arsine iodide and shake well; then add 2 mL of stannous chloride solution and mix again. Allow to stand for 15 minutes. Transfer 5 mL of the absorption solution into an absorption tube and insert a gas guide tube into it. Add 4 g of arsenic-free zinc granules to the hydrogen arsenide generation bottle, and immediately connect the gas guide tube to the generation bottle to ensure that the reactor is airtight. The reaction was maintained at room temperature for 1 hour to ensure complete release of arsenic. Chloroform was added to bring the volume of the absorbent solution to 5.0 mL. The absorbance of the solution was measured at a wavelength of 530 nm using a 10 mm cuvette with chloroform as the reference; the absorbance value obtained was then subtracted from that of the blank test. The arsenic content in the sample was determined from the calibration curve, and the results are shown in Table 2. Table 2 Results of determination by sulfuric acid-nitric acid digestion 1234 Mean Value Standard Deviation Relative Deviation/% 0.076 0.079 0.070 0.077 0.074 0.00375 Experiment 3: Determination of sulfite-containing samples using potassium permanganate for digestion (1) Pretreatment: Take 50 mL of a water sample to which 1 mL of Na2SO3 has been added, place it in a hydrogen arsenide generation bottle, add several glass beads, and add potassium permanganate solution until a slight pink color appears. Boil for several minutes; if the red color fades, continue adding potassium permanganate solution until the slight pink color remains unchanged. (2) Determination: The method is the same as that used in Experiment 2; the results are shown in Table 3. Table 3 Results of determination by potassium permanganate digestion method 1234 Average Value Standard Deviation Relative Deviation/% 0.069 0.073 0.070 0.072 0.071 0.0018 2.5 Experiment 4: Waste water samples from the sulfuric acid production plant were treated with potassium permanganate and compared with those that were not treated. Wastewater samples from Feiyan Chemical Co., Ltd. were taken for preliminary qualitative testing; they contained a certain amount of sulfite. 25 mL of these water samples were taken and diluted to 50 mL. Oxidation treatment with potassium permanganate was carried out on some of these samples, while others were left untreated. The methods used were the same as those described earlier; the specific results are shown in Table 4. Table 4 Comparison Table of Analysis Results for Sample Treatment Methods. Pretreatment method, Arsenic content/(mg·L-1), Average value/(mg·L-1), Relative deviation/%: Untreated treatment: 0.124, 0.130, 2.62; 0.132, 0.133. Treatment with potassium permanganate: 0.139, 0.137, 0.135. Results and Discussion: (1) When sulfite is present in sulfuric acid industrial wastewater samples, it can interfere with the determination of arsenic. When the sulfite concentration exceeds 190 mL/L, it causes severe interference with the determination of arsenic, making it impossible to measure it. (2) When the sulfite concentration in sulfuric acid industrial wastewater is high, pretreatment is necessary. (3) When preprocessing samples for arsenic determination, using sulfuric acid and nitric acid for digestion results in a complex procedure; moreover, this digestion process generates harmful gases such as nitrogen oxides and sulfur dioxide, leading to secondary pollution. Therefore, in the case of interference solely from sulfite ions, it can be simply treated using the potassium permanganate oxidation method, with fairly satisfactory accuracy. 5 Some experiences: (1) In the production of sulfuric acid, the pH level of the wastewater has a significant impact on arsenic levels. When the pH of the wastewater rises to 6, the arsenic content decreases significantly; when the pH reaches 8–9, the removal rate of arsenic from the wastewater can exceed 99.5%. (2) When determining arsenic, the dirt in the capillary of the gas guide tube is difficult to remove; it can be cleaned with blank chloroform. After drying, it can be rinsed once with a small amount of anhydrous ethanol after being cleaned, and then it can be used. References 1 **Department of Scientific and Technical Standards, Environmental Protection Agency. Standard Work Manual for Water Environment Analysis Methods. 1998** 2 **Environmental Protection Agency, Editorial Committee for Methods of Monitoring and Analyzing Water and Wastewater. Methods of Monitoring and Analyzing Water and Wastewater. 4th edition. Beijing: China Environmental Science Press, 2003** 3 Liu Shaowu, Zhao Shuqi. Purification of Flue Gas and Absorption of Sulfur Trioxide. Beijing: Chemical Industry Press, 1990. Author: Zheng Weixing, male, born in 1973, bachelor’s degree, engineer; mainly engaged in work related to environmental monitoring and environmental impact assessment.

Some companies also use a method of first carrying out sulfidation and precipitation followed by neutralization; the resulting arsenic filter cake is then processed to produce products such as copper arsenate or arsenic trioxide.

Why doesn’t the original poster consider resin adsorption? Those interested can contact 15951777817@163.com

These seem to be problems that every company faces

The acid is concentrated to a certain concentration, and arsenic ions are removed from it using chemical methods; it is then used as a raw material for further processing of arsenic, while the waste acid is recycled as a chemical raw material. Reduce the tonnage-based pollution caused by calcium slag and iron salt slag.

To deal with the sulfide (arsenic) slag generated by copper smelting systems, one can adopt the treatment methods used by Jiangxi Copper Industry. Arsenic can be produced in the form of arsenic trioxide, and valuable metals such as copper, bismuth, and rhenium can also be recovered from this sulfide-arsenic slag. The acid obtained after arsenic removal from the sulfides can further have fluoride and chloride removed from it and then concentrated to produce sulfuric acid that can be used in various industries!

Do you know anything about Jiangtong’s acid treatment system on the upper floor? Are there detailed operating parameters? In particular, can copper and arsenic be separated during the sulfidation precipitation process?

Enough with the bragging; these techniques can only be seen in databases, and doing this probably results in total losses

I can recover arsenic trioxide in a hydrochloric acid system