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Treatment method of arsenic-containing wastewater

by:BOQU     2023-03-15
When it comes to arsenic-containing wastewater, it mainly comes from the mining and smelting of arsenic and arsenic-containing metals, the production of glass, pigments, technical materials, paper, and coal combustion that use arsenic or arsenic compounds as raw materials. In this paper, manufacturers of online water quality monitors come to learn with you the treatment methods of arsenic-containing wastewater, and how to monitor its content to ensure water quality and arrange discharge! Treatment method of arsenic-containing wastewater 1. Lime method is generally suitable for acid wastewater with high arsenic content. Adding milk of lime reacts with arsenate or arsenite ions to form insoluble precipitates of calcium arsenate or arsenite. The wastewater is mixed with milk of lime for precipitation. When the dosage of milk of lime is appropriate and the reaction is complete, the quality of the effluent can reach the secondary standard for comprehensive sewage discharge (GB8978-88). The advantage of this method is that the operation unit is low and the cost is low; the disadvantage is that the amount of sediment is large, the treatment effect on trivalent arsenic is poor, and it is easy to cause secondary pollution. 2. The lime-iron salt method can generally be used to treat wastewater with a low arsenic content and a pH value close to a neutral or weakly alkaline wastewater. The use of arsenate and arsenite can form stable complexes with metals such as iron and aluminum, and it has an adsorption time for the hydroxides of metals such as iron and aluminum to precipitate and remove arsenic. when pH> At 10, arsenate, arsenite and hydroxyl are replaced, so that part of arsenic is soluble in water, so it is best to control the end point at pH< 10.3. Vulcanization method Under acidic conditions, arsenic exists in the form of cations. After adding a vulcanizing agent, an insoluble AS2S3 precipitate is formed. The content of arsenic in wastewater can be reduced to below 0.05 mg/L by sulfidation. However, sulfide precipitation must be carried out under acidic conditions, otherwise the precipitate is difficult to filter, and the excess sulfide ions in the supernatant need to be treated before they can be discharged. 4. The pyrolusite method uses the pyrolusite method (natural manganese dioxide) to oxidize trivalent arsenic to pentavalent arsenic, and then add milk of lime to generate manganese arsenate precipitation, namely: H2SO4+MnO2+H3AsO3→H3AsO4+MnSO4 +H2O3H2SO4+3MnSO4+6Ca(OH)2→6CaSO4↓+3Mn(OH)2+6H2O3Mn(OH)2+2H3AsO4→Mn3(AsO4)2↓+6H2O Specific working method: the wastewater is heated to 80°C and aerated 1h, then add ground pyrolusite powder to oxidize for 3h, finally add 10% milk of lime, adjust the pH value to 8-9, settle for 30-40min, the arsenic in the effluent water quality can be reduced to below 0.05mg/L. 5. Comprehensive recovery method At present, many mines are evaporating, concentrating, crystallizing, and centrifuging dehydrating waste water containing arsenic to obtain sodium arsenate, that is, the comprehensive recovery process. This treatment measure not only reduces the arsenic pollution in the water environment, but also turns harm into benefit, and has certain economic benefits. In addition to the above methods, some mines use phosphate method to remove arsenic, some mines use activated carbon and activated aluminum to absorb arsenic, some mines use reverse osmosis method to remove arsenic, and ion exchange method to remove arsenic, and the effect is also very good. So how to monitor the content of arsenic in wastewater to see if it meets the standard? The arsenic online analyzer in water can be used for this work. The instrument uses optical colorimetry to perform the operation. The working principle is that after the sample is filtered, it is pumped into the reactor, and the reducing agent is first injected to reduce the pentavalent arsenic to trivalent Arsenic; then add a gas generating agent to convert the arsenic to be measured into gas and be expelled, the expelled arsenic-containing gas is absorbed by the solution in the colorimetric cell, after absorption, the arsenic-containing gas and the absorption liquid undergo a color reaction, the analyzer according to the solution The color of the solution is used to calculate the absorbance of the solution, and then the concentration of total arsenic in the sample is calculated according to the stored correction factor.
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