Research On Oxidation And Separation Of Sulfur In Arsenic Sulfide Slag

Arsenic sulfide slag（ASS）used in this study is taken from the treatment of wastewater with sulfuric acid contamination in a non-ferrous metals company.Based on the research of ASS oxidation phenomena and the change of elemental sulfur,the effects on the ASS by temperature,water washing and air flow rate had been studied,and it is analysised the reason of ASS oxidation.In order to research the effects on ASS oxidation by oxidant,Hydrogen peroxide（H2O2）,sodium hypochlorite（NaCl O）,potassium permanganate（KMnO4）and ferric chloride hexahydrate（FeCl3·6H2O）had been studied.Base on the conversion rate of sulfur,the paper studies the best oxidation conditions of ASS.By alkaline leaching and extraction of organic compounds,the best separation process of elemental sulfur and arsenic had been studied about ASS after oxidation.The major contents and conclusions are summarized as follows:1)The elemental sulfur does not exist in the new generation of ASS.In the natural environment,there is a redox reaction in part of ASS due to natural factors（oxygen in the air mainly）and generates elemental sulfur and As₂O₃.By changing the temperature,air,water or not,the effects on the efficiency of sulfur ions into elemental sulfur in ASS had been studied.The results show that: When ASS was placed 12 days in the natural environment,the highest efficiency of sulfur ions into elemental sulfur is 61.37 %.Temperature can effectively influence the rate of sulfur ions into elemental sulfur,but influence little on the efficiency of sulfur ions into elemental sulfur.Under the temperature of 60 ℃ and 105 ℃,the efficiency of sulfur ions into elemental sulfur are both 65.18 %,higher than the efficiency in natural environment,the order of factors of influencing the oxidation rate of sulfur ions into elemental sulfur is: 105 ℃ > 60 ℃ > natural environment.When ASS is not washed by water,the rate of sulfur ions into elemental sulfur is faster,and there is smaller influence on the conversion efficiency of sulfur ions into elemental sulfur,the efficiency of sulfur ions into elemental sulfur are both 61.41 %.The increase of air convection velocity is helpful for the oxidation of sulfur ions.2)ASS piled up for long time in the natural environment were continued to be oxidized dy oxidant.Hydrogen peroxide,sodium hypochlorite,potassium permanganate and ferric trichloride are added to oxidize ASS respectively,and the optimal oxidation conditions of sulfur ions into elemental sulfur had been studied.The results show that: Four kinds of antioxidants can effectively oxidize sulfur ions.When Hydrogen peroxide,sodium hypochlorite and ferric trichloride oxidize sulfur ions,trivalent arsenic is not oxidized to pentavalent arsenic,but Potassium permanganate can do so.Sodium hypochlorite,potassium permanganate and ferric trichloride obviously effected the oxidation reaction of sulfur ions,the sulfur ions are oxidized into elemental sulfur,but also generated the forms of sulfate and sulfite.The best conditions are solid-liquid ratio 1:2,H2O2 concentration 18 wt.%.At above condition,the elemental sulfur content of the ASS might increase from 27.8 % to 48.0 %,elemental sulfur oxidation rate might improved from 57.8 % to 99.8 %.3)Arsenic from alkaline leaching of ASS after oxidation in the As-S-NaOH-H2 O system are analysed by thermodynamics.Using the alkali leaching to recovery arsenic and sulfur in ASS after oxidation,the paper discusses the effects of solid-liquid ratio,concentration of NaOH,leaching time and temperature on the leaching rate of arsenic and the recovery rate of elemental sulfur,and found the optimum process conditions of separation of arsenic and the of elemental sulfur from ASS after oxidation.The results show that the best conditions are that solid-liquid ratio 1:20,NaOH concentration 0.3 mol/L,leaching temperature 50 ℃ and leaching time 1 h.Under the conditions,arsenic leaching rate as high as 99.99 %,the recovery rate of elemental sulfur is 78.54%.After leaching liquid evaporation crystallization,the main existence form of the arsenic are NaAsO2 and As2（SO4）3.Based on the similar dissolve mutually theory between elemental sulfur and carbon disulfide and xylene,the samples retrieves by the solid liquid extraction recovery from ASS after oxidation,the recovery efficiency of elemental sulfur was 98.52 % and 90.10 % by carbon disulfur and xylene respectively.The dominant composition of product after separation recycling are As₂O₃ and elemental sulfur.