Technological Study Of Preparation Of As₂O₃ From Arsenic-containing Waste Residue By Alkali Leaching

Currently,the arsenic sulfide residue with high content of arsenic(40?50%),which is generated in the purification process of phosphoric acid production,has not been properly treated.To promote the comprehensive utilization of arsenic resource,reduce the pollution of arsenic residue on environment,and eliminate the hidden trouble of arsenic pollution,a new technology was developed on the basis of previous studies and comparative analysis.In this paper,arsenic was recovered from arsenic sulfide residue to produce As2O3 product by alkaline leaching-oxidation-reduction process with using NaOH as leaching agent,air,oxygen or H2O2 as oxidant,and SO2 as reductant.Combined with practical industrial application,the influences of different factors on evaluating indexes of alkaline leaching,oxidation and reduction processes were studied respectively with a single factor experiment method.By the discussion and analysis for experiments,the results were obtained as follows:(1)The arsenic could be recovered from arsenic sulfide residue for producing As2O3 product by the process of alkaline leaching-oxidation-reduction.(2)Using NaOH solution as leaching agent,the optimum conditions of this process were determined as leaching temperature 70?,molar ratio of NaOH/As2S3 of 6.0:1,liquid to solid ratio of 6.0:1,reaction time 30 min.Under these conditions,the arsenic leaching rate could reach 97.1%.(3)Using air as oxidant,the optimum conditions of the oxidation process were determined as oxidation temperature 30?,oxidation time 12 h,air flow of 120 L/h and hydroquinone dosage of 1.5 g/L.Under these conditions,the sulfur yield could reach 54.71%.Using Oxygen as oxidant,the optimum conditions of the oxidation process were determined as leaching temperature 30?,reaction time 6 h,oxygen flow of 60 L/h and hydroquinone dosage of 1.5 g/L.Under these conditions,the sulfur yield could reach 56.52%.Using H2O2 as oxidant,the optimum conditions of the oxidation process were determined as oxidation temperature 30?,oxidation time 1 h,H2O2 dosage of 150 mL/L.(4)Using SO2 as reducing agent and the desulfurizing liquid oxidized by air for the investigation of reduction process,the optimum conditions of the reduction process were determined as pH=0,reducing time 2 h,reduction temperature 30?and arsenic concentration of 66.55 g/L.In these conditions,the one-time crystallization rate of HAsO2 was 76.58%,and As2O3 content in the dried product was 99.93%.(5)Under the optimized conditions,the quality of As2O3 products reached first-grade(As2O3-1)by using air and oxygen as the oxidant,and the quality of As2O3 products reached second-grade(As2O3-2)or third-grade(As2O3-3)by using H2O2 as the oxidant.The selection of oxidants was the key to whole reaction process,it could be determined according to the factory needs and product quality standards.