Study On Separation And Recovery Of Arsenic And Antimony From Arsenic Alkali Residue By Calcification Transformation And Carbon Reduction

Arsenic alkali residue is a hazardous solid waste generated during the antimony refining process.Currently,China has stockpiled over 200,000 tons of arsenic alkali residue,which contains a substantial amount of highly toxic sodium arsenate that easily dissolves in water,as well as antimony and alkali with high utilization value.However,this waste not only leads to the squandering of valuable resources but also poses a significant threat to the surrounding environment.The traditional wet process has limited processing capabilities due to the similarities between arsenic and antimony in the residue.Consequently,it becomes challenging to separate and enrich arsenic,antimony,and alkali.The fire process is the optimal solution for large-scale arsenic alkali residue treatment.Nevertheless,the direct reduction of arsenic alkali residue leads to the wrapping of molten sodium salt,resulting in ineffective arsenic-antimony reduction and separation.To improve the reduction rate and separation of arsenic-antimony in arsenic alkali residue,a short process of"calcification phase transition arsenic fixation-step reduction fine control separation of arsenic-antimony"was adopted.This process effectively enhances the reduction and separation of arsenic-antimony by calcification transition.The findings of this study are as follows:Thermodynamic calculations were used to analyze the choice of calcifying agents and reduction pathways of calcified slag for arsenic alkali residue calcification.The study aimed to support the investigation of the calcification transition of arsenic alkali residue and carbon thermal reduction process of calcified slag.The results showed that Ca Cl₂ can effectively calcify sodium arsenate and sodium antimonate in arsenic alkali residue at temperatures up to1000℃.In contrast,Ca O requires CO₂ participation,while Ca（OH）₂ has difficulty in calcifying arsenic alkali residue.The carbothermal reduction reaction of calcium slag was analyzed,revealing that it does not undergo direct decomposition up to 1500℃.When the calcified slag reacts with carbon powder,calcium arsenate is reduced to calcium arsenite and further to produce arsenic vapor volatilization.Meanwhile,calcium antimonate is directly reduced to antimony vapor volatilization.the carbothermal reduction of calcified slag generates gaseous monomers of arsenic and antimony in the form of As₄（g）and Sb₄（g）,respectively.As₄（g）requires temperatures below 600℃to condense into solids,facilitating the separation of arsenic and antimony monomers during reduction.In summary,this study provides insights into the calcification transition of arsenic alkali residue and carbon thermal reduction process of calcified slag.The choice of calcifying agents significantly impacts the calcification process of arsenic alkali residue.The carbothermal reduction pathway of calcified slag was elucidated,and the separation of arsenic and antimony monomers during reduction was highlighted,providing guidance for practical applications.Based on the results of thermodynamic analysis,an experimental study was conducted to investigate the calcification transformation of arsenic alkali residue from antimony smelting.The results demonstrated that the calcification effect of arsenic alkali residue was significantly influenced by the type of calcifying agent used,as well as the reaction temperature,reaction time,and calcium addition amount during the calcification process.In this experiment,Calcifying sodium arsenate and sodium antimonate with calcium oxide as the calcifying agent,the calcification rate of sodium antimonate reached 95.35%at 900℃,2 h reaction time,180m L/min CO₂ flow rate,and 0.32 calcium-to-dross ratio.In comparison,the calcification rate of sodium arsenate only reached 75.57%under more favorable conditions.Meanwhile,using calcium chloride as the calcifying agent,the calcification rate of sodium arsenate and sodium antimonate in the arsenic alkali residue reached 99.67%and 98.74%,respectively,under the conditions of a reaction temperature of 1000℃,reaction time of 120 min,and a mass ratio of calcium chloride to arsenic alkali residue of 0.5.These conditions effectively achieved the desired calcification effect.X-ray diffraction analysis of the calcified slag indicated that the main physical phases in the slag were Ca₅（As O₄）₃Cl and Ca₂Sb₂O₇.An experimental study was conducted to investigate the preparation of arsenic and antimony metals through carbon thermal reduction of calcined slag at high temperature.Using optimal reduction conditions of N₂ gas as the protective gas,950℃reaction temperature in the reduction zone,120 min reaction time,and 0.16 mass ratio of carbon powder to calcined slag,the reduction rate of arsenic and antimony reached 99.55%and 99.13%,respectively.By adjusting the condensation temperature in the condensation zone of the three-temperature tube furnace and the vacuum of the reaction system during the reduction process,the arsenic and antimony were initially separated and purified.The purity of collected arsenic was 99.26%and the purity of antimony was 98.87%at a condensation zone temperature of 400℃and a vacuum of 200 Pa.The collected arsenic and antimony metals were further purified using a vacuum distillation process,resulting in both elements obtaining a purity level exceeding 99.8%.