| A massive amount of arsenic-alkali residue（AAR）is produced in the antimony smelting process every year,which has caused serious environmental pollution.In this study,a novel roasting process for antimony sulfide concentrate is proposed,in which arsenic is retained in the slag at low temperature,and antimony is volatilized to soot at high temperature.This study aims to effectively immobilize arsenic at the source of antimony smelting and significantly reduce the amount of arsenic in the refining process of crude antimony.The main research details and conclusions are as follows:（1）Thermodynamic calculations was performed to clarify the phase transformation mechanism in the roasting process.The results show that the volatile roasting of antimony sulfide concentrates should be carried out at a low oxygen concentration and high temperature.In the absence of Ca O,arsenic is volatilized into the soot along with antimony.In addition,the amount of calcium compounds exerts an essential effect on the mechanism and products of arsenic fixation.Furthermore,the low temperature is favorable to the arsenic fixation reaction.The sulfur,antimony,and arsenic all react with Ca,and the reaction priority of the three（sulfur,antimony,arsenic）with Ca changes with the oxygen concentration.Meanwhile,calcium compounds also exert a effect on the volatilization of antimony.（2）The effects of roasting atmosphere,temperature,material size,and roasting time on the volatilization efficiency of antimony were studied in700-900℃.The results show that the roasting atmosphere and temperature exert an essential effect on the volatilization efficiency of antimony.The difficult-to-volatilize Sb2O4 and Fe Sb2O6 are generated at oxygen concentrations higher than 5 vol.%,which leads to the loss of antimony in the slag.The Volatile efficiency of antimony at the optimized conditions(W（O2）≤5 vol.%、T=800℃)is 96.28%,the retention efficiency of arsenic is 2.03%.（3）The Coats-Redfern kinetic model and TG-DSC testing were applied to study the kinetic behavior of the roasting process of antimony sulfide concentrate.The results show that the kinetic control steps of the roasting process can be divided into three types:chemical reaction control（440-490℃）,internal diffusion control（500-550℃）,and chemical reaction control（560-580℃）.The activation energies of the three stages are 16.40-18.79 k J·mol-1,120.86-195.96 k J·mol-1,and 24.00-28.31k J·mol-1,respectively.The oxidation reaction of antimony sulfide concentrate occurs mainly in two stages:490-530℃and 560-580℃.（4）The effects of roasting atmosphere,temperature,time,and Ca O amount on the volatile efficiency of antimony and retention efficiency of arsenic were studied in 300-550℃.The results show that,the retention of arsenic and volatilization of antimony by the two-step roasting process is feasible in the presence of Ca O.In this process,arsenic is transformed into arsenate that stayed in the slag,while antimony is volatilized as Sb4O6.The roasting atmosphere and Ca O dosage exert essential effects on the roasting process.The efficiency of antimony volatilization and arsenic retention is93.06%and 70.12%at optimized conditions(W（O2）=5 vol.%、T=450℃、t=75 min、W（Ca O）=10 wt.%).（5）Sulfuric acid&nitrate acid method,horizontal vibration method,seawater leaching method,and TCLP method were employed to discriminate the thorny toxicity of roasting slag.The results show that the leaching amount of all metal elements in the slag does not exceed the standard value,so the roasted slag is not a hazardous waste.Furthermore,the leaching concentration of arsenic in the roasted slag at different leaching methods is less than 5 mg·L-1,which is far lower than that in AAR(915 mg·L-1).This work tries to reduce the generation of AAR at the source of antimony smelting.And these findings provide a novel insight to mitigate the arsenic contamination caused by antimony smelting. |
