Investigations into high temperature separation of antimony from metal oxide varistors

Very little research has been done into methods for recycling antimony from end of life products. This study investigates separation of antimony from metal oxide varistors (MOVs), where antimony is present between 3 and 5 wt%. In MOVs, antimony is found in spinel (Zn2.33Sb0.67O4, Zn7Sb2O12) and pyrochlore (Zn2Bi3Sb3O14) compounds. Due to the low concentration of antimony in MOVs, a leaching pretreatment using dilute sulfuric acid was performed where antimony remained in an insoluble solid. The leaching pretreatment resulted in a more than fivefold increase in the antimony concentration. In order to separate antimony from the MOV leaching residue, it was subjected to a simple thermal treatment and carbothermal reduction at temperatures of 500-1300 °C. Results showed that 80% of antimony can be separated from the leach residue by heat treatment at 1100 °C, while 85% of antimony can be separated from the leach residue at 1100 °C using carbothermal reduction. Once separated, antimony can be recovered from the gaseous phase due to its volatile nature. Results show that antimony recycling from MOVs is a promising source of secondary antimony.