Effect of O2, H2 and CO pretreatments on leaching Rh from spent auto-catalysts with acidic sodium chlorate solution

Rh extraction from spent auto-catalysts in an efficient and economical way is still an unresolved problem. In this work, the spent auto-catalyst samples were pretreated with O2, H2 and CO under certain temperatures. After the pretreatments, the samples were leached with acidic sodium chlorate solutions to extract Rh. The Rh extraction for the sample without any pretreatment was 56%. The optimal temperature, time and flow rate of O2 for the O2 pretreatment were 300 °C, 3 h and 200 mL/min, respectively, and the Rh extraction under these conditions was 69%. Following O2 pretreatment under optimal condition, H2 or CO pretreatment was also carried out, respectively. The optimal temperature, time and flow rate of H2 for the H2 pretreatment were 300 °C, 3 h and 200 mL/min, respectively, and the Rh extraction in this case was 82% . The optimal temperature, time and flow rate of CO for the CO pretreatment were 300 °C, 1 h and 150 mL/min, respectively, and the Rh extraction in this case was 80% . In addition, the effects of pretreatment with H2 and CO only on Rh extraction were also studied. It was found that pretreatment with O2 only was more effective than pretreatment with H2 and CO only, and O2 pretreatment plus a following H2 pretreatment was the most effective means to raise Rh extraction. Additionally, the possible mechanisms involved in pretreatment effects were also investigated.