Rhodium recovery from automobile exhaust catalyst leaching solution in the process of cementation by copper powder

Rhodium pertains to the platinum-group metals (PGM) and has a special catalytic activity to reduce nitrogen oxides (NOx) to N2. Hence, more than 80% of total rhodium demand is now used for the production of autocatalysts. As regards, rhodium is one of the rarest elements in the earth's crust and its natural resource deposits are strictly limited, so, their recycling process from secondary resources must be considered. In this study, car exhaust catalyst, in the presence of HNO3 and HCl was dissolved by the leaching process. All species and rhodium complexes formation were analyzed by Phreeqc software. The recovery of rhodium from leach solution containing Mg, Mn, Pb, Ni, Fe and Al was done through cementation with metallic copper powder. At an ambient temperature, a stirrer speed of 150 rpm, a stoichiometric ratio of Cu to Rh 15 and at a time of 240 minutes about 70% of rhodium on copper powder particles were recovered. By increasing the temperature to 60 ° C, the rate of recovery increased up to 95 percent and cementation of rhodium was shown to be a feasible process to achieve a high degree of rhodium recovery. Analysis SEM / EDAX confirmed rhodium formed in the presence of copper by the dendritic and multi-layer structures with a purity of 87 percent rhodium.