Preliminary study on PGM leaching from used autocatalytic convertors using AlCl3 and HOCl

Collins Saguru, Sehliselo Ndlovu

The use of the platinum group metals (PGMs) as catalysts in exhaust lines of fossil fuel engines to reduce the amount of toxic gases emitted by the engines has been growing. This increase has consequently resulted in a simultaneous demand for PGMs and an alternative ever-growing source of PGMs in end-of-life autocatalytic convertors. Pyrometallurgical recycling of PGMs from autocatalytic convertors has enjoyed a relatively high industrial adoption; however the challenges associated with this approach necessitate a new and better recycling option.

This study was therefore aimed at developing a hydrometallurgical leaching process route, which has a minimal environmental footprint, to be applied in the recovery for platinum, palladium and rhodium from used autocatalytic convertors. Consequently platinum (Pt), palladium (Pd) and rhodium (Rh) were leached using a chloride solution under acidic, oxidizing conditions.

The lixiviant solution used consisted of aluminium chloride (AlCl3) as the source of chloride ions and proton donor and of dissolved calcium hypochlorite (Ca(OCl)2) as the oxidant. Maximum leaching efficiencies of 15 %, 78 % and 86 % for Rh, Pt and Pd respectively were obtained. Response surface analysis of data from the full factorial CCD was used to describe and illustrate the effects of temperature, AlCl3 and Ca(OCl)2 concentrations on individual Pt, Pd and Rh leaching efficiencies. A statistical model describing the effect of the three factors on the leaching efficiency has been drawn up.