Target Recovery Of Precious Metals From Waste And The Application Of Ion Exchange In The Leaching Process

The decrease in mineable precious metals (PMs) causes the increase in price and growing awareness of environmental sustainability has been a driving force into the advancement into recovery and recycling. A major point of interest is developing an environmentally sustainable system recovering PMs from waste or other competing metals. Development into more sustainable methods introduced the use of ion exchange resins with resins showing affinity towards PMs. In recent years, the research into deep eutectic solvents (DES), a more benign lixiviant, has grown immensely. Combining the resins with DES, this method has the potential to recover PMs more sustainably.
Five different ion exchange (IX) resins, Purolite® A200, Lewatit® MonoPlus TP 214, Puromet™ MTS9140, Dowex™ M-4195 and Lewatit® VPOC 1026, were screened for their affinity towards gold from a simulant pregnant leach solution. MTS9140 and M-4195 was found to have the highest affinity towards gold. These resins were then used in addition to DES to create the new recovery system for PMs recovery. The DES synthesised and investigated were ChCl (choline chloride): ethylene glycol (EG), ChCl: urea (Ur), ChCl: thiourea (TU) and Lactic Acid (lac). DES was used for leaching of rhodium (Rh) and platinum (Pt) from cobalt on a spent catalyst. It was determined that ChCl: Lac, ChCl: Ur and ChCl: TU had the highest affinity towards Rh and Pt. The addition of oxidants, sodium peroxide and Iodine, was investigated with a slight decrease of leaching. The combination of the resins and DES were investigated in resin-in-leach (RIL) and resin-in-pulp (RIP) systems and tested with a range of temperatures 30C -80C. It was determined to be successful via RIL at 60C in combination of MTS9140 and ChCl:Lac, with RIP also showing high recovery of Rh and Pt from cobalt.