Recovery of rare earths and precious metals from waste electrical and electronic equipment by acid leaching and immobilized chelating agents

A natural smectite mineral clay (STx-1b) was modified by intercalating different concentrations of Pentaethylenehexamine (PEHA) with the final aim of synthesizing new solid materials for the recovery of valuable metals, in particular Rare Earths (REs), from Waste Electrical and Electronic Equipment (WEEE). The modified clays were then contacted with a model solution of Lanthanum (chosen as representing element of REs family). Finally, release tests were performed on the different samples in order to verify the organo-clay capability not only to capture but also to recover metal ions. The results showed that the experimental procedure was appropriate to intercalate the polymer in the clay for every initial polymer concentration considered. Furthermore, the obtained organo-clays were effective in both uptake (efficiencies up to 99 %) and release processes (efficiency around 80 % contacting with acid solutions). The organo-clay system with polymer content of 0.4 mmolpolymer/gclay was selected as that of choice to guarantee the highest global process efficiency, ensuring a Lanthanum recovery of 80 %. The adsorbed and released metal ions were calculated by ICP-OES while the amounts of intercalated polymer were estimated by COD (Chemical Oxygen Demand) analysis of the residual amounts in solution and deduced by difference. All the solid materials were characterized by X-ray diffraction (XRD)