Recycling of platinum group metals from spent auto-catalyst using “dry aqua regia”

Authors
Yoshimura, Akihiro; Matsuno, Yasunari

Abstract
Platinum group metals (PGMs), e.g. platinum (Pt), palladium (Pd), etc., are important for auto-catalyst because of their high catalytic activity and corrosion resistance. Since the production of PGMs is quite energy intensive, the recovery of PGMs from spent auto-catalyst is operated. The conventional hydrometallurgical and pyrometallurgical procedures have challenges in reducing process cost and environmental impacts. Therefore, the authors proposed a novel recycling process of PGMs using “dry aqua regia”, i.e. molten salt consisted of iron chloride (FeCl3) and chloride compound. In this paper, the authors summarize the developments of the recycling process of PGMs using dry aqua regia. First, as the fundamental studies, the dissolution of Pt and Pd using dry aqua regia was conducted at 600-650 K under ambient pressure. The dissolved Pt and Pd were successfully recovered by the addition of ammonium chloride (NH4Cl). Second, Pt-Pd alloy were dissolved in dry aqua regia and recovered. The recovered Pt and Pd were separated from each other using the solubility difference of their compounds in water. Third, the authors applied this process to spent auto-catalyst and confirmed the recovery of Pt and Pd separated from each other. A preliminary LCA was conducted to quantify the energy consumption and GWP of this process. Considering these results, dry aqua regia enables an effective and eco-friendly recovery procedure of PGMs from spent auto-catalyst.