Establishment of a Novel Recycling Process for Iridium Using “Dry Aqua Regia”

Abstract

Iridium is one of the most refractory platinum group metals (PGMs) used in crucibles, catalysts, and ignition tips for spark plugs. Refining and recycling of iridium are energy-intensive processes with high environmental impacts; therefore, a novel recycling process is desirable to expand the utilization of iridium.Previously, we established a novel process for recycling platinum and palladium using "dry aqua regia", which is a molten salt consisting of iron(III) chloride and potassium chloride. This process can recycle PGMs more easily than conventional recycling processes.In this study, we employed "dry aqua regia" for the recycling of iridium. Iridium was dissolved in molten salt and recovered by precipitation using ammonium chloride as the precipitant and nitric acid or hydrogen peroxide as the oxidant. Consequently, it was dissolved by dry aqua regia treatment at 630-670 K, and the dissolved iridium was recovered by precipitation using ammonium chloride and hydrochloric acid with oxidants. The recovery ratio reached 28.3% and 45.7% using nitric acid and hydrogen peroxide, respectively, as oxidants. Based on these findings, we established the fundamental process of recycling iridium using "dry aqua regia".