Fundamental Study of Palladium Recycling Using “Dry Aqua Regia” Considering the Recovery from Spent Auto-catalyst

Abstract

In this research, a recycling process for palladium using “dry aqua regia,” which consists of iron(III) chloride–potassium chloride, was proposed. Palladium was dissolved in “dry aqua regia,” and the dissolved palladium was recovered by leaching with potassium chloride solution with added ammonium chloride and nitric acid. Palladium was almost completely dissolved in 3 h at 600 K, and the recovery ratio of dissolved palladium was up to 80%. In addition, the dissolution of palladium in coexistence with platinum and the dissolution of platinum-palladium alloy by “dry aqua regia” were also tested. The dissolved palladium and platinum were separated and recovered by solid–liquid separation technique using the difference in solubility of their compounds in potassium chloride and sodium chloride solutions. As a result, pure compounds of each element were recovered. This result suggested the possibility of using “dry aqua regia” for the separation of platinum-group metals. Graphical Abstract

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

“…10,21) In our previous study, we successfully recovered platinum and palladium. 15,16) In this study, we have applied the same procedure for iridium recovery.…”

“…Considering these challenges, we proposed a mixture of iron chloride (III) (FeCl 3 ) and potassium chloride (KCl) as a novel "dry aqua regia". 15,16) The dry aqua regia can chlorinate and dissolve platinum or palladium directly, and the dissolved platinum and palladium were recovered as high-purity compounds via precipitation using ammonium chloride. This process can be used to treat platinum and palladium under milder conditions than conventional processes.…”

“…In addition, platinum and palladium can be separated by simple solid-liquid separation in cases of simultaneous or alloy treatment. 16) Complex and multistage procedures using solvent extraction are used in the case of conventional treatment of multiple elements. 17) The procedure using "dry aqua regia" can simplify the process and is expected to reduce the environmental impact.…”

Environmental Impact of Remanufacturing Mining Machinery

“…The environmental load of the cleaning process has been further reduced by developing and using a cleaning method [29]. In addition, if remanufacturing or direct reuse is not possible, a new value can be created by reusing the components among different industries, such as automotive lithium-ion batteries, catalysts, and smartphones, which can make a significant contribution to the circularity of resources [30][31][32].…”

Noble Metals Dissolution Catalyzed by [AlCl4–]-Based Ionic Liquids

“…The concept of green and recyclable development is currently the main focus of modern academic society. Clearly, the recycling of noble metals such as gold (Au), palladium (Pd), and platinum (Pt), important metals for jewelry, coins, and other industrial applications, is an important part of such development. − These metals are essential for sustainable applications as active sites of numerous catalysts used in various industrial areas, but their limited reserves and production monopolies in certain countries have restrained their large-scale use in practical industries . The dissolution of noble metals from secondary resourcescatalysts in this caseis necessary for the recyclable use of noble metals.…”