Platinum recycling through electroless dissolution under mild conditions using a surface activation assisted Pt-complexing approach

Abstract

High industrial demand and limited global abundance of precious metals (PMs) make their recycling essential for industrial and societal sustainability. Owing to their high surface-to-volume ratio, recycling of nanoparticulate precious metals through dissolution in dilute acids at room temperature is quite relevant. However, their dissolution by approaches such as the cyclic oxidation–reduction of metal surfaces through surface potential manipulation may not be suitable for large-scale production. Here, we demonstrate fast dissolution of Pt-nanoparticles under mild conditions (normal temperature and pressure) in Cl⁻ containing dilute acidic/neutral baths without using cyclic oxidation–reduction. We demonstrate that the dissolution of Pt nanoparticles through [PtCl_x]²⁻ complexing is hindered by blockage of the Pt surface due to adsorption of non-oxide species (impurities), a phenomenon termed herein as non-oxide passivation (NOP). The nanoparticles can be kept active for the [PtCl_x]²⁻ complexing through removal of the adsorbed species by surface activation, a process to remove the NOP layer by application of cyclic/continuous perturbation. As an example, average % dissolution rate (calculated on initial Pt loading) increases from ∼10% per h (∼30% dissolution in 3 h) for dissolution without NOP removal to ∼19% per h (∼55% dissolution in 3 h) for dissolution through cyclic activation of the Pt surface by HCl–water cycling. The approach may be implemented with a range of cost-efficient and non-toxic reagents for industrial-scale and environmentally friendly recycling of Pt.