Recovery of platinum-group metals from spent catalysts by microwave smelting

The feasibility of a facile route to recover platinum-group metals (PGMs) from spent catalyst by microwave smelting of spent catalyst with the additions of nickel matte as metal collector and sodium salts as fluxes was verified, based on the thermodynamic and experimental analyses which evaluated the dielectric properties, conductivities/resistances and viscosities of the materials involved in the smelting process. The results showed that the combined use of sodium salts reduced the viscosity and smelting temperature effectively by breaking the silicon-oxygen tetrahedron structure which facilitated the collection of PGMs and the separation of PGMs-enriched nickel matte from smelting slag. In association with the eddy current loss and swirling sedimentation effect produced by microwave heating, 98.59% of Pt, 97.91% of Pd and 97.16% of Rh were collected under the optimal smelting conditions of the mass ratios of nickel matte, Na2B4O7 and Na2CO3 to spent catalyst of 1.25, 0.575 and 0.125, respectively, temperature of 1250 degrees C, time of 2 h, and N-2 atmosphere. This new strategy enabled rapid collection of PGMs from spent catalyst at the low temperature within a short time, contributing to energy conservation and environmental protection.