Two-step method for recovering dispersed noble metals

Abstract

A two-stage method of recovering the noble metal content of a mixture of noble metals, for example, platinum, palladium, and rhodium, this mixture being, for example, comprises on or throughout a pellet or on or throughout a ceramic monolith of a spent catalyst, the method comprising first reductive chlorination at an elevated temperature by a gaseous chlorinating agent in the presence of a reducing agent (preferably the reducing agents sulfur dioxide and carbon monoxide in stages); minimizing the amount of aluminum trichloride formed from either washcoat or underlying ceramic chlorination, and separating the aluminum trichloride or other washcoat chlorides from the products of chlorination of the noble metals, as by sublimation of the former in a reducing atmosphere at a temperature below the vaporization temperatures of the latter, thereby recovering the noble metal chlorides in a concentrated form. As a second stage, temperature is further increased in an atmosphere of chlorine alone to volatilize rhodium trichloride for collection seperately from the palladium and platinum chlorides volatilized previously in the first-stage reductive chlorination.

Dependencies are inferred from the claim text.