GB1090294A - Recovery of palladium, platinum and gold - Google Patents

Abstract

At least one of the metals Pd, Pt or Au is recovered from a catalyst comprising at least one of the metals supported in finely divided form on a carrier by dissolving the metal by contacting it in an aqueous medium with HCl and H2O2 at a temperature such that reaction with the metal occurs and below 80 DEG C., separating the catalyst carrier from the resulting aqueous phase containing the dissolved metal and recovering the metal from the aqueous phase. In an embodiment of the process, a slurry of the catalyst is formed in 5 to 70% HCl, the amount of HCl being in excess of that needed to form the salt of the highest valency of the metal or metals present in the catalyst. H2O2 sufficient to give a concentration of from at least 0.1% to 50% in the medium is introduced. The preferred dissolution temperature is 60 DEG to 80 DEG C. The carrier is filtered off when reaction is complete and the metal or metals recovered from the filtrate by conventional methods. If the metal is present as oxide in the catalyst, it is reduced to metal by digestion with aqueous NaOH/formaldehyde prior to applying the process of the invention or, alternatively, by forming a catalyst/HCl slurry and introducing a metal more electropositive than H2, e.g. Al or Zn, into the slurry, which is then stirred prior to introduction of H2O2. In the latter reduction process, the slurry may be filtered after the stirring stage. The recovered solids are then slurried in HCl and H2O2 is added. Specified carriers are silica, silica gel, silica/alumina, sodium aluminium silicate and alumina. Pt or Pd may be recovered by this method from catalysts used in the hydrogenation stage of cyclic anthraquinone-quinol processes for production of H2O2.ALSO:Palladium, platinum or gold is recovered from a catalyst comprising one of these metals supported on a carrier by contacting the catalyst with an aqueous medium containing HCl and H2O2 to dissolve the metal, separating the carrier from Me resulting aqueous phase containing dissolved metal, and recovering the metal from said phase. When the metal is in oxide form in the catalyst, it is reduced to metal form, e.g. by reaction with Al, Zn or an NaOH/formaldehyde solution prior to being reacted with HCl and H2O2. The process is particularly applied to the recovery of Pd or Pt from catalysts used in the hydrogenation step of the anthraquinone-quinol process for the production of H2O2.