Recovery and separation of palladium from spent catalyst

Abstract

An efficient and complete separation of precious metals from the containing secondary materials has a vital economic impact. Palladium loaded on alumina carrier is usually used as a catalyst in fertilizers industry where the recovery of the metals from the spent catalyst is practically important. Palladium was partially dissolved from the spent catalyst in hot concentrated hydrochloric acid where a large amount of aluminum is also dissolved. The main objective of this work is to find out the optimum conditions for efficient dissolution of palladium with minimum attack to the alumina carrier. Palladium can form different soluble chloro-complexes which can enhance the dissolution process if an oxidizing agent is added. We interestingly found that, when dilute hydrochloric acid is used, a small amount of hydrogen peroxide could greatly improve the dissolution of palladium while the alumina carrier was left nearly unaffected. Complete dissolution of palladium was achieved by leaching with a solution contains 7 % hydrochloric acid and 5 % hydrogen peroxide at 60°C for 2 hours with a liquid/solid ratio of 10/1. The leach liquor contained 0.04 % palladium and 0.5% aluminum and the filtered solids was a pure aluminum rich residue. Palladium could be separated from the leach liquor by reduction with formic acid which does not contaminate the solution. Heating the solution increased the efficiency of palladium reduction and also produced larger palladium particles those can be easily separated by filtration. Palladium powder of 98% purity was produced with efficiency > 99 %.