Rhodium recovery from rhodium-containing waste rinsing water via cementation using zinc powder

The present work proposes the recovery of rhodium from rhodium-containing waste rinsing water through cementation with metallic zinc powder. The effects of zinc content, reaction temperature, reaction time and shaking on rhodium recovery are investigated in detail. In addition, the cementation kinetics of rhodium is studied, and its activation energy was found to be 30 kJ/mol. After a detailed observation of the dissolution behavior of the zinc powder during the cementation process, it is demonstrated that most of the zinc is preferentially consumed by free acid, a finding corroborated by pH measurements. The proposed process is simple, straightforward and economically feasible.

Research Highlights
► The rhodium in waste rinsing water can be recovered via cementation with zinc powder.
► Ten times the stoichiometric amount is not enough to recover all of the rhodium.
► Zinc is consumed by the free acid in the solution.
► Solution pH approaches to neutral due to zinc dissolution in the acidic solution.