The effect of tri-sodium citrate on the cementation of gold from ferric/thiourea solutions

The gold cementation by iron powder from thiourea solutions in the absence and presence of ferric ion was investigated. Ferric ion affects significantly the cementation reaction kinetics. The gold cementation without the presence of ferric ion obeys the first-order kinetics and is a diffusion controlled process. Ferric ion increases significantly the redox potential of the solutions, which results in the remarkable decrease of gold recovery. Tri-sodium citrate was used to overcome the negative effect of ferric ion on gold cementation reaction, which is attributed to its role of lowering the redox potential of the solutions with the formation of iron (III)-citrate complexes.