Pilot and full scale plant trials using thiourea enhanced Zadra stripping of activated carbon

Bench scale tests have been carried out to determine ways of improving the relatively slow kinetics of elution of gold from activated carbon. These indicate that a solution of 3.0 wt% thiourea, 2.0 wt% NaOH and 0.05 wt% NaCN represents the best prospects for greatly improved throughout in industrial cells. This paper presents the results of pilot plant trials of this solution. Pilot plant results reflected the results obtained in the laboratory and encouraged the subsequent introduction of the solution as a modification to the commercial Zadra plant operation. Although the initial plant trials were disappointing slight modifications to allow for staged additions of the NaCN and increased flow rates did result in significant improvement in the elution rates. This improvement in the kinetics of elution is reflected in the overall recovery and consequently in the throughput rates for the plant.