Development of activated carbon from coffee residue for gold extraction

The activated carbon was prepared from the disposed coffee residue by atmospheric pyrolysis and activated with zinc chloride. The obtained activated carbon was characterized by surface area analysis and found to have the surface area and the pore diameter of 355 m2.g-1 and 1.9 nm respectively. These activated carbons were subsequently modified by impregnation with ammonium thiosulfate (ATS). Various parameters were optimized around the preparation and utilization of this modified carbon for gold extraction in both batch and column methods. The maximum sorption capacity of gold derived from Langmuir adsorption isotherm was approximately 129.27 mg.g-1. The adsorption of gold by the modified sorbent was relatively free from interference ions commonly found in gold jewelry waste. The sorbent was subsequently packed into a larger scale column and used for the extraction of gold from real jewelry wastes and successful recoveries of gold (>90%) were achieved.