Adsorption of the gold–thiosulfate complex ion onto cupric ferrocyanide (CuFC)-impregnated activated carbon in aqueous solutions

• 1 The studies showed an innovative approach to modify the activated carbon, which can be adsorption of [Au(S2O3)2]3 −.
• 2 The gold adsorption capacity on the AC-CuFC was reached to 1.474 kg/t at temperature of 30°C.
• 3 The adsorption process of [Au(S2O3)2]3 − was correspond with the Freundlich model and pseudo-second order kinetic model.
• 4 The adsorption mechanism was ion-exchange reaction for Au and Cu, and Au(I) was reduction to native gold.

In this technical note, the adsorption of the gold–thiosulfate complex ion ([Au(S2O3)2]3 −) on cupric ferrocyanide (CuFC)-impregnated activated carbon in aqueous solutions was investigated to identify a better adsorbent for the gold thiosulfate process. This study was performed using cupric ferrocyanide (CuFC)-impregnated activated carbon (AC-CuFC) and an artificial, aqueous solution of [Au(S2O3)2]3 −. Variation in major factors was investigated for the determination of the appropriate dosages of cupric salts, potassium ferrocyanide, impregnation time and roasting temperature to obtain a high recovery of gold from simulated thiosulfate leach solutions. The experimental results have shown that [Au(S2O3)2]3 − strongly adsorbs onto the AC-CuFC and the adsorption capacity of [Au(S2O3)2]3 − on the AC-CuFC in aqueous solution increased with increasing temperature, leading to a gold adsorption capacity for AC-CuFC of 1.474 kg/t at a gold concentration of 100 mg/L at 30 °C. It was determined that the adsorption followed the Freundlich isotherm well, and a pseudo-second order kinetic model is suitable for the adsorption kinetic. That finding indicates that the gold adsorption is multimolecular chemical adsorption. EDX and FTIR suggested that the adsorption process consisted of two steps: first, [Au(S2O3)2]3 − diffused to the surface of AC-CuFC, and ion-exchange reaction for Au and Cu happened, then Au(I) was likely reduced to native gold by carbon or [Fe(CN)6]4 −.