Factors affecting the elution of Pt, Pd and Au cyanide from activated carbon

• Elution curves for Pt and Pd cyanide ions from activated carbon are given.
• The effect of eluant temperature and ionic strength on PGM elution are shown.
• The effect of the NaCN and NaOH pre-treatment concentrations are determined.
• The effect of impurities such as copper and KSCN on the elution are discussed.
• Acid pre-treatment, carbon loading and where the PGMs will report to are included.

Several factors affecting the elution of Pt, Pd and Au cyanide complexes in a manner similar to the AARL process have been investigated. Temperature, the cyanide pre-treatment concentration and the ionic strength of the eluant have been found to affect Pt and Pd elution substantially and will be critical factors in the design of an elution process. An acid (HCl) pre-treatment step increased the elution percentage for all cases investigated while no PGMs were eluted by the acid. The presence of Cu did not have a negative effect on the elution of Pt, Pd or Au at strong pre-treatment (2% NaCN and 0.6% NaOH) conditions but at weak pre-treatment conditions (0% NaCN), the elution percentage of Pt and Pd were reduced by between 10% and 18% after five bed volumes when Cu was present. The presence of 100 mg/L KSCN salt added to the leach solution during the adsorption stage reduced the elution percentage for Pt and Pd by seven and 10%. Carbon loaded to equilibrium resulted in slower elution kinetics.