Recovery of KAu(CN)2 from granular activated carbon using supercritical CO2

The recovery of KAu(CN)2 preloaded onto activated carbon by pure and cosolvent entrained supercritical carbon dioxide (sc-CO2) was investigated using a laboratory-size supercritical extractor. Gold on the carbon surface was monitored by SEM-EDS, while either ICP-MS or AA was employed to detect gold in the corresponding extracts. Recovery was improved by TBP (or TBP-HNO3 adduct) used as a stand-alone extractant or as a cosolvent to sc-CO2, but no more than 10% of the preloaded gold could be extracted, contrary to higher yields of recovery from other types of matrices claimed in the literature. This is ascribed to a surface related limitation in view of observations made on modifying the surface area of the activated carbon.