HEATS OF ADSORPTION OF GOLD CHLORIDE AND CYANIDE COMPLEXES FROM AQUEOUS-SOLUTIONS ON GRAPHITIZED CARBON-BLACK AND A COCONUT ACTIVE-CARBON

It was found that the graphitic carbon strongly adsorbs chloroauric acid (HAuCl4) and sodium aurocyanide (NaAu[CN]2) with the production of high heats of adsorption at low surface coverages. As the graphitized carbon possesses only a very small amount of polar surface sites, the adsorption is ascribed to the formation of surface complexes of the gold compounds with the basal plane sites. The work was carried out in a new model of the Microscal Flow Microcalorimeter to measure the heats of adsorption and desorption of the gold complexes from aqueous solutions onto graphitized carbon black (Graphon). The gold complexes can be eluted (desorbed) from the carbon by aqueous solutions containing anions that are competitively adsorbed on the basal plane sites. Thus CN- (in NaCN) can easily desorb Au(CN)2- from the Graphon, but not SO4 = (in Na2SO4), which is not preferentially adsorbed from the solutions. It is concluded that flow microcalorimetry has potential for the prediction of the selectivity of various carbons for soluble gold complexes in the presence of other compounds competing for the carbon surfaces. This should help in the evaluation of the effectiveness of various carbon adsorbents offered for gold recovery applications.