Retention of aurocyanide and thiourea-gold complexes on activated carbons obtained from lignocellulosic materials

The rate and equilibrium retention of potassium dicyano aurate(I), K[Au(CN)(2)] and bis-thiourea-gold(I) chloride, [Au(CS(NH2)(2))(2)]Cl, in aqueous media on two series of lignocellulosic activated carbons were studied. Activated carbons with different burn-off were obtained by steam activation of carbonized peach stones and Eucalyptus globulus charcoal. Textural and chemical properties of the adsorbents were used to explain the gold retention of both complexes. From the study of the influence of some process variables on the gold retention rate, a pore diffusional control was confirmed. Thus, Eucalyptus activated carbons, with an important higher macroporosity, showed a higher gold retention rate. The equilibrium gold retention was mainly a function of both the pore distribution and the chemical properties of the activated carbon surfaces. The gold retention rate in all cases was higher for cyanide than for the thiourea complex but the equilibrium retention was higher for the thiourea complex.