In this paper a fundamental study has been made of the adsorption of potassium gold cyanide from water onto industrial activated carbon widely used for the recovery of gold. We examined the thermodynamic reversibility of the adsorption of gold complexes by determining the adsorption/desorption isotherms of Au, Au(CN)(2)(-), and potassium counterion from pure KAu(CN)(2) in deionized water solution at pH = 6.0 and T = 298 K. This study was supplemented by the determination of pH and conductivity variations of the bulk phase, surface charge modifications of the loaded solid pal-tides, and enthalpic changes upon gold complex adsorption. The occurrence of two distinct and successive or overlapping mechanisms of adsorption in the studied range of concentrations at room temperature has been experimentally proved. For very low equilibrium concentrations, gold is adsorbed as Au(CN)(2)(-) anions and the adsorption has been found to be fully irreversible. The experimental results are consistent with an anionic exchange mechanism between Au(CN)(2)(-) ions and some anions initially present on the activated carbon surface. The measurements of the enthalpies associated with the adsorption process confirm the occurrence of the irreversible mechanisms of adsorption. For relatively concentrated solutions, above a given surface coverage ratio, the adsorption of gold complexes becomes partly reversible, which indicates that, in this second stage, gold complexes are physically adsorbed. Moreover, in this stage, the adsorption of potassium counterion is occurring and Is associated with a constant value of the pH, conductivity of the bulk phase, and electrophoretic mobility of the loaded solid particles. The experimental results prove that the reversibility is due to the physisorption of neutral molecular species (KAu(CN)(2)) on the less active parts of the activated carbon surface.