Adsorption of gold on activated carbon in bromide solutions

Adsorption of gold on activated carbon from gold bromide solutions was examined as a function of pH, particle size, amount of carbon, initial gold bromide concentration, bromine concentration, temperature, and various cations and anions. The pH did not have any effect on gold adsorption below pH = 6. Above pH = 6, pH had a dramatically negative effect. The adsorption occurred according to a first-order reaction-rate model. The reaction-rate constant was proportional to the inverse of carbon particle radius, the amount of carbon, and independent of the initial gold concentration. Temperature had very little effect on the rate of gold adsorption. Cations (Cu²⁺, Fe³⁺, Ca²⁺, Mg²⁺, and Na⁺) and anions (SO ₄ ² , Cl^-, Br^-) did not have any effect on gold adsorption. Free bromine had a very negative effect on gold uptake. Gold bromide is very stable and stays in this form on the carbon surface. Contrary to this, gold chloride is unstable, and elemental gold precipitates on the carbon surface. Loading capacity of carbon depended on the presence of free bromine. In the presence of free bromine, it was further dependent on temperature (increased with increasing temperature). AtT = 25 °C, gold loading was 27 to 64 kg Au/t carbon. In bromine-free solutions, gold loading was 174 to 315 kg Au/t carbon.