Gold recovery from chloride solutions with XAD-7: Competitive adsorption of Fe(III) and Te(IV)

In this study, competitive adsorption of metal chloro complexes on the polymer adsorbent XAD-7 has been investigated. Au(III), Fe(III) and Te(IV) dissolved in HCl and alkali metal chloride solutions were used as the model compounds. Adsorption equilibria were measured for individual elements as well as for binary pairs and the data were correlated in terms of activities of the adsorbable complexes. Finally, the equilibrium model together with the experimentally determined apparent diffusion coefficients was utilized in simulation of break-through curves of multicomponent mixtures. tion of gold and iron can be explained satisfactorily by taking into account the formation equilibria of the tetrachloro complexes and the difference in their acid strengths. The uptake of the weakly acidic HAuCl4 depends only slightly on the HCl concentration and adsorption was substantially stronger in NaCl solutions. The opposite trends observed for iron were due to the lower stability and higher degree of dissociation of HFeCl4. The adsorbable complex of Te(IV), HTe(OH)Cl4, has lower affinity for the adsorbent, but at high concentrations it can reduce substantially the adsorption capacity for Au(III) and Fe(III). This effect was confirmed with the adsorption column runs, and the change in the break-through behavior of Au(III) and Fe(III) can be explained quantitatively by the simulation model.