Adsorption of Co2+ and Zn2+ ions on hydrous Fe(III), Sn(IV) and mixed Fe(III)/Sn(IV) oxides .1. Characteristics of the hydrous oxides, apparent capacity and some equilibria measurements

Hydrous ferric oxide (HFO), stannic oxide (HSO) and mixed ferric/stannic oxide (HMO), obtained by precipitation with ammonia from metal chloride solutions, were all found to be microporous. Analysis (X-ray, infra-red, thermal) has shown that HFO and HMO are amorphous, whereas HSO is microcrystalline. It also showed that all the samples are oxides containing adsorbed H2O molecules and surface OH groups. In addition, it revealed that HMO is not a simple mixture of HFO and HSO, a conclusion which was also supported by the data on porous texture, intrinsic surface ionization constants, pH(PZC) and apparent capacity. For all the oxides, the apparent Zn2+ capacity is generally higher than the Co2+ capacity, in agreement with a stronger interaction of Zn2+ with O2- or OH- On the surface. Equilibria measurements point to the adsorption of both Co2+ and Zn2+ on all oxides with the release of two protons.