Adsorption of cadmium and humic acid onto hematite

Cadmium adsorption onto α-Fe2O3 (hematite) is successfully described using a non-electrostatic surface complexation model (NEM). Humic acid (Aldrich) adsorption onto hematite decreases with increasing pH, exhibiting ligand-exchange surface complexation characteristics. In ternary systems, the presence of humic acid (HA) leads to an increase in Cd(II) adsorption, dependent on HA concentration. The substrate loading order is observed to have noticeable effect on metal uptake at higher Cd(II) concentrations in the ternary systems, the general trend with respect to Cd(II) adsorption being: Cd(II) before HA > simultaneous adsorption ≈ HA before Cd(II). EDTA complexation significantly reduces the Cd(II) adsorption in the HA/hematite system.