Trace metal adsorption onto acid mine drainage iron oxide

Trace metal (Cu, Pb, Zn & Cd) adsorption onto pure hydrous iron oxide has been compared to adsorption onto a natural sulphate-rich iron oxide from an acid mine drainage system, and onto synthetic schwertmannite (a poorly crystallised oxyhydroxysulphate of iron:). For Cu, Zn and Cd, the natural oxide is a more efficient adsorbent than pure iron oxide, enhancing adsorption through the formation of Cu and Zn ternary complexes with SO4 at the oxide surface, and an additional, possibly bacterially mediated, mechanism. For Pb, natural schwertmannite is a less efficient adsorbent than pure iron oxide. Although there is evidence for the formation of Pb ternary surface complexes with SO4, adsorption on the natural oxide appears to be adversely affected by the relatively low surface area, and reduced availability of binding sites.