Geochemistry of Cu, Zn and Fe in the Tambo River, Australia I. Oxidation of Fe(II)-rich water entering the river

Abstract. The behaviour of Fe, Cu and Zn was studied during the laboratory oxidation of an acidic (pH 5.8) sample of naturally contaminated water from the Tambo River (Victoria, Australia). Changes in the concentrations of the dissolved, colloidal and particulate fractions of these metals were followed over 288 h. The initial concentrations of dissolved Cu (18.5 mg L−1) and Zn (22.6 mg L−1) were ∼15-fold greater than that of the dissolved Fe (1.13 mg L−1). Dissolved Fe was completely removed from solution in 60 h, with removal following the well established first order oxidation kinetics for Fe(II). A relatively small amount of the dissolved Cu (18%) and dissolved Zn (14%) was removed from the solution, although the removal mechanisms appear to be different. A ‘co-precipitation-surface precipitation ’ mechanism is proposed to explain the behaviour of the Cu and Zn, with Cu(II), Zn(II) and Fe(III) co-precipitating to form colloidal Fe(OH)3-Cu(OH)2-Zn(OH)2 particles following the initial oxidation of Fe(II) to Fe(III)