Cementation treatment of copper in wastewater: mass transfer in a fixed bed of iron spheres

The cementation of cupric ions from dilute copper sulfate using a fixed bed of iron spheres was studied. The extent of copper recovery and excess of iron consumption in similar conditions to those of copper bearing wastewater was experimentally determined. Determinations were made over a large range of cupric ions concentrations, for different solution flow rates and beds with different heights. The cementation reaction was found to proceed with two different regimes: a steady regime and unsteady regime with different initial cupric ions concentration. The rate of cementation for each regime were calculated and represented by the product ¯kae of the overall mass transfer coefficient ¯k and the effective surface area ae.The values for unsteady regime was found to increase with increasing initial cupric concentration and decrease with bed height especially at high flow rates, while they stay nearly constant in the steady regime. Empirical correlations giving the factor JD of the mass transfer as a function of the Reynolds numbers for each regime are proposed by introducing an apparent mass transfer coefficient. The correlations equations obtained were thus compared to the prediction of other empirical models when possible.