Optimization of the Iron Electro-Coagulation Process of Cr, Ni, Cu, and Zn Galvanization By-Products by Using Response Surface Methodology

Abstract

An electrocoagulation laboratory scale system was studied for the removal of inorganic pollutants from a mixture of galvanic process-based by-products. Response surface methodology based on a five-level, four-variable central composite rotatable design was employed for optimization with respect to four important variables—reaction time, agitation velocity, current density, and pH. The electrocoagulation process response was evaluated on the basis of chemical oxygen demand (COD), turbidity, total suspended solid, and element concentration values. Interaction effects between reactor operating variables and response variables were evaluated by using 3-D response surface analysis Second-order models were validated by ANOVA. Predicted yields were in a good agreement with the experimental ones. The reactor optimal performance was achieved at 35 min reaction time, 170 rpm agitation velocity, 97.7 Am⁻² current density, and 6.5 initial pH. Under these conditions 100% color and turbidity, 90% COD and total suspended solids, 100% chromium and nickel, and almost 99% zinc and copper were removed. A pseudo-first-order rate model was applied to describe the metal removal kinetics. The EC treatment of heavy metal solutions proved to be more cost-effective than the conventional one, indicating clearly that the method of electro-coagulation is a very promising alternative for industrial applications.

Keywords:

• electro-coagulation
• galvanic wastewater
• response surface analysis

ACKNOWLEDGEMENTS

F.R. Espinoza-Quiñones and A.N. Módenes thank CNPq for financial support. We gratefully acknowledge the Brazilian Light Synchrotron Laboratory (LNLS) for partial financing of this study through the 9074 project.