Removal of Copper from Aqueous Solution Using Electrocoagulation: Importance of Stirring Effect

Abstract

Electrocoagulation with aluminum and stainless steel electrodes was investigated. Electrocoagulation tests were performed to treat synthetic wastewater containing heavy metallic ions (Cu2+), with concentrations ranging from 100 to 600 ppm. Concentrations of the remaining copper and coagulant (Al3+), generated by electrochemical oxidation of the anode, were optimized by an experimental design methodology. The study was conducted using a Doehlert matrix. The factors considered are: the initial concentration of copper (CCu0); the stirring speed (N); the current density (J); and the electrolysis time (t). As for the response functions measured by atomic absorption, they imply the final concentration of the metallic ions of copper (Y1) and of the metallic ions of aluminum accumulated in the wastewater after electrocoagulation treatment (Y2). The isoresponse curves and the optimum path study of the two retained responses showed that the two optima were found to be opposite. In order to minimize the two responses and determine the conditions of electrocoagulation that satisfy the requirements of the Tunisian standard for effluent discharges NT-106-02 (≤1 ppm for copper and ≤ 10 ppm for aluminum), multicriteria optimization using the desirability function was achieved. In so doing, the determined optimal operating conditions for the process of electrocoagulation were: CCu0 = 421.43 ppm, N = 44.19 rpm, J = 656.41 mA dm−2 and t = 65.12 min, while the corresponding estimated response values were 0.25 ppm and 3.38 ppm for cooper and coagulant (Al3+), respectively. The removal efficiency over 98% was reached for copper. In addition, the results of the study demonstrate that a simultaneous increase of the current density and the stirring speed notably reduces not only the concentration of the remaining copper but also the treatment duration, without inducing a strong increase of the sludge.