The removal of phosphates using electrocoagulation with Al−Mg anodes

Abstract

The removal of phosphates, to levels below the detection limit, was achieved over a 30 to 60min period, depending on the initial phosphate concentration, with Al−Mg anodes in an electrocoagulation cell at 11.0mAcm−2 with a surface area to volume ratio of 11.7m−1. The Al−Mg alloy performed well in low chloride concentrations of 4.2mM NaCl and the complete removal of phosphates from two real water samples was achieved after a 15−min period. The removal efficiency, although depending on the initial pH, appears to depend on the evolution of pH during electrocoagulation with more efficient removal at a final pH of 7.5. Using the Freundlich adsorption model, the adsorption capacity, kF, was computed as 146mgg−1, corresponding to the adsorption of 146mg of phosphate per gram of the aluminium−hydroxy coagulant. The efficient removal of the phosphates was attributed to the low corrosion potentials and the lack of a passive region observed using polarisation and cyclic polarisation experiments, which in turn facilitate dissolution of the anode.