The removal of phosphates using electrocoagulation with Al - Mg anodes

The removal of phosphates, to levels below the detection limit, was achieved over a 30 to 60 min period, depending on the initial phosphate concentration, with Al-Mg anodes in an electrocoagulation cell at 11.0 mA cm(-2) with a surface area to volume ratio of 11.7m(-1). The Al-Mg alloy performed well in low chloride concentrations of 4.2 mM 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, k(F), was computed as 146 mg g(-1), corresponding to the adsorption of 146 mg 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.