An Electrochemical Study of Ammonium Dihydrogen Phosphate on Mg and Mg Alloy Electrodes

In this work, the electrochemistry of ammonium dihydrogen phosphate in aqueous solution on Mg and Mg AZ31 alloy (Al 3 wt%, Zn 1 wt%, balanced Mg) electrodes was studied using electrochemical characterization similar to electro-agglomeration and physical characterization to shed some light on the electrochemical mechanism of struvite formation as phosphate precipitation in waste. It was found that the Mg AZ31 alloy exhibited higher corrosion current densities (j_corr), and thus higher Mg dissolution rates and corrosion rates (v_corr) when compared with pure Mg. This finding was confirmed by ion chromatography (IC) analysis. Results also showed a phosphorus removal efficiency (P_Rem) of 16.8% together with ~53 mL H₂ production for pure Mg and 17.2% with ~61 mL H₂ production for Mg AZ31 alloy. The precipitates formed on the two Mg electrode materials were physically characterized by SEM, XRD, XPS, and energy-dispersive X-ray spectroscopy, which indicated the formation of struvite (magnesium ammonium phosphate hexahydrate-MgNH₄PO₄*6H₂O). It was found that (i) the thickness of the films was influenced by the applied scan rates, which also had a significant impact on the morphology, and (ii) hydrogen bubble formation influenced the precipitates, whereby the film thicknesses were negatively impacted. Graphical abstract: [Figure not available: see fulltext.].