Abstract
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 (jcorr), and thus higher Mg dissolution rates and corrosion rates (vcorr) when compared with pure Mg. This finding was confirmed by ion chromatography (IC) analysis. Results also showed a phosphorus removal efficiency (PRem) 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
Highlights
Nutrients are essential substances that provide nourishment necessary for the maintenance of life and growth, where nitrogen (N) and phosphorus (P) are critical nutrients to the agricultural sector
The objective of this work was to investigate the electrochemical mechanism of struvite formation in synthetic wastewater and its effects on the anode performance, by studying the electrochemistry of ammonium dihydrogen phosphate on two different types of sacrificial anode compositions: pure Mg and AZ31 magnesium alloy (Al 3 wt%, Zn 1 wt%, balance Mg), using the cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS) methods
The crystal structure analysis was performed via x-ray diffraction (XRD) on a Philips PW1830 double system diffractometer equipped with a Cu cathode
Summary
Nutrients are essential substances that provide nourishment necessary for the maintenance of life and growth, where nitrogen (N) and phosphorus (P) are critical nutrients to the agricultural sector. In the case of P, it has been recently estimated that as early as the 2030s, global demand will exceed supply, due to the fact that demand will continue to increase with a growing world population, but the P fertilizer rate of production will decrease when rock phosphate resources become depleted [1,2,3,4]. The recovery of nutrients in a concentrated form such as in the inorganic precipitate struvite is seen as a desirable process because it would allow eventual agricultural reuse. Known as magnesium ammonium phosphate hexahydrate (MgNH4PO4*6H2O), or MAP, is a white, orthorhombic, poorly soluble crystal and is considered an economically viable product, a slow-release fertilizer, in agriculture [19, 20]. The general reaction may be expressed as follows: Mg2+ + NH+4 + HnPOn4−3 + 6H2O → MgNH4PO4 ∗ 6H2O ↓ +nH+
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