When magnesia is introduced into the system, pH increases due to the predominant MgO and Mg(OH)2 dissolution reaction. This might be supported by the high phosphorous concentration at the beginning of the reaction, which increases the solubility of MgO due to the ion pair formation of magnesium and phosphate ions. Furthermore, the solution’s initial acidic condition contri- butes to the fast depletion and dissolution of the Mg(OH)2 layer .
MgðOHÞ2 þ2Hþ -Mg2þ þ2OH ð4Þ The dissolution process causes high supersaturation, which
induces rapid struvite precipitation. Precipitation becomes the predominant phenomenon when pH reaches its maximum. This results in a subsequent decrease in pH, according to the following