New method of treating dilute mineral acids using magnesium–aluminum oxide

Mineral acids, such as H3PO4, H2SO4, HCl, and HNO3, were treated with magnesium–aluminum oxide (Mg–Al oxide), which behaved as a neutralizer and fixative of anions. Anion removal increased with increasing Mg–Al oxide quantity, time, Mg/Al molar ratio, and initial acid concentration. Up to 95% removal of anions was achieved in 0.5 N acids using a stoichiometric quantity of Mg0.80Al0.20O1.10 for H3PO4, 1.75 stoichiometric quantities for H2SO4, or 2.5 stoichiometric quantities for HCl or HNO3 at 20°C over a period of 6 h. The final solutions were found to have a pH in the range of 8–12. Selectivity of acid removal was found to follow the following order: H3PO4>H2SO4>HCl>HNO3. The equivalent of acid removal per 1 g of Mg–Al oxide decreased as the Mg/Al molar ratio of Mg–Al oxide increased.