Application of Mg-Al layered double hydroxide for treating acidic mine wastewater: a novel approach to sludge reduction

To reduce sludge volume, Mg-Al layered double hydroxide (LDH) was used to remove pollutants from mine wastewater. Mg-Al LDH can remove both cations and anions from mine wastewater via co-precipitation and anion exchange mechanisms, respectively. We herein investigated the difference in removal efficiencies between Mg-Al LDH and Ca(OH)(2). Initial As and Fe concentrations of 8.4 and 308.6 mg/L led to final concentrations of <0.001 and 15.4 mg/L, respectively, when 5 g/L LDH with an Mg/Al molar ratio of 2:1 was employed. This suggests that As was removed in the form of , which exchanged with intercalated in the Mg-Al LDH structure, while Fe was removed by the formation of Fe-Al LDH via co-precipitation. In contrast, treatment with 5 g/L Ca(OH)(2) gave As and Fe concentrations of 0.1 and <0.01 mg/L, respectively. Thus, under Ca(OH)(2) treatment, As is removed by the co-precipitation of arsenate with the formation of ferric oxyhydroxide (FeO(OH)), while Fe is removed by co-precipitation of the formed Fe(OH)(3). The sludge volume obtained using Mg-Al LDH was approximately ten times lower than that obtained when using Ca(OH)(2).