Sb(III) and Sb(V) removal from water by a hydroxyl-intercalated, mechanochemically synthesized Mg-Fe-LDH

Antimony enrichment in aquatic environments is of great concern to international community. High-temperature geothermal waters usually contain excessive Sb, which are apt to contaminate the groundwaters or surface waters used as drinking waters in and around a hydrothermal area. However, Sb removal from geothermal water is rarely documented and the effect of high temperature on Sb removal has not received much attention. In this study, batch sorption experiments were conducted to investigate Sb removal from water by a hydroxyl-intercalated, mechanochemically synthesized Mg-Fe-LDH (i.e. Mg-Fe-OH-LDH) capable of avoiding secondary pollutions commonly related to other Mg-Fe-LDH intercalated by undesirable anions, such as Cl- and NO3-. The sorption capacities of Mg-Fe-OH-LDH for Sb(III) and Sb(V) were up to 48.7 and 30.0 mg/g, respectively. Notably, Mg-Fe-OH-LDH performed even better in removing aqueous Sb(V) at higher temperatures, superior to sorption of Sb by iron oxides that is generally exothermic and tends to be inhibited by increasing reaction temperature. The removal of Sb(V) existing as Sb(OH)(6)(-) by Mg-Fe-OH-LDH was attributable to its exchange with interlayer hydroxyl, and therefore could be impaired to some degree by coexisting anions with stronger electronegativity or smaller ionic radii. In contrast, anion exchange didn't contribute so much to Sb(III) sorption, because the main Sb (III) species at pH < 10 is neutral Sb(OH)(3). XPS analyses confirmed that inner-sphere complexation between sorbed Sb(III) and Fe on Mg-Fe-OH-LDH layers was formed, which was hardly affected by competitive anions. Mg-Fe-OH-LDH is promising to be practically applied in removing both Sb(III) and Sb(V) from contaminated natural waters, wastewaters, or geothermal waters potentially acing as a pollution source.