Sorption-desorption studies on alumina pretreated with acids: II. Oxyanions on HNO3-treated alumina

Sorption-desorption behaviour of three oxyanions (MnO₄⁻, CrO₄^2- and VO₃⁻) on chromatographic alumina pretreated with HNO₃ is described. The sorption is found to be pH dependent, and has maxima at surface pH values of 3.5 (MnO₄⁻), 2.5 (VO₃⁻) and 2.0 (CrO₄²⁻). The affinity of MnO₄^- and CrO₄^2- is almost negligible at surface pH values of 5.5 or more. However, VO₃^- shows affinity for the substrate in the pH range 5.0 - 8.8. The monovalent anion appears to be sorbed, primarily via electrostatic interaction with the surface sites created by the acid treatment. The CrO₄^2- appears to involve ion exchange and weak chemical interactions. Mixtures of the oxyanions have been separated (binary and ternary) by column chromatography using inorganic electrolytes as eluents.