Removal of vanadium(V) ions from acidic water using reusable manganese oxide sorbents

Manganese oxide (MnOx) was studied for its ability to adsorb vanadium (V) ions for applications in acidic water treatment. Three MnOx types: naturally-occurring (NatMnO), commercially-derived (ComMnO), and laboratory synthesised (SynMnO) were examined in batch systems under varying pH, adsorbent dosage, ionic strength, and contact time. The greatest V sorption occurred at acidic pH, following the order: NatMnO > SynMnO > ComMnO, with maximum adsorption capacities of 54.0, 26.0, and 10.4 mg/g, respectively (at pH 3.0, mass/volume ratio of 2 g/L, concentration of 100 mg/L, 24 hours). Adsorption equilibrium data best fit the Freundlich isotherm, indicating multilayer adsorption, while kinetic data followed a two-constant rate model, suggesting both physical and chemical sorption. Solution pH was found to have a significant impact, with V removal by MnOx most effective at low pH, likely due to the negative zeta potential of the MnOx under such conditions. MnOx reusability was investigated using repeated sorption and desorption experiments with 0.1 M HCl, 0.1 M NaOH, and deionised water to regenerate the MnOx. The regenerated MnOx exhibited similar or enhanced ability to sorb V ions from solution. Overall, these results confirm the unique ability of MnOx as a reusable sorbent for V removal from acidic water, while also enhancing our mechanistic understanding of the removal process. This finding supports the development of sustainable solutions for acidic water treatment, contributing to efforts to address this critical environmental challenge.