Understanding the As(III) oxidative performance of MnO2 polymorphs (α, β, and γ) and synthesis of an efficient nanocomposite of iron ore slime derived 2-line ferrihydrite and γ-MnO2 for sequestration of total arsenic from aqueous solution

Abstract

The present research was performed with a primary objective to study the performance of different MnO2 polymorphs for oxidative transformation of As(III). Five different MnO2 polymorphs with distinct morphologies were hydrothermally synthesized by altering the precursor and synthesis condition. The As(III) oxidative reactivity of MnO2 polymorphs, as confirmed by the kinetic experiment, were found to be in the order: γ-M2 > α-M2 > α-M1 > γ-M1 > β-M1. The study confirms that the surface Mn(III) content, crystallinity, reducibility, and synthesis temperature are the primary deciding factors that regulate the As(III) oxidative performance of MnO2. In addition, 2-line ferrihydrite nanoparticles were synthesized from iron ore slime for removal of As(V). A new nanocomposite of 2-line ferrihydrite and γ-MnO2 was prepared for the removal of both As(III) and As(V). The nanocomposite with high As(III) and As(V) removal affinity, excellent reusability and outstanding performance in groundwater environment demonstrate its potential as a front-line arsenic removal material.