Uptake of Traces of Selenite by Manganese Dioxide from Aqueous Solutions

Abstract

Sorption of selenite onto manganese dioxide has been investigated with respect to shaking time, concentration of sorbent and sorbate, nature of electrolyte, and influence of cations and anions. The sorption of other metal ions has been studied using optimal conditions selected for maximum sorption of selenite. The surface area, average pore diameter, porosity, and solid phase density of the sorbent have been measured. The sorption data followed only the Dubinin–Radushkevich (D–R) sorption isotherm among all the isotherms tested. The sorption capacity of 51.2 nmol·g−1 and a constant β related to sorption energy have been estimated to be −0.007521 mol2·kJ−2. The sorption energy is found to be 8.15 kJ·mol−1. The kinetics of the sorption follows the Lagergren equation in the initial stages. The first-order rate constant, k′, was evaluated to be 0.498 min−1 and of intraparticle diffusion rate 3.06 × 10−5 mol·g−1·min−2. Among all the anions and cations tested, only carbonate, Fe(III), and citrate reduced the sorption significantly. The sorption data for other metal ions showed that Te(IV) can be separated from ions showing higher degree of sorption; especially Se(IV), As(III), Sb(V), and Eu(III). It can be concluded that manganese dioxide may be used for the separation of certain metal ions, their preconcentration from very dilute solutions, and for decontamination and treatment of industrial effluents.