Mechanism study on manganese(II) removal from acid mine wastewater using red mud and its application to a lab-scale column

Abstract

Red mud, a by-product produced in the alumina industry, has been considered as a serious environmental burden. In this study red mud and three modified samples were used as adsorbents to remove Mn(II) from acid wastewater, and the removal ability of raw red mud were investigated in a lab-scale column after prepared as immobilized beads. Compared with the unmodified red mud, Mn(II) removal rate of the Fe(III)-modified, heat-treated and acid-activated red mud decreased by 34.26%, 65.34%, and 54.93%, respectively. Characterization of the adsorbents before and after reaction indicated that BET surface area of red mud did not play the main role in Mn(II) sorption, whereas O–C–O, Si–O–Al and Fe–O groups were significant for Mn(II) chemisorption process. However, minerals containing these active groups were decomposed and transformed partly in the modified samples. The maximum adsorption capacity of unmodified red mud in batch experiment was calculated to be 56.81 mg·g−1 at initial Mn(II) concentration of 95 mg·L−1 and pH of 6.0. Freundlich model gave a better fit to the adsorption data, and the whole adsorption behavior was closer demonstrated by pseudo-second-order kinetic model. Column experiments demonstrated that Mn(II) removal ability of immobilized red mud was at least 1.81–3.19 times larger than that in batch experiment, probably due to the generation of active manganese oxide and use of sodium alginate beads.