Potential removal of heavy metal ions from polluted water using Bauxite

Abstract

Bauxite, the principal ore of aluminum is a potential low-cost sorbent for treating heavy metal-contaminated water. We studied the ability of raw bauxite to adsorb Pb2+, Cu2+, and Co2+ ions in natural waters and the dependency of the adsorption efficiency on the metal concentration in water, contact time, the ‘type’ of bauxite, and the effect of coexisting metals. Goethite-rich (B1) and kaolinite-rich (B2) bauxites were sampled in Mississippi, USA and analyzed in order to use in adsorption experiments. Bauxite was able to remove ions (Pb2+, Cu2+, and Co2+) from water. The percent adsorption decreased with increasing metal concentration in water. This observation was prominent for both Pb2+ and Cu2+ with a noticeable reduction in percent adsorption (from >90% to ∼20-40%). Metal uptake generally increased with increasing metal concentration in water, but the increment between the 100 ppb and the 500 ppb metal levels was often less pronounced. The adsorption by B1 was more dependent on the metal concentration in water than B2. Overall, the removal efficiency of B2 was slightly higher than B1. Adsorption did not show a clear dependency on the bauxite-metal ion contact time. Bauxite was selective towards Cu2+ and Pb2+ but the near-complete removal of Cu2+ in some systems suggests that Cu2+ is favored. The removal efficiencies of both bauxites decreased in the presence of multiple metal ions in water. Fe-Al oxyhydroxide and clay surfaces are the probable adsorption sites that bind metals via specific adsorption and ion exchange mechanisms. Based on this study, raw bauxite is a promising low-cost sorbent to remove Cu2+, Pb2+, and Co2+ from water, where adsorption depends on the bauxite composition, metal ion concentration in water, and the coexistence of metal ions.