Lead(II) removal from aqueous solutions and battery industry wastewater by sorption using seawater-neutralized red mud

The present study aims to investigate the feasibility of using seawater-neutralized red mud-a waste-based byproduct from bauxite refining to produce alumina-for the removal of Pb(II) from a battery manufacturing wastewater. The results showed the ability of the neutralized red mud to sorb Pb(II) from model aqueous solutions and battery manufacturing wastewater. The highest Pb(II) removal was obtained at pH 5, a dose of 0.5 g adsorbent per 50 mL solution, and a contact time of 30 min, while the maximum sorption capacity for Pb(II) was calculated as 49.5 mg/g. The formation of inner-sphere complexes and precipitation are considered the main processes of Pb(II) removal. The presence of various monovalent and divalent competing ions did not cause a significant reduction in the Pb(II) removal efficiency. The sorption isotherm (L-type) showed a favorable affinity of Pb(II) toward the red mud. The Pb(II) sorption was rapid and the process kinetics was well fitted with the pseudo-second-order model, suggestive of chemisorption as the main mechanism of Pb(II) removal by the red mud. The experiments conducted on real battery industry wastewater showed that at least 91% of initial Pb(II) was sorbed by the red mud and the pH of the treated wastewater raised up to permissible pH = 6.2 according to Iran regulations. In conclusion, the neutralized red mud can be considered an efficient adsorbent product for the depuration of Pb-rich battery industry wastewaters.