Enhanced Cr(VI)-removal mechanism of nano MgO recycled from high-magnesium slag by titanium synergy

Among many pollution sources, Cr(VI) has captured much attention because of its strong toxicity, bioaccumulation and carcinogenicity. In recent years, nanoscale magnesium oxide has shown great potential in removing Cr(VI) pollution in water by virtue of its excellent adsorption and environmental friendliness. In this study, a high‑magnesium slag produced during the nitric acid pressure leaching process of laterite nickel ore was utilized as raw material for nano MgO preparation. A nano MgO-based adsorbent material (T-MgO) was prepared via the modification of MgO by nano TiO 2 which was synthesized use low-grade titanium slag as titanium source. Adsorption results demonstrated that T-MgO exhibits rapid adsorption performance, reaching adsorption equilibrium within 60 min. The kinetic adsorption conforms to the pseudo-second-order (PSO) model, revealing a chemisorption-dominated mechanism. According to the Freundlich model analysis, saturated adsorption capacity of the T-MgO for Cr(VI) reached 241.53 mg/g. The T-MgO material also possesses excellent reusability and selectivity to Cr(VI) adsorption. Furthermore, an in-depth analysis was performed to elucidate the Cr(VI) removal mechanism. Cr(VI) existing as HCrO 4 − and Cr₂O₇ 2− species under pH = 2 is electrostatically adsorbed on the protonated active sites of T-MgO. With the participation of free electrons generated by the nano-TiO 2 semiconductor, Cr(VI) is reduced to low-toxicity Cr(III), forming Mg-O-Cr bonds. The study achieved the purposes of superior and economic removal of Cr(VI) and high value-added utilization of the magnesium and titanium secondary resources.