Effective remediation of low-concentration cadmium in groundwater using nano-scale magnesia.

Cadmium (Cd), one of the hazardous elements in groundwater, is a severe threat to human health and ecological systems even at low concentrations. This study explores the effectiveness of commercial and self-synthesized nano-scale magnesia (NMgO) for remediating low-concentration Cd in groundwater as well as their associated removal mechanisms. The sorption kinetic data for both NMgOs were well fitted to the pseudo-second-order model and the calculated q values matched the experimental q values for both commercial and self-synthesized NMgOs. The sorption equilibrium data for both NMgOs were well fitted to the Langmuir isotherm model, with the maximum Cd sorption capacity (q ) of 19.25 and 16.54 mg/g at an initial concentration range of 5-200 μg/L and a temperature of 25 °C, for commercial and self-synthesized NMgOs, respectively. The combined sorption kinetics and equilibrium data suggest that the sorption onto both NMgOs follows a monolayer chemisorption. The scanning electron microscope-energy dispersive X-ray (SEM-EDX), Fourier transform infrared spectroscopy (FTIR), and X-ray diffractometer (XRD) analyses show that the chemisorption of Cd onto commercial NMgO is due to the formation of Cd(OH), which precipitates on the sorbent surface. For the self-synthesized NMgO, it was demonstrated that the hydroxyl group plays a role in the chemisorption process and the amount of Cd sorbed on the sorbent was quantified. The results of batch experiments showed that both NMgOs removed Cd effectively, obtaining a removal efficiency of more than 99%, under different experimental conditions of pH, sorbent dosage, co-existing ions, and simulated groundwater. Results from both the sorption isotherm and desorption experiments indicated strong bonding between Cd and both NMgOs, suggesting that NMgOs are safe, effective, and practical sorbents to remediate Cd in groundwater.