Synthesis of a unique nanostructured magnesium oxide coated magnetite cluster composite and its application for the removal of selected heavy metals

The removal of heavy metal such as lead (Pb), cadmium (Cd), and copper (Cu) was assessed using magnesium oxide cores with silica coated nano-magnetite (MTM) prepared by a simple method using chemicals such as iron(II) sulfate heptahydrate (FeSO₄·7H₂O), magnesium (II) nitrate hexahydrate [Mg(NO₃)₂·6H₂O], tetraethyl orthosilicate (TEOS), and urea. The MTM was characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), and alternating gradient magnetometer (AGM) analyses. The isotherm, kinetic, and intra-particle diffusion studies indicated that the MTM had excellent removal capacities towards heavy metals (Pb, Cd, Cu) and the adsorption capacities were as high as 238 mg g⁻¹ (1.15 mmol g⁻¹) for Pb, 85.1 mg g⁻¹ (0.75 mmol g⁻¹) for Cd, and 33.5 mg g⁻¹ (0.5 mmol g⁻¹) for Cu. The intra-particle diffusion, FE-SEM, XPS, and XRD results indicated that the mechanism of heavy metal removal was mainly substitution, followed by precipitation. A leaching test revealed that MTM showed no leaching of Fe ions at pH > 2. This material is cheap, simple, and can be produced in massive amounts. MTM can be used for the large-scale remediation of waste water containing heavy metals via applying a simple and fast magnetic separation.