Magnetized manganese oxide nanocomposite for effective decontamination of Cd(II) from wastewaters

In this study, a composite with magnetic properties has been successfully synthesized by a novel and environmentally friendly route and is applied to Cd(II) adsorption for water decontamination. The quantification of the phases obtained by Rietveld refinement has shown the presence of 84% of Mn₃O₄ and 16% of Fe₃O₄. Transmission electron microscopy image shows an aggregate of Mn₃O₄ nanoparticles without specific orientation and the predominance of octahedral morphology with nanoparticles size estimated around 25-30 nm. The Cd(II) adsorption isotherm is fitted using the Langmuir-Freundlich model. The estimated maximum adsorption capacities of Cd(II) at pH 6 and 7 are similar (0.28 ± 0.02 and 0.31 ± 0.02 mg/m², respectively). The kinetic results show that the studied system follows the pseudo-second-order model. The Raman results indicate that Cd is being specifically adsorbed by the Mn₃O₄ in the composite. The hysteresis curve of the composite Mn₃O₄/Fe₃O₄ has changed when compared to the pure magnetite; however, the coercive field after the addition of manganese oxide remains unaltered and does not change with a value around 158 Oe. The turbidity tests showed that the magnetic sedimentation was efficient and promising for wastewater treatment in large scale. These materials can be conveniently recovered by magnetic separation, avoiding the filtration steps, which will make easier the solid-liquid separation operation that follows the adsorption process.