Single and Ternary Removal of Heavy Metals from Aqueous Solution Using Fe3O4 Magnetic Nano-particles

Abstract

This research aims to investigate the use of magnetic iron nano-particles (FeN) for the removal of heavy metals under single and ternary scenarios. The methodology includes synthesis of FeN using chemical precipitation approach, batch experiments for single and ternary metals removal, isotherm and kinetic studies, thermos-dynamic study and assessing the effect of different parameters on the adsorption process. The results showed that the maximum removal for As and Hg was achieved at a pH of 7, while a pH of 6 provided a slightly higher removal of Cd than a pH of 7 at an optimum mixing time of 120 minutes. The optimum adsorption capacities of As, Cd and Hg at the initial concentration of 200 ppm were 260, 280 and 75.0 mg/g in the case of single metal removal against 91.5, 237.8 and 341.5 mg/g in the case of ternary combination, respectively. The removal of all metals increased with increasing the FeN dose and the mixing time, while it decreased with the increase of the initial concentration. The removal efficiency was affected strongly by the presence of multiple metals, while As removal decreased sharply and Hg removal increased significantly. Adsorption selectivity is affected negatively by the increase in atomic weight and atomic radius. In the case of single-metal removal, fitting of isotherm models can be ranked as Langmuir>Freundlich>Temkin>D-R for As and Cd and Temkin>Freundlich>D-R>Langmuir for Hg, while contradictory results were obtained in the case of ternary combination. Kinetic studies found that the adsorption follows the pseudo-second-order model with R2=0.99. For all metals, the adsorption process is highly favourable at higher temperatures and is endothermic in nature with (ΔHo) of 10.91, 23.86 and 0.163 for As, Cd and Hg, respectively. Coating of FeN with silica resulted in lower removal efficiency for all metals up to 50%. It can be concluded that FeN can be successfully used for the removal of heavy metals either through the single or ternary approach, but the single approach provides a higher performance. KEYWORDS: Nano-materials, Magnetite iron, Adsorption, Arsenic, Cadmium, Mercury, Lead.