Remediation of Wastewater Containing Divalent Heavy Metals using Silica-Embedded Metal Oxide Nanoparticles
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Date
2019-05-20
Authors
Abuhatab, Saqr
Hamdan, Hana
Ziad, Wessal
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Abstract
Abstract
In this study, the adsorption of Zn2+, Cu2+, and Cr2+ metal ions in synthetic wastewater samples and Cr2+ ions in real wastewater sample onto NiO-MgO silica-based nanosorbcats (SBNs) has been studied. The real wastewater sample was treated without any pre-treatment as collected from leather tanning plant and it was found that it contains an initial concentration of 2000 mg/L Cr2+ ions, as confirmed by atomic absorption spectroscopy (AAS). The effect of solution pH, initial concentration, contact time and coexisting ions on the adsorbed amounts of single Zn2+, Cu2+, and Cr2+ ions have been investigated within an array of batch mode experiments. The adsorption of Cr2+ was very fast, and equilibrium was achieved within 2 min compared to Cu2+ and Zn2+ which needed 30 and 60 min to reach equilibrium, respectively. The adsorption equilibrium data fitted very well with the Sips adsorption isotherm model for Cu2+ and Zn2+, and the BET model for Cr2+ ions. The maximum uptake was maintained at 7.23, 13.76, 41.36 (molecules per nm2) for Zn2+, Cu2+, and Cr2+, respectively. This equals to 37.69, 69.68, 209.51 (mg adsorbate per g adsorbent), respectively. The adsorption uptakes increase with increasing the pH in range of (7 to 11) for all investigated metal ions. The thermodynamics parameters; such as Gibbs free energy (∆G^o), enthalpy (∆H^o), and entropy (∆S^o) were determined. The adsorption of Zn2+, Cu2+, and Cr2+ was spontaneous, endothermic and physical for Cu2+ and Cr2+, exothermic and chemical in nature for Zn2+.The concentration of the Cr2+ ions in the real wastewater sample dropped from 2000 to 44 mg/L for each 50 mg NiO-MgO SBNs, the sample was treated without any pre-treatment. The regeneration and reusability study has proven that the NiO-MgO SBNs can be employed for the adsorptive of these metals repeatedly without impacting the adsorption capacity.