Reusable granulated silica pillared clay for wastewater treatment, selective for adsorption of Ni(II)

Abstract

The article presents a study on the suitability of silica pillared clay (SPC) encapsulated with biopolymers, such as alginate, chitosan, or a combination of both, for the adsorption of Ni(II) from aqueous solutions. In the current age of stringent environmental regulations, there is an urgent requirement to identify novel sorbents that can be readily commercialized and employed in large-scale systems to efficiently remove and recover metal compounds from wastewater. Therefore, the study aimed to encapsulate powdered silica pillared clay to produce stable granules via a modified solution casting method, which was confirmed through various characterization studies (FESEM, XRF, XRD, BET, and FTIR). The study found that ALG-SPC showed the best adsorption capacity, owing to its relatively high specific surface area and the negative charge of the alginate. In contrast, encapsulation with chitosan resulted in poor performance due to a significant reduction in porosity. The study also investigated the behaviour of ALG-SPC in a binary solution containing both Ni(II) and Cr(VI) and found that it exhibited selectivity for Ni(II) over Cr(VI). The presence of Cr(VI) did not negatively affect Ni(II) adsorption; in contrast, Ni(II) helped to Cr(VI) adsorption under a limited pH range. The study also conducted adsorption mechanism, kinetic, and equilibrium modelling. Recovery of adsorbed Ni(II) from saturated ALG-SPC was most effective in acidic solutions in comparison with electrolyte solution and methanol. The study's findings have important implications for the development of effective and selective adsorbents for heavy metal removal and recovery from wastewater.