Calcium Alginate Encapsulated Pillared Clay Beads for Adsorption of Ni(Ii) from Aqueous Solution

In the search for new adsorbents for wastewater treatment, a modified clay-based adsorbent for the adsorption of Ni(II) was proposed in the present study. Silica pillared clays (SPCs) are adsorbents with high specific surface area and thermal stability, which have not been thoroughly investigated for their metal adsorption capacity. SPC was prepared by intercalating tetraethoxysilane (TEOS) as a silica source and a cationic surfactant (ethyl hexadecyl dimethylammonium bromide) between layers of a Na-saturated Iranian clay, followed by calcination. In order to make SPC a more efficient adsorbent for use in large-scale commercial applications, the present study addresses the conversion of a powdered SPC adsorbent into a granular one (ALG-SPC) by entrapping it in a polymeric matrix of calcium alginate and then using it for the adsorption of Ni(II) from aqueous solutions. The process of pillarization/granulation increased the specific surface area of the clay from 40 m2/g to 506 m2/g. A strong pH dependence of Ni(II) adsorption on pH was observed, showing the role of electrostatic interaction as the dominant mechanism in Ni(II) adsorption. The pseudo-second order model was the most appropriate kinetic model to describe Ni(II) adsorption. The isotherm models of Sips and Freundlich fit the equilibrium data best. According to the isotherm model of Sips, the maximum adsorption capacity was 52.58 mg/g. Some preliminary binary adsorption experiments were performed, which showed the negative effect of the presence of aniline in the solution on Ni(II) adsorption. Further investigations on multicomponent and continuous adsorption can be carried out.