Ultraefficient removal of Ni 2+ ions from wastewater using ZnO embedded and tannic acid modified composite material: an experimental design approach

Surface functionalization is a promising approach for modulating the electronic and surface properties of metal oxide-embedded composites. In this study, sodium alginate (SA) and tannic acid (TA), in the presence of calcium chloride as a crosslinker, were used to synthesize ZnO-embedded composite gel beads material (SA@ZnO/TA) for the removal of nickel (Ni2+) ions from industrial wastewater (IW). The resulting adsorbent materials were characterized using FT-IR, SEM, and EDS. Adsorption experiments were performed in fixed-bed column mode by optimizing various parameters that influence adsorption capacity, including pH, flow rate, and Ni2+ ions concentration, using a central composite design (CCD) based on response surface methodology (RSM). Under the optimized conditions (120 mg L−1, 5.4, and 4 mL min−1 for Ni2+ initial concentration, pH, and flow rate, respectively), the maximum adsorption capacity obtained from CCD-RSM was 187.13 mg g−1, while breakthrough analysis of the fixed-bed column yielded a dynamic adsorption capacity of 14.93 mg g−1. The SA@ZnO/TA composite material exhibited significantly greater adsorption of Ni2+ ions than the unmodified composite beads (SA@ZnO). A regeneration study of SA@ZnO/TA using various desorption eluents shows that approximately 99% desorption efficiency was achieved using 0.2 M HCl solution after 10 adsorption-desorption cycles. The synthesized, functionalized and highly reusable material was carried out in a fixed bed column and the optimized system was applied to wastewater samples.