Polysaccharides Encapsulate Metal Oxides/Sulphides Based Nano-composites Beads for Cd(II) Sorption from Industrial Wastewater

Polysaccharides are one such biodegradable polymers, which have been extensively exploited for the preparation of nanoparticles (NPs) for several wastewater treatment applications. Many biopolymers are used as adsorbents and encapsulation of nanoparticles onto them can increase their efficiency and durability. In this study, zinc oxide/sulphide, and titanium (III) oxide were incorporated on alginates beads (Alg) along with Arabic gum (AG) to produce efficient sorbents for heavy metal ions extraction. The sorbents were characterized microscopically using a scanning electron microscope (SEM) accompanied by energy dispersive X-ray (EDX). The point of zero charges (PZC) was measured for the prepared adsorbents to identify the effect of surface charge on the sorption mechanism and it was found that each bead has a different charge and most adsorption activity occurred in pH > 4. The as-prepared sorbents were investigated as a sorbent of cadmium Cd(II) from their single solution and wastewater samples. The adsorption kinetics of the selected metal ions onto the prepared beads showed that beads are a good fit with PSORE and IPDE, while sorption equilibrium fitted with Langmuir and showed the homogenous properties of the synthesized beads. The maximum sorption capacity towards Cd(II) of 39.6%, 40.92% and 88.4% was found for the beads of Alg/ZnO-ZnS, Alg/ZnO-ZnS/AG, and Alg/ZnO-ZnS-Ti2O3, respectively. The sorbents were tested for heavy metal removal from wastewater samples. These test results show remarkable affinity and the investigated metal ion. Cadmium ions Cd(II) successfully desorbed using different concentrations of HNO3, the beads recorded decrease with 22.7%, 21.09% and 24.54% for Alg/ZnO/ZnS, Alg/ZnO/ZnS/Ti2O3 and Alg/ZnO/ZnS/AG respectively and allow re-use with limited loss in sorption capacity.