Preparation and characterization of bioadsorbent beads for removing selected heavy metal ions from wastewater

Abstract

Rapid industrialization is one of the major threats to water pollution worldwide, as discharge effluents contain large amounts of toxic metal ions. Heavy metals are highly toxic to the ecosystem and human even at very low concentrations. We focused on easily available, green and eco-friendly with low operational cost materials to remove heavy metals from industrial wastewater. Chitosan is considered an alternative and sustainable adsorbent due to its highly efficient adsorption capacities for heavy metals. In this particular study, chitosan was successfully modified by using diatomaceous earth and then fabricated as spherical beads using the drop-wise method. Pristine chitosan (CS) beads and chitosan coated diatomaceous earth (CSDE) beads were used to remove zinc, chromium, lead, and nickel ions from aqueous solutions in batch and continuous adsorption processes. The prepared adsorbents were characterized by using scanning electron microscopy (SEM) B Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and zeta potential. The results showed that the prepared adsorbents were porous in nature and the total surface area were increased from 1.9 m2/g for pristine chitosan to 14.4 m2/g for chitosan coated diatomaceous earth. The performance of prepared adsorbents was investigated at different temperatures, initial pH of the solution, contact times, initial metal concentrations. The pseudo-second-order kinetic model is more likely to predict the kinetic behavior of the metal ions adsorption process for the whole used contact time range, and the adsorption isotherm data of CS and CSDE beads were well fitted to Langmuir model. The maximal adsorption capacities of prepared CSDE beads were found to be pH dependent as follows: - Zinc ion - 127.4 mg/g at initial Zn(II) concentration 500 mg/L and pH 6. - Chromium ion - 84.23 mg/g at initial Cr(VI) concentration 1000 mg/L and pH 3. - Lead ion - 175.22 mg/g at initial Pb(II) concentration 400 mg/L and pH 7. - Nickel ion - 149.64 mg/g at initial Ni(II) concentration 400 mg/L and pH 6. Successful desorption and regeneration of prepared adsorbents were achieved (with common chemicals) and possessed excellent reusability (up to 10 cycles without a significant loss in adsorption capacity). The common anions and cations coexisting ions have insignificant impact on the removal capacity of prepared adsorbents. Overall, these results suggest that the environmentally friendly materials might be recognized as effective adsorbent and sustainable means for the separation of heavy metals from wastewater streams. That will lead to a new solution to water pollution required in the modern industrial society.