Chapter 9 - Removing chromium (VI) from contaminated water using a nano-chitosan–coated diatomaceous earth

Abstract

Access to clean water is a major challenge in many developing countries partly due to municipal and industrial pollution. Thus, developing low-cost technologies to provide clean water is vital. Hexavalent chromium, Cr(VI), is a toxic substance that is not biodegradable and greatly affects the ecosystem and human health. In this work, chitosan-coated diatomaceous earth (CCDE) granules were synthesized at 20 and 30 wt% and characterized by Fourier transfer infrared, scanning electron microscopy, and thermogravimetric analysis. CCDE is used for Cr(VI) ion removal from an aqueous solution in batch processes. Several parameters have been studied, such as solution-pH, initial Cr(VI) ion concentration, the mass of adsorbent, and contact time to investigate the efficiency of Cr(VI) removal. In batch studies, CCDE achieved 99% removal efficiency of Cr(VI), and adsorption capacity was 18.69 mg Cr(VI)/g. The adsorption followed pseudo-second-order and was well fitted to the Langmuir isotherm model, indicating monolayer adsorption behavior. Anions in the solution had an insignificant effect on Cr (VI) ion uptake by CCDE powder achieving clean water standard from initial Cr(VI) concentrations of 1 mg/L. The removal efficiency increased at lower pH, and the optimal pH was 4. Adsorption equilibrium was reached after approximately 60 min, and the adsorption kinetics was well fit by a pseudo-second-order model for Cr(VI). This study demonstrated that natural-based adsorbents could be employed as a low-cost, sustainable, and excellent alternative material for removing heavy metals from contaminated water.