Efficient removal of hexavalent chromium from water: Insights into novel adsorbents, health risks and vulnerability studies

Abstract

This study aims to develop a cost–effective and sustainable approach for hexavalent chromium [Cr(VI)] removal from contaminated water using adsorption technology. An Electrical Resistivity Tomography (ERT) survey and boring tests confirmed the predominance of sandy, sandy loam, and gravel layers in the study area. Soil samples from a 0–20 cm depth were selected for adsorption experiments. Initial batch equilibrium studies indicated low Cr(VI) adsorption capacity in the natural soil, posing a potential groundwater contamination risk. A subsequent health risk assessment, based on residual Cr(VI) concentrations, suggested elevated cancer risks through ingestion exposure pathways, emphasizing the need for effective remediation. To improve adsorption performance, iron–oxide nanoparticles were synthesized via a co–precipitation method at three temperatures (25°C, 60°C, and 90°C) and characterized for their structural, chemical, and magnetic properties. Despite minor variations in morphology and magnetism, adsorption capacities were comparable, with 25°C nanoparticles selected for further studies. Equilibrium studies demonstrated Cr(VI) removal efficiencies of 81.78%, 82.29%, and 83.82% for 10 mg/L initial concentrations using nanoparticles synthesized at 25°C, 60°C, and 90°C, respectively. A composite adsorbent, combining iron– oxide nanoparticles, chitin biopolymer powders, and natural soil, was developed to enhance removal efficiency. Single–factor batch adsorption experiments evaluated the effects of adsorbent dose, pH, contact time, and initial Cr(VI) concentration. The Box–Behnken Design (BBD) within the Response Surface Methodology (RSM) framework optimized adsorption efficiency and analyzed parameter interactions, identifying Cr(VI) concentration as the most influential factor. The adsorption mechanism was further examined through isotherm and kinetic models. Additionally, a socio–economic vulnerability assessment evaluated the implications of Cr(VI) contamination on local communities. A Socio–Economic Vulnerability Index for Cr(VI) [SeVICr(VI)] was developed using 28 indicators across five domains: demographic, social, physical, economic, and exposure. A structured survey of 35 groundwater–dependent households revealed that those near landfill sites, factory workers, and individuals affected by COVID–19 experienced higher exposure risks, regardless of income stability.