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.
