Iron modified coal gangue for light assisted attenuation of aqueous hexavalent chromium

Abstract

Coal gangue is a potential mineral precursor for water-treatment materials, but the effect of iron modification on aqueous hexavalent chromium [Cr(VI)] attenuation requires evaluation. This study compares a calcined and acid-washed gangue-derived material (SA) with its iron-modified counterpart (SAF) under white light-emitting diode irradiation. SAF was prepared by treatment with an iron nitrate precursor in N,N-dimethylformamide at 200 °C for 15 h, followed by centrifugation, drying, and calcination in air at 600 °C for 6 h. Powder X-ray diffraction showed similar dominant mineral reflections for SA and SAF, while surface spectroscopy and elemental mapping detected iron in SAF. Relative to SA, SAF exhibited a higher transient photocurrent and a smaller electrochemical impedance arc under the measurement conditions. The concentration profiles indicate faster aqueous Cr(VI) attenuation by SAF at pH 7 than by SA, with a steeper decline for acidified SAF at pH 3. Quantitative rate comparisons require validated sampling and concentration measurements. These observations do not independently establish complete chromium removal, a specific iron oxide phase, or a zeolite heterojunction. A possible contribution from light-driven electron transfer is discussed alongside adsorption and iron-mediated reactions. The findings identify an iron-modified gangue-derived material for further investigation, with chromium mass balance, iron leaching, independent replication, and authentic wastewater testing required to establish environmental applicability.

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