The Use of Hematite for Chromium(VI) Removal

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Abstract
The ability of hematite to remove Cr(VI) from aqueous solutions has been studied at different concentrations, temperatures and pH. The maximum removal (97%) was observed at 40 °C and pH 2.7 with initial concentrations of 19.23 μmol/L Cr(VI) and 40 g/L hematite. The equilibrium data obey the Langmuir isotherm for the present system. The reaction dynamics have been studied and the process involves both film and pore diffusion to different extents. Mass transfer and diffusion coefficients have been determined. Thermodynamic parameters indicate the spontaneous and endothermic nature of the process. The uptake of Cr(VI) increases as pH decreases and the maximum removal has been attributed to the formation of positively charged aquacomplexes of iron at the surface and a subsequent interaction with the dominant HCrO4 ‐species. An empirical equation has been developed to predict equilibrium adsorption capacity from knowledge of equilibrium adsorbate concentration.