Interaction of Cr(VI) species with thermally treated brick clay

PURPOSE: The purpose this research is to investigate the interaction of Cr(VI) species, present as Cr₂O₇ ²⁻, at ambient temperature with brick clay pre-fired at different temperatures. METHODS: A multi-technique approach was used for this investigation. Experiments such as surface titrations, Langmuir and Freundlich adsorption isotherms, mass-firing temperature investigation, scanning electron microscopy, Fourier transform infrared spectra, X-ray fluorescence spectra, and X-ray diffraction were conducted in this investigation. RESULTS: Fired brick clay, which bears a negative charge according to surface titration measurements, shows affinity towards Cr(VI) species despite the negative charge of the source of Cr(VI). The Cr(VI)—brick clay heterogeneous system, which shows the strongest interaction with brick clay fired at 200°C, obeys both the Langmuir and the Freundlich adsorption isotherms with high regression coefficients. Investigation on surface charge, constituents of brick clay, acid treatment of clay particles, and the effect of firing temperature suggests that the reduction of Cr(VI) to Cr(III) by reducing agents present in brick clay makes a significant contribution for adsorption of chromium species followed by subsequent removal. Scanning electron microscopic images support the adsorption of chromium species, and further, many metal ions are released as a result of Cr(VI)—brick clay interaction according to X-ray fluorescence studies. CONCLUSION: It is concluded that fired brick clay shows strong adsorption capacity on Cr(VI), having the maximum interaction with brick clay fired at 200°C. It is proposed that this methodology be extended for treatment of effluents containing Cr(VI) species.