Abstract
Natural goethite and thermally treated goethite at different temperature (200–500 °C) was used for removal of Cr(VI). This study was investigated based on the X-ray diffraction (XRD), N2 adsorption/desorption isotherm, high resolution transmission electron microscope (HRTEM), Fourier-transform infrared (FTIR) spectroscopy and adsorption experiments. The result indicates that goethite was unaltered up to 200 °C and transformed to hematite at 300 °C. Natural goethite developed slit-shaped pore at 200 °C and became dominant at 300 °C. With further increase in temperature, pores became spherical. The BET surface area and pore volume also reached maximum at 300 °C and decreased further with increase in temperature. Thus, the goethite calcined at 300 °C showed greater uptake with capacity of 2.053 mg/g as compared to that of natural goethite (0.569 mg/g). The pseudo-second-order kinetic model best described the sorption process. The FTIR and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) further confirms the uptake of Cr(VI) by forming inner-spheric complex.
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