REMOVAL OF HEXAVALENT CHROMIUM IN AQUEOUS SOLUTIONS USING DIFFERENT BIOCHARS AND CHARACTERIZATION OF THE PRODUCTS OF THE CR (VI) ADSORPTION AND REDUCTION
In this study, biochars pyrolyzed from different feedstocks were used to remove Cr(VI) from aqueous solutions. The dried biomasses were pyrolyzed at 300 and 700°C in a pyrolizer. Proximate analysis, including moisture content, mobile matter, resident matter and elemental composition, including C, N, H, S, and O were calculated for the biomasses and biochars. Molar ratios of H/C and O/C were also calculated. The Brunauer-Emmett-Teller and the Barret-Joyner-Halender methods were followed to determine the specific surface area, pore volume, and pore diameter. Structural analysis was performed using Fourier transform infrared spectroscopy. Batch sorption studies (in 0.1 M NaNO3) were carried to quantify the pH effects (pH 2 – 10) on Cr(VI) adsorption to biochars.
Our results showed that soybean stover has higher moisture content, fixed matter, C and O content, and H/C and O/C ratios than that of burcucumber. High Cr(VI) removal percentages were achieved by soybean stover derived biochars, due to their relatively high surface areas. However, when the adsorption data were normalized to the surface area, burcucumber biochar produced at 3000C showed the maximum adsorption (17.61 mg m-2), which may be due to the availability of surface functional groups. Because of permissive evidence from adsorption studies that a fraction of Cr(VI) is irreversibly bound to the biochar, we studied the valence state of Cr using synchrotron-based X-ray absorption spectroscopy. Our work points to combined adsorption and reduction mechanisms of Cr(VI) at the surface of biochars, which has significant implications on the use of biochars in treating Cr-contaminated waters.