X-ray absorption spectroscopy study of chromium recovered from Cr(VI)-containing water with rice husk

The characteristics of the richness in silica and the high porosity of rice husk enable its application as a good, yet cheap, heavy metal adsorbent from wastewater. This study used rice husk to sorb Cr(VI) from wastewater that contained 2000 mg Cr(VI) l^-1. Results of a scanning electron microscopy (SEM) experiment indicate a considerable morphology alteration of the rice husk after the sorption experiments. ¹³C-nuclear magnetic resonance (NMR) measurements show significant decrease in intensity of all the following peaks: carbonylic, carboxylic, aromatic, polysaccharides, carbohydrates and aliphatics. The X-ray absorption near edge structure (XANES) result indicates that about 70% and 90% of the Cr(VI) sorbed on the rice husk after the 12 and 48 h sorption experiments, respectively, were in Cr(III) forms. In the 12 h sorbed rice husk sample, the chromium species distribution is 41% organic Cr(III) +27%Cr(OH)₃+32%CrO₃, while in the 48 h sorbed one, it is 57% organic Cr(III) +31%Cr(OH)₃+12%CrO₃.