Sorption and Reduction of Hexavalent Chromium by Black Carbon Derived from Rice Straw.

Black carbon (BC) is a carbonaceous material arising from incomplete combustion of various organic precursors. One of the major precursors for BC in soils is rice straw, which is a by-product of rice production. In Taiwan, annual production of rice straw is estimated to be 2 million tons, which would yield a large quantity of carbonaceous material as a potential contaminant adsorbent in soils. This work evaluated the Cr(VI) sorption of BC derived from rice straw in relation to the surface characteristics of BC. Rice straw were burned in the air and then treated with HCl/HF solution to remove soluble salts and Si. Sorption of Cr(VI) on black carbon was investigated under various experimental conditions. The results of Cr K-edge XANES suggested that sorbed Cr(VI) on BC was reduced to Cr(III). XPS and FT-IR spectra were obtained for the sorbents before and after reaction to identify the functional groups responsible for sorption and reduction of Cr(VI) on the surface of the sorbent. The results showed that BC derived from rice straw is an effective sorbent for Cr(VI) and thus may play an important role in determining the fate of Cr(VI) in soils.