Enhanced chlorophenol sorption of soils by rice-straw-ash amendment

Rice-straw burning is a common post-harvest practice on rice paddy land, which results in the accumulation of rice-straw ash (RSA) in paddy soil. Because the occurrence of RSA in soil may affect the fate and transport of contaminants, this study investigated the sorption of 3-chlorophenol (3-CP) on RSA and RSA amended soils to evaluate the sorptive properties of RSA in soils. The results showed that the sorption of 3-CP to RSA proceeds through a surface reaction rather than through partitioning and that the neutral form of 3-CP is preferentially sorbed to the surface when compared to the deprotonated anionic form of 3-CP. The addition of RSA to the soils enhanced the overall 3-CP sorption, indicating that RSA amendment may be applied to retard the movement of 3-CP in contaminated soils. As the RSA content in the soils was increased from 0% to 2%, the Langmuir sorption maximum of the soils increased from 18-80 to 256-274 mg kg−1. Thus, RSA contributed more to the total sorption of the soils than other major components in the soils. Nonetheless, the 3-CP sorption of the soils containing RSA was less than the combination of pure RSA and the soils, thereby indicating that the 3-CP sorption of RSA was suppressed. This may be attributed to the competition of organic matter or other soil components for the surface binding sites of RSA.