title: Simultaneous adsorption of phenol and cadmium on amphoteric modified soil.
abstract: Surface modification is an effective way to enhance adsorption of pollutants by soil. In this study, we investigated the individual adsorption of cadmium ion (Cd(2+)) and phenol and also in combination by the clay layer of a loessial soil treated with the amphoteric modifier, duodalkylbetaine (BS-12). Three levels of BS-12 modification were compared in this experiment: (1) unmodified soil (CK), (2) modification with an amount of BS-12 equivalent to 50% of the soil's CEC (50BS) and (3) modification with an amount of BS-12 equivalent to 100% of the soil's CEC (100BS). Cd(2+) adsorption was 0.92-1.70 times higher in the amphoteric modified soil compared to unmodified soil. Adsorption isotherms for Cd(2+) displayed a L1-type shape. Phenol adsorption was 1.25-4.35 times higher in the amphoteric modified soil compared to the unmodified control. The adsorption isotherms of phenol on amphoteric modified soils were generally linear, but changed to L1-type isotherms for modified soil in the Cd(2+)+phenol treatment at 40 degrees C. The results clearly showed that amphoteric modified soil had the ability to simultaneously adsorb Cd(2+) and phenol. Cd(2+) adsorption by the amphoteric modified soil was related to the initial concentration of Cd(2+) in the supernatant. Cd(2+) adsorption in the 100BS treatment exceeded adsorption in the 50BS treatment when Cd(2+) initial concentrations were higher than approximate 200 microg mL(-1). Phenol adsorption by modified soils decreased in the order: 100BS>50BS>CK and was primarily determined by the surface hydrophobicity of the soil. For the unmodified soil, total adsorption in the Cd(2+)+phenol treatment was slightly lower compared to treatments that contained only Cd(2+) or phenol. This indicated an antagonistic effect between the adsorption of Cd(2+) and phenol, which was reduced after amphoteric modification. A comparison of temperature effects on Cd(2+) and phenol adsorption indicated that Cd(2+) was both physically and chemically adsorbed by the amphoteric modified soil, but phenol was primarily adsorbed physically.
authors.affiliation: College of Science, Northwest A & F University, Yangling, Shaanxi 712100, PR China. zfmeng@hotmail.com
authors.forename: Zhao-Fu
authors.initials: ZF
authors.lastname: Meng
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Zhang
authors.forename: Zeng-Qiang
authors.initials: ZQ
authors.lastname: Zhang
mesh_terms: D000327:Adsorption; D002104:Cadmium / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D019216:Metals, Heavy / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D013501:Surface-Active Agents / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D019216:Metals, Heavy; D010636:Phenols; D012987:Soil; D013501:Surface-Active Agents; D002104:Cadmium