Sorption of humic acid （HA） on mineral surfaces has a profound interest regarding the fate of hydrophobic organic contaminants （HOCs） and carbon sequestration in soils. The objective of our study is to determine t...Sorption of humic acid （HA） on mineral surfaces has a profound interest regarding the fate of hydrophobic organic contaminants （HOCs） and carbon sequestration in soils. The objective of our study is to determine the fractionation behavior of HA upon sorption on mineral surfaces with varying surface properties. HA was coated sequentially on kaolinite （1：1 clay）, montmorillonite （2：1 clay）, and goethite （iron oxide） for four times. The unadsorbed HA fractions were characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy （DRIFT）, and solid state 13C nuclear magnetic resonance spectroscopy （NMR）. The mineral-HA complexes were characterized by DRIFT. Polarity index [（N＋O）/C] revealed higher polarity of the unadsorbed HA fractions after coating on kaolinite, reflecting that relatively higher polarity fractions of HA remain unadsorbed. Sorption of aiiphatic alcohol fraction along with carbohydrate was prominent on kaolinite surface. DRIFT results of the unadsorbed HA fractions indicated more sorption of aiiphatic moieties on both kaolinite and montmorillonite. DRIFT results of the unadsorbed HA fractions after sorption on kaolinite and goethite showed the sorption of the proteinaceons fractions of HA. The HA fractions obtained after coating on goethite showed significant sorption of carboxylic moieties. The results mentioned above comply reasonably well with the DRIFT spectra of the minerai-HA complexes. ^13C NMR results showed higher sorption of anomeric C on kaolinite surface. Higher sorption of paraffinic fraction waS observed on montmorillonite. NMR data inferred the sorption of carboxylic moieties on goethite surface. Overall, this study showed that aliphatic moieties of HA preferentially sorbed on kaolinite and montmorillonite, while carboxylic functional groups play a significant role in sorption of HA on goethite. The sorbed fractions of HA may modify the mineral surface properties, and thus, the interaction with organic contaminants.展开更多
基金supported by the Federal Hatch Program, USA (No.MAS 8532)the Cheung Kong Scholar Program, Ministry ofEducation of Chinathe CSREES, USDA National Research Initiative Competitive Grants Program, USA (No.2005-35107-15278).
文摘Sorption of humic acid （HA） on mineral surfaces has a profound interest regarding the fate of hydrophobic organic contaminants （HOCs） and carbon sequestration in soils. The objective of our study is to determine the fractionation behavior of HA upon sorption on mineral surfaces with varying surface properties. HA was coated sequentially on kaolinite （1：1 clay）, montmorillonite （2：1 clay）, and goethite （iron oxide） for four times. The unadsorbed HA fractions were characterized by elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy （DRIFT）, and solid state 13C nuclear magnetic resonance spectroscopy （NMR）. The mineral-HA complexes were characterized by DRIFT. Polarity index [（N＋O）/C] revealed higher polarity of the unadsorbed HA fractions after coating on kaolinite, reflecting that relatively higher polarity fractions of HA remain unadsorbed. Sorption of aiiphatic alcohol fraction along with carbohydrate was prominent on kaolinite surface. DRIFT results of the unadsorbed HA fractions indicated more sorption of aiiphatic moieties on both kaolinite and montmorillonite. DRIFT results of the unadsorbed HA fractions after sorption on kaolinite and goethite showed the sorption of the proteinaceons fractions of HA. The HA fractions obtained after coating on goethite showed significant sorption of carboxylic moieties. The results mentioned above comply reasonably well with the DRIFT spectra of the minerai-HA complexes. ^13C NMR results showed higher sorption of anomeric C on kaolinite surface. Higher sorption of paraffinic fraction waS observed on montmorillonite. NMR data inferred the sorption of carboxylic moieties on goethite surface. Overall, this study showed that aliphatic moieties of HA preferentially sorbed on kaolinite and montmorillonite, while carboxylic functional groups play a significant role in sorption of HA on goethite. The sorbed fractions of HA may modify the mineral surface properties, and thus, the interaction with organic contaminants.
