Adsorption characterizations of fulvic acid fractions onto kaolinite
LI Aimin , XU Minjuan , LI Wenhui , WANG Xuejun , DAI Jingyu
DOI:
Received July 04, 2007,Revised September 07, 2007, Accepted , Available online
Volume 20,2008,Pages 528-535
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Fulvic acids extracted from a typical rice-production region near Taihu Lake of China were fractionated into three fractions including
F4.8, F7.0 and F11.0 (eluted by pH 4.8 bu er, pH 7.0 bu er and pH 11.0 bu er, respectively). Sorption of fulvic acid (FA) fractions onto
kaolinite was studied by batch adsorption experiments, and characterizations of kaolinite before and after adsorption were investigated
using scanning electron microscopy (SEM). Adsorption isotherms of kaolinite for three FA fractions fit well with the Langmuir
adsorption model. The adsorption density of the three fractions was positively correlated with the ratio of the amount of the alkyl
carbon to that of carboxyl and carbonyl carbon in FA fractions and followed an order of F11.0 > F7.0 > F4.8. Hydrophobic interaction
was one of the control mechanisms for the sorption of FA fraction onto kaolinite. SEM images confirmed that compared to blank
kaolinite samples, kaolinite samples coated by a FA fraction displayed an opener and more dispersed conformation resulting from the
disruption of the floc structure in complex. Dispersion of kaolinite after adsorption was due to the repulsion between negatively charged
FA-coated particles, which is closely related to the amount of FA fractions absorbed on kaolinite.
