title: Effects of pH and phosphate on the adsorptive fractionation of purified Aldrich humic acid on kaolinite and hematite.
abstract: The molecular weight (MW) fractionation of purified Aldrich humic acid (PAHA) resulting from adsorption on kaolinite and hematite was investigated for different solution pH and phosphate conditions. Adsorption was highly pH-dependent, with higher uptake at lower pH values. For all pH conditions, the weight-average MW (MWw) of residual PAHA remaining in solution after adsorption deviated from the original MWw, indicating that preferential adsorption of certain MW components occurred. The extent of preferential adsorption depended on the percent carbon adsorption at a given pH condition. For similar percent carbon adsorption ranges, a greater extent of preferential adsorption of the higher MW PAHA components was observed with higher pH values as demonstrated by the lowest residual MWw value occurring at pH 9. Detailed analyses of selected residual PAHA samples clearly showed that adsorption selectivity for particular MW components was strongly influenced by solution pH. The extent of preferential adsorption of lower MW PAHA components decreased in the presence of a small amount of phosphate. This effect was more evident for hematite than kaolinite, and became greater with lower solution pH irrespective of the mineral type. The different fractionation patterns observed for PAHA were reasonably well explained by the physicochemical trends occurring in its MWw fractions and the underlying sorption processes.
authors.affiliation: Departments of Environmental Engineering & Science and Geological Sciences, School of the Environment, Clemson University, Clemson, SC 29634-0919, USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Hur
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schlautman
mesh_terms: D000327:Adsorption; D005290:Ferric Compounds / Q000737:chemistry*; D006812:Humic Substances / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D008970:Molecular Weight; D010710:Phosphates / Q000737:chemistry*; D013499:Surface Properties; D013696:Temperature
chemical_list: D005290:Ferric Compounds; D006812:Humic Substances; D010710:Phosphates; C000499:ferric oxide; D007616:Kaolin