title: Concept model of the formation process of humic acid-kaolin complexes deduced by trichloroethylene sorption experiments and various characterizations.
abstract: To explore the interactions between soil organic matter and minerals, humic acid (HA, as organic matter), kaolin (as a mineral component) and Ca(2+) (as metal ions) were used to prepare HA-kaolin and Ca-HA-kaolin complexes. These complexes were used in trichloroethylene (TCE) sorption experiments and various characterizations. Interactions between HA and kaolin during the formation of their complexes were confirmed by the obvious differences between the Qe (experimental sorbed TCE) and Qe_p (predicted sorbed TCE) values of all detected samples. The partition coefficient kd obtained for the different samples indicated that both the organic content (fom) and Ca(2+) could significantly impact the interactions. Based on experimental results and various characterizations, a concept model was developed. In the absence of Ca(2+), HA molecules first patched onto charged sites of kaolin surfaces, filling the pores. Subsequently, as the HA content increased and the first HA layer reached saturation, an outer layer of HA began to form, compressing the inner HA layer. As HA loading continued, the second layer reached saturation, such that an outer-third layer began to form, compressing the inner layers. In the presence of Ca(2+), which not only can promote kaolin self-aggregation but can also boost HA attachment to kaolin, HA molecules were first surrounded by kaolin. Subsequently, first and second layers formed (with inner layer compression) via the same process as described above in the absence of Ca(2+), except that the second layer continued to load rather than reach saturation, within the investigated conditions, because of enhanced HA aggregation caused by Ca(2+).
authors.affiliation: School of Water Resources and Environment, and Beijing Key Laboratory of Water Resources and Environment Engineering, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, PR China. Electronic address: coleanie@cugb.edu.cn.
authors.forename: Xiaojing
authors.initials: X
authors.lastname: Zhu
authors.affiliation: School of Water Resources and Environment, and Beijing Key Laboratory of Water Resources and Environment Engineering, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, PR China. Electronic address: jthe@cugb.edu.cn.
authors.forename: Jiangtao
authors.initials: J
authors.lastname: He
authors.affiliation: School of Water Resources and Environment, and Beijing Key Laboratory of Water Resources and Environment Engineering, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, PR China.
authors.forename: Sihui
authors.initials: S
authors.lastname: Su
authors.affiliation: School of Water Resources and Environment, and Beijing Key Laboratory of Water Resources and Environment Engineering, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, PR China.
authors.forename: Xiaoliang
authors.initials: X
authors.lastname: Zhang
authors.affiliation: School of Water Resources and Environment, and Beijing Key Laboratory of Water Resources and Environment Engineering, China University of Geosciences (Beijing), 29 Xueyuan Road, Beijing 100083, PR China.
authors.forename: Fei
authors.initials: F
authors.lastname: Wang
mesh_terms: D000327:Adsorption; D002118:Calcium / Q000737:chemistry*; D006812:Humic Substances; D007616:Kaolin / Q000737:chemistry*; D012989:Soil Pollutants / Q000737:chemistry*; D014241:Trichloroethylene / Q000737:chemistry*
chemical_list: D006812:Humic Substances; D012989:Soil Pollutants; D007616:Kaolin; D014241:Trichloroethylene; D002118:Calcium
keywords: Ca(2+); Humic acid; Kaolin; Organo-mineral complexes; Trichloroethylene sorption