title: Transport and interactions of kaolinite and mercury in saturated sand media.
abstract: To evaluate the potential of Hg release and co-transport by colloids, it is important to understand how Hg, colloids and Hg-loaded colloids migrate in soils. Hg sorption by kaolinite and sand were nonlinear and fit the Langmuir model, with the maximum Hg sorption capacity being 1.2mg/g kaolinite and 0.11 mg/g sand. Co-transport of Hg and kaolinite was evaluated using: (1) 1 or 100 mg/L Hg or 100mg/L kaolinite, (2) 1 or 100 mg/L Hg mixed with 100mg/L kaolinite, (3) 1 or 100 mg/L Hg presorbed onto kaolinite, and (4) 25 0mg/L kaolinite in Hg-loaded sand columns. The presence of kaolinite (100 mg/L) reduced Hg's mobility through sand column by increasing deposition rate of Hg-loaded kaolinite. At 100 mg/L Hg, soluble Hg dominated Hg transport; but at 1 mg/L Hg, colloidal Hg (Hg sorbed on kaolinite) affected Hg transport. Preloading 100 mg/L Hg onto kaolinite (0.43 mg/g) reduced kaolinite's mobility with low recovery rate (78%), with Hg retardation (R=1) in Hg-loaded kaolinite being lower than Hg retardation at 100 mg/L Hg (R=1.287). The Hg recovery rate (93%) from Hg-loaded kaolinite at 1mg/L Hg was higher compared to 22% from 1 mg/L Hg. Kaolinite can serve as a carrier to enhance Hg transport in porous media, with 250 mg/L kaolinite mobilizing ~2.4% Hg presorbed onto sand media. Correlation analysis revealed that desorbed Hg was significantly correlated with kaolinite (r=0.81, P<0.0001). Hence kaolinite enhanced Hg transport in the sand media serving both as a carrier (Hg was loaded before transport) and as mobile colloids stripping Hg off the sand media (Hg was loaded during transport).
authors.affiliation: Soil and Water Science Department, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Yingjia
authors.initials: Y
authors.lastname: Zhu
authors.forename: Lena Q
authors.initials: LQ
authors.lastname: Ma
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.forename: J C
authors.initials: JC
authors.lastname: Bonzongo
authors.forename: Willie
authors.initials: W
authors.lastname: Harris
authors.forename: Binhe
authors.initials: B
authors.lastname: Gu
mesh_terms: D000327:Adsorption; D000465:Algorithms; D001965:Bromides / Q000737:chemistry; D003102:Colloids; D007616:Kaolin / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D015233:Models, Statistical; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D013535:Suspensions; D013816:Thermodynamics
chemical_list: D001965:Bromides; D003102:Colloids; D013535:Suspensions; D007616:Kaolin; D012822:Silicon Dioxide; D008628:Mercury