Sorption on clay minerals

There are several natural processes that can remove arsenic from groundwaters and other natural waters. These processes were introduced in Chapter 3 and include (1) precipitation and association with sulfides, (2) sorption on clay minerals, and (3) carbonate associations. This section discusses these processes in further detail. Additional discussions occur in Chapter 7, where some of the processes are utilized in treatment technologies for removing arsenic from water. 

Teppen et al. [89] have used a flexible model for clay minerals that allows full movement of the M-O-M bonds in the clay structure, where M represents Si, Al, or other cations in the octahedral sheet. This model was used in MD simulations of interactions of hydrated clay minerals with trichloroethene [90, 91]. The simulations suggest that at least three distinct mechanisms coexist for trichloroethene sorption on clay minerals [90], The most stable interactions of trichloroethene with clay surfaces are by full molecular contact, coplanar with the basal surface. The second type more reversible, less stable is adsorption through single-atom contact between one chlorine atom and the surface. In a third mechanism, trichloroethene interacts with the first water layer and does not interact with clay surface directly. Using MC and MD simulation the structure and dynamics of methane in hydrated Na-smectite were studied [92], Methane particles are solvated by approximately 12-13 water molecules, with six oxygen atoms from the clay surface completing the coordination shell. 

Neubauer, U., Nowak, B., Fuirer, G.. and Schulin, R. (2000). Heavy metal sorption on clay minerals affected by the siderophore desferrioxamine B. Environ. Sci. Technol. 34, 2749-2755. 

Cygan, R.T. 1998. Molecular models of metal sorption on clay minerals, p. 127-176. In J.D. Kubicki and W.F. Bleam (ed.) Molecular modeling of clays and mineral surfaces. Clay Miner. Soc., Boulder, CO. 

Ni Sorption on Clay Minerals A Case Study. Initial research with Co/clay mineral systems demonstrated the formation of nucleation products using XAFS spectroscopy, but the stmcture was not strictly identified and was referred to as a Co hydroxide-like stmcture (11,12). Thus, the exact mechanism for surface precipitate formation remained unknown. Recent research in our laboratory and elsewhere suggests that during sorption of Ni and Co metal ions, dissolution of the clay mineral or aluminum oxide surface can lead to precipitation of mixed Ni/Al and Co/Al hydroxide phases at the mineral/water interface (14,16,17,67,71). This process could act as a significant sink for metals in soils. The following discussion focuses on some of the recent research of our group on the formation kinetics of mixed cation hydroxide phases, using a combination of macroscopic and molecular approaches (14-17). 

Active sites involved in NAC sorption on clay minerals can be divided into two broad categories of surface sites polar and nonpolar. Polar sites originate from isomorphic substitution sites and from broken edges. Nonpolar sites, on the other hand, occur on the surfaces of neutral mineral surfaces. Current evidence would suggest that NAC accessibility to both types of surface sites is a prerequisite to sorption. 

The most important leachate reactions are dissolution and precipitation of solids and minerals, redox (reduction/oxidation) reactions with organic matter, and ion exchange and sorption on clay minerals and organic matter. 

Sorption of cesium in synthetic groundwater on clay minerals ... 

Sorption Behavior of Tri valent Actinides and Rare Earths on Clay Minerals ... 

G. D., "Sorption Behavior of Trivalent Actinides and Rare Earths on Clay Minerals," ACS Symposium Series on Radioactive Waste in Geologic Storage, R. F. Gould, Ed., Miami Beach, Florida, Sept. 11-15, 1978. 

Zhuang, J. and Yu, G.-R. (2002) Effects of surface coatings on electrochemical properties and contaminant sorption of clay minerals. Chemosphere, 49(6), 619-28. 

Figure 3.7. Phenanthrene sorption isotherms on (A) the whole Amherst peat soil humic acid, (B) montmorillonite and a montmorillonite-humic acid complex (5 1 ratio), and (C) kaolin-ite and kaolinite-humic acid complex (5 1 ratio). Insets in parts B and C are the respective isotherms presented on a linear scale. Reprinted from Wang, K., and Xing, B. (2005). Structural and sorption characteristics of adsorbed humic acid on clay minerals. J. Environ. Qual. 34, 342-349, with permission from the Soil Science Society of America.

Feng, X., Simpson, A. J., and Simpson, M. J. (2005). Chemical and mineralogical controls on humic acid sorption to clay mineral surfaces. Org. Geochem. 36,1553-1566. 

Wang, K., and Xing, B. (2005). Structural and sorption characteristics of adsorbed humic acid on clay minerals. J. Environ. Qual. 34, 342-349. 

Zavarzina, A. G. (2001). Sorption of soil-originated humic acids on clay minerals, Proceedings. Eleventh Annual V. M. Goldschmidt Conference, May 20-24, Hot Springs, Va. 

Sparks et al. (1980b) introduced a continuous flow method (next subsection) that is quite similar in principle to liquid-phase column chromatography. This method was used to study potassium adsorption dynamics on soils and clay minerals (Sparks and Jardine, 1981 Sparks and Rechcigl, 1982 Jardine and Sparks, 1984 Ogwada and Sparks, 1986a,b,c), silicate sorption on soils (Miller et al., 1986), S04 sorption and desorption on soils (Hodges and Johnson, 1987), and Al reactions on clay minerals and peat (Jardine etal., 1985a). 

Nagy, N. M., J. Kdnya, and Gy. Wazelischen-Kun. 1999. The sorption and desorption of carrier-free radioactive isotopes on clay minerals and Hungarian soils. Coll. Surf. 152 245-250. 

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