Adsorption aluminosilicate minerals

Adsorption of Metal Ions and Complexes on Aluminosilicate Minerals... 

As far as adsorption properties are concerned, aluminosilicate minerals may be divided into 3 general groups -... 

Sorption processes are influenced not just by the natures of the absorbate ion(s) and the mineral surface, but also by the solution pH and the concentrations of the various components in the solution. Even apparently simple absorption reactions may involve a series of chemical equilibria, especially in natural systems. Thus in only a comparatively small number of cases has an understanding been achieved of either the precise chemical form(s) of the adsorbed species or of the exact nature of the adsorption sites. The difficulties of such characterization arise from (i) the number of sites for adsorption on the mineral surface that are present because of the isomorphous substitutions and structural defects that commonly occur in aluminosilicate minerals, and (ii) the difference in the chemistry of solutions in contact with a solid surface as compound to bulk solution. Much of our present understanding is derived from experiments using spectroscopic techniques which are able to produce information at the molecular level. Although individual methods may often be applicable to only special situations, significant advances in our knowledge have been made... 

The retardation of subsurface transport of TNT arises from this compound s absorption into NOM and adsorption onto mineral siloxane surfaces covered with weakly hydrated cations like potassium (but not sodium and calcium). While components of feldspars exhibit some siloxane surfaces, here we anticipate that most of the silox-anes occur in the aluminosilicate clay minerals (e.g., illite) because these particles have such high specific surface areas (Table 11.3). Hence, the total for TNT may be found at this site ... 

In cases where neutral or alkaline mine drainage predominates, problems may arise because of elevated concentrations of SO4, iron, manganese, and other solutes that are derived from sulfide oxidation or from reactions with carbonate or aluminosilicate minerals. Dissolved iron and aluminum may precipitate as the pH increases, and these precipitates can act as substrates for adsorption and co-precipitation (Stumm and Sulzberger, 1992 Foos, 1997 Brake et al., 2001). The dissolution of siderite,... 

Aquifer solids are rarely composed of discrete mineral phases such as quartz, feldspar, or clay minerals. Over time, weathering reactions produce complex mixtures of different minerals of varying degrees of crystallinity. Since adsorption implies a surface or near surface phenomena, it is the mineral surfaces of aquifer solids that are of principal concern. These surfaces can consist of mixtures and coatings of various oxides, aluminosilicate minerals, carbonates, and organic matter (Coston et al., 1995 Farmer et al., 1991 Jeime, 1976 Taylor, 1987). 

Cationic contaminants include numerous heavy metals and transition metals and several alkaline earth and alkali metals. The adsorption reactions of Pb, Cd2+, Co- . 1 Ig- C Cu- -. Zii- C i-". L Oz- - Sr- C Cs+, and NpO+ onto different oxide, hydroxide, and aluminosilicate minerals have all been investigated using XAS. The nature of the surface complexes formed has been found to be a function of crystal structure, sorbing cation, ligands present in solution, and surface coverage. 

Zeolite Any of the minerals of the zeolite group. Aluminosilicate minerals with an open framework structure that allows for easily reversible hydration, gas adsorption, and either cation or anion exchange. 

The major components of most soils are silicate and aluminosilicate minerals. Under natural conditions, these components have negative charges. Anionic pollutants are less attracted to negatively charged surfaces. The high solubility of anionic pollutants and low adsorptive capacity of soils can result in the persistence of high concentration of anionic pollutants, including d , Cr(VI), NOi, Se(VI), Se(IV), As(V), As(III),Tc(VII), Mo(VI), POi, F-, ClOj, and SOj (Blowes et aL, 2000). 

A zeolite, of course, is a crystalline aluminosilicate mineral with a very open pore structure and a very large water adsorption capacity. It possesses two well-defined chemical properties. First, it can be reversibly hydrated and dehydrated. Second, it has a high reversible ion exchange capacity. This capacity corresponds to one equivalent of cation per A1 atom in the anionic framework. The anionic nature of the framework derives from the substitution of trivalent A1 atoms for Si atoms in the tetracoordinated structure. 

The name of zeolites, which originates from the Greek words zeo (to boil) and lithos (stone), was given some 250 years ago to a family of minerals (hydrated aluminosilicates) that exhibited intumescence when heated in a flame. However, the history of zeolites really began 60 years ago with the development of synthesis methods. Commercial applications in three main fields—ion exchange, adsorption, and catalysis—were rapidly developed, the corresponding processes being more environmentally friendly than their predecessors. 

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