Aluminosilicate minerals complexes

Site-binding constants have been determined for only a limited range of simple oxides with only one type of surface site. Multiple-surface site minerals occurring in the deep-well environment such as silicates, aluminosilicates, and complex oxides (such as manganese oxide) will require much more complex TLMs. 

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

In addition to stabilizing organic products by reaction with metal-exchanged clays, as indicated above, aluminosilicate minerals may enable the preparation of metal organic complexes that cannot be formed in solution. Thus a complex of Cu(II) with rubeanic acid (dithiooxamide) could be prepared by soaking Cu montmorillonite in an acetone solution of rubeanic acid (93). The intercalated complex was monomeric, aligned with Its molecular plane parallel to the interlamellar surfaces, and had a metal ligand ratio of 1 2 despite the tetradentate nature of the rubeanic acid. 

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. 

Al3+ The dominant species are A13+-S02 complexes in low pH, high SO4- water (TS-3, MW-86) and Al(OH)3 in low SO4- and near neutral waters (MW-36, MW-15, MW-12, MW-14). It is wise to bear in mind that accurate analyses for dissolved Al are very difficult to perform. Because of its very low dissolved concentrations, particulate and colloidal particles containing Al can dominate an analysis, unless great care is taken. Driscoll and Postek (1996) note that . .. because particulate minerals exhibit a continuous size distribution, no absolute distinction between dissolved and particulate forms can be made, and results show a strong dependence on filter pore size . In the absence of other errors, analyses for Al should be regarded as maximum possible values, from the point of view of geochemical modeling. It should also be noted that if an Al content is not reported (commonly the case), no conclusions at all can be reached about the saturation state of any aluminosilicate mineral. 

Mica is a generic term for any of several complex hydrous aluminosilicate minerals characterized by their platy shape and pronounced basal cleavage. This per-... 

SA Carroll. The dissolution behavior of corundum, kaohnite, and andalusite A surface complex reaction model for the dissolution behavior of aluminosilicate minerals in diage- netic and weathering environs. PhD thesis, Northwestern University, 1989. P Fletcher, G Sposito. Clay Mineral 24 375-391, 1989. 

At the surface of the raised bog, the pore waters are derived primarily from recharging precipitation, and are high in dissolved organic acids from the oxidation of plant material. pH is low (<5), and dissolved aluminum is high, whereas dissolved silicon and alkaline earth cation concentrations are low. Examination of silt grains from the peat show that aluminosilicate minerals are chemically weathered but quartz is not. In this type of water, aluminum is mobilized as organic-aluminum complexes at acidic pH, and... 

The earth s surface contains rocks and minerals, as well as clays and soils. The minerals may take many forms, including primary aluminosilicate minerals and other complex species that makeup the hard surface, or crust, of the planet. Aluminosilicates are made from aluminum, silicon, and oxygen and account for approximately 82% of the earth s crust by weight. Because of their structure, the soil surface chemistry is dominated by the reactions that occur on oxide and hydroxide-rich surfaces. These surfaces are extremely hydrophilic, layers of adsorbed water molecules surrounded by varying volumes of bulk water. 

---