Chromium kaolinite

The adsorption of transition metal complexes by minerals is often followed by reactions which change the coordination environment around the metal ion. Thus in the adsorption of hexaamminechromium(III) and tris(ethylenediamine) chromium(III) by chlorite, illite and kaolinite, XPS showed that hydrolysis reactions occurred, leading to the formation of aqua complexes (67). In a similar manner, dehydration of hexaaraminecobalt(III) and chloropentaamminecobalt(III) adsorbed on montmorillonite led to the formation of cobalt(II) hydroxide and ammonium ions (68), the reaction being conveniently followed by the IR absorbance of the ammonium ions. Demetallation of complexes can also occur, as in the case of dehydration of tin tetra(4-pyridyl) porphyrin adsorbed on Na hectorite (69). The reaction, which was observed using UV-visible and luminescence spectroscopy, was reversible indicating that the Sn(IV) cation and porphyrin anion remained close to one another after destruction of the complex. 

Treatment of many materials results in the liberation of the trace elements into the environment, which can have an impact on health. Coal is a particularly useful example of a major source of trace elements poured into the environment from coal combustion. Coal contains an alphabet soup of trace elements, including arsenic, mercury, uranium, selenium, and chromium. Pyrite is a ubiquitous mineral found in coal, but coal can also contain a variety of other mineral phases. West Virginia coal, for example, includes clay minerals such as kaolinite (35%) and illite (35%i), quartz (18%i), pyrite (7%), and calcite (3%). A number of projects that utilize coal for power generation while minimizing the impact on the environment have been described. An excellent example is the SNOX (trademark owner Haldor Topsoe) demonstration project, which utilizes high-sulfur coal (2.8%). The demonstration project of this technology, equally funded by the U.S. Department of Energy and participants at a total cost... 

Clams, oysters, and mussels accumulate chromium from the medium or from contaminated sediments at comparatively low concentrations. For example, oysters subjected to 5.0 (xg Cr+ /L for 12 weeks contained 3.1 mg Cr/kg DW in soft parts and retained 52% of the accumulated chromium after they were transferred to chromium-free seawater for 28 weeks. Mussels (Mytilus edulis) subjected to the same dose-time regimen contained 4.8 mg/kg, but retained only 39% after 28 weeks of depuration. Both oysters and mussels contained higher residues after exposure to 10.0 jig Cr /L for 12 weeks 5.6 and 9.4 mg Cr/kg DW in soft parts, respectively, and both contained substantial (30-58%) residues after 28 weeks in a chromium-free environment. In studies with mussels and softshell clams (Mya arenaria), it was demonstrated that chromium in New Hampshire sediments (contaminated with Cr+ from tannery wastes) was bioavailable to clams by diffusion from seawater, and that both diffusion and particulate uptake were important pathways for mussels. Accumulation was observed at sediment chromium concentrations as low as 150.0 mg/kg. Kaolinite sediments containing up to 1200.0 mg Cr+ /kg produced the most pronounced adverse effects on filtration rates and ciliary activity of bivalve mollusks, leading the authors to conclude that chromium that has accumulated in areas affected by industrial wastes might have serious consequences to filter feeding bivalves. 

The matrix of the till on Mt. Sirius is composed of quartz, plagioclase, K-feldspar, kaolinite, montmoril-lonite, and illite (Hagen 1988, p. 22). The sand-size fractions (1.0-0.0625 nun) contain heavy minerals including pyroxene, hornblende, garnet, tourmaline, rutile, zircon, apatite, sphene, magnetite, ilmenite, hematite, pyrite, and chalcopyrite. A bulk sample of the heavy mineral fraction of till on ML Sirius in Table 19.1 is composed primarily of iron, titanium, and manganese with lesser concentrations of chromium, zinc, copper, and nickel (Hagen 1988). Additional analyses of the heavy-mineral fractions of till in the Transantarctic Mountains were published by Faure et al. (1995). 

Clays and metal oxides and salts such as talc, kaolinite, mica, zinc oxide, titanium oxide, iron oxide, hydrated chromium oxide, cobalt blue, ultramarine blue, calcium carbonate, barium sulfate, etc. are widely used as pigments for cosmetics. Since these pigments possess acidic and basic surface properties, and hence catalytic activity, cos-... 

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