Smectite-rich clays

Clays, like most other natural substances, have some beneficial and some hazardous impacts on the environment. As described in Part 1, clays have a tendeney to adsorb and immobilize ions. This property enables clays to remove ions of pollutants and contaminants from leachates and waste water, thus reducing pollution and contamination. It also facilitates the use of clays in different pollution control measures like carriers of pesticides, liners in waste disposal etc. Clays can also be used in nuclear waste management clay buffers are built from smectite-rich clays into which the containers of radioactive wastes can be safely disposed (Pusch, 2006). 

The cylindrical masses of radioactive wastes are enclosed in containers, separated from one another by smectite-rich clays. These containers are placed in vertical boreholes or long horizontal bored or blasted tunnels. For high-level radioactive wastes, the containers are stored at a depth of 300-800 m. Low- and medium-level waste has shorter lifetimes and can be stored at smaller depth. 

The following properties of smectite-rich clays make them suitable for this purpose ... 

Samples of the red clay having uniform physical and chemical characteristics were provided by G. R. Heath of the University of Rhode Island. The samples were obtained from core LLUU-GPC-2, collected on October 11, 1976, at 30° 20.9 n, 157° 50.85 w, water depth 5821 meters, and are representative of the smectite-rich region of the red clays which occurs in the sediment at depths below about ten meters. In this region, the sediment appears to contain about five to six percent by weight leachable iron and manganese in the form of hydrous oxides. The remaining material appears to be dominated by iron-rich smectite and lesser, varying amounts of phillipsite (2). The results of a semi-quantitative (precision in data is within a factor of 2) elemental analysis... 

The mineralogical composition of Sahara dust particles shows the predominance of aluminosilicates (clays). Illite is also present in many cases while quartz particles are rare. Scanning Electron Microscopy (SEM) results on dust composition transported over different regions in the Mediterranean Basin have shown that Al-rich clay minerals such as illite and kaolinite are very common in PM10 for Cypms and dominant for Crete. Dust particles are also very rich in calcium which is distributed between calcite, dolomite and sulphates and Ca-Si particles (e.g. smectites) whereas iron oxides are often detected [43]. 

As mixed-layer I/S clays become smectite-rich, their ion exchange and swelling properties approach those of the pure smectites. Other three-layer clays, including the chlorites and vermiculites, also commonly occur in soils in mixed-layer form (e.g., mixed-layer chlorite-smectite [-vermicu-lite]) (cf. Wilson and Nadeau 1985 Drever 1988). 

Sandstones in the central basin, with the highest initial porosities and permeabilities, were the first to experience extensive cementation. Presumably these were flow pathways and, considering the pore fluid volumes required for extensive cementation, it is not surprising that this relationship occurs. The basis for this observation is that sandstones with early high-volume cements are notably clay free (relatively low elemental Al content) compared with adjacent uncemented sandstones (Boles, 1989). The clay is a smectite-rich mixed-layer smectite/illite clay, believed to be detrital on the basis of its... 

Anchizone after Kibler (1964, 1968), a transitional zone between the diagenetic zone and the epizone as defined by IC mean values between 0.42 and 0.25 A°20. [Kaolinite and/or dioctahedral illite/smectite interstratified clay mineral with more than about 10% expandable layers are absent in normal clastic rocks, but they may persist in carbonate rocks, and in organic matter-rich, Na-rich and K-poor shales.]... 

The clays found in sedimentary phosphate rocks include illite, kaolinite, smectites, and magnesium-rich clays such as palygorskite and sepiolite. Illite often appears to be a detrital mineral. Kaolinite, smectites, and magnesium-rich clays often appear to occur in zones within phosphate deposits. This zonation may be related to weathering and the general alteration of deposits under surface or near-surface conditions [15,16]. Clay-Iike minerals such as the zeolite clinoptilolite occasionally are found in phosphate rock. 

Bentonite is a rock rich in montmorillonite that has usually resulted from the alteration of volcanic dust (ash) of the intermediate (latitic) siliceous types. In general, reUcts of partially unaltered feldspar, quartz, or volcanic glass shards offer evidence of the parent rock. Most adsorbent clays, bleaching clays, and many clay catalysts are smectites, although some are palygorskite [1337-76 ]. 

In some pipe deposits in geothermal power plants, arsenic is associated with clays or other silicate minerals rather than sulfides or (oxy)(hydr)oxides. Pascua et al. (2005) found that about 80 % of the arsenic in pipe scales from a Japanese geothermal power plant was associated with Mg-rich smectite clays. The arsenic (mostly III) was probably located in the crystalline structures of the clays and/or present as submicron inclusions. 

Mineralogically the sediments of the laminite series consist of carbonates (mainly dolomite and calcite), various clay minerals, zeolites, opal, quartz and rare gypsum (8). The occurrence of gypsum, based on our X-ray diffraction (XRD) data, is restricted to the marl unit. Deposition, according to Jankowski (8), occurred in a periodically evaporitic, stagnant lake. The high bitumen concentrations most probably were responsible for the preservation of unusual minerals such as Mg-rich calcites (up to 25% Mg 9) and bituminous smectites (Muller, G., University of Heidelberg, personal communication, 1989). 

Evidences for electron transfer from surface tg bulk. According to the nature of the clay, variable amounts of Fe are present in the lattice. Glauconite, which is an iron rich member of the dioctahedral smectite family, reacts at pH 7 with sodium... 

Saponite is a naturally occurring phyllosilicate clay of the smectite (montmorillonite) group. It is a magnesium-rich hydrated aluminum silicate and is present as a component of some commercial magnesium aluminum silicate clays. Saponite is a mineral with an approximate empirical formula owing to the variability in cation substitution see Table I. 

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