Clay minerals in coal

Clay Minerals. The clay minerals in coal all contain water bound within their lattices. Kaolinite contains 13.96%, illite 4.5%, and mont-morillonite 5% bound water. In addition, the montmorillonite in the mixed-layer clays also contains interlayer or adsorbed water. All of the water is lost during the high-temperature ashing. 

The usual method utilized to identify the clay minerals in coal is X-ray diffraction of the low-temperature ash (LTA), but because of the poor crystallinity of the clays in the coal, the technique cannot be used for quantitative measurements. The Mossbauer effect does not provide much improvement owing to the small iron content of the clays. A coal rich in clays is shown in Figure 7 (about 10% mineral matter). The two peaks at higher... 

Gluskoter, H. J., Clay Minerals in Illinois Coals, J. Sediment Petrology... 

There are two types of minerals in coal (1) extraneous mineral matter and (2) inherent mineral matter. Extraneous mineral matter consists of materials such as calcium, magnesium, and ferrous carbonates pyrite marcasite clay shale sand and gypsum. Inherent mineral matter represents the inorganic elements combined with organic components of coal that originated from the plant materials from which the coal was formed. 

A large number of distinct mineral phases have been reported in various coals (Table 5.1), although lists of minerals in coal may contain as many as 50 to 60 minerals, most fall into one of five groups (1) aluminosilicate minerals (clay minerals), (2) sulfide and sulfate minerals, (3) carbonate minerals, (4) silicate minerals (principally quartz), and (5) other minerals that include minerals that may occur in trace amounts or may be specific to a particular coal having originated because of the localized deposition and maturation conditions (Speight, 1994, and references cited therein). 

The major minerals in coal are clays. Kaolinite is usually present in coal, but its identification by Moessbauer spectroscopy is very difficult due to the small amount of iron present and to surface contamination of the clay grains with iron oxides, mainly goethite. The other clay minerals present in coal are il-lite, chlorite and mixed clays. Their identification is not always easy. We have used a simple method, carrying out Moessbauer measurements at low temperatures and applying an external magnetic field to resolve the spectra and distinguish, for example, between illite and chlorite (11). 

Clays are volumetric ally the most abundant mineral group in coal. They can be authigenic or detrital in origin. Kaolinite is the most common clay and the most common authigenic mineral in coals. The silicon and aluminum in kaolinite are, perhaps, residual from the dissolution of ferromagnesian minerals and feldspars. Illite and mixed layer clays in coal are almost exclusively detrital in origin. Chlorites, smectites, and other clay minerals may be abundant locally. 

Figure 14 Backscattered SEM image depicting detrital clay and quartz grains in a bituminous coal. Most minerals in coal are only (1-2 pm) in diameter (scale bar = 10 pm).

The Lower Kittanning coal contains kaolinite (well-crystallized), illite/mica and expandable clays. Low total clay contents are observed in the center of the study area, where the coal is rich in pyrite, and in the north-central region where high quartz contents are observed. High total clay contents are seen on the northwestern and eastern margins of the basin. Because clay mineral data are presented as a percentage of the low-temperature ash, variations in the quartz and pyrite contents influence the proportionate distribution of the clays. To avoid this problem, the relative amounts of individual clay minerals in the clay (less than 2 micron) fraction were examined. As this size fraction contains only clays, variations in quartz and pyrite do not influence the results. 

Clay minerals, quartz, calcite, siderite, and pyrite/marcasite are the most common minerals in coals. All naturally occurring elements have been found in coal. 

The most common minerals in coal (e.g., ilUte clay, pyrite, quartz, and calcite) are made up of these most common elanents (in rough order of decreasing abundance) oxygen, aluminum, silicon, iron, sulfur, and calcium. These minerals and other less common minerals usually contain the bulk of the trace elanents present in coal (Finkelman, 1982,1993 Davidson and Clarke, 1996 Davidson, 2000). 

Although much is known about the minerals in coal, much remains to be learned about their occurrence, abundance, origin, and composition. For example, the type of clay mineral in a coal, whether montmorillonite or illite, determines how a coal will react when burned. 

Minerals of great variety have been studied using TA techniques - particularly clay minerals and coal, lignite, and wood. Traditionally, the simultaneous methods have been applied in these cases, but increasingly, new methods such as sample controlled TA are becoming more prominent, particularly for studies of pyrolysis and combustion of coals. The rationale for using SCTA over conventional TA for the study of coal is simply related to overcoming the... 

Very finely divided minerals may be difficult to purify by flotation since the particles may a ere to larger, undesired minerals—or vice versa, the fines may be an impurity to be removed. The latter is the case with Ii02 (anatase) impurity in kaolin clay [87]. In carrier flotation, a coarser, separable mineral is added that will selectively pick up the fines [88,89]. The added mineral may be in the form of a floe (ferric hydroxide), and the process is called adsorbing colloid flotation [90]. The fines may be aggregated to reduce their loss, as in the addition of oil to agglomerate coal fines [91]. 

On the earth itself, however, hydrogen is not the most common I element it is only the tenth most common on the basis of weight, and only third in the number of atoms. Hydrogen, chemically combined with other elements, is found in huge quantities in coal. and petroleum, in clay and some minerals, and in all plant and animal matter. If you weigh 100 pounds, 10 pounds of you is hydrogen. 

But the founders were not concerned merely with balance sheets. They drew their inspiration from the gurgling of water, the perfume of damp earth, and every vegetable and mineral in the earth. Could health, personal beauty — yes, even universal brotherhood — be created by two dozen men of dynamic chemical genius They believed it could, By 1925, they had nursed food from arid lands, made fats and fuels from coal and water, and were dreaming of making copper out of clay. 

Clay fillers, for PVC polymers, 25 675 Clay liners, in landfill design, 25 879 Clay minerals, 6 685-686 in coal, 6 718... 

Cadmium is found naturally deep in the subsurface in zinc, lead, and copper ores, in coal, shales, and other fossil fuels it also is released during volcanic activity. These deposits can serve as sources to ground and surface waters, especially when in contact with soft, acidic waters. Chloride, nitrate, and sulfate salts of cadmium are soluble, and sorption to soils is pH-dependent (increasing with alkalinity). Cadmium found in association with carbonate minerals, precipitated as stable solid compounds, or coprecipitated with hydrous iron oxides is less likely to be mobilized by resuspension of sediments or biological activity. Cadmium absorbed to mineral surfaces (e.g., clay) or organic materials is more easily bioaccumulated or released in a dissolved state when sediments are disturbed, such as during flooding. 

The occurrence of non-carbonaceous material in coals has been the subject of much research, especially in relation to its effect on utilization and ash formation (4-14). In contrast to high rank coals in which minerals constitute almost all of the non-carbonaceous fraction, the low rank coals have two categories of non-carbonaceous material minerals which occur as discrete particles of quartz, marcasite, clays, etc. and inorganics which occur as w er soluble salts and exchangeable ions such as NaCl,... 

The use of BSE images on the SEM screen was ideal for the detection of minerals in low rank coals. The difference in atomic number between the major components of the coal matrix (C, H, N and 0) and the elements present in the mineral species (Si, Al, Fe, Ca) causes the minerals to appear bright against the dark coal background Variations in the BSE brightness between minerals was such that the different minerals present were also distinguishable. However, it is difficult to differentiate between quartz and clay (kaolinite) just from a BSE image. 

Equations such as equation (1) above imply that the oxidative dissolution of pyrite is congruent, directly liberating Fe2+, SO4, and H+ to solution. However, in the common circumstance that water is insufficiently abundant to immediately transport the oxidation products away from the mineral surfaces, pyrite oxidation more commonly results initially in the accumulation of various hydroxysulphate evaporite minerals. These minerals form efflorescent crusts, typically white and yellow in colour, on the surfaces of pyrite-rich coals and mudstones (Fig. 1), and they effectively store the oxidation products in a readily soluble form until some hydro-logical event delivers sufficient water to dissolve and transport them away. Because pyrite often occurs in mudstones, where Al-bearing clay minerals are in contact with acidic pyrite oxidation waters, A1 is frequently released from the clays and is also stored in these hydroxysulphate phases. When these minerals finally dissolve, they result in abrupt and extreme increases in dissolved acidity. For this reason, they have been termed acid generating salts (AGS) (Bayless... 

Coal contains detrital minerals that were deposited along with the plant material, and authigenic minerals that were formed during coalification. The abundance of mineral matter in coal varies considerably with its source, and is reported to range between 9.05 and 32.26 wt% (Valkovic 1983). Minerals found in coal include (Table 2) aluminosilicates, mainly clay minerals carbonates, such as, calcite, ankerite, siderite, and dolomite sulphides, mainly pyrite (FeS2) chlorides and silicates, principally quartz. Trace elements in coal are commonly associated with one or more of these minerals (see Table 2). 

Mullite is almost twice as abundant in low-Ca fly ash when compared to high-Ca fly ash, mainly due to differences in the Al content of the clay minerals associated with the coal (McCarthy et al. 1990). Using atomic absorption spectroscopy (AAS) and scanning electron microscopy /electron microprobe analyses (SEM/ EMPA) Stevenson Huber (1987) found a correlation between the elemental composition of ash particles and the clay mineral species in the raw coal. They concluded that the geologic origin of the coal had a significant impact on the microchemical composition of the ash. 

The molar ratio of Al Si in clay minerals is variable, kaolinite (0.85), mica-illite (0.61), and smectitic clays (0.35) (McCarthy et al. 1987). Bituminous coal tends to have higher concentrations of kaolinite, while lignite and subbituminous coals contain mica-illite or smectitic clays. McCarthy et al. (1987) predicted that the higher the Al Si ratio of the clay minerals the... 

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