Mineral matter nature

Finally, selective separation and dewatering of one suspended substance in a slurry containing different minerals or precipitates is possible by selectively adsorbing a magnetic material (usually hydrophobic) onto a soHd that is also naturally or chemically conditioned to a hydrophobic state. This process (Murex) was used on both sulfide ores and some oxides (145). More recently, hydrocarbon-based ferrofluids were tested and shown to selectively adsorb on coal from slurries of coal and mineral matter, allowing magnetic recovery (147). Copper and zinc sulfides were similarly recoverable as a dewatered product from waste-rock slurries (148). 

Cellulose is the most abundant of naturally occurring organic compounds for, as the chief constituent of the eell walls of higher plants, it comprises at least one-third of the vegetable matter of the world. The cellulose eontent of such vegetable matter varies from plant to plant. For example, oven-dried cotton contains about 90% cellulose, while an average wood has about 50%. The balance is composed of lignin, polysaccharides other than cellulose and minor amounts of resins, proteins and mineral matter. In spite of its wide distribution in nature, cellulose for chemical purposes is derived commerically from only two sources, cotton linters and wood pulp. 

Atmospheric particulate emissions can be reduced by choosing cleaner fuels. Natural gas used as fuel emits negligible amounts of particulate matter. Oil-based processes also emit significantly fewer particulates than coal-fired combustion processes. Low-ash fossil fuels contain less noncombustible, ash-forming mineral matter and thus generate lower levels of particulate emissions. Lighter distillate oil-based combustion results in lower levels of particulate emissions than heavier residual oils. However, the choice of fuel is usually influenced by economic as well as environmental considerations. 

Fuerstenau (1980) found that sulphide minerals are naturally floatable in the absence of oxygen. Yoon (1981) ever attributed the natural floatability of some sulphide minerals to their very low solubility. Finkelstein et al. (1975) considered that the natural floatability of sulphide minerals are due to the formation of elemental sulphur and related to the thickness of formation of elemental sulphur at the surface. Some authors reported that the hydrophobic entity in collectorless flotation of sulphide minerals were the metal-deficient poly sulphide (Buckley et al., 1985). No matter whichever mechanism, investigators increasingly concluded that most sulphide minerals are not naturally floatable and floated only under some suitable redox environment. Some authors considered that the natural floatability of sulphide minerals was restricted to some special sulphide minerals such as molybdenite, stibnite, orpiment etc. owing to the effects of crystal structure and the collectorless floatability of most sulphide minerals could be classified into self-induced and sulphur-induced floatability (Trahar, 1984 Heyes and Trahar, 1984 Hayes et al., 1987 Wang et al., 1991b, c Hu et al, 2000). 

The above conclusions based on SEM-AIA measurements of association in terms of particle surfaces are somewhat more tentative than the conclusions drawn from bulk association distributions. There are more analytical difficulties when characterizing the particle surfaces than when characterizing the bulk sample. In addition, the factors determining the overall surface nature of a particle are more complex than just the relative amount of the phases present on the particle surface. However, the SEM-AIA results can still provide a useful and heretofore unavailable insight into the nature of mineral matter in coal. 

Summarizing the above discussion, the dissolved mineral matter in most natural waters consists mainly of calcium in the form of bicarbonate or temporary hardness and chlorides and sulfates as permanent hardness. The tendency of the water to deposit scale when made alkaline by heating or to attack metals corrosively depends on the balance of these various constituents. 

The presence of extraneous mineral matters is detected as follows 4-5 grams of the powdered substance are shaken in a test-tube with chloroform and then left to stand any mineral matter then settles at the bottom of the tube, wliilst the starch floats at the surface of the liquid. Analysis of the ash of the product by the ordinary methods indicates the nature of the inorganic substances. 

In the Parr formula for moist, mineral-matter-free calorific value, the moisture basis used is that of the inherent moisture of the coal in the seam (natural bed moisture, capacity moisture) ... 

Extrinsic mineral matter, which is purely adventitious, is derived from the roof and floor of the coal seam and from any noncoal or inorganic material that may be associated with the seam itself. It consists generally of pieces of stone, clay, and shale together with infiltrated inorganic salts that have become deposited in the natural fissures in the coal seam (e.g., pyrite, ankeritic material). Such material can be reduced very much in amount by suitable methods of coal cleaning and, indeed, may be separated from the coal completely, provided that it can be broken apart from coal particles. 

Various processes that result in a reduction of the mineral matter and sulfur content can be employed to clean coal. The ash content of raw coal is often used to select the best cleaning method, and the ash content of the cleaned coal is used to measure the effectiveness of the cleaning process. In the commercial pulverization of coals, the amount and nature of ash is considered carefully before selecting pulverizing equipment or setting up the process. 

The evaluation of coal mineral matter by the ashing technique can be taken further insofar as attempts can then be made to determine the individual metal constituents of the ash. On the occasion when the mineral matter has been separated from the coal successfully, it is then possible to apply any one of several techniques (such as x-ray diffraction, x-ray fluorescence, scanning electron microscopy and electron probe microanalysis) not only to investigate the major metallic elements in coal but also to investigate directly the nature (and amount) of the trace elements in the coal (Jenkins and Walker, 1978 Prather et al., 1979 Raymond and Gooley, 1979 Russell and Rimmer, 1979 Jones et al., 1992). Generally, no single method yields a complete analysis of the mineral matter in coal and it is often necessary to employ a combination of methods. 

Although porosity dictates the rate at which methane can diffuse out of the coal (in the seam) and there may also be some influence during preparation operations in terms of mineral matter removal, the major influence of the porous nature of coal is seen during the utilization of coal. For example, during conversion, chemical reactions occur between gas (and/or liquid) products and surface features, much of which exists within the pore systems. 

Thermal conductivity increases with increasing apparent density, volatile matter, ash, and mineral matter content. Due to the high porosity of coal, thermal conductivity is also strongly dependent on the nature of gas, vapor, or fluid in the pores, even for monolithic samples (van Krevelen, 1961). Moisture has a similar effect and increases the thermal conductivity of coal since its thermal conductivity value is approximately three times higher than that of dry coal (Speight, 1994, and references cited therein). However, the thermal diffusivity of coal is practically unaffected by moisture since the /Cp value is not essentially changed by moisture. 

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