Adventitious mineral matter

The silicate species occur in coal chiefly as separate strata and large particle inclusions, and this mode of occurrence is termed the "adventitious" mineral matter. Figure la shows a typical sample of the adventitious silicate mineral particles, density separated from pulverized coal. The density separation technique does not remove the small silicate particles, chiefly alumino-silicate species, the "inherent" mineral matter, in the coal substance (Figure lb). 

Ash particulates are formed from mineral matter due to three different mechanisms. First, part of the mineral matter is found in layers or bands separate from the organic matter. This is called adventitious mineral matter, and it can be partially separated from the coal after crushing and fine grinding. The adventitious mineral matter is transformed directly to ash in the combustor, and the shape is semirounded. Second, mineral matter in coal is contained within the organic matrix in the form of chemically bound molecules and submicron crystals. Grinding does not liberate this intrinsic mineral matter. Third, some of the mineral matter is vaporized during combustion and condenses on cooler surfaces such as turbine blades. 

Adventitious mineral matter is transformed directly to ash in the combustion zone. Depending on the temperature-time history, the ash particles will be spherical or semirounded. The size distribution of this ash depends on the size distribution of the adventitious mineral matter. Intrinsic mineral matter forms ash nodules in the pores of the char, and as char burnout proceeds, the ash nodules coalesce on the surface of the char. 

Adventitious (Non-essential) mineral matter (clayey or silicious) present in mud or water in contact with the decomposing vegetation (during the anaerobic decay state) gets intimately mixed with coal or is present as dirt bands alternate, with purer coal layers. The amount of adventitious ash varies widely and may go upto 10%. The inherent and adventitious mineral matter cannot be removed by cleansing operations and together constitute what is know as Fixed AslT. 

The mineral matter and the ash in coal have often been informally classified as inherent (stemming from the plant material in the coal swamp) or as adventitious (added after the deposition of the plant material in the swamp). This classification is misleading and difficult to apply, especially for those minerals that are contemporaneous with the peat swamp but were not incorporated by the plants. 

Horton and Aubrey (34) handpicked pure vitrain samples from coals and separated them into five different specific gravity fractions. They then analyzed these for 16 minor elements. They concluded that for the three vitrains they studied, beryllium, germanium, vanadium, titanium, and boron were contributed almost entirely by the inherent (organically combined) mineral matter and that manganese, phosphorus, and tin were associated with the adventitious (inorganically combined) mineral matter. 

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. 

Figure 1. Mineral matter in coal. (a) Adventitious (b) inherent white particles.

Raw cotton contains, in addition to cellulose, the usual constituents of a vegetable cell. These are oil and wax, pectoses and pectins, proteins and simpler related nitrogen compounds, organic acids, mineral matter, and natural colouring matter. Cotton yarns or piece goods may contain, in addition, adventitious dirt, size, and machine oil. The approximate composition of raw cotton is as follows ... 

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