controls on coal washing difficulty

8/2/2019 Controls on Coal Washing Difficulty

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CONTROLS ON COAL WASHING DIFFICULTY(82G/15 93L/ll)By Barry D. Ryan

p-.-mKEYWORDS: Coal washing, washing di&olty,dispersed minetil matter, lithotypes, detrital macerals,coal-forming ewironments.

The second part of the paper examines a wzyof estimating washing difficulty, using small samples.New data from the Elkview and Quintl::tte min~:r: areintroduced and data from the Corbin, @insam andTelkwa properties are re-interpreted.INTRODUCTIONCoal seams are a mixture of pure coal and rock.The coal scientist may be interested in the relationshipbetween the co&rock mixhue and the environment inwhich the coal formed. The mining engineer is moreinterested in how easy it will be to separate the coalfrom the rock and how much coal wil l be lost in theprocess. A number of papers (Sanders and Brookes,

1986; Sarkar and Das, 1974) have attempted to bridgethe gap between the interests of ,the scientist and theengineer by looking at the linkage betweenenvironmental controls on coal formation and washingdifficulty. These papers may be of some interest to theengineer, but he or she is more interested in predictingthe washing characteristics of a particular coal seamthan in finding a genetic explanation for thecharacteristics.

Washing difliculty is not the wne as plantrecovery, which is the main concern of the plantengineer. Plant recovery is dependent on:l the type of wash plant used;l the size-consist of the run-of-min: coal ~(ROlvlcoal);l the amount of rock mixed into the coal 19. themining process (in-seam and out-of-::eam dilntion);. the washing difficulty of the coal.

The first three elements are 1arg:ly under thecontrol of the operator the last is largely an inhxntpropelty of the coal seam.

The first part of this paper looks at some possibleenvironmental controls of washing difliculty of BritishColumbia coals. Lithotype and mace& evidence areobtained from a number of published papers and therelationship between these data and the amount ofdispersed mineral matter is discussed. It is generallyconsidered that it is the amount and distribution of thefinely dispersed mineral matter that most effectswashing difficulty. If the coal contains a higher thannormal amount of tinely dispersed mineral matter thenit will be difIic:ult to wash. There is no universaldefinition of this material. It is probably present in thecoal as fine particles associated with the different coalmacerals, as fillings in the coal mace& and aschemically bound components in the coal molecularstructure. Changes in washabi lity are caused bychanges in the amount and distribution of this material.

The difficulty of washing coal is related to thedegree of liberation of rock from coal in the size-waist(range of particle sizes) that enters the p: ant. If there isincomplete liberation of rock from coal then whatev:rthe washing process in the plant, some: rock wil l IKmisplaced in the clean product and sxne coal wllescape with the reject material. Rwk splits aregenerally easy to liberate from the coal and an increasein their amount in the R.OM coal decreases plantrecovery but does not make the coal owe difficult towash. It is the amount of dispersed mineral matins thatmost influences washing difficulty.A wash plant can respond to chaltging w:z;hingcharacteristics of ROM coal by making processadjustments or by blending differen. seams withdiierent washing difliculty The key is foreknowlS:d,:eof changes in the washing characteristii:s of the warasto be mined. The method of prediting wtxihingdiiculty proposed in this paper helps in this respe:t.

The dispersed mineral matter has a number oforigins:. wind blown;. water transport;. original component of the vegetation;. introduced rubsequent to the start of coali fication(syngenetic or epigenetic emplacement)The source and amount of the dispersed mineralmatter and the environment in which the coal formedare related and therefore there wil l be some relationshipbetween washing difficulty of the coal and thedepositional enwonment in the coal swamp.

PART 1 ENVIRONMENTALCONTROLS ON WASHTNGDIFFICUILTYRELATIONSHIP BETWEEN LITEIOTYP~?S:AND DISPERSED MINERAL MAYTER

Coal seams can be subdivided into lithotypes \rhi,:hare. outcrop mappable zones of coal within the mm,distinguished by brightness, banding and guwalappearance. Terms such as bright, banded or bandeddull are used. Lithotype mapping is a solnewhat !tedicus

Geological Fieldwork 1995, Paper 19961 Z!5!)


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controls on coal washing difficulty

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