Washability, coal, curves

All of the washability curves shown are drawn with the ordinates the same length and the origin at zero concentration so that the slopes can be compared and interpreted. Figure 3, which shows beryllium in the Davis Coal Member, presents a flat washability curve and also a relatively uniform histogram. Beryllium is, therefore, rather evenly distributed in the clean coal samples and is also present, in somewhat lesser amounts, in the heavier sink fractions. 

Nickel in a sample from the Colchester (No. 2) Coal Member (Figure 4) is definitely concentrated in the heavier specific gravity fractions. However, the washability curve remains well above the abscissa and does not appear to approach the origin in the cleanest fraction (purest... 

The final washability curve and histogram (Figure 5) are of arsenic in a sample from the Herrin (No. 6) Coal Member. The washability curve shows an intense concentration of arsenic in the heavier fractions. The curve approaches the abscissa and if extrapolated would intersect the ordinate near the origin. Arsenic is one of the least organically related elements in all four of the coals studied. 

Float-and-sink analysis separation of crushed coal into density fractions using a liquid of predetermined specific gravity washability curves are prepared from these data (ASTM D-4371). 

Figure 1. Washability Curves for the Most Common Minerals in a Northern West Virginia High Volatile Bituminous Coal.

The shape of the primary washability curve and the M-curve is an indication of the ease or difficulty of cleaning the coal. The more the shape approximates the letter... 

The primary washability curve for the difficult-to-clean coal (c) exhibits only a gradual change in slope revealing a large proportion of middlings. 

FIGURE 10 Primary washability and M-value curves for (a) ideal separation, (b) easy-to-clean coal, (c) difficult-to-clean coal, and (d) impossible separation. 

Curve A is the primary washability curve. Curve B is the clean-coal curve and shows the theoretical percent ash of the clean-coal product at any given yield. Curve C (the cumulative sink ash) shows the theoretical ash content of the refuse at any yield. Curve D, plotted directly fi om the cumulative percent yield of floats versus density, gives the yield of floats at any separation density. Curve E, the curve of near-density material, gives the amount of ma-... 

The yield and quality of the clean-coal product from an industrial coal preparation plant and the theoretical yield and quality determined fi om washability curves are known to be different. In the ideal cleaning process, all coal particles lower in density than the density of separation would be recovered in the clean product, while all material of greater density would be rejected as refuse. Under these conditions the product yield and quality from the actual concentration process and the yield and quality expected from the washability curves would be identical. 

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