Washability 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.

Washability curves Graphical presentation of the float-sink test results. Two types of plots are in use Henry-Reinhaid washability curves and M-curves. 

In the example shown in Fig. 7, five heavy liquids with densities from 1.3 to 1.8 are used. The weight yields of six density fractions are calculated (ki, yi, .., ye), and their ash contents ate determined (A,], A2,..., Ae). The results are set out graphically in a series of curves referred to as washabihty curves (Henry-Reinhard washability curves or mean-value curve, M-curve, introduced by Mayer). 

The constraction of the primary washability curve (Henry-Reinhard plot) is shown in Fig. 8. It is noteworthy that the area below the primaty curve (shaded) represents ash in the sample. The shaded area, changed into the rectangle of the same surface area, gives the mean-ash content in the sample (a = 16.44% in our example). 

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 8 Construction of the primary washability curve (Henry-Reinhard washability diagram). 

The washability curve can be used in conjunction with the specific-gravity-yield curve (curve D) and the 0.1 near-density curve (curve E) as demonstrated in the example given in Table III and plotted in Fig. 11. 

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-... 

FIGURE 11 Complete set of washability curves (for data given in Table III). 

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. 

Washability curves are prepared from these data. 

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