5.1 Although the determination of the washability characteristics of coal is not an exact science, this washability test method can be used to investigate the cleaning characteristics of coarse- and fine-coal fractions. However, especially with the fine-coal fractions, this test method may not be applicable for low-rank coals for reasons explained in 1.2.

5.2 The usefulness of this test procedure and the usefulness of the results derived from washability testing are directly related to the care exercised in developing and following the sampling regime while taking into consideration the desired degree of precision. For more exacting work, it will be necessary to know the general washability characteristics of the material in question. This can be done only through pilot testing as described in 9.6 and Annex A3.

5.3 This test method, in conjunction with the advice of experts and with knowledge of the particle size analysis (see Test Method D4749), is used for the engineering design of coal preparation facilities.

5.4 This test method is also used to assist in process control and to determine the efficiency of operating preparation plants.

5.5 This test method is used in core studies to determine the quality washability characteristics of coal reserves; however, in these instances the typical mass of raw coal from Table 1 may be neither applicable nor practical. For this reason, core diameter should be as large as possible and subdivision of the core section by any means or for any purpose prior to washability testing should be avoided. Care must be exercised in the design of the coring programs, including the consideration of appropriate geostatistics, in order that the potential recovery and quality of the coal reserves, as defined by the washability analysis of the cores, have any practical significance.