Centrifugal Float-Sink Testing of Fine Coal: An Interlaboratory Test Program

The Pittsburgh Energy Technology Center (PETC) recently completed an interlaboratory test program (ITP) involving eight laboratories that are currently performing washability analyses of coals finer than 500-microns top size using a centrifugal float-sink technique. With current and future development of fine coal cleaning technology, there is a growing need to determine the washability of coals in extremely fine sizes, in some cases as fine as several microns by zero. However, much uncertainty exists about limitations relative to particle size and the viability of centrifugal float-sink procedures in achieving "ideal" specific gravity separations (i.e., the perfect separation of particles according to their density). The objective of this work was to develop an understanding regarding the variables affecting the procedure and initiate a process for obtaining a standard procedure. A Pittsburgh No. 8 coal from Belmont County, Ohio, was ground to four different top sizes: 217, 83, 48, and 14 microns. Two 200-gram samples of each top size were sent to each participating laboratory. Each laboratory then utilized its own centrifugal float-sink procedure to obtain specific gravity splits at 1.30, 1.40, and 1.60, and returned the fractions to PETC where they were analyzed for ash, pyritic sulfur and total sulfur. These results indicated that (1) wide differences in weight and other parameters between laboratories can occur at even relatively coarse sizes (e.g., 217µm), but particularly at the finer sizes; (2) each laboratory using an organic heavy liquid medium obtained extremely low float 1.30 sg yields (between 1-20 percent) for the 14 µm × 0 coal; and (3) each of the three laboratories using a medium of an aqueous solution of cesium chloride with a surfactant produced float 1.30sg percent yields in the 60s for the 14 µm × 0 coal. Fine coal, Float-sink, Gravity separation.