Preperation - The Operation of a Froth Flotation Pilot Plant on Washery-water Solids (Contribution 132, with discussion)

Large quantities of fine anthracite with associated impurities are discharged with the waste water from the coal-cleaning plants in the Pennsylvania anthracite region. Furthermore, for many years this fine material has accumulated and formed silt banks. The difficulty of removing the impurities from the fine material and the lack of adequate markets are responsible for the waste of this material. In view of a larger demand for fine coal, mainly for pulverized fuel, the Lehigh Navigation Coal Co. Inc. decided to investigate the froth flotation process for recovery of fine coal from these waste solids. A test plant was constructed and operated for six months during 1942 in order to determine the practicability of recover ing coal from the waste water of a a plant (breaker) by froth cleaning and to obtain operating data for designing a commercial plant if the results were favorable. Preliminary Investigation Before the pilot plant was constructed information was obtained by field and small-scale laboratory tests to serve as a guide in the design and operation of the pilot plant. Size and ash analyses of a representative sample of the material discharged in the wash water from a cleaning plant are given in Table. The refuse content increases progressively as the size of the particles decreases The larger particles (+35 m.) are low in ash content and could be marketed without cleaning. Since these solids are discharged from the breakers with 90 to 95 per cent water by weight, the first step in the recovery of the coal was that of reducing the quantity of water so that water in excess will not have to be handled. Furthermore, it was found that the removal of most of the minus 200 mesh high-ash material was desirable to permit the most efficient flotation of the cod. Classification tests were run and showed that a hydroseparator overflow rate of 12 ft. per hour* was sufficient to elimi-,late much of the minus 200-mesh material while allowing the coarser material to settle and be thickened,