Abstract
Molten caustic leaching (MCL) of coal has been studied under a variety of conditions, many of which studies have been conducted using a large excess of liquid caustic (3:1 caustic/coal or higher) so that, with stirring, coal is suspended in it. This provides a uniform temperature throughout the mixture and is preferred for chemical research. Some development studies have made use of lower ratios of caustic, such as TRW`s 20 lb/hr kiln work by Meyers, and the studies of Chriswell and Markuszewski at Ames Laboratory and by Kusakabe in Japan. In the Japanese work, Illinois No. 6 coal was impregnated with mixed KOH and NaOH (52:48 parts by weight) from an aqueous solution to give 51 wt% caustic on the dry coal which after MCL treating, 2 hr at 375{degrees}C, produced a coal having only 0.50 wt% total sulfur. Less caustic should help in reducing the cost of an MCL process. Moreover, at high ratios much more caustic is present than necessary to form salts of sulfur and mineral matter in coal. We have calculated that to form the sodium salts of the sulfur and mineral matter present in an 8% ash, 4.2% sulfur, Pittsburgh No. 8 coal would takemore » about 0.15 parts of sodium hydroxide for one part of dry coal. This does not take into account carbonate formation nor cleavage of carbon-oxygen bonds which also can occur. The objectives of this work were to examine molten caustic leaching under conditions that could be used for commercial chemical coal cleaning. This has meant using low levels of acid water and caustic.« less
Published Version
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