Beneficiation of coal from impounded coal waste

The potential for recovery and purification of fine coal particles from the impounded waste of a coal cleaning plant using a two-stage, two-solvent system was investigated. The two-solvent system consisted of a first-stage fluid (a mixture of n-dodecane and 2-propanol) used to separate fine coal particles from ash-forming impurities, and a second-stage fluid, the U.S. Environmental Protection Agency (EPA) toxicity characteristic leaching procedure (TCLP) solvents, used to remove sulfur and mineral impurities from the recovered coal. The degree of separation of organic matter from inorganic impurities was examined as a function of the fraction of n-dodecane in the first-stage fluid, and settling time. The results show a general trend of increasing organic matter recovery with increasing fraction of n-dodecane. The most ash removal was obtained with a first-stage fluid of 4% n-dodecane and 96% 2-propanol by volume. Mineral and sulfur removal from the recovered coal was negligible. Further treatment with TCLP solvents in the second stage showed significant removal from the recovered coal (over 70%) of iron, manganese, and sodium Sulfur and calcium removal was poor (less than 50%); it is likely that these are bound in the organic matrix. The energy content of the final recovered coal product was 34.9 MJ/kg, an increase of 22.2% over the 28.59 MJ/kg of the impounded waste.