Surface Modification of Coal With Carbon Dioxide and Its Application to Advanced Coal Cleaning

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Four coals from different localities (Datong, Wandoan, Illinois and Shenmu) were used in this study. Immersion time measurements were carried out to assess wettability of coal surface using 100-200 mesh coals. Flotation tests were conducted by introducing air, nitrogen and carbon dioxide gases, respectively. After sparging the gases into coal slurries, the slurries were chemically analyzed. For flotation and chemical analysis fine coals (mean particle size : about 30mum) were used. Some of the coals were treated with 0.6kgf/cm^2 of carbon dioxide gas prior to the experiments. The collectors used were kerosene for Datong and Shenmu coal, and heavy oil A for the other coals.The hydrophobicity of four coals treated with carbon dioxide became slightly higher than that of untreated coal. When sparging carbon dioxide gas, the highest amounts of calcium and magnesium were dissolved from Datong and Wandoan coals and the amounts of bassanite and calcite in the coals were simultaneously decreased. By flotation with carbon dioxide, the maximum yield was obtained for the coals treated with carbon dioxide than the untreated coals. In the case of Shenmu coal containing calcite and dolomite, separation efficiency of combustibles from mineral matters became higher with decreasing pH.Fine grinding of four coals were investigated. The ground product with a mean size of 2mum was obtained at a suitable operating conditions for all coals. The wear loss of the grinding media and vessel depended strongly on the amount of the hard minerals disseminated in coal, such as quartz, pyrite and iron oxide.