Waste materials from conventional and advanced low-rank coal utilization processes are characterized from pilot scale coal combustion tests. Elemental and mineral analyses were followed by leaching tests. Trace element immobilization studies identified additives and treatment processes to reduce leaching of arsenic and selenium in a solid waste disposal site setting. The results indicate that low-rank coal fly ashes produced from coals mined at different sites vary moderately in elemental and mineral compositions and greatly in leachate composition. The ash data was analyzed for mineral phase relationships, and for correlations between the major and trace elements. Solid wastes from several advanced low-rank coal utilization and flue gas clean-up processes were also characterized. These included fly ashes from hot-water-dried coal water slurry combustion tests, fly ashes from direct furnace injection tests using pressure hydrated lime for SO/sub 2/ capture, and fly ashes from flue gas injection tests using NH/sub 3/ and SO/sub 3/ to enhance fine particulate collection in a baghouse. Liquid and solid wastes produced from the incineration of concentrated coal gasification wastewater were also characterized.