The presence of large portions of pyritic sulfur in coals extracted from the Illinois coal basin has been a deterrent in utilizing flotation circuits to recover ultrafine (minus 0.15 mm) coal in coal preparation plants. While gravity-based separation processes are very effective in separating pyrite from coal for coarse particles due to the large density difference between pyrite and coal, the flotation process fails to effectively reject the fine pyrite. Previous studies have indicated that the spiral concentrator can be utilized to remove fine pyrite in the flotation feed. These studies also indicated that the pyrite can be concentrated in low-volume streams through cyclone classifying and screening operations, thus minimizing the required spirals capacity. A full-scale classifying cyclone, a full-scale spiral, and two pilot-scale flotation cells were tested at an Illinois plant to evaluate various circuit configurations for pyrite rejection. This paper reviews the results of the evaluations and the performance of the various circuit configurations for rejecting ash, sulfur, and water. Flowsheet design criteria and operating guidelines are also discussed.
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