The slurry-column coal beneficiation process

The slurry column is a second-generation process developed at the Idaho National Engineering Laboratory (INEL) for the beneficiation of fine (60 mesh x 10 mu m) coal by a combination of the physical separation of mineral matter and the biooxidation of pyrite. The bioreactor is a slurry-type airlift, specifically designed to allow the large liberated inclusions of pyrite and other insoluble minerals to settle out. They are transferred to a similar reactor, called the rougher/propagator, that gives a second stage of physical separation, as well as the longer residence time for the biodegradation of the large pyritic inclusions and the associated bacterial growth. The bioreactors operate in sequencing-batch mode, and also serve as settlers for coal/water separation when the air is turned off. This separation allows counter-current flow of coal and water, which minimizes the volumes of water consumed and wastewater generated. The complete flow sheet incorporates two-stage washing to remove sulfate and bacteria from the product coal, and recycle of bacteria into the process to inoculate the feed coal. A description of the process illustrates some general principles applicable to the optimum design of any coal bioprocess. (C) 1997 Elsevier Science B.V.