Dry Processing using an Air-Magnetite Dense Medium in the Reflux Classifier
Traditionally, small coal (less than 4 mm) has been processed using water based media to separate the coal from the mineral matter. There has been much interest in developing a method for coal processing that does not require the use of water, given the growing concerns over water shortages throughout Australia. Further, by not introducing water into the process, many other problems associated with dewatering are overcome, transport costs are reduced, and heating values increased. The reflux classifier is a fluidized bed arrangement with parallel inclined channels located above. The inclined channels provide for an increase in the effective vessel area and an improvement in the separation performance due to the favorable re-suspension of low density particles. The technology has been successfully deployed in water based processing. In the present study, however, the objective is to operate the device using an air based medium. In the presence of an air medium only, the separation proceeds on the basis of the particle size. We have discovered that the performance is significantly improved through the use of relatively coarse magnetite with the air flow. However, it is necessary to maintain a steady flow of the air-magnetite medium through the system, maintaining both flows at all times. The paper reports on the beneficiation achieved for a coal in the size range from 0.25 to 4.0 mm. These results are reported with respect to that achievable by water based processing and with respect to the coal washability data.