Dry electrostatic beneficiation of Illinois coal and Eastern oil shales

The objective of this study was to investigate a dry electrostatic process to beneficiate the high-sulphur and/or high-ash Illinois coals and the Eastern oil shales. The basis of our electrostatic beneficiation method is the observation that carbonaceous matter present in either coal or shale can be made to acquire a positive charge, while mineral matter, including pyrites, can be charged negatively with a copper tribocharger. Hence, application of a high voltage electric field causes a clear separation, once the pyrites and minerals have been liberated from the organic matrix by grinding or by other means. The typical grain size of mineral inclusions present in coal and shale, determined using scanning electron and optical microscopes, was found to be in the range of 5 to 10 ;The electrostatic force, principally responsible for the separation, is a product of the surface charge of the particles and the applied electric field strength. The surface charge on the particles was imparted using a copper tribocharger. The magnitude and the polarity of charge was found to depend primarily on the work functions and, to a lesser degree, on elastic and electrical properties of the particle and the material of the tribocharger. A semi-empirical approach was developed to correlate the charge with these properties and to choose a suitable material for the tribocharger. The surface charge of the particles was measured using a Faraday cage and a parametric study was conducted to investigate the effect of various process variables on particle charging.;A continuous electrostatic separator with perforated electrodes was designed and tested for both coal and shale desulfurization. Significant pyrite removals were achieved. The coal recoveries obtained with this device were, however, poor because of improper hydrodynamic conditions.;The separation tests in a batch separator showed about 80% ash and pyrite removal from the Illinois ;A simple mathematical analysis of the batch electrostatic separator showed that the efficiency of the separation can be enhanced by increasing (a) the inter-electrode spacing, (b) electric field strength and (c) the surface charge of the particles. Finally, a conceptual design of a continuous separator to beneficiate coal and shale was identified.