An evaluation of separation methods for the selective coagulation of ultrafine coal

Abstract

A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, which is known as Selective Hydrophobic Coagulation (SHC), differs from oil agglomeration, shear or polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. In most cases, simple pH control is all that is required to (i) induce the coagulation of coal particles and (ii) effectively disperse particles of mineral matter. If the coal is oxidized, a small dosage of reagents may be used to enhance the coagulation process.

During the SHC development, it was discovered that the hydrophobic coagula were very difficult to separate from dispersed mineral matter due to their very small size and their susceptibility to breakage. Using the SHC technique, an evaluation of new methods for coagula recovery was conducted. In this effort, several methods for improving the separation of the coal coagula from dispersed mineral matter were examined. These included lamella thickening, centrifugal sedimentation, vacuum filtration, drum screening, and froth flotation. Each separation method was optimized using statistically-designed test matrices to determined the best separation method based on overall process performance. The thickener was found to be the best method for separating hydrophobic coagula from dispersed mineral matter based on overall process performance (e.g., recovery and grade), unit capacity, and engineering feasibility. Further testing of the thickener separation unit was conducted in an attempt to improve the process performance and the unit throughput.