Development of the selective hydrophobic coagulation process. Technical progress report for the ninth quarter, October 1--December 31, 1993

Abstract

A novel technique for selectively coagulating and separating coal from dispersed mineral matter has been developed at Virginia Tech. The process, known as Selective Hydrophobic Coagulation (SHC), has been studied under the sponsorship of the U.S. Department of Energy since 1986 (Contracts DE-AC22-86PC91221 & DE-AC22- 9OPC90174). The SHC process differs from oil agglomeration, shear flocculation, polymer flocculation, and electrolytic coagulation processes in that it does not require reagents or additives to induce the formation of coagula. Often, simple pH control is all that is required to (i) induce the coagulation of coal particles, and (ii) effectively disperse particles of mineral matter. When the coal is superficially oxidized, a small dosage of reagents may be used to promote coagulation. During the past quarter, stability calculations were carried out to develop a better understanding of the selective coagulation of fine coal and associated mineral matter. The calculations were performed for interactions involving coal, silica and clay particles. The analyses suggest that the heterocoagulation of the edges of clay particles with coal particles controls the overall selectivity of the SHC process. In Subtask 3.3, froth flotation was explored as a possible technique for recovering hydrophobic coagula. Experimental test data obtained using this techniquemore » were analyzed using a statistical regression program. The analyses indicate that froth flotation can be used to successfully recover hydrophobic coagula provided that adequate precautions are taken to minimize coagula breakage due to turbulence. Recommendations include the use of low aeration rates and little or no additions of wash water.« less