Magnetic Enhancement and Demineralization of Eastern Coals. Second Yearly Technical Progress Report

摘要

We now have our first successful indications that selective microwave heating of coal pyrite improves the reduction of sulfur by high gradient magnetic separation (HGMS). The clean coal products of our magnetic separations have significantly reduced values of SO sub 2 /10 sup 6 BTU's in all three coals: Upper Freeport, Pittsburgh and Illinois No. 6. There is a clear improvement in this sulfur reduction when microwave pretreatment is applied before HGMS for the first two coals and a preliminary indication of such an effect for the Illinois No. 6. This improvement has been achieved only at high values of input microwave power but can be achieved in very short times thus keeping the energy expended at a reasonable level. Experiments have been conducted on heating pyrite to try to understand the mechanism of the conversion to a more magnetic state. The results show the existence of a ''critical temperature'' above which very high values of magnetization can be reached. Moessbauer and electron microprobe studies show that highly magnetic pyrrhotite is produced when pyrite is heated to temperatures above this critical temperature. Small particles appear to be completely converted while larger ones have surface inclusions of pyrrhotite. 8 figs. (ERA citation 11:035400)