Processing of high-sulfur coals using microbubble column flotation

Abstract

Sulfur dioxide emissions, which are produced through the combustion of coal, are thought to be a leading contributor to acid rain. A number of postcombustion techniques for the reduction of sulfur dioxide emissions are being tested; however, the reduction in the pyritic sulfur content of coal through physical cleaning methods may be the most economically viable alternative to the S02 problem.

In this investigation, the microbubble column flotation process (MCF), developed at VPI&SU, was tested as a means of reducing the pyritic sulfur content of several high-sulfur coals targeted by the u.S. Department of Energy. A wide variety of pyrite rejection schemes were tested including the use of pyrite depressants, dispersants and elevated pH conditions. The overall efficiency of the MCF process was characterized using a technique known as "release analysis".

This technique was used to provide the optimum grade versus recovery relationship for a given coal and a given set of reagent conditions. It was also used as a means for evaluating the various schemes for rejecting coal pyrite. The results of this work indicate that the MCF process is capable of producing a separation very close to that generated by release analysis. The release analysis technique was also found to be an effective means of characterizing pyrite liberation and pyrite rejection for a given coal. In general, it was found that liberation was the most important factor in the rejection of pyrite, although elevated pH conditions seemed to provide improvements for some coals.