Control of pyrite surface chemistry in physical coal cleaning. Fifth quarterly progress report, September 1, 1990--November 30, 1990

The successful separation of pyrite from coal by flotation is dependent to a large extent upon the selectivity of the process, and the use of a pyrite depressant is one of the most important and cost-effective techniques for achieving this. This report evaluates the effects of three factors on the floatability of pyrite. These are (1) the superficial oxidation of pyrite, (2) the contamination of pyrite surfaces by carbonaceous matter, and (3) pulp redox potentials. XPS (x-ray photoelectron spectroscopy) and IR spectrometry have been used to identify surface reaction products. Microflotation, laboratory-scale conventional flotation and microbubble column flotation were used to quantify the effects of these factors. It was found that low (reducing) pulp potentials are effective depressants of pyrite (more so for fresh, unoxidized samples than for oxidized samples), whilst at the same time do not materially affect coal flotation.