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Methods for determining fundamental chemical differences between iron disulfides from different geologic provenances.

Hammack-RW; Lai-RW; Diehl-RJ
Mine Drainage and Surface Mine Reclamation. Volume I: Mine Water and Mine Waste. Vol. I. Pittsburgh, PA: U.S. Bureau of Mines, 1988 Apr; :136-146
X-ray photoelectron spectroscopy (XPS), evolved gas analysis (EGA), and froth flotation tests were used to compare iron disulfides of hydrothermal, sedimentary/hydrothermal, and sedimentary origin. A specimen composed of equal amounts of pyrite and marcasite was also evaluated. The susceptibility of iron disulfide surfaces to oxidation was measured using XPS and EGA techniques. XPS analyses indicated the following order of increasing oxidation rate at 21 pet oxygen and 88 pet relative humidity: sedimentary/hydrothermal pyrite (0.70 mg S04-2/hr per gram of FeS2)< hydrothermal pyrite (0.83 mg S04-2/hr per gram of FeS2)< hydrothermal pyrite/marcasite (1.34 mg S04-2/hr per gram of FeS2)< sedimentary pyrite (3.53 mg S04-2/hr per gram of FeS2)' Oxidation rates measured by XPS are based solely on the sulfate/sulfide ratios at the surface, where oxidation is not inhibited by mass transfer limitations. Therefore, these rates are much higher than previously published rates based on bulk iron disulfide content. The comparison of EGA results with oxidation rates measured by XPS showed that for sedimentary pyrites, higher temperatures of S02 evolution corresponded to lower oxidation rates. Weathering rates for hydrothermal iron disulfides appear to be independent of S02 evolution temperatures. In flotation tests with an anionic fluorosurfactant collector, hydrothermal pyrite floated and sedimentary pyrite was depressed. Hydrothermal pyrite floated because it developed a positive surface charge in solution that allowed the attachment of the anionic collector. The negative charge developed by sedimentary pyrite in this solution repelled the anionic collector, depressing sedimentary pyrite. This research provides a better understanding of iron disulfide oxidation and illustrates inherent differences in physical and chemical properties that significantly alter the behavior of pyrites of different geologic provenance.
Iron-compounds; Spectroscopes; Gas-sampling; Oxidation; Sulfates; Sulfides; Waste-treatment
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IH; Conference/Symposia Proceedings
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Mine Drainage and Surface Mine Reclamation. Volume I: Mine Water and Mine Waste