Evolved Gas Analysis--a New Method for Determining Pyrite, Bicarbonate, and Alkaline Earth Carbonates.
Proceeds 8th Ann W V Surface Mine Drainage Task Force Symp Morgantown West Virginia, 4/7-8/87 Surface:16 pages
The U.S. Bureau of Mines has developed an evolved gas analysis technique that may be useful for the simultaneous determination of pyrite, bicarbonate, and alkaline earth carbonate in geologic materials. Although the technique has only been applied to ideal, reagent-grade samples and its applicability to actual geological samples with complex matrices is untested, the technique may potentially improve conventional methods of predicting acid mine drainage potential. The technique employs a programmable tube furnace for heating samples in a 10-pct oxygen atmosphere. The evolutions of sulfur dioxide from the oxidation of pyrite and carbon dioxide from the decomposition of carbonate and bicarbonate are monitored with respect to time and temperature using a quadrupole mass spectrometer. Sulfur dioxide peaks attributable to the oxidation of coal-derived pyrite occur between 380 and 440 deg c; sulfur dioxide peaks attributable to the oxidation of hydrothermal pyrite are present between 475 and 520 deg c. Carbon dioxide evolution resulting from the decomposition of bicarbonate is present between 100 and 200 deg c; carbonates decompose with carbon dioxide evolution between 250 and 700 deg c. Alkaline earth carbonates can be distinguished from transition metal carbonates and organic combustion on the basis of higher temperatures of carbon dioxide evolution. Calibration curves prepared by plotting evolved gas peak areas versus the concentration of pyrite, bicarbonate, and alkaline earth carbonate were linear.
Proceeds, 8th Ann. W.v. Surface Mine Drainage Task Force Symp., Morgantown, West Virginia, 4/7-8/87