REFINEMENT OF ADTI-WP2 STANDARD WEATHERING PROCEDURES, AND EVALUATION OF PARTICLE SIZE AND SURFACE AREA EFFECTS UPON LEACHING RATES: PART 2: PRACTICAL AND THEORETICAL ASPECTS OF LEACHING KINETICS

摘要

Most previous coal mine drainage leaching studies have not investigated the effect of surface area, effects of elevated Pco_2, which are typical of mine spoil, and solubility constraints on water chemistry. The leaching column and humidity cell tests were designed to evaluate the importance of these parameters. Surface area was examined on three rock types before and after leaching: the Brush Creek shale; a well-indurated calcareous sandstone; and a coal refuse. The surface area, as measured by BET, for the shale was an order of magnitude greater than the other rock types. Surface area after leaching decreased slightly for the shale, and by half for the refuse. The sandstone area remained the same. Plots of sulfate concentration through time closely resemble those expected for diffusioncontrolled kinetics. Plots of alkalinity through time are characteristic of a material that dissolves quickly at first and then approaches or reaches saturation. Saturation with respect to calcite was confirmed by equilibrium calculations. The water in the leaching columns was undersaturated with respect to gypsum, indicating that sulfate was a conservative parameter and could be used to measure pyrite oxidation rates. The target 10 percent CO_2 was achieved in the column tests, but not achieved in the humidity cell tests. At the end of 12 to 14 weeks, between 1.5 and 2 percent of the calcite and between 4 and 6 percent of the sulfur in the rock had been removed by weathering. Predictions, based on power function equations, indicate that the Brush Creek shale sample would remain alkaline even if weathered for years. Comparisons between leaching chemistry and field data for the Brush Creek shale and the coal refuse sample showed similar water chemistry.