Leaching pyrite from coal waste: results of diagnostic study.
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9569, 1995 Jan; :1-49
The U.S. Bureau of Mines conducted an experimental and theoretical study of coupled chemical kinetic and mass transport processes during leaching of pyrite from coal in a counterflow, "trickle-bed" column reactor. Spatial and temporal data on reactant and product concentrations were used as solutions to appropriate continuity equations, which in turn define chemical kinetic reaction rates. Data from four 180- by 30-cm column leaching experiments using coal, coal waste, and air-water and air-FeCl lixiviants have been analyzed. The rate of leaching was found 3 to be diffusion limited (probably by Fe ) and not controlled by bacterial action. Rates of pyrite oxidation were 3+ found to vary with elapsed time (80 to 225 days) and followed a bell-shaped curve, sometimes with a delay before start of reaction. Maximum rates of reaction ranged from 3 to 10 (mmol/d)/L (column) for coal waste and 0.4 (mmol/d)/L (column) for coal. Reaction was 30 to 80 pct complete, probably due to precipitation of product salts (e.g., jarosites), which impede transport of oxidant through the coal. An absorption-desorption model of solids leaching, which considers the role of heterogeneous porosity in solids leaching, was used to describe time-dependent leaching rates.
Mining-industry; Chemical-extraction; Chemical-reactions; Coal-mining; Waste-treatment; Environmental-protection
Report of Investigations
NTIS Accession No.
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI 9569