The U.S. Bureau of Mines examined the oxygen dependence of abiotic and biotic pyrite oxidation on three scales: (1) pyrite surfaces to a depth of 20 angstroms, (2) 5-g quantities of pyrite in small columns, and (3) 175-kg quantities of pyritic shale in large columns. Results of these studies indicated that the initial abiotic oxidation of fresh pyrite surfaces was independent of oxygen partial pressures above 10 pct (0-order reaction) and was proportional to oxygen partial pressures below 10 pct (first-order reaction). However, the rates of abiotic oxidation measured in small columns were proportional to oxygen partial pressures between atmospheric (21 pct) and 5 pct. Small-column and large-column results indicated that with bacteria present, the rate of pyrite oxidation was independent of oxygen partial pressures down to 1 pct. Below 1 pct oxygen, the reaction rate was proportional to oxygen partial pressures (first-order reaction). The oxygen-impermeable and oxygen-consumptive barriers other than water that are economically feasible at present are not capable of maintaining oxygen levels below 1 pct. Therefore, no reduction in the rate of pyrite oxidation would be realized using these techniques unless bacteria were inhibited. The best method for limiting pyrite oxidation was to place pyritic material below a permanent water table. Results of large-column experiments indicated that a 96-pct reduction in pyrite oxidation could be realized by inundating the pyritic material.
Proceeds 1990 Mng. & Reclamation Conf. & Exhibition. West Virginia Univ. Pub. Services, V. 1, PP. 257-264