Acid Mine Drainage From Reclaimed Coal Strip Mines 1. Model Description

Abstract

A model describing the long‐term oxidation of pyrite and the removal of reaction products from reclaimed coal strip mines is presented. Both direct‐oxygen and ferric iron oxidation of pyrite are considered. The pyrite oxidation rate is assumed to be controlled by first‐order, solid‐liquid kinetics and the rate of simple diffusion of oxidant into reactive, coarse, stone fragments. The oxygen supply into the reclaimed profile is considered to be governed by one‐dimensional gas diffusion. Ferric iron is produced by both purely chemical and bacterial oxidation of ferrous iron. Activity of the iron‐oxidizing bacteria is controlled by the energy available from ferrous oxidation, as measured by the ferric/ferrous ratio, and from a combination of potentially inhibiting factors: the oxygen concentration in the spoil air, the hydrogen ion concentration in solution, and the spoil temperature. Bacterial activity and pyrite oxidation are linked through a shared environment. The side reactions considered include the complexation and precipitation of ferric iron and the interaction between hydrogen ion in solution and the spoil matrix. Soluble reaction products are removed from the reclaimed profile by percolating water.