Edafología. Volumen 5. Diciembre 1998. pag 71-82.
AGUAS DE DRENAJE DE MINA AFECTADAS POR LA OXIDACIÓN DE SULFUROS. VARIACIONES ESTACIONALES DE SU COMPOSICIÓN
C. Monterroso y F. Macías
Universidad de Santiago, Dpto. Edafología y Química Agrícola, 15706 Santiago de Compostela.
Abstract
The oxidation of the sulfides represents one of the biggest environmental problems associated with surface mining. In this study mine drainage streams emanating from a coal mine dump (As Pontes, NW Spain) was analysed, at monthly intervals over a 2-years period. Geochemical processes which determine its composition and seasonal variations were examined. During this period pH values ranged between 2.1 and 8.0 and redox potential values between 150 and 750 mV. Four groups of streams were distinguish in which the level of inffluence of the sulfide oxidation and the level of the neutralization reached were variable feacture. The main group of streams were strongly affected by sulfide oxidation and undergo litte neutralization (pH 2.5-3.5 and Eh 600-750 mV). These waters displayed lower pH and higher Eh in the summer than in other times, as well as the higher Fe 3+:Fe 2+ ratio. These results reflect the increasing of the sulfide oxidation rate during the warm months. The group of neutralized streams (pH=5.7-7.1) displayed seasonal trends contrary to those in acidic waters. Some of these seasonal changes were associated to the natural development of a little weatland which was actuing as a natural water cleaner.
Key words: Acid mine drainage, pyrite oxidation, coal mining