Abstract
Solutions obtained from minesoils originating from the opencast lignite mine dump at As Pontes (Galicia, NW Spain) were studied. Spoils were very heterogeneous and there were a wide range of environments. Generally, solutions showed high electrical conductivity, often with large quantity of weathering products derived from pyrite oxidation (Fe, SO 4 2−, H +), as well as Al and Si originating from mineral alteration. The Al fractioning showed (a) in the most acid areas (pH < 5.0) AlSO 4 was the dominant complexeand Al 3+ was the second most common; (b) at pH values between 5.0 and 6.0, AlF monomers were the most abundant complexes; (c) at pH values > 6.0, AlOH species were most common. The distribution of Fe species was chiefly determined by the EhpH conditions and SO 4 2− contentss in the solution. Generally, in areas with a pH < 4.0 and Eh > 600 mV, Fe was found as FeSO 4 complexes, while in areas with a pH > 6.0 the only species present were Fe-hydroxy-monomers. The Al 3+ activity in soil solution seems to be controlled by a jurbanite-type mineral at pH < 4.0, while amorphous Al(OH) 3 seems to exercise this control at pH > 5.0. With regards to Fe, in the most acid (pH < 4.0) and oxidizing (pe < 9) environments, none of the minerals studied, could control their solubility, FeSO 4·7H 2O being the mineral phase closest to the equilibrium.
Published Version
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