SOILS AFFECTED BY ACID-MINE WATERS IN GALICIA (NW SPAIN)

Contaminated soils and surface waters, from copper mining in Galicia, are acidic, high in sulphate and increase appreciably in the concentration of elements such as Al, Fe, Ca, Mg, K, Mn, Cu and Zn by contact with soils and fragments of rock of an amphibolic composition. Application of activity data to mineral equilibrium diagrams illustrates the instability of Al-hydroxides and aluminosilicates compared to Al-sulphates of the alunite and jurbanite type, in the waters which are most acid and display sulphate activities close to 10(-2) M. The solution extracted from soils around the spoil heaps reflects the strong influence of the most heavily contaminated run-off waters, with little or no buffering by the solid phase. This aspect may be accounted for by both a brief time of residence and a real decrease of the acid buffering power of these soils, whose primary minerals undergo strong acidolysis. Neoformation of Al-sulphate (and Fe-sulphate) is observed both in soils and in the channels of the contaminated streams, above all the points of contact with non-acid or slightly acid waters.