Samples of sediment from Estero Rungue, north of Santiago, were analyzed during January 2007. The studied zone is affected by acid contamination. Analysis of the sediment by XRD detected the presence of rozenite (FeSO(4)center dot 4H(2)O) and gypsum (CaSO(4)center dot 2H(2)O). The experiments were carried out according to the criterion established for the first Step of the sequential extraction proposed by the SMT, using Ca, Cu, Fe, Ni and Zn sulfates in the form of M(lambda)SO(4)alpha H(2)O as a model sediment. The results suggest that it is possible to extract up to similar to 99% of the sulfates because of the low pH (similar to 3). Analysis of the sediment by XRD before and after the first Step of the sequential extraction showed that the sulfates disappear after the treatment, extending the interpretation of the first Step of the sequential extraction to elements that are interchangeable, adsorbed on carbonates, and present as sulfates.