Natural attenuation of arsenic in the Tinto Santa Rosa acid stream (Iberian Pyritic Belt, SW Spain): the role of iron precipitates Asta Andrés, María Pilar Ayora, Carlos Román-Ross, Gabriela Cama, Jordi Acero, Patricia Gault, Andrew G. Charnock, John M. Bardelli, Fabrizio Arsenic Natural attenuation Speciation Publicado en 2010, el embargo ya terminó. No obstante, se sube última versión del autor MPA was financially supported by the Spanish Government with a PhD fellowship. G. R.-R. thanks the Spanish Minister of Science and Innovation and the Ramon y Cajal Programme. This research was funded by project CTM2007-66724-C02-01/TECNO from the Spanish Government. Acid waters and sediment of the Tinto Santa Rosa acid stream (Iberian Pyritic Belt; SW, Spain) were analysed to determine the role of sedimentary phases in the behaviour of arsenic. Aqueous arsenic and iron concentrations decreased markedly from the adit mouth to 300 m downstream indicating iron minerals precipitation as well as arsenic sorption onto these newly‐formed phases. This was confirmed by the high arsenic concentrations observed in bed stream precipitates, which play a major role in controlling arsenic mobility. To unravel the complex nature of the AMD sediments a combination of techniques including X‐Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), total solid digestions, X‐Ray Fluorescence (XRF) and X‐ Ray Absorption Spectroscopy (XAS) were employed. Results showed that (1) arsenic was present predominantly in its pentavalent state; (2) upstream arsenic was sorbed onto the main phase, schwertmannite, whereas downstream it was chiefly associated with goethite and jarosite; and (3) changes in arsenic speciation with depth were observed in the consolidated terrace sediments, where arsenic appeared primarily associated with schwertmannite in the upper part of the terraces, but with goethite at depth. Arsenic mobilization was controlled by sorption onto newly formed precipitates (schwertmannite, goethite and jarosite), causing natural arsenic attenuation. 2026-02-18T08:09:03Z 2026-02-18T08:09:03Z 2010 journal article Published version: María P. Asta. Natural attenuation of arsenic in the Tinto Santa Rosa acid stream (Iberian Pyritic Belt, SW Spain): the role of iron precipitates. Chemical Geology Volume 271, Issues 1–2, 1 March 2010, Pages 1-12. https://doi.org/10.1016/j.chemgeo.2009.12.005 https://hdl.handle.net/10481/111147 10.1016/j.chemgeo.2009.12.005 eng http://creativecommons.org/licenses/by-nc-nd/4.0/ open access Attribution-NonCommercial-NoDerivatives 4.0 Internacional Elsevier