Boletín de la Sociedad Geológica Mexicana

Volumen 67, núm. 3, 2015, p. 447-456

Understanding Copper speciation and mobilization in soils and mine tailings from “Mineral La Aurora” in central Mexico: contributions from Synchrotron techniques

René Loredo Portales1, Gustavo Cruz Jiménez1, Hiram Castillo Michel2,*, Diana Olivia Rocha Amador1, Katarina Vogel Mikuš3, Peter Kump4, Guadalupe de la Rosa5,+

1 Department of Pharmacy, University of Guanajuato, Noria alta, 36050 Guanajuato, Guanajuato, Mexico. 2 ID 21, European Synchrotron Radiation Facility, Avenue des Martyrs 71, 3800 Grenoble, France.
3 Department of Biology, University of Ljubljana, Večna pot 111, 1000 Ljubljana, Slovenia. 4 Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
5 Biomedical and Electrical Engineering, University of Guanajuato, Lomas del Bosque 103, 37150 Leon, Guanajuato, Mexico.

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Potentially toxic elements are usually present in mine tailings in concentrations that may threat environmental and human health. In this research, mine tailings and soils from the mine "La Aurora" located in central Mexico were studied. This mine was exploited for Pb, Zn, Ag, Cu and Au and abandoned since their last cycle in 1957. For this purpose, a combination of sequential extraction procedure (SEP), Flame Atomic Absorption Spectroscopy (FAAS), and X-ray synchrotron techniques (XAS) were used. Cu is present in mine tailings and soils in a range respectively between 125 ± 21 and 1763 ± 10 mg·kg-1 and 22 ± 2 and 88 ± 5 mg·kg-1. Repartition of Cu in mine tailings determined by SEP followed this general trend: Water soluble > Residual > Organic Bound > Exchangeable > Fe-Mn oxides bound > Carbonates bound. In contrast, Cu in soils was mainly retained in the residual fraction and followed this general trend: Residual > Organic bound > Fe-Mn oxides bound > Carbonates bound > Water soluble > Exchangeable. X-ray Absorption Near Edge Spectroscopy (XANES), showed that Cu is present as Cu2+, forming highly mobile species, and in minor proportion as Cu+species, as oxides and sulphides. Cu content in mine tailings is available for plants and bioaccessible with percentages higher than 50% in almost all the points tested. The calculated dose limit, that involves gastrointestinal disorders for chronic exposure is surpassed in all mine tailings tested.

Keywords: Copper, mine tailings, X-ray absorption spectroscopy.