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

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.