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

Resumen

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.