Speciation of Chemical Elements in the Waters of the Herberz Historical Mine, Karelia, Russia: Thermodynamic Calculations and Fractionation

Abstract

The speciation of chemical elements in the waters and its dependence on the dissolved organic matter were studied by a complex of methods, involving thermodynamic calculations and experimental fractionation. The waters were studied at the abandoned and flooded Herberz Mine in the Pitkäranta district, Karelia, Russia. The regional natural waters are typically highly humified. In combination with the unique metallogeny of the rocks, this makes the mine suitable for solving the formulated problems. The eastern shaft of the Herberz Mine was sampled to a depth of 20 m to trance the changes induced by changes in the redox conditions. One of the geochemical characteristics of the waters is their relatively high concentrations of trace elements and a low salinity (TDS, total dissolved solids). All water samples from the Herberz Mine contain elevated concentrations of Zn, Fe, Mn, Cu, Ni, As, and W. Experimental fractionation and thermodynamic simulations of the speciation of chemical elements led us to identify metals whose accumulation most strongly depends on organic matter (OM). Both methods have demonstrated that U, Th, Cu, Ni, and Y show a high chemical affinity to OM. Metals (Cd and Fe) weakly bonded to the functional groups of natural OM, with the predominance of electrostatic bonding and a higher proportion of carboxyl bonds, are most susceptible to transformations with changes in geochemical conditions.