Concentration and mobility of copper and zinc in the hypergenic zone of a highly urbanized area

Abstract

Common occurrence of copper and zinc in groundwater and their diverse mobility in the environment make these metals sensitive indicators of industrial and municipal pollution of freshwaters. An analysis of the collected data allowed for a description of the factors and processes that induce changes in the concentration of these metals in the soil, rock and groundwater. Sorption, ion exchange and oxidation–reduction processes, dissolution and precipitation of minerals, and reactions involving organic matter significantly affected the mobility of copper and zinc. The study employed hydrogeochemical methods to obtain comprehensive interpretative data. Its results showed that the variability of the composition of exchangeable cations was due to instability of chemical composition of precipitation. Different activities of Cu and Zn in the solution introduced into the rocks led to the establishment of new quasi-equilibrium states between the adsorbent and the adsorbate. At very low copper and zinc concentrations in groundwater, zinc was more easily retained in the solid phase, and it was more difficult to extract. In contrast, a laboratory static batch experiment utilizing high concentrations of the elements in the solutions showed their different behavior. The sorption of copper occurred more easily than the sorption of zinc, as evidenced by the study results and the calculated parameters of sorption maximum, binding constant, and degree of surface coverage of the solid phase by adsorbed copper and zinc according to a single Langmuir equation.