BEHAVIOR OF SOME MACROELEMENTS, TRACE-ELEMENTS AND RE IN THE WATER-SEDIMENT SYSTEM

The aim of this work was to estimate the processes of sorption or desorption which take place when water of slightly higher temperature and elevated concentrations of some elements, compared to groundwater, comes into contact with aquifer sediments under aerobic conditions. The behavior of some macro-elements, trace elements and RE in the water/sediment systems, prepared as five different granulometric fractions of the sediment, was followed by INAA, AAS and titrimetric methods, under simulated natural conditions. It was found that, for the majority of elements, desorption takes place. Opposite to this, Mg and Zn are sorbed from water on all sediment granulometric fractions. The concentration of Ca as a major cation is lingering about its initial value. Na, K, Ba, Sr, Fe, Hg, Au, Sc, Sb, U, La and Ce are desorbed from all sediment fractions. The desorption from finer sediment phase was less pronounced for Fe, Hg, Au, Sc, Sb and Ce. Sorption of some elements (like Co, Cr and Zr) on smallest sediment fraction (<90 m) appears. Sorption-desorption processes, as well as water pH changes, are time dependent, continuing for some weeks, especially in.the coarse sediment system. The extents of sorption and desorption for most of the determined elements indicate that the specific surface area is not a key parameter determining these processes in natural aquifer systems. In the present case cation exchange capacity better describes sorption/desorption processes for most elements. The fact that the finest sediment phase generally shows good sorption properties in laboratory experiments, becomes less significant in real situation of the alluvial aquifer. Due to granulometric composition with large percentage of coarse particles, the contribution of coarse sediments to the sorption-desorption processes and thus to the element transport with water through the underground medium, cannot be neglected.