Sorption of Pb and Cd by sediments of the polygenetic river valleys of the eastern part of the Polish Lowland

Abstract

Sediments, filling the polygenetic, melt-out river valleys of the eastern part of the Polish Lowland and adjacent areas are characterised by various sorption capacities in relation to Pb and Cd. Valley bottoms and ice-dammed basins within the morainic plateau are built of peats, mucks and warps, which bond 98% of the added heavy metals from the input solution with concentrations of 1 to 20 mg/dm3 . These sediments, occurring also in the form of horizontal and continuous layers, form natural isolation barriers protecting the groundwaters against pollution with lead and cadmium. Deposits which build the adjacent morainic plateau and which contain over 20% of clay fraction also possess very high sorption capacities in relation to Pb and Cd. Sandy sediments of kames and kame terraces are characterised by the lowest sorption capacities to lead and cadmium. The content of organic matter and to a lesser extent the clay mineral composition determines the sorption capacities of lacustrine and marsh sediments. In the case of the clastic deposits of the morainic plateau, the value of this parameter depends on the quantity and composition of the clay fraction, and on the presence of CaCO3 and oxides and hydroxides of Fe, Al and Mn. The sorption of lead by peats and warps for delivered input solutions (5-100 mg/dm3 ), in most cases, are described by Henry's isotherms whereas the sorption of cadmium is described by Freundlich's isotherms. The sorption of lead as well as cadmium by mineral and organic-mineral sediments are described by Freundlich's isotherms.