Kinetics of the desorption of mercury from selected freshwater sediments as influenced by chloride

Abstract

The kinetics of Hg desorption from selected freshwater sediments in the Canadian Prairies as influenced by a range of chloride concentrations (0, 10−4, 10−3, 10−2, 2×10−2, 4×10−2, 6×10−2, 8×10−2, 10−1 M) were studied. The extent of the influence of Cl− concentrations on the increase of the rate of Hg release from the sediments in the fast desorption and slow desorption processes varied from 2.5 to 10.5 times and 2.0 to 8.5 times, respectively. An abrupt increase in the Hg release from the sediments was observed when the Cl− concentration was 2×10−2 M and higher. The increase of Hg release with increasing Cl− concentrations was attributed to the dissolution of the adsorbed Hg through its complexation with Cl−. The release of Hg was not affected by the ionic strength and the Na concentrations in the systems studied. The influence of Cl- concentrations on the kinetics of the release of the sediment-bound Hg varied with the nature and properties of the sediments. The data indicate that short-range ordered oxides of Al, Fe, and Mn and their complexes with organic components merit close attention in studying the influence of Cl−, whose sources include deicing salts, fertilizers, animal wastes, and sewage effluents, on the rate of the dispersion of Hg from freshwater sediments.