SORPTION OF ZINC ON SUSPENDED PARTICLES ALONG A SALINITY GRADIENT - A LABORATORY STUDY USING ILLITE AND SUSPENDED MATTER FROM THE RIVER RHINE

The adsorption of zinc on suspended matter from the river Rhine has been studied. High rates of adsorption were apparent during the first hours of the experiments, but during the next few days adsorption kinetics were much slower. The adsorption could be described by a Freundlich isotherm, indicating surface heterogeneity. In subsequent experiments, desorption of previously adsorbed Zn was investigated in solutions of various salinities. These experiments showed that the largest desorption effect occurred in the low salinity range (S=0-5). The adsorption reaction was not completely reversible. Our results indicate that desorption of Zn is to be expected in an estuary due to the presence of a salinity gradient. In field measurements, however, adsorption of Zn is often observed. This apparent contradiction is caused by additional processes that are not taken into account in laboratory studies.