Removal of Heavy Metal Impurities from Dredged River Sediment

Abstract

This article shows the results of a study that aims to remove the sediment fraction containing heavy metals from river sediment by flotation. Different parameters such as pH, flotation time, different collectors, distilled water, tap water, and different salts were investigated to achieve a high separation efficiency. Explanations are suggested for the obtained results. Results of flotation revealed that 63 % by weight of the input dredged sediment can be safely and successfully separated, thus, meeting the standard environmental requirement of current Flemish (Belgium) regulation “bodemsaneringsdecreet” (February 1995). This dredged fraction could not be achieved before a flotation time of 15 min. Increasing flotation time would impart less metal content but with a lower yield. In the case of applying the settling technique, 55 % by weight of the dredged sample meeting the same standard specification was obtained. Results are explained in the light of a model, which assumes that sediment contains organic matter together with heavy metals, clay, and sand. Upon aeration, air bubbles are adsorbed on hydrophobic particles, which carry them up to the froth layer with the hydrophilic particles left behind in the pulp. The use of an organic collector has a minor effect on flotation process. Results of the settling technique are discussed.