Removal of heavy metal impurities from dredged river sediment

This article shows the results of a study that aims to remove the sediment fraction containing heavy metals from river sediment by flotation. Differen t parameters such as pH, flotation time, different collectors, distilled wa ter, tap water, and different salts were investigated to achieve a high sep aration efficiency. Explanations are suggested for the obtained results. Re sults of flotation revealed that 63% by weight of the input dredged sedimen t can be safely and successfully separated, thus, meeting the standard envi ronmental requirement of current Flemish (Belgium) regulation "bodemsanerin gsdecreet" (February 1995). This dredged fraction could not be achieved bef ore 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 s pecification was obtained. Results are explained in the light of a model, w hich assumes that sediment contains organic matter together with heavy meta ls, clay, and sand. Upon aeration, air bubbles are adsorbed on hydrophobic particles, which carry them up to the froth layer with the hydrophilic part icles left behind in the pulp. The use of an organic collector has a minor effect on flotation process. Results of the settling technique are discusse d.