Flotation as a remediation technique for heavily polluted dredged material. 1. A feasibility study

The flotation behaviour of highly polluted dredged material was investigated at different pH values by mechanical agitated (Denver) flotation. Up to 80% of cadmium, copper, lead and zinc could be concentrated in the froth layer which represented only 30% of the total mass. The maximum specificity for heavy metals, defined as the concentrating factor, was obtained at pH 8-9. The maximum recovery of heavy metals on the other hand was found to be reached at elevated pH values (pH 12). In addition the specificity of the flotation process for the transition metals could be assigned to their presence as metal sulphides in the dredged material. However, the interaction with organic matter is an important factor in determining their flotability. The carbonate fraction was irrelevant for the flotation behaviour of heavy metals.