The removal of heavy metals from dredged sediments by mechanical Denver flotation: the contribution of true flotation and entrainment
Mathias Vanthuyne and André Maes

This study investigated the possibility of removing Cd, Cu, Pb and Zn from four Belgian anoxic sedi-ments, using Denver flotation. The sediments were sampled in, respectively, the River Schijn, the Gent–Terneuzen Canal, the Zuid-Willemsvaart Canal, and the Brussels Docks, all of which have a different (in situ) particle-size distribution. Two froth fractions were collected after froth stabilization: froth 1 (during the first five minutes) and froth 2 (during the second five minutes). For all sediments, the heavy-metal-concentrating factors decreased in froth 2 to values close to 1, which means an absence of flotation selectivity. Except for Cd, higher heavy-metal flotation selectivities were observed in froth 1 for the River Schijn sediment (with concentrating factors of 2.87–3.15) compared with the other three sediments (with concentrating factors of 1.71–2.17) and at similar mass recover-ies (20.4–25.5%). The heavy-metal recoveries by entrainment were predicted for froth 1 and froth 2, based on the experimental Fe-concentrating factors of froth 2. For all sediments, the total heavy-metal recoveries in froth 2 were shown to be entirely due to entrainment. The higher Cu, Pb and Zn flotation selectivity in froth 1 from the River Schijn sediment was ascribed to the higher heavy-metal recoveries by true flotation (65.7–68.9%), as compared with the other three sediments (23.9–49.2%), and was explained by the observation that a higher heavy-metal fraction was present in the >20-µm particle-size fraction. For the sediments from the Gent–Terneuzen Canal, the Zuid-Wille-msvaart Canal, and the Brussels Docks, the large contribution of entrainment (50.8–76.1%) strongly decreased the heavy-metal flotation selectivities in froth 1.

Key words: entrainment, flotation, heavy metals, remediation, sediment

Land Contamination & Reclamation, 15 (1), 15-30 (2007)

DOI 10.2462/09670513.844

© 2007 EPP Publications Ltd

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Article code 844