Ionic exchange desorption of mercury from contaminated dredging sludge (at 393K and ambient temperature)

ABSTRACT

In this work, we reported results obtained during experimental tests to introduce a new approach to the treatment of dredging sludge polluted by mercury. A slurry of dredging sludge was treated by cationic exchange procedures both at ambient temperature and distilled at 393K with the aid of some different exchange salts: three inorganic (NaCl, CaCl_2, and CaI₂) and two organic Tetrabutylammonium chloride [(C₄H₉)₄NCl] and Ethyl Viologen diiodide (1,1′-Dietil-4,4′-bipyridinium diiodide) [C₁₄H₁₈I₂N₂], having different cationic exchangeable part and different molecular weights. A similar (15% w/w) solution was used to treat mercury-polluted sludge considering 2, 24, and 48 h of reaction time.

The removal efficiencies of the inorganic/low molecular weight monovalent salts were minimal at the tested temperatures, while higher removal was reached when CaI₂ and Viol-I2 were used at ambient temperature with maximum treatment efficiencies over 70% in 48 h treatment. A recovery/reuse of the exchanging solutions was also tested finding good recovery potential of the salt slurry.

KEYWORDS:

• Dredging sludge
• mercury pollution
• cation exchange
• ambient desorption
• remediation

Acknowledgements

The authors would like to thank Erasmus students and Dr Arianna Gattesco for their laboratorial contribution and to Ing. Federica Gubiani for sludge characterization.