In this study, we tested a new procedure for the decontamination of mercury-polluted dredging sludge
(Marano-Grado Lagoon, northeastern Italy) based on cationic exchange associated with thermal desorption
at a low temperature. Four mercury-polluted sludge slurries were treated using thermal desorption
at 393 K for 2 h. Three different salts, NaCl (sodium chloride), (CH3)4NCl (tetramethylammonium chloride)
and (C4H9)4NCl (tetrabutylammonium chloride) were used as exchangers. The selected salts have a
monovalent cationic part that progressively increases in molecular weight. The results show that the association
of cationic exchange with thermal treatment leads to a significant improvement in the removal of
mercury from the contaminated material at a low temperature compared to samples that were not treated
with salt. The highest levels of decontamination were attained were obtained when the slurries, which
had mercury pollution ranging from 20 to 200 ppm, were treated with a 15% solution of (C4H9)4NCl. The
efficiency of the removal at 393 K (from 24% up to 60%) depended on the nature of the sample. When the
samples were treated at a similar temperature without the salt, no remediation of mercury was detected.
Our results show that the thermal decontamination temperature can be significantly lowered by this
remediation approach, which is the first example based on cationic exchange of the pollutant with an
appropriate salt.
