Sequential solidification/stabilization and thermal process under vacuum for the treatment of mercury in sediments

Abstract

Purpose Millions of cubic meters of sediments are dredged every year in the world. About 10–20%onweight basis of this material is contaminated by organic and/or inorganic pollutants. This work presents the laboratory tests performed to study a system for the remediation and reuse of mercurycontaminated sediments. The treatment is based on a cementbased granulation step (solidification/stabilization (S/S)), followed by a thermal process under vacuum during which volatile and semi-volatile compounds are removed. The experiments focused on: (1) cement hydration reactions; (2) pollutant removal efficiencies; and (3) leaching behavior, in relation to temperature and duration of the thermal process. Mercury speciation was also investigated.\ud Materials and methods Dredged at the marine harbor of Augusta (SR, Italy), the sediments used in the experiments were highly polluted by mercury (200 mgkg−1dry weight (d.w.)). The recipe applied in the S/S step was based on the particle size distribution of the resulting granulates. An indirectly–heated batch system operated under vacuum (2.6±1.3 103 Pa) at: (1) 150°C for 16 h; (2) 200°C for 6 h; (3) 250°C for 4 h; or (4) 280°C for 4 h. X-ray diffraction spectroscopy and scanning electron microscopy were used to study cement hydration reactions. Total mercury concentration and leaching tests were carried out to assess the effects of the different treatment conditions.\ud Results and discussion The best results were obtained by treating the granulate at 250°C for 4 h. Under these conditions, mercury final concentration was 49 mgkg−1 d.w., resulting in a removal efficiency of 63% referred to the granular material before thermal treatment, and 75% referred to the sediment. The concentrations measured in the leachate were compatible with the Italian requirements for reuse, with some exceptions (pH, chlorides, nickel, copper, and COD) ascribed to the specific nature of the sediment. Mercury speciation analyses pointed out changes after both the treatment steps.\ud Conclusions The final granulates accomplish most Italian requirements for reuse, even though an improvement in the S/S step or an additional washing step would help for the exceptions mentioned above. Different reuse options in civil engineering (e.g., filling material, road material, concrete aggregates, etc.) will be evaluated also taking into consideration the mechanical properties. Further studies will be carried out to assess the long-term leaching behavior and leaching under different pH conditions

Remediation of Hg-contaminated marine sediments by simultaneous application of enhancing agents and microwave heating (MWH)

“…PAH, TPH and heavy metal concentrations were below the Italian regulatory limits, whereas the Hg level was much higher than the limit of 1 mg kg −1 . Physical characterization and the nature of the contamination found are consistent with characteristics of coastal sediments of the SW zone of Augusta Bay [4,24,43]. In terms of dielectric properties, the observed relatively high dielectric constant ( ') and loss factor ( ") of 11.3 and 0.6, respectively, are due to the high percentage of CaCO3 and the presence of Al and Fe oxides in the sediment composition.…”

“…Careghini et al [43] reported a maximum Hg removal of 63% from marine sediments dredged from Augusta Bay applying a sequential S/S and thermal process for 4 h. Similar removals were found by Comuzzi et al [64] testing a decontamination procedure of Hg-polluted dredged sludge from Marano-Grado Lagoon (NE Italy), based on cationic exchange associated with low temperature thermal desorption. Hg removals between 24 and 60% were observed when the samples were treated with a 15% solution of tetrabutyl-ammonium chloride.…”

Thermal Treatment of Mercury Mine Wastes Using a Rotary Solar Kiln

“…Besides, thermal treatment of mercury contaminated sediments showed that the percentage of mercury removal raises with the temperature during the treatment of solid matrices [9,10]. Furthermore, the treatment of mercury wastes from the chloralkali industry showed that treatment for 1 h at 800 °C allowed for a removal efficiency above 99.7% [11].…”

Removal of Hg from Real Polluted Sediments Using Enhanced-EK Decontamination: Verification of Experimental Methods and Batch-Test Preliminary Results

“…At the present, 57 National Priority Sites (NPSs) have been issued in Italy in order to achieve the management of the characterization and remediation procedures under the direct responsibility of the Ministry of the Environment. Twenty-nine of these sites (i.e., 60 km 2 in Brindisi, 100 km 2 in Priolo, 900 km 2 in the Sulcis area, 80 km 2 in Taranto, and 75 km 2 in the Venice lagoon) require either sediment containment or treatment activities [1]. High levels of polychlorobiphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), high molecular weight (C 12 -C 40 ) petroleum hydrocarbons, and heavy metals, such as mercury, were generally found in contaminated sediments [2].…”

“…Technically and economically feasible treatment strategies need to be identified. The commonly employed and emerging techniques for mercury ex situ remediation are stabilisation/solidification (S/S), thermal desorption, soil washing, or phytoremediation [1]. However, these alternatives could be extremely expensive or long time requiring.…”