Thermal-Treated Soil for Mercury Removal: Soil and Phytotoxicity Tests

Abstract

Mercury (Hg) contamination of soils and sediments is one of many environmental problems at the Oak Ridge Reservation, Oak Ridge, TN. Mercury‐contaminated soil from the Lower East Fork Poplar Creek (LEFPC) at the Oak Reservation was treated thermally to reduce Hg concentration to a below target level (20 mg kg−1) as a pilot scale thermal treatment demonstration. As a part of performance evaluation, the soil characteristics and plant growth response of the untreated and treated soil were examined. The soil treated at 350°C retained most of its original soil properties, but the soil treated at 600°C exhibited considerable changes in mineralogical composition and physicochemical characteristics. Growth and physiological response of the three plant species radish (Raphanus sativus L.), fescue (Festuca arundinacea Schreb.), and oat (Avena sativa L.) indicated adverse effects of the thermal treatment. The addition of N fertilizer had beneficial effects in the 350°C treated soil, but had little beneficial effects in the 600°C treated soil. Some changes of soil characteristics induced by thermal treatment cannot be avoided. Soil characteristics and phytotoxicity test results strongly suggest that changes occurring following the 350°C treatment do not limit the use of the treated soil to refill the excavated site for full‐scale remediation. The only problem with the 350°C treatment is that small amounts of Hg compounds (<15 mg kg−1) remain in the soil and a processing cost of $45/Mg.

Mercury removal from contaminated soil by thermal treatment with FeCl 3 at reduced temperature

“…As shown in Table 2, after heating at 400°C, the soil pH changed from being slightly acidic (5.2) to near neutral (6.5), while heating at 700°C resulted in a pH that was more basic (9.8). The changes in pH may be attributed to the oxidation of certain elements, the dehydration of colloids, the decrease of buffer capacity, and the release of ions from organic matters in the treatment process (Roh et al, 2000). Total organic carbon content in the soil treated at 400°C was 64% that of the original soil, whereas no organic carbon was detected in the soil treated at 700°C.…”

“…Several treatment technologies, including stabilization/solidification (Piao and Bishop, 2006;Randall and Chattopadhyay, 2009;Zhang et al, 2009), soil flushing and soil washing (Wasay et al, 1995;Sierra et al, 2011), thermal treatment (Rose et al, 1995;Roh et al, 2000;Kucharski et al, 2005;Chang and Yen, 2006;Huang et al, 2011), and in situ vitrification , have been employed to remediate mercury-contaminated soils. Among these technologies, thermal treatment, using heat to http://dx.doi.org/10.1016/j.chemosphere.2014.08.012 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.…”

“…Among these technologies, thermal treatment, using heat to http://dx.doi.org/10.1016/j.chemosphere.2014.08.012 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved. convert solid mercurial compounds into volatile mercury, has been often used due to its high removal efficiency and quick turnaround time (Roh et al, 2000;Huang et al, 2011).…”

“…Currently, to decrease residual mercury concentration to a low level (e.g., <1.5 mg kg À1 ), thermal treatment requires the heating of mercury-contaminated soils at temperatures above 600°C (Rose et al, 1995;Chang and Yen, 2006), which is energy intensive. Moreover, experimental results have shown that dramatic changes in soil properties, including increase in soil pH, dehydration of silicate clay minerals, and reduction in the content of organic carbon and nitrogen, were observed when soils were treated at 600°C, thus making the soils unfavorable for agricultural reuse (Roh et al, 2000). Up to now, no study has been reported to decrease the concentration of residual mercury to a low level (e.g., <1.5 mg kg À1 ) by thermal treatment at a reduced temperature.…”

Citric acid facilitated thermal treatment: An innovative method for the remediation of mercury contaminated soil

“…The available remediation technologies for soil contaminated with mercury include phytoremediation [6][7][8], stabilization/solidification [9,10], soil washing [11,12], thermal treatment [13][14][15][16][17][18], and electrokinetics [19,20]. Stabilization/solidification changes soil properties dramatically and makes the treated soil unsuitable for agricultural reuse.…”