Thermal-treated soil for mercury removal: Soil and phytotoxicity tests

Mercury (Hg) contamination of soils and sediments is one of many environmen tal problems at the Oak Ridge Reservation, Oak Ridge, TN, Mercury-contamina ted soil from the Lower East Fork Poplar Creek (LEFPC) at the Oak Reservati on was treated thermally to reduce Mg concentration to a below target level (20 mg kg-L) as a pilot scale thermal treatment demonstration. As a part o f performance evaluation, the soil characteristics and plant growth respons e of the untreated and treated soil were examined. The soil treated at 350 degrees C retained most of its original soil properties, hut the soil treat ed at 600 degrees C exhibited considerable changes in mineralogical composi tion and physicochemical characteristics. Growth and physiological response of the three plant species radish (Raphanus sativus L.), fescue (Festuca a rundinacea Schreb.), and oat (Avena sativa L.) indicated adverse effects of the thermal treatment. The addition of N fertilizer had beneficial effects in the 350 degrees C treated soil, hut had little beneficial effects in th e 600 degrees C treated soil. Some changes of soil characteristics induced by thermal treatment cannot be avoided. Soil characteristics and phytotoxic ity test results strongly suggest that changes occurring following the 350 degrees 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 de grees C treatment is that small amounts of Hg compounds (<15 mg kg(-1)) rem ain in the soil and a processing cost of $45/Mg.