The vaporization mechanisms of water-insoluble Cs in raw ash and Cs-doped ash during thermal treatment with CaCl addition was systematically examined in a lab-scale electrical heating furnace over a temperature range of 500-1500 °C. The results indicate that the water-insoluble Cs in the ash was associated with aluminosilicate as pollucite. Addition of 10% CaCl caused the maximum vaporization ratio of Cs in the raw ash to reach approximately 80% at temperatures higher than 1200 °C, whereas approximately 95% of Cs was vaporized at temperatures higher than 1300 °C when 30% CaCl was added. The formation of an intermediate compound, CsCaCl, through the chemical reaction of Cs with CaCl was responsible for Cs vaporization by means of the subsequent decomposition of this intermediate upon the increase in temperature. The indirect chlorination of Cs by the gaseous chlorine released from the decomposition of CaCl was insignificant. A high CaCl content in the resulting annealed products with 30% CaCl addition delayed the decomposition of CsCaCl and thus lowered the Cs vaporization ratio compared to that with 10% CaCl addition at 900-1250 °C. Thermal treatment with CaCl addition is a proposed method to remove Cs from Cs-contaminated incineration ash.
Phytoremediation is the direct application of green plants and their associated micro-organism to stabilize or absorb contaminants from soils, sludge, sediments, surface water, or groundwater. Boron and fluoride were listed to the soil standards a few years ago in Japan; however, few researches have been reported about phytoremediation on the above elements. In this paper, the authors report the experimental results of accumulation and tolerance ability of green plants focusing on the fluoride and boron contamination. In the pot laboratory tests, the growth rate of Chinese cabbage was not affected by low fluoride concentration (<15 mg/L) or low boron concentration (<5 mg/L). In the hydroponics tests, fluoride content in both stems+leaves and roots increased 3–10 times higher than control. Fluoride is easy to be concentrated in the roots. Boron content in both stems+leaves and roots increased 1.2–1.5 times higher than control. Boron is easy to be concentrated in the upper portion. Especially, Phytolacca Americana, Ambrosia trifida L., and Commelina communis can accumulate boron with higher efficiency. The boron content in soil was 480–550 mg/kg, and the boron content in these grasses was 2–3 times higher than that in soil. These results show they can accumulate boron and fluoride, and phytoremediation can be adopted for relatively lower contamination.
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