Thermal immobilization of copper contaminants in soil analogue minerals, quartz and kaolin, at low temperatures such as 300 ℃ is studied to corroborate its technical feasibility as a method for soil remediation. We use a synchrotron-based, X-ray absorption spectroscopy (XAS) technique to study the speciation of and the local structure around copper in the soil analogues that are thermally treated at 300-900℃ for 1 h. The toxicity characteristic leaching procedure (TCLP) method is employed to investigate the leaching behavior of copper compounds. CuO, being predominately transformed from Cu(OH){sub}2 with a lesser amount from Cu(NO{sub}3){sub}2 by 1-h heat application at 300-900℃, is identified by the spectroscopy of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) as the key species that is leaching-resistant due to its low solubility and its chemisorption onto the soil analogue minerals. Fourier transform of EXAFS spectrum of the Cu-doped kaolin heated at 900℃ for 1 h indicates that the intensity of Cu-Cu peaks (2.50 and 5.48 A, both without phase shift correction) is either relatively smaller or disappearing as compared with that of kaolin samples heated at 300 and 500 ℃. The EXAFS analysis suggests that the Cu solid phase in the 900 ℃ kaolin sample is different from the lower temperature samples, the 900 ℃ SiO{sub}2 sample, and the Cu standards. The leaching studies also support the formation of a less soluble phase in the 900 ℃ kaolin sample. An increase of heating temperature, in the range of 105-900℃, reduces the Cu leaching percentage; this reduction trend is more marked for Cu-doped kaolin than for Cu-doped SiO{sub}2.
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