Study of thermally immobilized Cu in analogue minerals of contaminated soils

Thermal immobilization of copper contaminants in Soil analogue minerals, qu artz and kaolin, at low temperatures such as 300 degreesC is studied to cor roborate its technical feasibility as a method for soil remediation. We use a synchrotron-based, X-ray absorption spectroscopy (XAS) technique to stud y the speciation of and the local structure around copper in the soil analo gues that are thermally treated at 300-900 degreesC for 1 h. The toxicity c haracteristic leaching procedure (TCLP) method is employed to investigate t he leaching behavior of copper compounds. CuO, being predominately transfor med from Cu(OH)(2) with a lesser amount from Cu(NO3)(2) by 1-h heat applica tion at 300-900 degreesC, is identified by the spectroscopy of X-ray absorp tion near-edge structure (XANES) and extended X-ray absorption fine structu re (EXAFS) as the key species that is leaching-resistant due to its low sol ubility and its chemisorption onto the soil analogue minerals. Fourier tran sform of EXAFS spectrum of the Cu-doped kaolin heated at 900 degreesC for 1 h indicates that the intensity of Cu-Cu peaks (2.50 and 5.48 Angstrom, bot h without phase shift correction) is either relatively smaller or disappear ing as compared with that of kaolin samples heated at 300 and 500 degreesC. The EXAFS analysis suggests that the Cu solid phase in the 900 degreesC ka olin sample is different from the lower temperature samples, the 900 degree sC SiO2 sample, and the Cu standards. The leaching studies also support the formation of a less soluble phase in the 900 degreesC kaolin sample. An in crease of heating temperature, in the range of 105-900 degreesC, reduces th e Cu leaching percentage; this reduction trend is more marked for Cu-doped kaolin than for Cu-doped SiO2.