Study of Thermally Immobilized Cu in Analogue Minerals of Contaminated Soils

Abstract

Thermal immobilization of copper contaminants in soil analogue minerals, quartz and kaolin, at low temperatures such as 300 degrees C 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 degrees C 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)2 with a lesser amount from Cu(NO3)2 by 1-h heat application at 300-900 degrees C, 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 degrees C 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 degrees C. The EXAFS analysis suggests that the Cu solid phase in the 900 degrees C kaolin sample is different from the lower temperature samples, the 900 degrees C SiO2 sample, and the Cu standards. The leaching studies also support the formation of a less soluble phase in the 900 degrees C kaolin sample. An increase of heating temperature, in the range of 105-900 degrees C, reduces the Cu leaching percentage; this reduction trend is more marked for Cu-doped kaolin than for Cu-doped SiO2.

X-ray absorption spectroscopy study of a copper-containing material after thermal treatment

“…Accordingly, we suggest that copper species in this sample is mainly in the form of cupric hydroxide due to the hydroxylation reaction of cupric ion. Previous studies also revealed that copper ions readily form cupric hydroxide through hydroxylation reaction at room temperature [7,9].…”

“…Previous studies indicate that a major portion of heavy metals can be effectively stabilized in some inorganic sorbents including aluminosilicates and silica through a heating process at 200-1300 • C [2][3][4][5][6][7]. The sintered or/and melted materials, depending on their composition, can be recycled as component resources for the manufacture of brick, porcelain, firebrick, and ceramics.…”

“…A previous study shows that, as inferred from the simulation of a sample XANES spectrum with a set of copper reference compounds, most of the artificially doped cupric nitrate was transformed into cupric hydroxide due to hydroxylation at room temperature [7]. After heating, the cupric oxide became the major copper species in samples; quantification of copper species is successful due to the intrinsic simplicity of the silica matrix used.…”

“…The objective of this study is to determine: (i) fraction of copper leached from heated samples, and (ii) copper species transformation in a real-world copper-containing solid material after thermal treatment up to 1100 • C. The real-world sample matrix in the present study is much more complicated than the previously studied model compound matrixes where the matrix sintering activity was minimal at 900 • C [7]. The real-world sample contains 13.6 wt.% copper, being much higher than the copper content in fly ashes, so it is very hazardous and imposes quite a challenge on immobilization technologies.…”

Evidence for a new mechanism of Fe2O3 decomposition in lightweight aggregate formation

“…The composition of the material simulates the elemental content (Si, Al, Fe, K, Na, and Ca) of a Taiwanese reservoir sediment sample already identified as a useful raw material for producing lightweight aggregates (Wei and Lin 2009). A study of the molecular environment using X-ray absorption spectroscopy can provide necessary information to identify longterm solutions for waste management and environmental remediation (US DOE 1995;Wei et al 2001Wei et al , 2002Wei et al , 2006a. X-ray absorption spectroscopy, including X-ray absorption near-edge structure and extended X-ray absorption fine-structure spectra, can reveal speciation, species distribution, and form transformations of target elements, such as Fe (US DOE 1995).…”