X-ray Absorption Spectroscopy Study of Immobilization Processes for Heavy Metals in Calcium Silicate Hydrates. 2. Zinc

Abstract

Tricalcium silicate (C3S), the major phase of cement-based materials, contains naturally a few hundred parts per million of heavy metals. An X-ray absorption spectroscopy (XAS) study at the Zn K-edge has been carried out to elucidate the binding mechanisms of Zn by calcium silicate hydrates, which is important to predict the long-term behavior of Zn. At low concentration, under the threshold of precipitation of the oxide, oxy hydroxide, and calcium zinc hydroxide, no retardation of the hydration of the C3S has been observed for C3S doped with Zn. A previous 29Si NMR (Moulin, I.; Stone, W. E. E.; Sanz, J.; Bottero, J.-Y.; Mosnier, J−Y.; Haehnel, C. Langmuir 1999, 15, 2829−2835) study has demonstrated that the structure of the hydrated C3S (called C-S-H for calcium silicate hydrates) does not change if Zn is present initially or not. XAS experiments have shown that Zn tetrahedra are incorporated within the matrix of C-S-H and linked directly at the end of the silicate chains through Zn−O−Si bonds. The Zn−Si distance is ≈3.1 Å. Extended X-ray absorption fine structure results have been confirmed by ab initio calculations including multiple scattering.

An assessment of Portland cement, cement kiln dust and Class C fly ash for the immobilization of Zn in contaminated soils

“…Also, the Zn ion can be incorporated into CSH compounds, which is the major phase in hydrated cement (Rose et al 2001). Therefore, if the TCLP solution is buffered enough by the S/S agents, effective Zn immobilization should be expected.…”

“…The Zn substitution occurs either by replacement of Ca 2? or by direct linkage to the end of the silicate chains through Zn-O-Si bonds (Moulin et al 1999;Rose et al 2001). Moreover, the formation of Zn 6 Al 2 (OH) 16 CO 3 Á4H 2 O and CaO[Zn(OH) 2 ]Á2H 2 O have been reported when the Zn(OH) 2 was blended with PC (Qiao et al 2007).…”

“…This precipitate covers cement grains and prevents their further hydration (Cocke and Mollah 1993;Yousuf et al 1995). Rose et al (2001) reported that Zn ions at low concentrations can be directly incorporated into calcium silicate hydrate (C-S-H) compounds. The Zn substitution occurs either by replacement of Ca 2?…”

In vivo speciation of zinc in Noccaea caerulescens in response to nitrogen form and zinc exposure

“…Spectra of Group 1 compounds were very similar and included all of the weakly-complexed Zn species: Znsalts, the carboxylates Zn-acetate, and Zn-succinate (both pH), and the amino acids Zn-Pro and Zn-Ala (pH 5.6). The differences between the spectra of individual or groups of reference compounds are attributed to variations detected by XANES in the electronic transitions from 1s to unoccupied 4p molecular orbitals which constitute the first coordination sphere of Zn (Rose et al 2001).…”

Nickel speciation in cement-stabilized/solidified metal treatment filtercakes

“…The application of XAS to complex matrices in relation to environmental fate and behavior of contaminants is still relatively rare, but it has been employed in a limited number of studies of the speciation of metals in cement pastes, including chromium [9], cobalt [10], copper [11], lead [12], neodymium [13], selenium [14], tin [15], uranium [16] and zinc [17], as well as nickel [18][19][20]. Apart from Rinehart et al [9], who examined the oxidation state of chromium in a s/s contaminated soil and showed that this was not affected by S/S, and Hsaio et al [11], who indicated that S/S respeciated CuCl2 and reduced forms of copper in municipal waste incinerator air pollution control residues to Cu(OH)2, other studies have all prepared hydrated cement pastes by mixing pure solutions of soluble metal salts with cement powder.…”