Sorption Mechanisms of Zinc to Calcium Silicate Hydrate:  X-ray Absorption Fine Structure (XAFS) Investigation

Abstract

In this study, X-ray absorption fine structure (XAFS) spectroscopy has been used to further elucidate the binding mechanisms of Zn(II) to calcium silicate hydrate (C-S-H), the quantitatively most important cement mineral. Such knowledge is essential for the assessment of the longterm behavior of cement-stabilized waste materials. XAFS spectra of the Zn(II) equilibrated with C-S-H(I) for up to 28 days are best modeled by tetrahedral coordination of Zn(II) by four O atoms in the first atomic shell. Beyond the first coordination shell, data analysis of more highly concentrated samples suggests the presence of two distinct Zn distances and possibly the presence of an Si shell. On the basis of the comparison with a set of reference compounds, this coordination environment can be reasonably related to the structure of hemimorphite, a naturally occurring zinc silicate, and/or the presence of gamma-Zn(OH)2. At the lowest Zn uptake, the above fitting approach failed and data could be described best with a Zn-Si and a Zn-Ca shell. Previous work has been able to show that Zn(II) diffuses into the C-S-H(I) particles and does not form discrete precipitates, so the findings appear to confirm the incorporation of Zn(II) in the interlayer of C-S-H(I).

Effects of in situ remediation on the speciation and bioavailability of zinc in a smelter contaminated soil

“…Under basic pH conditions, hydrozincite and smithsonite could possibly form in the soil. Bond distances and coordination numbers derived from non-linear least-square fitting compared well with values reported in the literature for these minerals (Ziegler et al, 2001;Roberts et al, 2002;Waychunas et al, 2002).…”

Micro-spectroscopic investigations of highly heterogeneous waste repository materials

“…Despite its undisputed relevance, a molecular-level studies on the geochemical and microbial processes responsible for radionuclide uptake and cement degradation-including the subsequent release of contaminant into the environment-are not commonly found in the literature (e.g., Allen et al, 1997;Bonhoure et al, 2002Bonhoure et al, , 2003Rinehart et al, 1997;Rose et al, 2000Rose et al, , 2001Rose et al, , 2003Scheidegger et al, 2000;Zhao et al, 2000;Ziegler et al, 2001). In our laboratory we have successfully conducted bulk XAS studies to gain information on the interactions of radionuclides (Ni, Zn, Sr, Se, and I) with hardened cement paste (HCP) and cement phases under highly alkaline conditions (pH = 12-14, high ionic strength) (Bonhoure et al, 2002(Bonhoure et al, , 2003Scheidegger et al, 2000;Ziegler et al, 2001).…”

“…In our laboratory we have successfully conducted bulk XAS studies to gain information on the interactions of radionuclides (Ni, Zn, Sr, Se, and I) with hardened cement paste (HCP) and cement phases under highly alkaline conditions (pH = 12-14, high ionic strength) (Bonhoure et al, 2002(Bonhoure et al, , 2003Scheidegger et al, 2000;Ziegler et al, 2001). An important reason for the lack of molecular-level process understanding in cementitious system is the fact that cement is a complex heterogeneous mixture consisting of mainly calcium (aluminium) silicate hydrates (C(A)SH phases (CaO) x (SiO 2 ) y (H 2 O) z ;~50 wt.%), portlandite (Ca(OH) 2 ;~20 wt.%) and calcium alumi-…”

“…It has been realized, however, that in order to obtain mechanistic or atomic/molecular-level information, macroscopic studies need to be coupled with analytical investigations. In our laboratory, X-ray absorption spectroscopy (XAS) has become an important research tool to elucidate chemical processes in waste repository systems (Bonhoure et al, 2002(Bonhoure et al, , 2003Dähn et al, 2002aDähn et al, ,b, 2003Scheidegger et al, 2000;Ziegler et al, 2001). XAS corresponds to a powerful collection of techniques able to provide molecular-level characterisation of material (Koningsberger and Prins, 1988;Saisho and Gohshi, 1996).…”

Viability Study of a Safe Method for Health to Prepare Cement Pastes with Simultaneous Nanometric Functional Additions

“…When there are not enough dissolved Zn ions, retardation ends and a greater acceleration of hydration occurs. In the same sense, various authors suggest that the CSH gel is the most probable site for metal fixation in cement and Zn 2+ is incorporated in the interlayer CSH (Stumm et al [37], Ouki and Hills [38], Ziegler et al [39], and Ziegler and Johnson [40]). …”