Speciation of cadmium in cement: Part I. Cd2+ uptake by C-S-H

Abstract Hazardous cadmium can be trapped in C-S-H, the main “phase” in Portland cement. Two kinds of Cd-containing calcium silicates were synthesized: Cd/Ca silicate hydrates prepared by coprecipitation and Cd-exchanged C-S-H. In Cd-exchanged C-S-H, chemical and structural studies (ICP-AES, XRD, extended X-ray absorption fine structure (EXAFS), and nuclear magnetic resonance (NMR)) show that up to 30 wt.% Cd uptake is possible, with little structural change. XRD patterns and 29Si magic angle spinning (MAS) NMR spectra are similar in Cd-free and Cd-containing C-S-H. Cd-EXAFS shows that the majority of Cd2+ atoms are homogeneously distributed within the C-S-H structure, although 113Cd cross-polarization (CP) MAS NMR cannot discriminate between Cd atoms in main layer location and Cd atoms in interlayer location. In Cd/Ca silicate coprecipitates, the structure is nearly amorphous and the silicate species do not polymerize to a C-S-H-like structure.

[1]  A. Benesi,et al.  Silicon‐29 Magic Angle Spinning Nuclear Magnetic Resonance Study of Calcium Silicate Hydrates , 1989 .

[2]  X. Cong,et al.  29Si MAS NMR study of the structure of calcium silicate hydrate , 1996 .

[3]  F. Glasser,et al.  Ion-exchange properties of 11-Å tobermorite , 1986 .

[4]  R. Roy,et al.  Al-substituted tobermorite: shows cation exchange , 1982 .

[5]  J. Rehr,et al.  Ab initio curved-wave x-ray-absorption fine structure. , 1991, Physical review. B, Condensed matter.

[6]  S. Komarneni,et al.  Sequestration of Cesium and Strontium by Tobermorite Synthesized from Fly Ashes , 1996 .

[7]  G. Maciel,et al.  Cadmium-113 NMR studies of solid cadmium(II) complexes , 1981 .

[8]  S. Komarneni,et al.  Reactions of some calcium silicates with metal cations , 1988 .

[9]  JOSEPH V. Smith,et al.  Nuclear magnetic resonance of silica polymorphs , 1983, Nature.

[10]  S. A. Hamid.  The crystal structure of the 11Å natural tobermorite Ca2.25[Si3O7.5(OH)1.5] · 1H2O , 1981 .

[11]  F. Glasser,et al.  Ion-exchange properties of Ca5Si6O18H2·4H2O , 1985 .

[12]  A. Nonat,et al.  C-S-H Structure Evolution with Calcium Content by Multinuclear NMR , 1998 .

[13]  Rustum Roy,et al.  27Al and29Si magic angle spinning nuclear magnetic resonance spectroscopy of Al-substituted tobermorites , 1985 .

[14]  N. Lequeux,et al.  Speciation of cadmium in cement: Part II. C3S hydration with Cd2+ solution , 2001 .

[15]  S. Komarneni,et al.  Selective cation exchange in substituted tobermorites , 1989 .

[16]  X. Cong,et al.  17O MAS NMR Investigation of the Structure of Calcium Silicate Hydrate Gel , 1996 .

[17]  P. Bonville,et al.  Superparamagnetic properties of a cement-derived synthetic Fe-substituted calcium silicate hydrate , 1997 .

[18]  É. Lippmaa,et al.  Solid-state high-resolution 29Si NMR spectroscopy of synthetic 14 Å, 11 Å and 9 Å tobermorites , 1982 .

[19]  É. Lippmaa,et al.  Solid-state high-resolution silicon-29 chemical shifts in silicates , 1984 .

[20]  S. Komarneni,et al.  Substituted Tobermorites: 27Al and 29Si MASNMR, Cation Exchange, and Water Sorption Studies , 1991 .

[21]  G. Sankar,et al.  Tracking in Detail the Synthesis of Cadmium Oxide from a Hydroxyl Gel Using Combinations of in Situ X-ray Absorption Fine Structure Spectroscopy, X-ray Diffraction, and Small-Angle X-ray Scattering , 1999 .

[22]  N. Labhasetwar,et al.  Ca2+ ⇌ Pb2+ exchange reaction of calcium silicate hydrate: Ca5Si6O18H2 · 4H2O , 1989 .

[23]  D. Macphee,et al.  Immobilization Science of Cement Systems , 1993 .