Aqueous and surface chemistry of calcium-metal hydroxides in high pH environments
- Lamar Univ., Beaumont, TX (United States)
There is considerable interest in the chemistry associated with hazardous waste treatment by cement. The hydration of Portland cement is retarded in presence of zinc, cadmium and lead ions. Mixed hydroxides of calcium, zinc, cadmium and lead have been recently identified in the high pH environments of hydrating cement. FTIR, XRD, SEM, and SPM have been used to characterize these systems. A chemical equilibrium model of the early hydration of a zinc-doped cement/water system, Na-K-Ca-ZnH-SO{sub 4}-OH-Zn(OH){sub 2}-Zn(OH){sub 3}-Zn(OH){sub 4}-H{sub 2}O, has been developed to better understand the mechanism of the surface formation of calcium hydroxyzincate (CHZ). The model is based on Pitzer`s semi-empirical method for calculation of ion-activity coefficients at high ionic strength. The Pitzer parameters for Na{sup +}-Zn{sup 2+}, Na{sup +}-Zn{sup 2+}-SO{sub 4}{sup 2{minus}} and K{sup +}-Zn(OH){sub 4}{sup 2{minus}} have been evaluated, and the results successfully predict the equilibria (solubilities) of Na{sub 2}SO{sub 4}-ZnSO{sub 4}-H{sub 2}O, NaOH-Zn(OH){sub 2}-H{sub 2}O and KOH-ZnO-H{sub 2}O systems. The chemical model clearly demonstrates that the formation of CHZ on the calcium-silica-hydrate (C-S-H) surface is critically controlled by the Ca{sup 2+} ion concentration as well as pH of the pore water system. The results of this study suggest that the growth of CHZ is preceded by surface complex formation. Sequential charge control and sequential structure development have been used to discuss the surface selectivity of these compounds and their control of cement hydration.
- Sponsoring Organization:
- Texas Advanced Technology Program, TX (United States); Welch (Robert A.) Foundation, Houston, TX (United States)
- OSTI ID:
- 500989
- Report Number(s):
- CONF-960401-; ISBN 1-55899-335-5; TRN: IM9732%%217
- Resource Relation:
- Conference: Spring meeting of the Materials Research Society (MRS), San Francisco, CA (United States), 8-12 Apr 1996; Other Information: PBD: 1997; Related Information: Is Part Of Aqueous chemistry and geochemistry of oxides, oxyhydroxides, and related materials; Voigt, J.A. [ed.] [Sandia National Labs., Albuquerque, NM (United States)]; Wood, T.E. [ed.] [3M Co., St. Paul, MN (United States)]; Bunker, B.C. [ed.] [Pacific Northwest Lab., Richland, WA (United States)]; Casey, W.H. [ed.] [Univ. of California, Davis, CA (United States)]; Crossey, L.J. [ed.] [Univ. of New Mexico, Albuquerque, NM (United States)]; PB: 384 p.; Materials Research Society symposium proceedings, Volume 432
- Country of Publication:
- United States
- Language:
- English
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