Kinetics of fly ash leaching in strongly alkaline solutions
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We have leached fly ash samples from six power stations in potassium hydroxide solutions at a water-to-solid mass ratio of 40 g/g. A wet chemical method was developed which provides for a detailed characterization of the reactivity of fly ash. The leaching process could be divided into three stages. In stage one, reaction progress measured by the relative mass of fly ash reacted (α) was controlled by the rate of glass network dissolution while very little gel formed (α < 0.1). In stage two, more gel (mainly oxides of Fe, Ca, Mg, and Ti) formed on the glass surface, and the rate of glass dissolution was limited by diffusion (0.1 < α < 0.45). In stage three, zeolite crystallized on top of the gel layer, and an aluminosilicate gel formed in situ, while diffusion continued to control reaction progress (α > 0.45). The data were modeled using a modified Jander equation and rate constants were calculated for each process. The rate constants for stage one reflect an intrinsic glass property, chemical durability, which increased linearly with increasing concentration of network formers in the glass phase of a fly ash.
KeywordsZeolite Geopolymer Relative Mass Reaction Progress Glass Phase
The authors are grateful for financial support of this project from the Vitreous State Laboratory (VSL) of The Catholic University of America (CUA). Chen Chen thanks the Chinese Overseas Fellowship Commission for financial support of his visit to VSL/CUA. The authors thank Dr. Hong Zhao, Dr. Andrew Buechele, and Dr. David McKeown (all VSL) for discussions and experimental support of this study. The authors are grateful to Dr. A. Barkatt (Department of Chemistry, CUA) for his comments and suggestions.
- 5.Pacheco-Torgal F, Castro-Gomes J, Jalali S (2008) Mater 22:1315Google Scholar
- 13.Bumrongjaroen W, Muller I, Schweitzer J, Livingston RA (2007) In: Proceedings of the 2007 world of coal ash (WOCA), Covington, 2007Google Scholar
- 17.Biernacki JJ, Williams PJ, Stutzman PE (2001) ACI Mater J 98:340Google Scholar
- 20.Pietersen HS, Fraay A, Bijen JM (1990) Mat Res Soc Proc Symp 176:139Google Scholar
- 23.Buchwald A, Kaps Ch, Hohmann M (2003) In: Proceedings of the 11th international congress on the chemistry of cement (ICCC) Durban, 2003, p 1238Google Scholar
- 28.Khawam A, Flanagan DR (2006) J Phys Chem B110:17315Google Scholar
- 30.Kondo R, Lee K, Diamon M (1976) J Ceram Soc (Japan) 84:573Google Scholar
- 34.Grambow B (1985) Mat Res Soc Symp Proc 44:15Google Scholar
- 42.Barkatt AA, Gibson BC, Macedo PB, Montrose C, Sousanpour CJW, Boroomand MA, Rogers V, Penafiel M (1986) Nucl Technol 73:140Google Scholar
- 43.Lasaga AC (1981) In: Lasaga AC, Kirkpatrick RJ (eds) Kinetics of geochemical processes. Mineralogical Society of America, WashingtonGoogle Scholar