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Chlorides behavior in raw fly ash washing experiments
Fenfen Zhu1, Masaki Takaoka, Kazuyuki Oshita
1Department of Urban & Environmental Engineering, Graduate School of Engineering, Katsura Campus, Kyoto University, Nishikyo-ku, Kyoto 615-8540, Japan. zhu@hse.gcoe.kyoto-u.ac.jp
Journal of Hazardous Materials
|February 23, 2010
Summary
Understanding chloride behavior in municipal solid waste incinerator (MSWI) fly ash is crucial for recycling. Washing effectively removes soluble chlorides like NaCl, KCl, and CaCl(2), but insoluble forms, primarily CaCl(2), are released more slowly.
Area of Science:
- Environmental Science
- Materials Science
- Analytical Chemistry
Background:
- Chloride content in municipal solid waste incinerator (MSWI) fly ash hinders its use as building material.
- Effective recycling of fly ash necessitates understanding chloride behavior during processes like washing.
Purpose of the Study:
- To investigate the behavior of chlorides in raw fly ash (RFA) during washing.
- To identify the chemical forms of chlorides in RFA and their transformation during washing.
Main Methods:
- X-ray absorption near edge structure (XANES) and X-ray diffraction (XRD) were employed.
- A combined XRD and XANES approach was used to analyze chloride speciation.
- Washing experiments were conducted at varying liquid-to-solid (L/S) ratios and washing frequencies.
Main Results:
- Raw fly ash (RFA) contained chlorides primarily as CaCl(2) (51%), NaCl (15%), KCl (10%), and Friedel's salt.
- Washing significantly reduced soluble chlorides (NaCl, KCl, CaCl(2)) with increased L/S ratio or washing frequency.
- Insoluble chlorides, mainly CaCl(2) and related compounds, were released more gradually but were promoted by washing.
Conclusions:
- The combination of XRD and XANES is effective for studying chloride behavior in fly ash washing.
- Washing is a viable method for reducing chloride content in fly ash, though insoluble forms require further consideration.
- CaCl(2) and Friedel's salt serve as reliable indicators for insoluble chlorides in MSWI fly ash.
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