Resource recovery of waste incineration fly ash: Synthesis of tobermorite as ion exchanger
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Resource recovery of waste incineration fly ash: Synthesis of tobermorite as ion exchanger Zhidong Yao, Chikashi Tamura, Motohide Matsuda, and Michihiro Miyakea) Department of Environmental Chemistry and Materials, Faculty of Environmental Science and Technology, Okayama University, 2-1-1 Tsushima-Naka, Okayama 700-8530, Japan (Received 16 June 1999; accepted 7 August 1999)
Tobermorite was synthesized successfully from waste incineration fly ash by hydrothermal treatment in the presence of sodium hydroxide solution. The tobermorite synthesis was examined as a function of reaction temperature, time, and NaOH concentration. The formation of tobermorite was identified in all of the fly ash treated with NaOH at 180 °C, followed by the minor generations of sodalite and cancrinite phases with increasing NaOH concentration and extending reaction time. The NaOH-treated fly ash revealed the uptake behaviors for Cs+ and NH4+, whereas the fly ash untreated with NaOH solution did not show that. The uptake amounts of resulting products were also determined: 0.40 mmol/g for Cs+ and 0.35 mmol/g for NH4+ in the fly ash treated with 2.0 M NaOH at 180 °C for 20 h. I. INTRODUCTION
The waste generated from our daily lives is continuously increasing year after year, about 75% of which is treated at municipal incinerators and then landfilled. It was reported in Japan that the waste incineration ash of over 6 million tons was produced in 1995, and is becoming a severe social problem.1 Although incineration reduces the volume of the waste by about 90%, it leaves considerable amounts of solid residues, consisting of fly ash and main ash. Fly ash is particularly problematic because it contains significant concentrations of heavy metals such as As, Pb, Sb, and Cd, regarded as hazardous in most countries.2 Therefore, fly ash was treated as a special disposal in Japan. It was subject to such pretreatments as melt and cement solidifications to stabilize those incorporated heavy metals prior to disposal. At present, however, securing new sites for landfill disposal is becoming difficult. Moreover, the heavy metals will leak from incineration ash when exposed for a long time to acid environment such as acid rain. Therefore, developing recycling technologies (i.e., converting the incineration fly ash into a resource) has become urgent. As far as resource recovery of fly ash is concerned, attempts to recycle fly ash as a raw material for cement synthesis have been limited due to its high chloride content, which has a detrimental influence on cement quality and results in degradation failures such as reinforcement corrosion and crack extension. The proposed solution was water-washing pretreatment.3 Also, slag formed by
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e-mail: [email protected] J. Mater. Res., Vol. 14, No. 11, Nov 1999
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melting incineration ash could be employed as concrete aggregate, nevertheless, the technology faces problems such as cost and quality.4 In addition, b
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