title: Dynamic formation of zeolite synthesized from fly ash by alkaline hydrothermal conversion.
abstract: This study was designed to characterize the dynamic formation of zeolite synthesized from fly ash (ZFA) and to identify the zeolitization mechanisms during a 160-h-long hydrothermal alkaline conversion at 95°C by using fly ash (FA) samples collected from four typical thermoelectric power plants in China, with the purpose of improving ZFA quality. The process of synthesizing ZFA can be fundamentally divided into five stages: induction stage (0-0.5 h), accelerating dissolution stage (0.5-12 h), nucleation and/or crystallization stage (12-24 h), crystal growth stage (24-72 h) and crystal transformation stage (72-160 h). The crystal growth stage determined the quality of zeolite crystallization, coupled with functions of re-assembling the silicon-aluminium tetrahedral network and developing submicro- and/or nanometer microstructure. A 48-h-long hydrothermal conversion generated ZFAs that had a greater specific surface area (26.0-89.4 times) and cation exchange capacity (29.6-71.0 times) than FA, which successfully sequestrated 41-95% of ammonium and 75-98% of phosphate from swine manure. However, over-reaction resulted in more stable hydroxysodalite and/or sodalite, surface agglomeration and cracking, and energy wasting. This work suggests that the reuse of recycled synthesis materials should occur during the fourth step (24-72 h).
authors.affiliation: 1Institute of Environmental Science, College of Environmental and Resource Sciences, ZheJiang University, HangZhou, ZheJiang Province, China.
authors.forename: ZhiJian
authors.initials: Z
authors.lastname: Zhang
authors.forename: Jiangli
authors.initials: J
authors.lastname: Li
authors.forename: Hongyi
authors.initials: H
authors.lastname: Li
authors.forename: Hang
authors.initials: H
authors.lastname: Wang
authors.forename: Jun
authors.initials: J
authors.lastname: Zhu
authors.forename: Qiang
authors.initials: Q
authors.lastname: He
mesh_terms: D002681:China; D060729:Coal Ash / Q000737:chemistry*; D003246:Conservation of Energy Resources / Q000379:methods*; D003460:Crystallization; D007220:Industrial Waste / Q000032:analysis*; D011210:Power Plants; D059027:Recycling / Q000379:methods*; D013054:Spectrophotometry, Atomic; D013696:Temperature; D013997:Time Factors; D014961:X-Ray Diffraction; D017641:Zeolites / Q000737:chemistry*
chemical_list: D060729:Coal Ash; D007220:Industrial Waste; D017641:Zeolites
keywords: Fly ash; alkaline hydrothermal; mechanism; synthesis process; zeolitization