Ions-Leaching Rates Rules of Low-Calcium Fly Ash in NaOH Solutions Based on ICP-OES
YIN Bo1, 2, KANG Tian-he1*, KANG Jian-ting1, CHEN Yue-juan1, 2
1. Institute of Mining Technology, Taiyuan University of Technology, Taiyuan 030024, China
2. School of Mining and Technology, Inner Mongolia University of Technology, Huhhot 010051, China
Abstract：The slow release of potential pozzolanic activity of low-calcium fly ash slows down its large-scale utilization, and enhance leaching rate of Si4+, Al3+ and Ca2+ of fly ash through alkali activation, which will play positive effects for accelerating the active release of low-calcium fly ash. In this study, low-calcium fly ash was soaked and activated in five NaOH solutions of different concentrations for different time periods. The leaching rules of Si4+, Al3+ and Ca2+, changes in chemical groups, hydration product formation and evolution of microscopic morphology were tested and analyzed via Inductively coupled plasma atomic emission spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction and Scanning electron microscopy. The results showed that the alkali activation effect can significantly increase the leaching rate of Si4+, Al3+ and Ca2+ ions from low-calcium fly ash, and the order of three ions leaching rates is Si4+＞Al3+＞Ca2+. The leaching rate of Si4+ and Al3+ increased with NaOH concentration, and increased logarithmically with leaching time. Ca2+ generate Ca(OH)2 precipitated in NaOH solution, which explained why the leaching rate of Ca2+ was high in water and low in NaOH solution. Fourier transform infrared spectroscopy can clearly characterize the change of chemical groups in the fingerprint zone (below 1 300 cm-1 of wavenumbers) of fly ash by alkali activation, and the changes were more obvious as the increase of the alkaline concentration and time in the activating fly ash process. Results of hydration products and micromorphology showed that the surface of fly ash particles were depolymerized under alkaline attack, and unstable ionic monomers were formed. The active Al3+ and Si4+ ions react under catalysis by OH- to form silicate and aluminate species. They would form the aluminosilicate oligomers sol by nucleophilic substitution reaction. Thereafter, the aluminosilicate oligomers and the alkali metal cation were further polycondensed via the action of a coordination bond or an electrostatic bond to form aluminosilicate gel, which accumulated gradually. The results of the study demonstrates that using inductively coupled plasma atomic emission spectrometry to test the ions leaching rate can be used as a fast and accurate method to evaluate the pozzolanic activity of fly ash.
尹 博，康天合，康健婷，陈月娟. ICP-OES分析低钙粉煤灰在NaOH溶液中离子浸出规律[J]. 光谱学与光谱分析, 2018, 38(09): 2943-2950.
YIN Bo, KANG Tian-he, KANG Jian-ting, CHEN Yue-juan. Ions-Leaching Rates Rules of Low-Calcium Fly Ash in NaOH Solutions Based on ICP-OES. SPECTROSCOPY AND SPECTRAL ANALYSIS, 2018, 38(09): 2943-2950.
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