ICP-OES分析低钙粉煤灰在NaOH溶液中离子浸出规律

Ions-Leaching Rates Rules of Low-Calcium Fly Ash in NaOH Solutions Based on ICP-OES

低钙粉煤灰潜在的火山灰活性释放缓慢限制了其大规模利用,通过碱激发提高粉煤灰中Si^(4+),Al^(3+)和Ca^(2+)等离子浸出率对于加快低钙粉煤灰活性释放具有积极作用。采用电感耦合等离子体发射光谱、傅里叶变换红外光谱、X射线衍射和扫描电子显微镜分别测试和分析了5种浓度NaOH溶液对低钙粉煤灰激发过程中Si^(4+),Al^(3+)和Ca^(2+)的浸出规律、化学基团变化、水化产物生成及微观形貌演化。结果表明:碱激发作用显著提高了低钙粉煤灰中Si^(4+),Al^(3+)和Ca^(2+)浸出率,三种离子浸出率大小为:Si^(4+)>Al^(3+)>Ca^(2+),其中Si^(4+)和Al^(3+)浸出率随NaOH浓度增加而增加,随浸出时间延长呈对数规律升高;Ca^(2+)由于在NaOH溶液中生成Ca(OH)_2沉淀,其浸出率大小表现为在水中高,在NaOH溶液中低。红外光谱清晰地表征出低钙粉煤灰受碱激发作用后化学基团在指纹区(波数1 300cm^(-1)以下)的变化,且随碱激发时间的延长和碱浓度的增加变化愈加明显。水化产物和微观形貌的结果显示出粉煤灰颗粒表面受到碱侵蚀发生解聚,在OH^-催化下,硅铝单体分子重新排列形成硅酸盐和铝酸盐低聚络合物,通过亲核取代反应形成铝硅酸盐的低聚态溶胶,并进一步与碱金属阳离子通过配位键或静电键的作用缩聚形成水化凝胶类产物。采用ICP-OES测试粉煤灰中离子浸出率可作为评价粉煤灰火山灰活性的一种快速和准确的方法。

The slow release of potential pozzolanic activity of low-calcium fly ash slows down its large-scale utilization,and enhance leaching rate of Si^4+,Al^3+and Ca^2+of fly ash through alkaliactivation,which will play positive effects for accelerating the active releaseof 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 Si^4+,Al^3+and Ca^2+,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 cansignificantly increase the leaching rate of Si^4+,Al^3+and Ca^2+ions from low-calcium fly ash,and the order of three ions leaching rates isSi^4+>Al^3+>Ca^2+.The leaching rate of Si^4+and Al 3+increased with NaOH concentration,and increased logarithmically with leaching time.Ca^2+generate Ca(OH)2 precipitated in NaOH solution,which explained why the leaching rate of Ca^2+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 Al^3+and Si^4+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 polycondensedvia 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.