Department of Environmental Science and Engineering, Tsinghua University, Beijing, China.
Waste Manag. 2011 Feb;31(2):311-7. doi: 10.1016/j.wasman.2010.05.015. Epub 2010 Jul 6.
The present research explored the role played by water-wash on geopolymerization for the immobilization and solidification of municipal solid waste incineration (MSWI) fly ash. The water-wash pretreatment substantially promoted the early strength of geopolymer and resulted in a higher ultimate strength compared to the counterpart without water-wash. XRD pattern of water-washed fly ash (WFA) revealed that NaCl and KCl were nearly eliminated in the WFA. Aside from geopolymer, ettringite (Ca(6)Al(2)(SO(4))(3)(OH)(12)·26H(2)O) was formed in MSWI fly ash-based geopolymer (Geo-FA). Meanwhile, calcium aluminate hydrate (Ca(2)Al(OH)(7)·3H(2)O), not ettringite, appeared in geopolymer that was synthesized with water-washed fly ash (Geo-WFA). Leached Geo-WFA (Geo-WFA-L) did not exhibit any signs of deterioration, while there was visual cracking on the surface of leached Geo-FA (Geo-FA-L). The crack may be caused by the migration of K(+), Na(+), and Cl(-) ions outside Geo-FA and the negative effect from crystallization of expansive compounds can not be excluded. Furthermore, transformation of calcium aluminate hydrate in Geo-WFA to ettringite in Geo-WFA-L allowed the reduction of the pore size of the specimen. IR spectrums suggested that Geo-WFA can supply more stable chemical encapsulation for heavy metals. Static monolithic leaching tests were conducted for geopolymers to estimate the immobilization efficiency. Heavy metal leaching was elucidated using the first-order reaction/diffusion model. Combined with the results from compressive strength and microstructure of samples, the effects of water-wash on immobilization were inferred in this study.
本研究探讨了水洗对水热合成地聚合物固化稳定化城市生活垃圾焚烧飞灰的影响。水洗预处理可显著提高地聚合物的早期强度，使未水洗的地聚合物具有更高的最终强度。水洗飞灰（WFA）的 X 射线衍射（XRD）图谱表明，NaCl 和 KCl 在 WFA 中几乎被去除。除了地聚合物，水热合成的以 MSWI 飞灰为原料的地聚合物（Geo-FA）中还形成了钙矾石（Ca(6)Al(2)(SO(4))(3)(OH)(12)·26H(2)O）。而在用水洗飞灰合成的地聚合物（Geo-WFA）中，则出现了水化铝酸钙（Ca(2)Al(OH)(7)·3H(2)O），而不是钙矾石。浸出的 Geo-WFA（Geo-WFA-L）没有出现任何劣化迹象，而浸出的 Geo-FA（Geo-FA-L）表面出现了可见的裂缝。裂缝可能是由于 K(+)、Na(+)和 Cl(-)离子在 Geo-FA 外的迁移以及膨胀性化合物结晶的负面影响所致。此外，水化铝酸钙在 Geo-WFA 中的转化为钙矾石在 Geo-WFA-L 中的转化，使得试样的孔径减小。红外光谱表明，Geo-WFA 可以为重金属提供更稳定的化学封装。进行了静态整体浸出试验来评估地聚合物的固定化效率。采用一级反应/扩散模型来阐明重金属的浸出情况。结合抗压强度和样品微观结构的结果，推断了水洗对固定化的影响。
