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19. Structural Evolution of Geopolymers Incorporated with Heavy Metals: Solidification Mechanism of Pb2+and Cd2+

Author

Wei, Xuankun, Sun, Yongqi, Su, Yiping, Shen, Xuehua, Tang, Yuanyuan, Yan, Feng, and Zhang, Zuotai

Abstract

Geopolymers have emerged as a promising solution for solidifying heavy metals; however, the underlying mechanisms remain elusive. In this study, we synthesized geopolymers incorporating Pb2+and Cd2+to unravel their solidification mechanisms. Leaching analyses demonstrated superior solidification efficacy for Pb2+(93.6%) compared to that for Cd2+(65.2%). The dissimilarity in solidification mechanisms can be attributed to variances in ionic potential and covalent interactions between the cations. Furthermore, Cd2+exhibited a higher ionic potential, facilitating its exchange with Na+in the geopolymer matrix. Triple-quantum nuclear magnetic resonance experiments revealed a weak affinity of the geopolymer structure toward Cd2+. Density functional theory calculations affirmed stronger interactions between Pb2+(−8.71 eV) and the matrix compared to those of Cd2+(−5.83 eV). Consequently, Pb2+demonstrated an enhanced covalent propensity within the geopolymer matrix, while Cd2+primarily underwent solidification via ion exchange. This research provides novel insights and concepts regarding the mechanisms involved in solidifying heavy metals in geopolymers.

Published
2023
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