Metakaolin-based geopolymers have attracted significant interest in decontaminating radioactive debris from the Fukushima nuclear accident. This study explored the incorporation of boron (B) into geopolymers using boric acid as the source, with the goal of developing B-enriched geopolymers for enhanced radionuclide immobilisation and neutron capture potential. The addition of boric acid lowered the pH of the alkali activator, reducing metakaolin solubility and impeding alkali-activated geopolymerisation. B formed an unstable BO4(xB, 4-xSi) structure with extra short-range Si tetrahedra in low-temperature curing conditions, making it prone to be leached out. High-temperature curing facilitated alkali-activated geopolymerisation, mitigating some negative effects of boric acid. It also promoted partial incorporation of BO4 into the framework, reducing leaching. Additionally, in acid-activated geopolymers, boric acid absorbed substantial reaction heat during the initial dealumination phase by reacting with PO4, thereby enhancing the overall geopolymerisation degree and increasing the relative content of near-Si terminal P and Al6 units. B could be incorporated into the framework by bonding with numerous Al-unsaturated Si tetrahedra to form a stable BO4(0B, 4Si) structure. Although B introduction slightly reduced the positive charge of the acid-activated geopolymer's structure, decreasing its capacity to immobilise anionic SeO32− through electrostatic adsorption, the decrease was negligible. Conversely, B introduction increased structural compactness, which improved Cs+ immobilisation through physical entrapment. Overall, the B-containing acid-activated geopolymer effectively incorporated B into the main matrix while maintaining radionuclide immobilisation capacity. This study provides valuable insights into the selection and incorporation mechanisms of the B-containing geopolymer matrix, contributing to effective strategies for radioactive waste disposal.

中文翻译：

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将硼掺入偏高岭土基地质聚合物中，用于放射性核素固定和中子俘获潜力


基于间高岭土的地质聚合物在净化福岛核事故中的放射性碎片方面引起了极大的兴趣。本研究以硼酸为来源，探讨将硼 （B） 掺入地聚合物中，目的是开发富含 B 的地聚合物，以增强放射性核素固定和中子俘获潜力。硼酸的添加降低了碱活化剂的 pH 值，降低了偏高岭土的溶解度并阻碍了碱活化的地聚合。B 在低温固化条件下形成了不稳定的 BO4（xB， 4-xSi） 结构，具有超短程的 Si 四面体，使其容易浸出。高温固化促进了碱活化地聚合，减轻了硼酸的一些负面影响。它还促进了 BO4 部分纳入框架，减少了浸出。此外，在酸活化地聚合物中，硼酸通过与 PO4 反应，在初始脱离阶段吸收了大量反应热，从而提高了整体地聚合度并增加了近硅末端 P 和 Al6 单元的相对含量。B 可以通过与许多 Al-unsaturated Si 四面体键合而掺入框架中，形成稳定的 BO4（0B， 4Si） 结构。尽管 B 的引入略微降低了酸活化地聚合物结构的正电荷，降低了其通过静电吸附固定阴离子 SeO32− 的能力，但这种降低可以忽略不计。相反，B 的引入增加了结构的致密性，从而通过物理包埋改善了 Cs+ 固定。总体而言，含 B 的酸性活化地质聚合物有效地将 B 掺入主基质中，同时保持放射性核素固定能力。 本研究为含 B 的地质聚合物基质的选择和掺入机制提供了有价值的见解，有助于制定放射性废物处理的有效策略。