Geopolymers are promising candidates for immobilizing radioactive borate waste (BW), but their performance needs improvement as borate negatively affects their physicochemical properties such as compressive strength and setting time. This study investigated the effect of Ca(OH)₂ on geopolymer waste forms by varying the Ca/Al ratio (0.25–1.0). At a Ca/Al ratio of 0.25, Ca(OH)₂ tripled the compressive strength (5 to 14 MPa) by promoting geopolymerization reaction and forming C-(A)-S-H gel. The increased pH and the reactive Ca ions led to the decomposition of immobilized BW. A low Ca/Al ratio caused minimal structural changes, while higher ratios promoted C-(A)-S-H gel formation. Characterization results confirmed the formation of extensive geopolymers and a compact microstructure. Notably, in the geopolymer waste form with a Ca/Al ratio of 0.25, the cumulative fraction leached of B decreased by more than twofold and the leachability index increased from 7.5 to 8.7, compared to the Ca-free geopolymer waste form. This research provides insights into the role of calcium in immobilizing radioactive BW in geopolymers, emphasizing the importance of optimizing the Ca/Al ratio to enhance immobilization performance.

中文翻译：

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Ca（OH）2 对偏高岭土基地聚合物废物形式中模拟放射性硼酸盐废物固定化的影响

地质聚合物是固定放射性硼酸盐废物 （BW） 的有前途的候选材料，但由于硼酸盐会对其物理化学性质（如抗压强度和凝固时间）产生负面影响，因此其性能需要改进。本研究通过改变 Ca/Al 比率 （0.25–1.0） 来调查 Ca（OH）₂ 对地质聚合物废物形式的影响。在 Ca/Al 比率为 0.25 时，Ca（OH）₂ 通过促进地聚合反应并形成 C-（A）-S-H 凝胶，使抗压强度增加了两倍（5 至 14 MPa）。pH 值升高和反应性 Ca 离子导致固定化 BW 分解。低 Ca/Al 比率引起的结构变化最小，而较高的比率促进 C-（A）-S-H 凝胶形成。表征结果证实了广泛的地聚合物和致密微观结构的形成。值得注意的是，与 Ca/Al 比为 0.25 的地质聚合物废料形式相比，B 的累积浸出分数降低了两倍以上，浸出性指数从 7.5 增加到 8.7。这项研究为钙在固定地质聚合物中的放射性 BW 中的作用提供了见解，强调了优化 Ca/Al 比率以提高固定性能的重要性。