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Barrier effect of coal bottom ash-based geopolymers on soil contaminated by heavy metals

机译：煤底灰聚合物对重金属污染土壤土壤的阻隔效应

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Coal bottom ash (CBA) was modified on the basis of the engineering problems of low resource utilization of CBA and difficulty in treating HMS through alkali activation to synthesize geopolymers and solidify heavy metal-contaminated soil (HMS). The optimal values of geopolymers were selected through response surface methodology. Their mineral compositions, microstructure, and binding energy were determined through X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy tests, respectively. The stress-strain curve, the leaching concentration and fraction of heavy metals, and the solidifying mechanism for remolded soil were determined through unconfined compressive strength, leaching toxicity, sequential chemical extraction, and infrared (IR) spectroscopy tests, respectively. Based on these experiments, the following conclusions were presented. The optimum ratios of CBA-based geopolymers were n(Si) : n(Al) = 2.666, n(Na) : n(Al) = 0.687, and n(water) : n(binder) = 2.422. The X-ray curves of the geopolymers were obvious hump-like protuberances at diffraction angles of 20-35 degrees and had a dense amorphous structure on the surface. The maximum binding energies of Si 2p and Al 2p decreased to 101.03 and 72.89 eV, respectively. A 3D network polymerized because of strong geopolymerization. The maximum axial stress of the remolded soil was 104.91% higher than that of the undisturbed soil, and the leaching concentration decreased by more than 45.88%. The leaching toxicity met the requirements of standard GB 5085.3-2007. The proportion of the acid-extractable fraction of heavy metals in the remolded soil decreased, whereas the proportion of residual fraction increased. The stretching vibration of Si-O-Si (Al) and the bending vibration of Si-O-Si appeared in the IR spectrum. The soil particles were completely encapsulated by a hardened geopolymer structure, thereby forming a multilayer space-skeleton barrier structure that could greatly improve the mechanical properties.
机译：煤底灰（CBA）根据CBA的低资源利用率的工程问题进行修饰，难以通过碱活化治疗HMS以合成地质聚合物并固化重金属污染的土壤（HMS）。通过响应面方法选择地质聚合物的最佳值。通过X射线衍射，X射线光电子能谱和扫描电子显微镜测试测定它们的矿物组合物，微观结构和结合能。通过非整齐的抗压强度，浸出毒性，连续化学提取和红外（IR）光谱检测，测定应力 - 应变曲线，重质金属的浸出浓度和分数，以及重形土壤的凝固机制。基于这些实验，提出了以下结论。基于CBA的地质聚合物的最佳比率为N（Si）：N（Al）= 2.666，N（Na）：N（Al）= 0.687，N（水）：N（粘合剂）= 2.422。地质聚合物的X射线曲线在20-35度的衍射角下是明显的驼峰状突起，并且在表面上具有致密的无定形结构。 Si 2P和Al 2P的最大结合能量分别降至101.03和72.89eV。由于强烈的地质聚合物化而聚合3D网络。再折叠土壤的最大轴向应力高于未受干扰的土壤的104.91％，浸出浓度降低超过45.88％。浸出毒性符合标准GB 5085.3-2007的要求。重形土壤中重金属的酸可萃取部分的比例降低，而残留率的比例增加。 IR光谱中Si-O-Si（Al）的拉伸振动及Si-O-Si的弯曲振动。土壤颗粒完全通过硬化的地质聚合物结构包封，从而形成多层空间 - 骨架阻挡结构，其可以大大改善机械性能。

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    《RSC Advances》 |2019年第49期|共9页
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