RM-BFS基地聚物固化复合重金属污染土稳定性

Stability of Composite Heavy Metal Contaminated Soil Cured by RM-BFS Based Geopolymer Under Influence of Environment

摘要:

针对传统水泥基固化剂在修复重金属污染土时面临的能耗大和耐久性欠佳等问题，通过碱激发方式制备赤泥（RM）-高炉矿渣（BFS）基地聚物，用于固化/稳定化复合重金属污染土，进而研究其在地下水位升降和降雨中酸碱物质变化等环境影响下的长期稳定性。为此，开展干湿循环和酸碱度影响试验，查明RM-BFS基地聚物固化体在不同环境影响下强度及重金属浸出质量浓度演化规律；结合宏微观测试阐明RM-BFS地聚物修复复合重金属污染土的机制和稳定性退化机制。结果发现，随着干湿循环次数增加，固化体UCS大幅降低，重金属浸出质量浓度显著增加，但随RM+BFS掺量增加，干湿循环后固化土壤UCS降幅减小，重金属浸出质量浓度增幅减小，固化效果增强；对于低/中质量浓度复合重金属污染土，随pH增加，除Cu（II）浸出质量浓度持续下降外，Cd（II）、Pb（II）和Zn（II）浸出质量浓度均先降低后增加；但无论pH值大小，四种重金属浸出质量浓度基本上均低于限定值，固化效果能够保持长久稳定。RM-BFS基地聚合物聚合反应产生的水化凝胶通过物理包裹吸附及化学沉淀等机制固定重金属污染物；环境影响下其内部孔隙连通、重金属吸附点位和赋存形态改变导致稳定性能退化。研究成果为工业固废固化复合重金属污染土的工程应用提供了重要参考。

Abstract:

High energy consumption and poor durability faced by traditional cement-based curing agent when repairing heavy metal contaminated soil， this study prepared red mud （RM） -blast furnace slag （BFS） based geopolymers ??solidifying/stabilizing composite heavy metal contaminated soil by alkali activation. However， the stability of soil solidification will decrease under the long-term environmental influence of ground water level and acids and alkalis in rainfall. Wet-dry cycling and pH tests were conducted to evaluate the evolution of strength and leaching concentration. The mechanism of solidification and stability degradation were also elucidated. With increasing dry-wet cycles， the UCS decreased， while the leaching concentration of heavy metal rose significantly. In contrast， a higher content of RM+BFS mitigated the strength loss and suppressed the increase in heavy metal leaching. For low/medium level contaminated soils， the leaching concentrations initially decreased and then increased with the increase of pH， except for the continuous decrease of Cu（II）. However， regardless of pH， the leaching concentration is basically lower than the limit value， and the curing effect can remain stable for a long time. The hydrogels generated through the polymerization can immobilize heavy metal pollutants through physical absorption， chemical precipitation， and other mechanisms. Environmental influences lead to changes in internal pore connectivity， heavy metal adsorption sites， and occurrence forms， resulting in the degradation of stability. This study serves as a significant reference for utilization of industrial solid waste in solidifying composite heavy metal contaminated soil.