改性膨润土防水毯阻隔赤泥渗滤液机理和服役性能研究

Bauxite residue leachates with hyperalkaline and high ionic strength cause serious deterioration in service performance of the geosynthetic clay liners (GCLs), which problem can be solved effectively by taking bentonite amendment actions. The containment performances of the GCL containing sodium-activated calcium bentonite amended with sodium hexametaphosphate and citric acid are subjected to experimental study and theoretical analysis in this proposal, and key issues below are expected to be addressed: (1) amendment mechanisms are revealed by systematically investigating interlamellar distance, functional group, and surface charge characteristics of the amended bentonite; and interaction mechanisms between the amended bentonite and the bauxite residue leachate are exposed by investigating variations in mineral composition of modified bentonite when attacked by the contaminated solution; (2) changes in hydraulic conductivity of the amended GCL subjected to bauxite residue leachate are investigated by conducting modified fluid loss tests and flexible-wall hydraulic conductivity tests. The control mechanisms of amendment on enhancing containment performance of the GCL and the effects of amendment on adjust pH value of the effluent are explored, and the modifier dosages are then optimized; and (3) the migration parameters of the aluminum and hydroxyl ions of the leachate passing through the amended GCL are evaluated by performing column tests and theoretical analyses, and the containment performances of the modified GCL are assessed quantitatively in aids of parameter studies. The obtained results are conducive to expanding the application of the GCL technology, and to yielding theoretical support for enhancing the level of bauxite residue disposal in China.

强碱性富多价阳离子赤泥渗滤液作用下传统膨润土防水毯(GCL)的安全服役性能将严重劣化，膨润土改性是解决该技术瓶颈的有效措施。本项目以六偏磷酸钠协同柠檬酸改性的钠化膨润土防水毯为研究对象，通过室内试验结合理论分析，拟解决如下关键问题：(1)系统研究改性膨润土晶面间距、主要官能团和表面带电特性，阐明改性机理，根据膨润土物相演化特征，揭示改性膨润土-赤泥渗滤液相互作用机制；(2)基于改进滤失试验和柔性壁渗透试验，明晰改性GCL渗透系数在赤泥渗滤液作用下的演变规律，揭示改性作用提升GCL防渗性能和调控渗出液碱性的控制机理，优化改性剂掺量；(3)通过土柱化学渗透试验和理论计算，对比分析改性前后GCL阻控渗滤液关键离子运移特性的差异，定量评价改性GCL的服役性能。研究成果有助于拓展GCL阻隔技术的应用范围，为提高我国赤泥安全处置水平提供重要的理论依据和技术支撑。

赤泥堆场渗滤液具有高碱性和富含铝离子的特征,渗入地下不仅会污染地下水,也会影响赤泥堆场下覆地基土土体工程特性。课题通过室内试验对赤泥渗滤液作用下，商用土工合成材料黏土衬垫材料（GCL）的工程特性、化学相容性和内部膨润土防渗性能和物理化学属性做了系统性研究。主要研究成果如下：（1）系统研究了羧甲基纤维素钠（CMC）、六偏磷酸钠（SHMP）、黄原胶（XG）改性膨润土的基本物理性质和膨润土泥浆的施工和易性。结果表明，CMC显著提升了膨润土膨胀性能，去离子水中膨胀指数SI达40 mL/2g，与商用GCL膨润土膨胀性能相当。（2）通过自由膨胀试验、改进API滤失试验和柔性壁试验，研究了预水化过程、水力梯度对GCL材料渗透系数的影响规律以及赤泥渗滤液对GCL材料化学相容性的影响特征。结果表明，预水化显著降低GCL渗透系数；GCL材料在赤泥渗滤液作用下化学相容性良好，kc/kw低于15，GCL材料在赤泥渗滤液作用下防渗性能卓越。（3）通过自由膨胀试验、改进滤失试验，研究了GCL膨润土、CMC聚合物改性膨润土、XG聚合物改性膨润土、SHMP聚合物改性膨润土在赤泥渗滤液作用下的化学相容性。各改性膨润土在赤泥渗滤液作用下膨胀性和防渗性均较素土有显著提升；其中CMC聚合物改性膨润土各项性能与GCL膨润土接近；SHMP聚合物改性膨润土以及XG聚合物改性膨润土在赤泥渗滤液环境中，防渗性能优于GCL膨润土。（4）通过X射线衍射分析、傅里叶变换红外光谱分析、扫描电镜分析，研究了赤泥渗滤液污染前后GCL膨润土的微观结构、表面官能团变化规律。试验表明，经过150天的赤泥渗滤液渗透，GCL膨润土片层结构破坏；膨润土中层间结合水无明显变化；赤泥渗滤液渗透后，膨润土颗粒孔隙尺寸增大，颗粒发生絮凝；离子强度大的赤泥渗滤液对于GCL材料的微观性能影响明显，与宏观试验结果一致。