De Windt Laurent, Badreddine Rabia
Ecole des Mines de Paris (ENSMP), CG-Hydrodynamics and Reaction Groups, 35 R. St-Honoré, 77300 Fontainebleau, France.
Waste Manag. 2007;27(11):1638-47. doi: 10.1016/j.wasman.2006.07.019. Epub 2006 Sep 26.
The paper aims at simulating the closed-system dynamic leaching of a cement-based monolith containing lead with the numerical reactive transport code HYTEC in a 3D-cylindrical geometry. The model considers, simultaneously, the chemical evolution of pore water, the progression of mineralogical alteration fronts, and the concomitant release of elements from the S/S waste. In good agreement with the experiment, element releases were found to be mainly controlled by either diffusion (Na, K, and, to a lesser extent, Cl), by surface dissolution (Ca, Si) or by a mixed evolution (Pb, SO4). All of the calculated mineralogical transformations take place in a thin layer beyond the monolith surface. Consequently, modelling of Ca, Si and SO4 releases was quite sensitive to the node size of the simulation grid and was improved by taking into account the increase of porosity and effective diffusion coefficient due to mineral dissolution in the leached layer. In agreement with experimental results, the deepest front corresponds under closed-system conditions to portlandite dissolution and calcium silicate hydrates CSH 1.8 transformation into CSH of lower Ca/Si ratio. A second, distinct and intermediate, front is made by ettringite dissolution. The network of CSH is globally preserved in the leached layer, complete dissolution occurring over a very small thickness only. Finally, hydrotalcite precipitation in the leached layer is expected by modelling due to pH drop.
本文旨在使用数值反应输运代码HYTEC，在三维圆柱几何结构中模拟含铅水泥基整体材料的封闭系统动态浸出过程。该模型同时考虑了孔隙水的化学演化、矿物学蚀变前沿的进展以及稳定化/固化废物中元素的伴随释放。与实验结果高度一致，发现元素释放主要受扩散（钠、钾以及程度较轻的氯）、表面溶解（钙、硅）或混合演化（铅、硫酸根）控制。所有计算出的矿物学转变都发生在整体材料表面之外的薄层中。因此，钙、硅和硫酸根释放的模拟对模拟网格的节点尺寸相当敏感，通过考虑由于浸出层中矿物溶解导致的孔隙率和有效扩散系数的增加，模拟得到了改进。与实验结果一致，在封闭系统条件下，最深的前沿对应于氢氧化钙的溶解以及硅酸钙水合物CSH 1.8向钙硅比更低的CSH的转变。第二个明显的中间前沿是由钙矾石溶解形成的。CSH网络在浸出层中总体上得以保留，完全溶解仅发生在非常小的厚度范围内。最后，通过模拟预计由于pH值下降，浸出层中会有水滑石沉淀。
