Chen Q Y, Tyrer M, Hills C D, Yang X M, Carey P
School of Environmental Science and Engineering, Donghua University, Shanghai 200051, PR China.
Waste Manag. 2009 Jan;29(1):390-403. doi: 10.1016/j.wasman.2008.01.019. Epub 2008 Mar 25.
Heavy metal-bearing waste usually needs solidification/stabilization (s/s) prior to landfill to lower the leaching rate. Cement is the most adaptable binder currently available for the immobilisation of heavy metals. The selection of cements and operating parameters depends upon an understanding of chemistry of the system. This paper discusses interactions of heavy metals and cement phases in the solidification/stabilisation process. It provides a clarification of heavy metal effects on cement hydration. According to the decomposition rate of minerals, heavy metals accelerate the hydration of tricalcium silicate (C3S) and Portland cement, although they retard the precipitation of portlandite due to the reduction of pH resulted from hydrolyses of heavy metal ions. The chemical mechanism relevant to the accelerating effect of heavy metals is considered to be H+ attacks on cement phases and the precipitation of calcium heavy metal double hydroxides, which consumes calcium ions and then promotes the decomposition of C3S. In this work, molecular models of calcium silicate hydrate gel are presented based on the examination of 29Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). This paper also reviews immobilisation mechanisms of heavy metals in hydrated cement matrices, focusing on the sorption, precipitation and chemical incorporation of cement hydration products. It is concluded that further research on the phase development during cement hydration in the presence of heavy metals and thermodynamic modelling is needed to improve effectiveness of cement-based s/s and extend this waste management technique.
含重金属废物在填埋之前通常需要进行固化/稳定化处理（s/s），以降低浸出率。水泥是目前最适合用于固定重金属的粘结剂。水泥和操作参数的选择取决于对系统化学性质的了解。本文讨论了固化/稳定化过程中重金属与水泥相之间的相互作用。它阐明了重金属对水泥水化的影响。根据矿物的分解速率，重金属会加速硅酸三钙（C3S）和波特兰水泥的水化，尽管由于重金属离子水解导致pH值降低，它们会阻碍氢氧化钙的沉淀。与重金属加速作用相关的化学机理被认为是H+对水泥相的攻击以及钙重金属双氢氧化物的沉淀，这会消耗钙离子，进而促进C3S的分解。在这项工作中，基于对29Si固态魔角旋转/核磁共振（MAS/NMR）的研究，提出了硅酸钙水合物凝胶的分子模型。本文还综述了重金属在水合水泥基体中的固定机理，重点关注水泥水化产物的吸附、沉淀和化学结合。得出的结论是，需要进一步研究重金属存在下水泥水化过程中的相发展以及热力学模型，以提高基于水泥的s/s的有效性并扩展这种废物管理技术。
