铅镉废渣机械化学稳定化过程及固相自由基反应机理

Lead smelting industry will produce a large amount of heavy metal-containing solid wastes, and its contamination is the most serious in non-ferrous metal metallurgy industry in China. More than 80% of lead, cadmium and other characteristics of heavy metal pollutants in the form of waste residues, dust is present in the solid waste. These wastes should be safely stored and disposed because several serious accidents of exceeding limits of children blood lead and cadmium containing rice happened in many parts of our country. Solidification and stabilization are the common methods to treat these wastes. The traditional solidification/stabilization method has the problem such as incompletely solidification and unstable structure. Therefore, we propose that utilization of mechano-chemical reaction will accelerate the stabilization process of lead slag with solid phase radicals. The reaction will facilitate the formation of non-bridge oxygen bond structure such as Si-O-Pb bond and Si-O-Cd bond, which will reduce the leaching toxicity of slag under acidic condition and achieve the stabilization of waste residue. However, the process and mechanism of this reaction is not clear yet. Solid microscopic characterization methods and quantitative analysis methods of reaction kinetics will be applied to investigate the intermediate products and reaction path. The contribution and promotion mechanism of solid radicals in heavy metal stabilization will be deeply illustrated. This research will provide new technology and theory basis for design and optimization of mechanochemical non-hazardous disposal of heavy metal waste residues.

我国有色金属行业中铅冶炼造成的重金属污染最为严重，引起了多起儿童血铅超标和镉大米等重金属污染事件。铅冶炼行业中铅镉等特征重金属污染物有80%以上以废渣、烟尘的形式存在于固体废物中，因此重金属废渣必须得到安全地储存和处置。固化稳定化技术是处理这一类危险废物的常用方法。针对传统的固化稳定化工艺存在固化不彻底、结构不稳定的问题，我们提出了将硅氧型固相自由基体系引入铅镉废渣的机械化学稳定化过程中。利用该反应生成含有非桥氧共价键结构的中间态（如Si-O-Pb键、Si-O-Cd键)，可降低其在酸性条件下的浸出毒性，有利于铅镉废渣的稳定化。目前这种稳定化的过程和反应机理尚不清晰，我们拟采用固体表征和自由基反应动力学定量分析手段，来进一步验证这种涉及硅氧型自由基反应的中间产物及路径，揭示固相自由基对重金属稳定化反应的贡献和驱动机制。本研究可为机械化学法处置重金属危险固体废物的工艺提供理论支撑和应用指导。

石英砂有较高的弹性模量（70-120 GPa），所以要想粉碎石英砂颗粒需要较大的机械能。而且这些能量一旦断裂Si-O键，就会释放出466 kJ/mol的解离能。当搅拌杆形状改进之后，球磨机对磨球提供的总动能以及磨球之间的撞击效果都有一定程度的提高，而且使用方形柱搅拌杆时，整个球磨反应器的应变能转化效率也有一定提高。搅拌杆形状的改进有助于提高机械化学降解反应效率。稳定化药剂均能降低浸出毒性，使得Pb的浸出浓度低于5mg/L以下。稳定率大于90%以上，使得产物无害化程度更高。机械化学稳定化机理及稳定化实验研究有点：1）整个试验过程处于干法试验条件，不添加额外的液体试验材料，整个试验过程环保，不会对土壤和地下水产生二次污染。2）具有对重金属重度污染土壤及含重金属的危险废渣的快速处置能力。