脱硫石膏中汞的赋存状态及资源化过程中的稳定性研究

Mercury in the flue gas desulfurization (FGD) gypsum from coal-fired power plants would release into the environment, which causes secondary pollution during its storage, processing and multipurpose utilization processes. To combat the negative impacts of mercury on the environment, we propose to systematically investigate mercury speciation and distribution in the FGD gypsum, transformation rules of mercury between the liquid and gaseous phases during the storage of desulfurization gypsum. The objectives of the project are five-fold, specifically, 1) we will continuously monitor the transition of different mercury species between exudative and gaseous phases, 2) we will examine the effects of parameters such as water content, pH, sulfite, chloride, iron, manganese, nickel and other metal ions on Hg2+ reduction to Hg0 in the FGD gypsum, and the reaction mechanisms of Hg2+ reduction to Hg0 and its subsequent release into the atmosphere, 3) we will experimentally explore how hydrated desulfurization gypsum promotes Hg2+ reduction to Hg0, 4) we will investigate the stability of mercury in the FGD gypsum during its processing and multipurpose utilization, with particular emphasis on mercury transformation during the FGD drying, heat treatment and acid rain-assisted corrosion processing, and 5) we will establish an optimal stabilization method of mercury in desulfurization gypsums to reduce secondary mercury pollution during its storage, processing and comprehensive utilization processes, which will provide the theoretical basis for the co-removal of highly-soluble oxidized mercury in the wet flue desulfurization and in the recycling of the FGD gypsum.

本项目针对燃煤电厂脱硫石膏在堆放、处理加工和综合利用等过程中，含有的汞可能再次释放到环境中从而造成二次污染的特点。研究典型脱硫石膏中汞的赋存状态特征；通过对渗滤液和挥发到气相中的不同形态汞的连续监测，研究脱硫石膏在堆放过程中汞在气相及液相中的迁移转化规律，探索脱硫石膏中含水率、pH、亚硫酸根、氯离子、铁、锰和镍等因素对Hg2+还原转化为Hg0的影响，并研究其还原再释放进入大气的反应机制；考察脱硫石膏在处理加工和综合利用过程中汞的稳定性，包括脱水干燥、热处理和酸雨侵蚀等过程中脱硫石膏中汞的转化、释放机制和影响因素；探索脱硫石膏中汞的稳定化方法，减少脱硫石膏在堆放、处理加工和综合利用过程中可能产生的汞二次污染，为湿法烟气脱硫同时脱汞以及脱硫石膏的资源化提供理论依据。

湿法烟气脱硫系统同步除汞是最经济的脱汞技术之一，被脱除的Hg2+在浆液中经历了复杂的迁移转化过程，并在气相、液相、固相中重新分布，而进入固相中的汞可能会增加脱硫石膏在资源化过程中的环境风险。本项目首先考察了浙江四个典型燃煤电厂脱硫石膏的基本理化性质和汞的赋存形态，包括水溶态、弱酸可提取态、可氧化态和残渣态。其次在实验室条件下探究了脱硫石膏中汞在酸雨侵蚀、热处理过程中的释放、还原规律。液固比、初始pH值均会影响浸出液中汞的含量，而酸雨类型对汞的释放影响不大。脱硫石膏中汞的释放随温度的升高而增加，在400℃时接近最大值，200℃处理后石膏中汞的浸出量反而有所增加。筛选出了性能优良的捕集剂，与脱硫石膏中的汞形成了稳定化合物，提高了脱硫石膏在堆放、处理加工和综合利用中汞的稳定性，为脱硫石膏的资源化利用提供理论依据。