【作者】 刘玉坤；

【导师】 禚玉群；

【作者基本信息】 清华大学 ， 热能工程， 2011， 硕士

【摘要】 燃煤电站消耗的煤中的痕量元素会部分迁移至脱硫石膏中，脱硫石膏中常含有害的Hg、As、Se、Pb、Cr和Cd等痕量元素，随着越来越多的燃煤电站使用湿法脱硫系统，产生的脱硫石膏越来越多。脱硫石膏可用于建材生产和土壤改良，在脱硫石膏进行再利用的过程中，其中所含的痕量元素对环境的影响已成为人们关心的一项重要内容。本文对脱硫石膏中痕量元素的环境稳定性进行研究，有利于人们认识脱硫石膏中的痕量元素在环境中的释放规律和可能产生的影响。本文以毒性较强的Hg、Pb、Cr、Cd、As、Se六种痕量元素为研究对象，首先采用美国EPA Method1312(TCLP方法)对脱硫石膏中的痕量元素进行研究，确定液固比和浸取液pH值是影响痕量元素浸出的主要因素。为研究脱硫石膏中痕量元素在各种条件下的浸出特性，研究中对TCLP方法进行改进，在不同液固比和pH值条件下进行浸出实验。研究中通过浸出实验研究脱硫石膏中醋酸可提取态的痕量元素浸出特性，通过BCR方法进行逐级提取实验研究脱硫石膏中各种赋存形态的比例，探索氧化还原条件对痕量元素迁移的影响。TCLP实验结果表明，浸出液中痕量元素的浓度远低于该方法规定的阈值（固体废弃物填埋的最高允许值），说明在现行的环保标准下，脱硫石膏中痕量元素完全满足填埋的环保要求，脱硫石膏不属于危险废弃物。浸出特性研究表明，脱硫石膏中痕量元素的浸出率在所研究的范围内随pH值的减小而增大，随液固比的增大而增大；而浸出液中痕量元素的浓度随pH值减小而增大，随液固比的增大而减小。赋存形态的研究表明，脱硫石膏中所含的在环境中能够稳定存在的残渣态痕量元素含量很低，而醋酸可提取态、可还原提取态、可氧化提取态的含量占据绝大部分。已有的研究表明，飞灰中的痕量元素主要以残渣态存在，这说明脱硫石膏和飞灰中痕量元素的赋存形态有很大差别，脱硫石膏中痕量元素的迁移能力要高于飞灰。更多还原

【Abstract】 Trace elements will be partially transferred to gypsum in coal-fired power plants withwet FGD devices, and consequently hazardous trace elements including Hg, As, Se,Pb, Cr and Cd commonly exist in FGD gypsum. The production of FGD gypsum hasbeen significantly increased since more and more coal-fired power plants adopted wetFGD technologies. FGD gypsum could be re-used as raw material for architecturalindustry, or reagent for soil amelioration in agriculture. During these processes, thetrace elements in gypsum may be re-emitted to environment, which has incurred greatpublic concern. This study focuses on the environmental stability of trace elements inFGD gypsum. The research outcomes could be helpful for people to understand there-emission characteristics of trace elements and their possible environmentalimpacts.This research focuses on the6most toxic trace elements, i.e. Hg, Pb, Cr, Cd, As andSe. EPA Method1312(TCLP) was first adopted in this study to investigate thebehaviors of trace element in FGD gypsum. Liquid-Solid Ratio (LSR) and pH valuehave been identified as the key factors affecting the behaviors of trace elements.Experiments of different LSR and pH values were performed. Leaching tests wereconducted to obtain the characteristics of acetate extractable trace element, whilstBCR tests were conducted to identify the existing status of trace element in FGDgypsum and the influences of reducing/oxidizing conditions.The TCLP experimental results indicated that the trace element concentrations inleachates are much lower than the permitted values specified in regulations,suggesting that FGD gypsum is safe for landfill and should not be characterized asHazardous Waste. The findings from leaching tests also revealed that the extractionrate of trace element in FGD gypsum increased with decreasing pH value andincreasing LSR. The trace element concentration in leachate also increased with decreasing pH value, however, it decreased with increasing LSR.The research on the existing status of trace element in FGD gypsum revealed that theportion of stable solid-state trace element was rather low. Most of the trace elementsin FGD gypsum could be extracted by acetate, or under reducing/oxidizing conditions.Comparing with the available research on fly ash where most of the trace elementswere in stable solid-state, it could be concluded that there was significant differencebetween the patterns of trace element in FGD gypsum and fly ash. The trace elementsin FGD gypsum seemed to be more active than those in fly ash.更多还原