燃煤烟气脱硫石膏农用的环境安全风险

中国从20世纪90年代后期开始利用燃煤烟气脱硫石膏改良碱化土壤。燃煤烟气脱硫石膏是来自于电厂的脱硫废渣,是对含硫燃料(主要是煤)燃烧后产生的烟气进行脱硫净化处理而得到的工业副产物。随着中国燃煤电厂除尘、脱硫和脱硝等烟气污染控制系统的安装,在解决燃煤燃烧过程中SO2等废气减排的同时,也会产生越来越多的脱硫石膏等脱硫副产物。燃煤烟气脱硫石膏资源化利用为燃煤电厂解决越来越多的脱硫残渣处置问题而受到关注。由于燃煤烟气脱硫石膏性质和天然石膏相似,因此有研究利用燃煤烟气脱硫石膏代替天然石膏进行盐碱地改良。然而,当企业采用燃煤烟气净化技术和协同脱汞工艺,煤中有害污染物在脱硫过程中富集到烟气脱硫副产物——脱硫石膏及飞灰中,导致燃煤烟气脱硫石膏中主要有汞(Hg)、氟(F)、氯(Cl)和硒(Se)等多种污染元素的富集;脱硫飞灰中主要有砷(As)、镉(Cd)、铬(Cr)、铜(Cu)、镍(Ni)、铅(Pb)和锌(Zn)等多种污染元素的富集。研究数据显示,我国部分烟气脱硫石膏中Hg、Cd、As、Se、F和Cl等含量存在不同程度超出国家土壤环境质量标准和地下水质量标准。为保障土壤健康、食品安全和环境安全,建议应严格控制脱硫剂来源、脱硫工艺、脱硫石膏使用量,并对农田土壤环境风险进行长期监测,防止土壤中污染元素累积;未经无害化处理、有害物质超标的、存在环境安全风险的不得直接施用于农田土壤,杜绝其进入食物链而危害人类健康。

Environment Risk for Application of Flue Gas Desulfurization Gypsum in Soils in China

Utilization of flue gas desulfurization (FGD) gypsum in China to improve alkaline soils started in the late 1990s. The FGD gypsum is a kind of desulfurized waste residue from power plant. It is an industrial by-product gypsum obtained by desulfurization and purification of flue gas produced by sulfur bearing fuel (mainly coal). With the increasing of installation of flue gas pollution control system, such as dust removal, desulfurization and denitrification in coal-fired power plants in China, more and more desulfurization by-product gypsum will be produced while reducing SO₂ emission and other harmful gases in the process of coal combustion. The utilization of FGD gypsum has attracted more attention for solving the problem with increased disposal of desulfurization residues in power plants. Because the nature of FGD gypsum is similar to that of natural gypsum, some researchers have tried to use it instead of natural gypsum in the improvement of saline alkali land. However, since some enterprises introduced flue gas purification technology and synergistic mercury removal process, several hazardous pollutants in coal would inevitably transfer into FGD by-products (FGD gypsum and fly-ash). The process of FGD and synergistic mercury removal causes the enrichment of several hazardous pollutants in FGD gypsum (mainly Hg, F, Cl, and Se), and in FGD fly-ash (mainly As, Cd, Cr, Cu, Ni, Pb, and Zn). Research results indicated that the enrichment of hazardous pollutants could result in high levels of hazardous pollutants (especially Hg, Se, F and Cl) in some FGD gypsum in China, inordinately beyond the limits of Environmental Quality Standards for Soils and the limits of Environmental Quality Standards for Ground Water. In order to ensure soil health, food safety, and environmental quality, it was suggested that those FGD by-products without any harmless treatment of pollutants should not be allowed to use as for soil remediation or conditioning directly into the farmlands by solid waste disposal methods; especially material source and technology of desulfurization, application rate in farmland and long-term environmental safety risk should be concerted, to prevent hazardous pollutants from entering food chain and harming to human health.