Migration and transformation of mercury in WFGD slurry from a coal-fired power unit and the effect of additive on mercury stability in gypsum
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摘要: 以某300 MW超低排放燃煤机组现场脱硫浆液为研究对象,考察了浆液中汞迁移转化及添加剂对其影响行为,探讨了固相石膏中汞的热释放特性和环境风险。结果表明温度升高仅导致气相Hg0增加,而浆液pH升高会导致气相和固相中汞含量均有增加,Cl−或
$ {\rm{SO}}^{2-}_{4} $ 浓度升高既可以抑制浆液中汞还原为Hg0也可以促进固相石膏中汞含量增加,而$ {\rm{SO}}^{2-}_{3} $ 浓度升高虽然有利于汞富集于固相但会引起Hg2+部分转化为Hg0。Na2S、EDTA-2Na或DTCR-4添加剂与Hg2+反应分别生成HgS、Hg(EDTA)2或[ −Hg-DTCR] −n,使浆液中75%以上汞转移至固相石膏中,并抑制了Hg2+还原为Hg0,其中DTCR-4对汞的固化效果最好,但热稳定性依次为Gypsum + EDTA-2Na < Gypsum + DTCR-4 < Gypsum + Na2S < Gypsum,主要原因是所生成Hg(EDTA)2、[ −Hg-DTCR] −n和HgS(black)的稳定性差异所致。进而采用TCLP、SPLP和MEP三种方法获得了样品中汞的化学稳定性为Gypsum < Gypsum + Na2S < Gypsum + EDTA-2Na < Gypsum + DTCR-4,其原因是石膏中水溶态汞、酸溶态汞和可氧化态汞含量的差异所致。Abstract: Slurry sample was collected from a 300 MW ultra-low emissions coal-fired power unit. The migration and transformation behaviors of mercury in the sample were investigated, and the effect of additive on the stability of mercury in solid gypsum was explored by considering the thermal release behavior and environmental risk. The results show that gaseous Hg0 is increased with the increase of slurry temperature, while Hg is increased in both gas phase and gypsum with the increase of slurry pH. The concentration of Cl− or$ {\rm{SO}}^{2-}_{4} $ increases in slurry could inhibit the reduction of Hg2+ to Hg0 and increase Hg proportion in gypsum. However, the increase of$ {\rm{SO}}^{2-}_{3} $ concentration is beneficial to the Hg enriched in gypsum and a part of Hg2+ reduced to Hg0. When Na2S, EDTA-2Na or DTCR-4 is added, Hg2+ is turned into HgS, Hg(EDTA)2 or [ −Hg-DTCR] −n, respectively among which more than 75% Hg is transferred to gypsum and Hg2+ is inhibited to reduce into Hg0. The thermal stability of Hg in gypsum can be ordered as Gypsum + EDTA-2Na < Gypsum + DTCR-4 < Gypsum + Na2S < Gypsum due to the stability difference among Hg(EDTA)2, [ −Hg-DTCR] −n and HgS(black). By using TCLP, SPLP and MEP, the chemical stability of Hg in gypsum can be ordered as Gypsum < Gypsum + Na2S < Gypsum + EDTA-2Na < Gypsum + DTCR-4 due to the concentration difference of water soluble mercury, acid soluble mercury and oxidizable mercury among gypsums.-
Key words:
- coal-fired power unit /
- WFGD slurry /
- mercury /
- migration and transformation /
- additive /
- gypsum /
- stability
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表 1 入炉煤的工业分析以及氯和汞含量
Table 1 Proximate analysis, chlorine and mercury content of feed coal
Proximate analysis w/% S content/% Cl content/ (mg·kg−1) Hg content/ (mg·kg−1) M A V FC 2.57 14.84 30.09 52.50 0.37 0.078 0.0621 not: air drying base 表 2 本研究测量的脱硫浆液基本物性参数
Table 2 Main properties of WFGD slurry measured in this study
Sample Hg/ (μg·L−1) Temperature/ ℃ pH Cl−/ (mg·L−1) $ {\rm{SO}}^{2-}_{3} $/ (mg·L−1) $ {\rm{SO}}^{2-}_{4} $/ (mg·L−1) Slurry 157 50 5.82 4414 296 1413 表 4 含汞化合物的释放温度特征
Table 4 Release temperatures of Hg-containing compounds
Hg-containing compounds Temperature range of Hg release/℃ Peak temperature of Hg release/℃ Hg2Cl2 110−220 119 ± 10 HgCl2 95−350 138 ± 4 HgS(black) 150−280 220 ± 11 HgS(red) 210−340 305 ± 12 HgO(yellow) 250−450 284 ± 7 HgO(red) 360−500 420 ± 10 HgSO4 495−600 560 ± 10 表 5 Hg2+与有机添加剂反应产物中汞的释放温度
Table 5 Release temperatures of mercury in the reaction products of Hg2+ and organic additives
Reaction product Temperature range of Hg release/℃ Peak temperature of Hg release/℃ Hg(EDTA)2 100−210 164 ± 4 [ −Hg-DTCR] −n 105−230 186 ± 4 -
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