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摘要: 以铂片为阴极，氟掺杂二氧化锡（FTO）玻璃为阳极，提出了一种新型酸液辅助电化学氧化法（AEO）脱除单质汞（Hg0）技术，探讨了酸类型、硝酸浓度、外加直流电压、电解质类型、SO2、NO和O2对脱汞效率的影响。研究结果表明，随着直流电压和硝酸液浓度的升高，脱汞效率逐渐上升；硝酸浓度增加至0.15 mol/L后，脱汞效率保持不变；SO2和NO抑制了AEO体系中Hg0的去除，但这种抑制是可逆的。与单独实验条件的脱汞效率相比，在0.1 mol/L硝酸、4 V直流电压的实验条件下，电化学氧化脱汞的效率可达96%，硝酸与直流电压的协同作用起关键作用。基于实验结果，分析了AEO系统中脱除Hg0的机理：在阳极，Hg0被阳极表面氧化反应产生的羟基自由基（•OH）氧化去除；在阴极，溶解性氧或吸附在Pt表面的O2经还原反应生成阴离子超氧自由基（•
${\rm{O}}_2^- $ ）。在酸性条件下，电子会促进•${\rm{O}}_2^- $ 生成•OH。自由基捕获实验表明，•${\rm{O}}_2^- $ 和•OH是酸液辅助电化学法去除Hg0的主要活性物质。研究有助于开发有效的工业除汞电化学技术和工业废酸的循环再利用。Abstract: As a global pollutant, mercury emission is increasingly restricted in recent years. It is urgent to explore a new and efficient mercury removal technology for coal-fired power plants. A new acid-assisted electrochemical oxidation (AEO) technique for mercury removal was proposed using platinum plate as cathode and fluorine-doped tin dioxide (FTO) glass as anode. The effects of acid type, acid concentration, applied direct current (DC) voltage, electrolyte type, SO2, NO and O2 on the Hg0 removal efficiency were carried out. The results indicated that the mercury removal efficiency increased with the increase of DC voltage and nitric acid concentration. When the concentration of nitric acid increased to 0.15 mol/L, the mercury removal efficiency remained unchanged. SO2 and NO inhibited the removal of Hg0 in AEO system, but the inhibition was reversible. Compared with the mercury removal efficiency under single experimental conditions, the mercury removal efficiency of electrochemical oxidation can reach 96% under the experimental conditions of 0.1 mol/L nitric acid and 4V DC voltage, suggesting that the synergistic effect of nitric acid and DC voltage plays a key role. According to the experimental results, the mechanism of Hg0 removal in AEO system was analyzed. At the anode, Hg0 was oxidized by hydroxyl radical (•OH) generated by the oxidation reaction on the anode surface. At the cathode, dissolved oxygen or O2 adsorbed on the surface of Pt is reduced to form anionic superoxide radicals (•${\rm{O}}_2^- $ ). Moreover, parts of •${\rm{O}}_2^- $ would produce •OH with the aid of electron at acidic condition. Free radicals capture experiments showed that •O$_2^- $ and •OH were the main active substances for the removal of Hg0 by acid-assisted electrochemical method. The research is helpful for the development of effective electrochemical techniques for industrial mercury removal and recycling of industrial acid waste.-
Key words:
- elemental mercury /
- wet removal /
- waste acid /
- electrochemical oxidation.
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Figure 2 Hg0 removal efficiencies under different experimental conditions (a), the corresponding linear fitted pseudo-first order plots (b), and the synergistic effect of nitric acid and DC voltage on Hg0 removal (c)
Figure 3 Hg0 removal efficiencies ((a), (c)) and linear fitted pseudo-first order plots ((b), (d)) under various types of acid and different nitric acid concentrations
Figure 4 Hg0 removal efficiencies under different DC voltages (a) and different electrolytes (b)
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