紫外活化过硫酸盐/甲酸体系还原水中Cr(Ⅵ)机理及影响因素

Mechanism and influencing factors of aqueous Cr(Ⅵ) reduction by carbon dioxide anion radical based on the UV-activated sodium persulfate/formic acid system

采用紫外活化过硫酸盐/甲酸体系所产生的还原性二氧化碳阴离子自由基(CO2·-),研究了水溶液中高浓度Cr(Ⅵ)的去除效果;使用电子自旋共振(ESR)技术,鉴定识别了体系中产生的活性自由基;分析了体系的活化机理及其对Cr(Ⅵ)的还原机制;考察了过硫酸盐投加量、初始pH、腐殖酸、无机阴离子(Cl-、HCO3-和NO3-)及初始Cr(Ⅵ)浓度等对Cr(Ⅵ)去除的影响。结果表明:紫外活化过硫酸盐/甲酸体系可以有效还原Cr(Ⅵ),当过硫酸钠与甲酸浓度分别为20 mmol·L-1和40 mmol·L-1,未调初始pH为2.4时,初始浓度为200 mg·L-1Cr(VI)在50 min内基本完全可被还原;此外,Cr(Ⅵ)还原去除率随过硫酸盐浓度升高而增强,在酸性条件下(pH=2.4),体系对Cr(Ⅵ)的还原效率最高,随着pH的增大,还原效率明显降低。进一步研究表明, Cl-、HCO3-和NO3-对Cr(Ⅵ)的还原都存在抑制作用,在相同浓度下,其抑制程度分别为HCO3->NO3->Cl-,腐殖酸也对Cr(Ⅵ)的去除存在抑制作用。紫外活化过硫酸盐/甲酸体系还原Cr(Ⅵ)过程符合零级反应动力学方程,其动力学常数为78.467μmol·(L·min)-1。本研究结果为Cr(Ⅵ)废水的处理提供了一种高效的还原新技术。

The removal of high concentration of Cr(Ⅵ)in aqueous solution was studied by using ultraviolet activated persulfate/formic acid system to produce carbon dioxide anion radicals(CO2·-).The active free radicals produced in the system were identified by Electron paramagnetic resonance(EPR),and the mechanisms of radical activation and Cr(Ⅵ)reduction in this system were also discussed.The effects of persulfate dosages,HCO3-,NO3-)and the initial concentration of Cr(Ⅵ)on Cr(Ⅵ)removal were systematically investigated.The results showed that an effective Cr(Ⅵ)reduction occurred in ultraviolet activated persulfate/formic acid system,and Cr(Ⅵ)with an initial concentration of 200 mg·L-1 could be almost completely reduced within 50 min at the sodium persulfate concentration of 20 mmol·L-1,formic acid concentration of 40 mmol·L-1,and the initial pH of 2.4(without the adjustment).In addition,the reduction efficiency of Cr(Ⅵ)increased with the increase of persulfate concentration.The highest reduction efficiency of Cr(Ⅵ)appeared at acidic conditions of pH=2.4.The reduction efficiency decreased significantly with the increase of pH.Further studies revealed that Cl-,HCO3-HCO3->NO3->Cl-,and humic acid was also an inhibition factor for the removal of Cr(Ⅵ)at the same concentration.Ultraviolet activated persulfate/formic acid system was well fitted with the zero-order kinetic equation with the kinetic constant of 78.467μmol·(L·min)-1,which provides an efficient new reduction technology for Cr(Ⅵ)wastewater treatment.