铁电絮凝中固相Fe(II)活化氧气产羟自由基的规律与机制

Electrocoagulation has drawn intensive attention because of the features such as simplicity, green and low cost. Although electrocoagulation is thought as a separation technology, the transformation and degradation phenomena of pollutants are still exist. At present, the understanding of oxidation mechanism of pollutants in Fe(0) electrocoagulation is limited to the direct oxidation on the iron anode, active chlorine oxidation, and oxidation induced by ferryl ion from Fe(II)/O2 reaction, while the oxidation induced by hydroxyl radical from solid-phase Fe(II)activated oxygen is still a blind spot. In this project, we first verify the existence of oxidation induced by hydroxyl radical in Fe(0) electrocoagulation using quenching tests and the detection of electron spin resonance spectroscopy. Next, we explore the effect of operating conditions and water chemical parameters using benzoic acid as a hydroxyl radical trapping agent. Subsequently, the solid-phase Fe(II) of activated oxygen was analyzed by means of chemical extraction and solid phase characterization, and the pathway of oxygen activation to produce hydroxyl radicals was studied. Finally, this oxidation mechanism is further verified and perfected in actual wastewater treatment. The research results of this project will supplement the transformation and degradation mechanism of pollutants in Fe(0) electrocoagulation, broaden the working mechanism of Fe(0) electrocoagulation technology, and provide a new theoretical basis for the application of decentralized water treatment systems.

电絮凝因其简便易行、绿色环保和成本较低等特点而备受关注。虽然电絮凝被认为是一种污染物分离技术，但其中依然存在污染物的转化和降解现象。目前对铁电絮凝中污染物氧化机制的认识有阳极直接氧化和析氯氧化，以及Fe(II)与O2反应产生Fe(IV)导致的氧化，而通过固相Fe(II)活化O2产生羟自由基导致的氧化仍是一个研究盲点。针对这一问题，本项目将通过淬灭自由基的对照实验和电子自旋共振光谱检测等手段证实羟自由基氧化机制的存在，并以苯甲酸为羟自由基捕获剂研究运行条件和水化学参数等对其影响，继而通过化学提取和固相表征手段对活化氧的固相Fe(II)进行分析，并对氧活化产生羟自由基的途径进行研究，最后在实际废水处理中进一步验证和完善此氧化机制。本项目的研究成果将补充污染物在铁电絮凝中的转化降解机理，拓宽铁电絮凝技术的工作机制，为应用于分散式水处理系统提供新的理论基础。

当今世界环境面临着多重挑战，有机污染物、重金属污染物往往同时出现，作为绿色吸附沉淀技术之一的电絮凝技术一直收到环境领域的关注。以铁材料为阳极的电絮凝过程中也存在高级氧化现象，而其作用机制尚不明晰。本项目首先以苯胺作为探针化合物，对其中的氧化机制进行了探究，发现了其主导作用的氧化物质为羟自由基，而羟自由基的主要来源是铁电解产生的二价铁离子，以及吸附在铁沉淀上的二价铁被氧气氧化所产生。这一过程在pH 8.5的碳酸氢钠电解质中尤其显著。另外，研究发现有机配体如草酸和EDTA对铁电絮凝产羟自由基具有较大的促进作用，且最佳的EDTA投加量为0.05 mM。项目继而研究了EDTA络合的重金属污染物如Fe(III)-EDTA和Cu(II)-EDTA在铁电絮凝体系中的去除机制。发现Cu(II)-EDTA能在大电流形成的缺氧铁电絮凝体系中被快速转化为Fe(III)-EDTA，继而在有氧体系中被羟自由基氧化降解。该项目的研究成果为拓展铁电絮凝体系的应用范围从吸附沉淀向氧化还原发展提供了基础证据。