污水中铜、镉和磷同步去除的高铁酸钾纳米特性混凝增效机制研究

Coagulation-filtration is one of traditional widely-used advanced techniques for wastewater reclamation in wastewater treatment plant (WWTP). However, it is an emergent problem that the lack of capacity to remove phosphorous (P), heavy metals, and excessive aluminum salts simultaneously, when the technique is employed. Based on the theories and methodology of instrument analysis, stoichiometry, and molecular simulation, this project focuses on the synchronous removal of copper (Cu), cadmium (Cd), and P from municipal wastewater and, especially, emphases some respects including charge neutralization and surface complexation of nano-crystalline produced from reduction/self-decomposition of potassium ferrate, reaction kinetics and mechanism of surface complexation between P and potassium ferrate, competition among Cu, Cd, and P on active sites of nano-crystalline, and the pathway of valence change as potassium ferrate self-decomposing, etc. This study aims to reveal the mechanism enhancing coagulation to synchronously remove heavy metals and P by potassium ferrate; and build up the innovative advanced wastewater treatment system based on potassium ferrate coagulation-magnetic separation. The project is expected to realize the high-efficient synchronous removal of P, Cu, and Cd from municipal wastewater without changing the basic units and arrangement of current WWTP. If so, it would be an essential improvement of traditional treatment.

混凝—过滤技术是污水处理厂污水回用常用的深度处理技术。目前，混凝-过滤技术在磷和重金属同步去除及铝盐安全方面存在不足。本项目将结合仪器分析、化学计量学、分子模拟的理论和方法，以城市污水为研究对象，以同步高效去除重金属铜、镉与磷为目标，重点研究高铁酸钾还原/自分解产物的纳米颗粒晶体的电中和及表面络合作用，高铁酸钾对磷的化学反应动力学和表面络合机理，重金属铜、镉与磷在纳米颗粒晶体上的活性点位竞争机制, 高铁酸钾还原自分解过程中铁的价态变化途径等。本研究旨在揭示高铁酸钾同步去除重金属和磷的混凝增效机制建立新型的高铁酸钾混凝-磁分离同步去除污水中重金属与磷的深度处理技术与工艺系统。该项目研究成果将在基本不改变现行污水厂处理单元结构前提下，实现水中磷、铜镉等污染物的同步高效去除，是对传统处理工艺的重要创新。

常规混凝技术在磷和重金属同步去除及有机物矿化存在不足且功能单一。高铁酸钾作为一种绿色的水处理剂，其多功能特性和污染物去除机制尚不明晰，为此，本项目选择城市污水中重金属铜、镉、磷和污水厂二级出水为研究对象，系统评价了高铁酸盐的自分解特性，对污染物的作用机理及基于高铁酸钾多功能特性的处理工艺。（1）高铁酸钾在水中的还原过程受溶液pH影响显著，在酸性及中性条件下自分解速率较高。分解产物主要为羟基氧化铁和水铁矿的微纳米颗粒，比表面积为250~600 m2/g。（2）高铁酸钾对总磷、溶解性总磷和溶解性正磷的去除率均达到90%以上。反应产物的特征谱峰P2p3/2的结合能为133.28eV, 特征谱峰Fe2p1/2和Fe2p3/2的结合能分别为724.98eV和711.48eV，反应产物稳定，证明磷主要通过高铁酸钾还原产物的吸附作用和生成FePO4沉淀去除。（3）在铜、镉共存，pH值一定的条件下，高铁酸钾对铜的去除具有优势，铜去除率达到98.92%，随着投加量的增加，镉去除率才达到99.45%。构建的反应体系中所有的电子均按自旋相反的方式配对充满壳层，通过构型优化和频率计算可知，由于[Cu(H2O)4]2+的EβLUMO=-5.315 eV小于[Cd(H2O)6]2+的EαLUMO=-2.016 eV，且FeO42--[Cu(H2O)2]2+的吉布斯自由能变-328.53975 KJ/mol小于FeO42- -[Cd(H2O)2]2+的-224.05425 KJ/mol， [Cu(H2O)4]2+、[Cd(H2O)6]2+同时存在时，FeO42-优先与[Cu(H2O)4]2+反应，验证了试验结果。（4）多级氧化催化工艺经过高铁酸钾的初级氧化后，分解产物FeOOH进一步催化臭氧分解，提高臭氧的氧化效率。相比单独高铁酸钾和臭氧的20.9%和23.2%的DOC去除率，最DOC的去除率达到52.7%，为“双碳”背景下，污水深度处理提供了基于绿色多动能试剂基础上的新思路和技术路线。