铸铁还原氯乙酸的影响因素与机制研究

氯乙酸是地表水与饮用水中一种常见的微量氯代有机污染,具有致癌性,浓度较高时对人体健康会产生一定的危害.为了更经济地去除水体中的氯乙酸,研究了铸铁废料去除氯乙酸的可行性,讨论了铁类型、预处理方法,振荡方式以及溶解氧等条件对还原效果的影响.结果表明传质过程比铁类型与酸处理对氯乙酸还原速率的影响更大.铸铁无氧去除三氯乙酸(TCAA)的主要产物为二氯乙酸(DCAA)而有氧存在时为一氯乙酸(MCAA).在纵向翻转下铸铁对氯乙酸的去除过程符合伪一级动力学,TCAA、DCAA与MCAA的无氧速率常数分别为0.46 h-1、0.03 h-1与0,有氧速率常数依次为1.24 h-1、0.79 h-1与0.28 h-1.不同氧含量环境中铸铁对氯乙酸的去除机制不同,无氧时为连续氢解,有氧时可能包括连续氢解与直接转化过程.

Influencing Factors and Reaction Mechanism of Chloroacetic Acid Reduction by Cast Iron

The chloroacetic acids are ubiquitous present as a class of trace chlorinated organic pollutants in surface and drinking water. Most of chloroacetic acids are known or suspected carcinogens and, when at high concentrations, are of great concern to human health. In order to economically remove chloroacetic acids, the degradation of chloroacetic acids by cast iron was investigated. Moreover, the effect of iron style, pretreatment process, shocking mode and dissolved oxygen on chloroacetic acids reduced by cast iron was discussed. Compared to iron source and acid pretreatment, mass transfer was more important to chloroacetic acid removal. Dichloroacetic acid (DCAA) and monochloroacetic acid (MCAA) were the main products of anoxic and oxic degradation of trichloroacetic acid (TCAA) by cast iron during the researched reaction time, respectively. With longtitudinal shock, the reaction kinetics of chloroaectic acid removal by cast iron conformed well to the pseudo first order reaction. The anoxic reaction constants of TCAA, DCAA and MCAA were 0.46 h^-1, 0.03 h^-1 and 0, and their oxic constants were 1.24 h^-1, 0.79 h^-1 and 0.28 h^-1, respectively. The removal mechanisms of chloroacetic acids were different under various oxygen concentrations, including sequential hydrogenolysis for anoxic reaction and sequential hydrogenolysis and direct transformation possible for oxic reaction, respectively.