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.