铁及超声辅助铁还原降解水中氯乙酸及其动力学研究

以二氯乙酸(DCAA)和三氯乙酸(TCAA)为目标污染物,研究了铁(Fe0)和超声辅助铁(US-Fe0)还原降解水溶液中氯乙酸,以及溶液初始pH值、Fe0投加量、反应温度、反应时间、氯乙酸初始浓度对降解率的影响,并对降解的动力学进行了初步研究。结果表明,Fe0还原氯乙酸的最佳条件是:pH值为4.0、铁投加量为4g·L-1,室温条件下反应16h。超声辅助对Fe0还原水中氯乙酸的反应具有显著促进作用。在初始浓度为50μg·L-1时,US-Fe0还原降解DCAA和TCAA的降解率分别为87.3%和82.0%。Fe0和US-Fe0还原降解氯乙酸均符合准一级反应动力学(对氯乙酸),降解的表观速率常数分别为1.03×10-3 s-1(Fe0还原DCAA)、5.70×10-3 s-1(US-Fe0还原DCAA)和5.63×10-4 s-1(Fe0还原TCAA)、2.58×10-3 s-1(US-Fe0还原TCAA)。TCAA脱氯生成DCAA是降解的速率控制步骤。

A Study on Reductive Degradation of Chloroacetic Acids with Fe~0 and Ultrasonically Aided Fe~0 and the Kinetics

Reductive degradation of dichloroacetic acid(DCAA) and trichloroacetic acid(TCAA) in aqueous solution with iron(Fe0) and ultrasonically aided iron(US-Fe0) is reported in this paper together with the kinetics.The influences of solution pH,dosage of iron,reaction temperature and time,and initial concentration of DCAA(or TCAA) on the degradation were studied.It was determined that,for reductive degradation of chloroacetic acids with Fe0,the optimal pH was 4.0,the best dosage of Fe0 was 4g L-1,and the most suitable reaction temperature and time were 25℃ and 16 h,respectively,while ultrasonification greatly promoted the degradation reaction.Under these conditions,the degradation efficiencies of DCAA and TCAA with US-Fe0 for an initial concentration of 50μg·L-1 were 87.3% and 82.0%,respectively.The degradation kinetics conforms to a pseudo first-order reaction,with apparent rate constants of 1.03×10-3 s-1(for reduction of DCAA with Fe0),5.70×10-3 s-1(for reduction of DCAA with US-Fe0),5.63×10-4 s-1(for reduction of TCAA with Fe0),and 2.58×10-3 s-1(for reduction of TCAA with US-Fe0).Dechlorination to produce DCAA is the rate-determining step of the reductive degradation of TCAA.