铁及超声辅助铁还原降解水中氯乙酸及其动力学研究

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

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。

Reductive degradation of dichloroacetic acid （DCAA） and trichloroacetic acid （TCAA） in a- queous 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 in- itial 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 degrada- tion 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 ap- parent rate constants of 1.03× 10-3 s-1 （for reduction of DCAA with Fe0）, 5. 70× 10-3 s-1 （for reduc- tion of DCAA with US-Fe0）, 5. 63 × 104 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.