关键词: 三氯乙烯, 螯合剂, 过硫酸钠, 降解, 反应动力学

Abstract: Trichloroethylene (TCE) was taken as a target pollutant to study its degradation characteristics in the environmentally friendly chelating agents, sodium citrate (TCD) and citric acid (CA), chelating ferrous ion (Fe²⁺)-catalyzed sodium persulfate (Na₂S₂O₈) system. The effects of the proportion of sodium persulfate, chelating agents, and pH value on the degradation of TCE were investigated, and the optimal proportion of all components and suitable pH value were obtained. Both TCD and CA had effectively chelated Fe²⁺-catalyzed sodium persulfate, which degraded TCE in water, and the degradation of TCE abided by the first-order kinetic reaction model. The optimal proportion in mole was 20:10:10:1 for Na₂S₂O₈/TCD/Fe²⁺/TCE and 20:5:10:1 for  Na₂S₂O₈/CA/Fe²⁺/TCE, respectively, at which both the degradation rate and the first-order reactive rate constant reached their
maximum values. The maximal degradation rate was 96.7% and 97.6% and the maximal reactive rate constant was 2.48×10^-2 and 2.68×10^-2 min-1 for the two reactive systems, respectively. Additionally, the usage of CA for the optimal proportion was only half of TCD. For small proportion, both degradation rate of TCE and the first-order reaction rate constant increased with the increasing amount of TCE, CA, or Na₂S₂O₈. However, excessive chelating agents could form an over-stabilized chelate with Fe²⁺, which reduced the catalytic effect of Fe²⁺ and the oxidative capacity of Na₂S₂O₈. Excessive amount of Na2S2O8 could generate much more sulfate radicals, and these sulfate radicals could consume internally, refraining the degradation reaction of TCE. In the system of Na₂S₂O₈/ Fe²⁺/TCE being 20:10:1, the catalytic effect would dwindle if the proportion in mole was greater than 10 for TCD and 5 for CA. In the system of TCD/Fe²⁺/TCE being10:10:1or CA/Fe²⁺/TCE being 5:10:1, the reaction would be refrained if the proportion in mole was greater than 20 for Na₂S₂O₈. A suitable range of pH value was necessary for the degradation of TCE in activated sodium persulfate system. Alkaline condition refrained the degradation reaction of TCE, while acid to neutral condition was helpful for the reaction.

Key words: trichloroethylene (TCE), chelating agent, sodium persulfate, degradation, reactive kinetics