Study On The Catalytic Degradation Of PCE By Iron Oxide In The Growth Ring Of Pipe Network

Perchloroethylene is some kind of non-degradable and volatile chlorinated olefin compounds.PCE has become one of the pollutants in the water.It is harmful to the health and could cause certain toxicological effects to human skin,lung,liver,kidney and so on.With the prolongation of the service time,irregular ring-like substances called growth ring will appear on the inner wall of the pipeline.The major components of the water supply pipeline growth ring are various precipitations,mental rusts,biological mucosa and metabolites.The main metal components are Lepidocrocite(?-FeOOH)and Goethite(a-FeOOH).The paper aimed at the studies of iron metal oxides in the growth ring used as some kind of catalyst to degrade perchloroethylene(PCE)cooperated with oxidants such as hydrogen peroxide and sodium persulfate.Based on the analysis of the growth ring and the preparation of two kinds of iron minerals in the laboratory,the efficiency and effectiveness of the degradation system has been explored.The mechanism of the degradation of Perchloroethylene(PCE)catalyzed by iron mineral were analyzed briefly.The two iron minerals prepared in the laboratory were detected as well-formed goethite and Lepidocrocite,in which goethite is more needle-like,Lepidocrocite is flocculent and snow-like.The specific surface area of goethite is 146.848 m2/g,pyrite is 168.812 m2/g,the goethite has a pHpzc=6.1,the Lepidocrocite has a pHpzc=5.4,and the mixed iron ore has a pHpzc=5.9.The system based on the Lepidocrocite,goethite and H2O2 has good degradation effect on PCE.The removal rate of PCE could reach 86.3%after 8h.The effect of degradation is most significantly affected by the pH.The concentration of HCO3 anion and dosage ratio of catalyst has less impact than pH value.The effect is least affected by amount of catalyst.The optimum conditions for the oxidation system are as follows:pH=4,catalyst dosage ratio is 2 goethite:1 Lepidocrocite,the concentration of HCO3 is 12mmol/L,catalyst dosage is 0.3g.The system based on the Lepidocrocite,goethite and Na2S2O8 has some kind of degradation effect on PCE.The removal rate of PCE could reach 61.3%after 8h.The effect of degradation is most significantly affected by the pH.The amount of catalyst and dosage ratio of catalyst has less impact than pH value.The effect comes from concentration of HCO3-anion is last.The optimum conditions for the oxidation system are as follows:pH=7,catalyst dosage ratio is 1 goethite:1 Lepidocrocite,the concentration of HCO3-is 8mmol/L,catalyst dosage is 0.2g.The system in which hydrogen peroxide is used to enhance the effect of sodium persulfate could gain the 92.1%PCE removal rate.It was proved that the synergy of oxidants could significantly improve the degradability of PCE.The degradation of PCE in the H2O2 or Na2S2O8 system conforms to the second-order reaction kinetics,and the remove of PCE in the presence of double oxidants conforms to the first-order reaction kinetics.The experiments using chemical probes show that·OH is the main effective oxidant in the system,and ·SO4-also participates in the process.The amount of iron ions in the Aqueous solution can reach 7.43mg/L therefore degradation of PCE should be mainly based on the dissolution of iron ions and the large amount of ·OH and ·SO4-produced after.