Dechlorination Of 2, 4-DCP By Zero-valent Iron In The Presence Of Humic Acid

Groundwater which contains chlorinated organic compounds remediation by nanoscale bimetallic metals has received increasing interest in recent years.This report presents the dechlorination of 2,4-dichlorophenol(2,4-DCP)by nanoscale bimetallic particles in the presence of humic acid(HA)to investigate the feasibility of using them for the in-situ remediation of contaminated groundwater.In the present paper is reported an efficient method of synthesizing nanoscale bimetallic particles.They were observed by transmission electronic microscopy(TEM) to determine the size.The results of using the synthesized nanoscale particles for the treatment of 2,4-DCP are showed.And the kinetics and mechanism of catalytic reductive dechlorination in the presence of HA is elucidated.The results are as following:1.Most of the nanoscale Ni-Fe and nanoscale Pd-Fe particles have sizes less than 100nm.2.Experimental results indicate that HA has an obvious inhibitory effect towards 2,4-DCP dechlorination by nanoscale bimetallic particles.And this inhibitory effect is obvious in low HA concentration,such as 5 mg L^-1.3.The effect of dechlorination reaction and reaction rate were dominated by the mass fraction of Ni(Pd)in the bimetal(ω(Ni(Pd))),the mass concentration of nanoscale bimetallic particles in the reaction mixture,reaction temperature and initial pH value.Higherω(Ni(Pd)),higher mass concentration of nanoscale bimetallic particles,higher reaction temperature and lower pH values condition favored the dechlorination reaction.Reaction rate increased asω(Ni(Pd)),mass concentration of nanoscale bimetallic particles and reaction temperature increased.No dependence was found between reaction rate and initial concentration of 2,4-DCP.Towards dechlorination,the appropriate mass fraction of Ni in the bimetal Ni-Fe and the appropriate mass fraction of Pd in the bimetal Pd-Fe are 1.5(wt)%and 0.15(wt)%4.Previous studies have shown that the degradeation rate of chlorinated solvents by nanoscale bimetallic particles follows a pseudo-first-order reaction.Kinetics for the dechlorination of 2,4-DCP by Pd-Fe bimetallic particles shows that k values for 2,4-DCP dechlorination dropped from 0.017,0.013,0.009,0.006 to 0.004 min^-1with the increasing of HA concentrations from 0,5,10,15 to 20 mg 1^-1.The relationship between HA dosage and k values can be described as linear model.5.The wastewater which contains 2,4-DCP,HA and nitrate were simultaneously treated by nanoscale Pd-Fe bimetallic particles.The experimental results showed in the presence of HA,reaction rate decreased as nitrate concentration increased.6.The dechlorination reaction of these 2,4-DCP over nanoscale bimetallic metals in the presences of HA progresses through catalytic reductive dechlorination.This model involves the hydrogen produced as a product of corrosion of iron with water.In the presence of Ni(Pd),H₂ is a facile reductant,and the corrosion reaction will contribute directly to dechlorination.2,4-DCP can be transformed to CP,then to phenol.The complexation between HA and the generated Fe(â…¡)may inhibit 2,4-DCP reduction by Fe(â…¡)or occupy the active surface sites and inhibit iron corrosion.