Iron nanoparticles: Reactions with lindane and the hexachlorocyclohexanes.

摘要

This research demonstrated the efficacy of nanoscale zero-valent iron (nZVI) at both the bench and field scales. This emerging technology utilizes iron particles of up to 200 nanometers (nm) in diameter to degrade redox-amenable contaminants via surface-mediated reduction reactions. Under development since 1996, nZVI represents a promising new remediation approach due to its: (1) enhanced reactivity relative to microscale and granular irons, (2) subsurface mobility potential, and (3) superior field deployment capabilities.; In aqueous batch studies, nZVI degraded gamma-hexachlorocyclohexane (gamma-HCH), a notorious organochlorine pesticide also known as lindane, within 24--48 hours by a reductive dihaloelimination process yielding gamma-3,4,5,6 tetrachlorocyclohexene (gamma-TeCCH). Using a pseudo first-order model, the lindane half-life was approximately 5 hours versus 24 hours with less reactive microscale iron. Balances on chloride, the principal product, generally were in the range of 0.50--0.75.; High gamma-HCH concentration studies in 95% ethanol demonstrated that nZVI can degrade lindane via both dihaloelimination non-reductive dehydrohalogenation in which gamma-2,3,4,5,6-pentachlorocyclohexene (gamma-PeCCH) was the only intermediate. Biphenyl was detected as an end product in the reductive pathway while the trichlorobenzenes (TCBs) were identified as surface-associated products in the non-reductive pathway. Lindane half-lives typically ranged from 2--5 hours. Chloride balances in the reductive pathway were approximately 0.55--0.75 but only 0.30--0.40 in the non-reductive pathway.; Nanoscale iron also effectively treated HCH-contaminated groundwater obtained from a pesticides manufacturing site in Florida. Summed HCH isomer (i.e. SigmaHCH) half-lives ranged from 3--16 hours depending upon nZVI dose as compared to approximately 30 hours with mZVI. The HCH isomers were removed by nZVI with varying effectiveness as follows: gamma > alpha > delta > beta.; The first-ever nZVI field demonstration involved the injection of slurried nanoiron (2.5 kg dry weight nZVI), under gravity-feed conditions, into trichloroethene (TCE)-impacted groundwater at a Trenton, NJ manufacturing site. During the ten-week study, aqueous TCE concentrations in the test area were reduced by up to 96.5%. Elevated levels of methane, ethane, and ethene were also detected. Moreover, reactions between nZVI and water caused the groundwater oxidation-reduction potential (ORP) to decline by 100--400 mV while the pH increased 0.5--1.5 standard units, depending on proximity to the injection well.