Transformation of chlorinated ethylenes by iron powder in 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer

Conference · Fri Dec 01 04:00:00 EST 1995

OSTI ID:126416

Schreier, C G; Reinhard, M ^[1]

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1. Stanford Univ., CA (United States)

Reduction of chlorinated organics by metals, particularly iron, has been shown to be an effective environmental remediation method. In this work, six chlorinated ethylenes were reduced by iron in HEPES buffer (pH 7) to ethene and ethane. Mass balances ranged from typically 50% for tetrachloroethylene (PCE) to 100% for vinyl chloride (VC). The only other products observed were trichlorethylene (TCE), a reactive intermediate of PCE transformation, and cis-dichloroethylene (cis-DCE), a reactive intermediate of TCE transformation. No vinyl chloride was seen with any of the substrates. Normalized rate constants ranged from 0.13/day for PCE to 0.50/day for trans-DCE using 36g/L iron at 50{degrees}C. The order of reactivity was VC < 1,1-DCE {approx} cis-DCE {approx} PCE < TCE < trans-DCE, which does not follow the typical pattern of reductive dehalogenation in which the more highly chlorinated compounds are be most reactive. A buffer was necessary for significant (>30%) transformation to occur. The role of buffer appears to be simply maintenance of pH rather than a source of reducible sulfur since decreasing the buffer concentration 10-fold resulted in only a minor change in rate (k{sub obs} = 0.056/day at 0.5M buffer; k{sub obs} = 0.045/day at 0.05M buffer).

• OSTI ID: 126416
• Report Number(s): CONF-950402--
• Country of Publication: United States
• Language: English

Related Subjects

40 CHEMISTRY
54 ENVIRONMENTAL SCIENCES
BUFFERS
CHEMICAL REACTIONS
CHLORINATED ALIPHATIC HYDROCARBONS
DECHLORINATION
ENVIRONMENT
IRON
OXIDATION
POWDERS
REACTION INTERMEDIATES
REDUCTION
REMEDIAL ACTION