Reductive dechlorination of chlorinated hydrocarbons as non-aqueous phase liquid (NAPL): preliminary investigation on effects of cement doses.
The reactivities of various types of iron mixtures to degrade chlorinated hydrocarbons (PCE, TCE and 1,1,1-TCA) in the form of non-aqueous phase liquids were investigated. The iron mixtures included a mixture of Fe(II) and Portland cement (Fe(II)-C), a mixture of Fe(II), Fe(III) and Ca(OH)(2) (Fe(II/III)-L), and a mixture of Fe(II), Fe(III), Ca(OH)(2), and Portland cement (Fe(II/III)-C). When the same amount of Fe(II) was used, Fe(II)-C was more reactive with chlorinated ethylenes (i.e. PCE and TCE) than Fe(II/III)-L. The reductive pathway for high concentrations of total PCE (i.e. above solubility) with Fe(II)-C was determined to be a combination of two-electron transfer, β-elimination and hydrogenolysis. Increasing the cement dose from 5% to 10% in Fe(II)-C did not affect PCE dechlorination rates, but it did favor the β-elimination pathway. In addition, when Fe(II/III)-C with 5%C was used, PCE dechlorination was similar to that by Fe(II)-C, but this mixture did not effectively degrade TCE. A modified second-order kinetic model was developed and shown to appropriately describe degradation of TCE at high concentrations. Fe(II/III)-L effectively degraded high concentrations of 1,1,1-TCA at rates that were similar to those obtained with Fe(II)-C using 10% C. Moreover, both increasing cement doses and the presence of Fe(III) increased dechlorination rates of 1,1,1-TCA, which was mainly through the hydrogenolysis pathway. The reactivity of Fe(II/III)-L was strongly dependent on the target compound (i.e. less reactivity with TCE, more with 1,1,1-TCA). Therefore, Fe(II/III)-L could be a potential mixture for degrading 1,1,1-TCA, but it should be modified to degrade TCE more effectively.
Department of Chemical Engineering, Hanyang University, Seoul 133-791, Republic of Korea. sihyun2@hanyang.ac.kr
Si-Hyun
SH
Do
Bill
B
Batchelor
D002126:Calcium Hydroxide / Q000032:analysis / Q000737:chemistry; D003252:Construction Materials / Q000032:analysis; D004787:Environmental Pollution / Q000517:prevention & control*; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry; D005296:Ferrous Compounds / Q000032:analysis / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008962:Models, Theoretical; D010084:Oxidation-Reduction; D012995:Solubility; D013750:Tetrachloroethylene / Q000032:analysis / Q000737:chemistry*; D014240:Trichloroethanes / Q000032:analysis / Q000737:chemistry*; D014241:Trichloroethylene / Q000032:analysis / Q000737:chemistry*
D005290:Ferric Compounds; D005296:Ferrous Compounds; D014240:Trichloroethanes; C024566:1,1,1-trichloroethane; D014241:Trichloroethylene; D002126:Calcium Hydroxide; D013750:Tetrachloroethylene