Reductive transformation halogenated aliphatic pollutants

Reductive Transformation of Halogenated Aliphatic Pollutants by Iron Sulfide... 

Studies in the last decade show that iron sulfide minerals are very reactive in the reductive transformation of chlorinated aliphatic pollutants. These minerals, present in sulfate-reducing anaerobic environments, likely contribute to in-sUu transformation of chlorinated aliphatic pollutants and have potential application in remediation technologies. Solution pH, the presence of organic co-solutes with functional groups representative of natural organic matter, and the thermodynamic or molecular properties of the halogenated aliphatic pollutant all influence the rates and/or products of pollutant transformation. 

This chapter reviews the literature to date on the reductive transformation of halogenated aliphatic pollutants, particularly chlorinated aliphatics, by iron sulfide minerals. 

Linear regression of one-electron reduction potentials (which are proportional to free energies for electron transfer reactions) with log kohs values for the transformation of 8 halogenated aliphatic compoimds by FeS produced only a weak LFER (R =0.48) (7 7). The poor R value and the small slope of the LFER were attributed to several factors, including the influence of thermodynamic or molecular parameters other than one-electron reduction potentials on reaction rates, different mechanisms of adsorption to the FeS surface for different pollutants, different reaction mechanisms at the FeS surface, and/or significant adsorption of certain pollutants to non-reactive FeS surface sites (77). 

Empirical linear correlation analysis has also produced results that may be used in predicting the rates of FeS-mediated pollutant transformation based on pollutant thermodynamic or molecular properties. One study (77) performed linear correlation analysis of log kohs values for 8 halogenated aliphatic molecules with five molecular properties one-electron reduction potentials, lowest unoccupied molecular orbital (LUMO) energies, fi ee energies of formation of aqueous phase radicals formed upon one-electron reduction, gas-phase homo-[ytic bond dissociation enthalpies, and aqueous solubilities. Of these parameters, homolytic bond dissociation enthalpies (7)r.x values) were best correlated with log obs values for FeS reductive dechlorination (R =0.82). The correlation between log obs and 7)r x is illustrated in Figure 4. Another parameter shown... 

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