Abstract
Ascorbic acid (AA) mediated electron transfer may induce reductive dechlorination of carbon tetrachloride (CCl(4)). This study investigated the role of AA in conjunction with the presence of iron minerals over a wide pH range for the reduction of CCl(4) in aqueous systems. The results indicate that CCl(4) was reduced by AA at a pH of 13 (>pKa(2, AA) of 11.79) and chloroform (CHCl3) was a transformation byproduct of CCl(4). When CCl(4) levels were reduced to near complete disappearance, the decrease of CHCl(3) was then observed. The degradation rate of CCl(4) and also the formation rate of CHCl(3) increased with increased AA concentrations. Analysis of reaction kinetics between CCl(4) and AA revealed an overall second-order reaction with a rate constant of 0.253 ± 0.018 M(-1) s(-1). Furthermore, the reduction rate of CCl(4) by AA at pH of 13 could be enhanced with the presence of iron minerals (Fe(3)O(4), Fe(2)O(3), FeOOH, and FeS2). In the absence or presence of iron minerals, the fraction of CCl(4) transformed to CHCl(3) was less than 1, indicating simultaneous one- and two-electron transfer processes. The end-products of AA at a pH of 13 included threonic acid and oxalic acid. This study highlights the potential of an alkaline AA solution for remediating chlorinated solvents.
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