Carbon Tetrachloride Degradation by Alkaline Ascorbic Acid Solution

Ascorbic acid (AA) mediated electron transfer may induce reductive dechlorination of carbon tetrachloride (CCl4). This study investigated the role of AA in conjunction with the presence of iron minerals over a wide pH range for the reduction of CCl4 in aqueous systems. The results indicate that CCl4 was reduced by AA at a pH of 13 (>pK(a2),(AA) of 11.79) and chloroform (CHCl3) was a transformation byproduct of CCl4. When CCl4 levels were reduced to near complete disappearance, the decrease of CHCl3 was then observed. The degradation rate of CCl4 and also the formation rate of CHCl3 increased with increased AA concentrations. Analysis of reaction kinetics between CCl4 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 CCl4 by AA at pH of 13 could be enhanced with the presence of iron minerals (Fe3O4, Fe2O3, FeOOH, and FeS2). In the absence or presence of iron minerals, the fraction of CCl4 transformed to CHCl3 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.