Electrochemical generation of perchlorate from chlorinated drinking water



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Texas Tech University


Texas Commission on Environmental Quality (TCEQ) discovered perchlorate contamination in an elevated drinking water storage tank in Levelland, Texas on April, 2002. The perchlorate contamination was found to be the result of the cathodic corrosion protection system. The main objective of this study was to characterize the production of perchlorate both quantitatively and qualitatively from an impressed current, corrosion protection system. Laboratory experiments were conducted in small-scale, batch reactors. Samples were taken at regular time intervals and analyzed for Cf, CIO', CIO2', CIO3', and CIO4". The influence of the anode material used, the aqueous ionic composition, and the electrical potential and current imposed required to generate perchlorate were studied. This study demonstrated that under certain conditions perchlorate was generated with cast iron and niobium anodes. There was minimal perchlorate production when titanium wire anodes were used. The ions Ca^2+, Mg^2+, and hypochlorite present in the water also had a significant influence on perchlorate production.

From the experimental analysis of the CIO4', CIO3", CIO", and Cl'data, the chemical mechanism and kinetics for a sequential production of perchlorate ions from chloride ions were derived. The order and reaction-rate constants for the formation of CIO", CIO3', and CIO4' reactions from their respective precursors were determined. The overall first-order reaction-rate constant for the perchlorate formation was found to be 0.005 to 0.1 hr. The findings from this study demonstrated the complex electrochemical process of perchlorate formation and perhaps suggest ways to mitigate perchlorate contamination.



Electrolysis -- Conductivity, Drinking water -- Contamination, Perchlorates -- Toxicity testing, Ammonium perchlorate -- Oxidation, Levelland Texas