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Comment on “Complete Degradation of Perchlorate in Ferric Chloride and Hydrochloric Acid under Controlled Temperature and Pressure” Gu et al. (1) presented the reduction of perchlorate (ClO4-) by ferrous iron in an FeCl3-HCl solution, which was used to regenerate the ion-exchange column, at an elevated temperature and/or pressure. We read the paper with great interest and would like to raise a few scientific and practical questions on the method delivered in the paper. First, the Materials and Methods section does not provide a detailed description of the initial condition of the experimental solution for others to reconstruct the experimental system to check the reproducibility of the work. At a minimum, the initial concentration of Fe(III) and pH before Fe(II) addition should have been mentioned and also marked on the figures. Second, the pressure of the systems recorded in the paper was caused by the experimental conditions in both batch and flow-through systems and seems to be not “controlled” as implied by the catchy title of the paper. Gu et al. (1) stated that the reaction rate of ClO4- could depend on pressure, yet did not independently consider temperature and pressure effects on the reaction rate. More supportive data will be needed to investigate the contribution of pressure. Third, the previous work regarding the reduction of perchlorate in acidic media should have been acknowledged. For decades, the reduction of perchlorate has been observed on aluminum, copper, and iron metal and on some metal electrodes in acidic media by chemists at room temperature (2). In other words, it is well-known that hydrogen ion promotes ClO4- reduction. In addition, Gurol and Kim (3) studied perchlorate reduction at acidic pH in the presence of phosphoric acid and iron metal or iron oxide. They concluded that perchlorate can be removed by up to 100% in the pH range of 2.0-2.5 in this system, possibly due to a complex formation between perchlorate and phosphoric acid. Finally, we doubt that the perchlorate reduction method described by Gu et al. (1) will have a widespread use in fullscale applications due to the following reasons: (i) highly
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acidic corrosive water with a pH of -4 will easily deteriorate any metallic structure in the treatment system, (ii) applying high temperature (170 °C) and pressure (20 atm) in the reactor would pose an operational nightmare and a great danger to operators, (iii) the required residence times of several hours to obtain more than 90% removal at the stated temperature and pressures may not prove economical in full-scale applications, and (iv) ClO4--contaminated regenerating solution with a concentration of ∼10 000 mg/L will still contain tens and hundreds of milligrams per liter of ClO4even after 99% treatment efficiency. The authors are also invited to comment on the technical and economical benefits of first transferring perchlorate to a resin and then trying to destroy perchlorate in the regenerating solution under the extreme conditions described above instead of using alternative methods (e.g., directly reducing perchlorate in water at ambient pressure and temperature by chemical reduction) as described by Gurol and Kim (3) or by biological reduction as described by Logan (4) and Rittman (5).
Literature Cited (1) Gu, B.; Dong, W.; Brown, G. M.; Cole, D. R. Environ. Sci. Technol. 2003, 37, 2291-2295. (2) Almeida, C. M. V. B.; Giannetti, B. F.; Rabockai, T. J. Electroanal. Chem. 1997, 422, 185-189. (3) Gurol, M. D.; Kim, K. In Perchlorate in the Environment; Urbansky, E. T., Ed.; Kluwer Academic/Plenum Publishers: New York, 2000; pp 99-107. (4) Logan, B.; et al. Biological Treatment of Perchlorate Contaminated Waters. Presented at the In-Situ and On-Site Bioremediation, the Fifth Symposium, San Diego, CA, April 19-22, 1999. (5) Rittman, B. The Use of Hollow-Fiber Membranes for Perchlorate Ex-Situ Treatment. Presented at the 7th Symposium in Groundwater Resources Association of California on Perchlorate in Goundwater: Occurrence, Analysis and Treatment, Sacramento, CA, July 31, 2003.
Kyehee Kim and Mirat D. Gurol* Department of Civil and Environmental Engineering San Diego State University San Diego, California 92182-1324 ES030691+
10.1021/es030691+ CCC: $27.50
2004 American Chemical Society Published on Web 02/14/2004
