C. Liu, E. Salhi, J.P. Croue, U. von Gunten
Environ. Sci. Technol., 48 (22), 13173-13180, (2014)
It has been shown previously that the disproportionation of halogen-containing oxidants (e.g., HOCl, HOBr, and ClO2)
is enhanced by a CuO-catalyzed process. In this study, the
transformation of iodine during chlorination in the presence of CuO was
investigated. There is no significant enhancement of the
disproportionation of hypoiodous acid (HOI) in the presence of CuO. The
formation rate of iodate (IO3–) in the CuO–HOCl–I–
system significantly increased when compared to homogeneous solutions,
which was ascribed to the activation of HOCl by CuO enhancing its
reactivity toward HOI. In this reaction system, iodate formation rates
increase with increasing CuO (0–0.5 g L–1) and bromide (0–2
μM) doses and with decreasing pH (9.6–6.6). Iodate does not adsorb to
the CuO surfaces used in this study. Nevertheless, iodate concentrations
decreased after a maximum was reached in the CuO–HOCl–I–(−Br–) systems. Similarly, the iodate concentrations decrease as a function of time in the CuO–HOCl–IO3– or CuO–HOBr–IO3–
system, and the rates increase with decreasing pH (9.6–6.6) due to the
enhanced reactivity of HOCl or HOBr in the presence of CuO. It could be
demonstrated that iodate is oxidized to periodate by a CuO-activated
hypohalous acid, which is adsorbed on the CuO surface. No periodate
could be measured in filtered solutions because it was mainly adsorbed
to CuO. The adsorbed periodate was identified by scanning electron
microscopy plus energy dispersive spectroscopy and X-ray photoelectron
spectroscopy.