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Chlorination of Iodide-Containing Waters in the Presence of CuO: Formation of Periodate
journal contribution
posted on 2014-11-18, 00:00 authored by Chao Liu, Elisabeth Salhi, Jean-Philippe Croué, Urs von GuntenIt
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.