A new
method for the concurrent treatment of Cr(VI)-contaminated
wastewater and production of the useful I2 chemical was
developed. The method is based on the redox reaction between Cr(VI)
and I– that occurs when an aqueous wastewater solution
containing Cr(VI) and I– is frozen, producing I2 and allowing for the effective removal of Cr. The redox reaction
occurs primarily because of the accumulation of Cr(VI), I–, and protons in the ice grain boundaries formed during freezing
(i.e., the freeze concentration effect). This effect was verified
by confocal Raman spectroscopy and the experiments varying I– concentration and pH. The reduction of Cr(VI) (20 μM) was
near complete after freezing at I– concentrations
≥ 100 μM, pH ≤ 3.0, and temperatures ≤
−10 °C. The freezing method (liquid cooling vs air cooling)
had little effect on the final Cr(VI) reduction efficiency but had
a significant effect on the Cr(VI) reduction rate. The freezing method
was also tested with Cr(VI)-contaminated electroplating wastewater
samples, and simultaneous Cr(VI) reduction and I2 production
proceeded rapidly in a frozen solution but was not observed in an
aqueous solution. Additionally, other substances in electroplating
wastewater did not reduce the rate and final efficiency of Cr(VI)
reduction and I2 production. Therefore, the freezing/Cr(VI)/I– system can be considered a feasible approach to water-energy
nexus technology for simultaneous I2 production and Cr(VI)-contaminated
wastewater treatment.
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