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DOI : ,    Vol.21, No.5, 79 ~ 90, 2013
Title
The Features of the Reduction-Precipitation Reaction of Highly Concentrated Dichromate Ion depending on Thermal Condition in Acidic Environment
유동주 Dong Ju You , 한혜정 Hye Jeong Han , 김동주 Dong Su Kim
Abstract
The variation of the features of the reduction-precipitation treatment reaction for highly concentrated acidic dichromate ion-containing wastewater has been investigated with temperature and pH condition. Cr2O72- and HCrO4- are mutually interchangeable depending on the degree of hydrolysis and the form of Cr(VI) ion is Cr2O72- at high concentration. The reduction of Cr2O72- to Cr3+ is promoted by decreasing pH and the lower limit of pH for this was estimated to be ca. 2.0 at equilibrium. The reduction of Cr2O72- was found to be promoted as temperature decreases and the precipitate-forming reaction of Cr3 ion was investigated to be demoted at high temperature. A kinetic model has been suggested for the precipitation reaction of aqueous ion and the time necessary for sedimentation was anticipated to reduce exponentially as temperature increases. The re-dissolution of Cr(OH)3 as Cr(OH)4- was examined to be accelerated as temperature and pH rise and it was thought to be necessary to control the temperature and pH conditions for each step of the reduction-precipitation treatment process of Cr(VI) ion by considering the characteristic of entire process including the main manufacturing process.
Key Words
Dichromate ion, Acidic condition, Thermal effect, Reduction-Precipitation treatment, Thermodynamic estimation
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