Cochenille red dye decoloration and chromate reduction simultaneously in acid medium

摘要

During the last century, the synthetic dyes have taken a pivotal role in many domains. Part of this class is the Cochenille Red dye. It can be used as such for wool, nylon, silk, inks, paper, plastics, wood stains, leather tanning and processing. But still in the above mentioned fields it is used as well or even with much better results as ligand being complexed with different metal cations. This domain has been approached by us in previous studies in various papers. The range of use areas is extended for foods drugs, cosmetics, hematology and histology stains and last but not least, in photography, too. Due to these multiple uses, we have found it useful to study its behavior in an acidic medium in the presence of an oxidizing agent. Chromate [Cr(VI)] and azo dyes like Cochenille Red are common pollutants which may co-exist in some industrial effluents. The degradation kinetics of the oxidation process of Cochenille Red dye using inorganic oxidizing agent (K_2CrO_4) have been investigated under various experimental conditions: different concentrations of H2SO4 [10-2 -5·10-1 M ] and temperatures [296 and 308 K]. A kinetic model for oxidation of Cochenille Red dye by the combination of chromate was developed based on experimental results. The thermodynamic activation energy was calculated from the rate constants of the oxidation process of the dye, measured at two different temperatures, 296 and 308 K. We concluded that the negative value of entropies of activation indicate that the reaction occurs between ions of similar charge. Based on our experimental and literature data , we conclude that the destruction of azo-chromophore group by the inorganic oxidizing agent (K_2CrO_4) is explained by the highest oxidation state of this dye.