Decoloring Mechanisms of Dye Stuff by Chemical Oxidation
This study utilizes sodium hypochlorite (NaOC1) to reduce the color of synthetic dye solutions. Five dyes including methyl red (MR), methyl violet (MV), methyl blue (MB), malachite green (MG) and methyl orange (MO) were studied. The color was measured using an automatic ADMI (American Dye Manufacturer Institute) measurement system. A visible spectrophotometer is connected to a personal computer so that samples can be scanned and the results are recorded automatically. During the batch decoloring study, several factors: ADMI, ORP, temperature and pH were also monitored continuously using the computer and makes it possible to have an automated decoloring process.
A modified Nernst equation was used to delineate the relationship between the degree of decoloring reaction and the solution ORP value. A “decoloring coefficient” (S) was proposed to represent the oxidative potential (or decoloring property) of the dyes studied. In this study, the oxidative or decoloring potential can be shown in the following order: MG>MV>MO> MR>MB. Using the on-line measurements of ORP, color and pH, the oxidation process can be automated to achieve a pre-selected percentage of color removal.
KeywordsMethylene Blue Methyl Orange Malachite Green Chemical Oxidation Sodium Hypochlorite
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