Discoloration of azo dye acid red 18 by fenton reagent in the presence of iron powder

The examined H₂O₂/Fe⁰ process was found to be very efficient for discoloration of simulated wastewater containing 100 mg/dm³ commercial azo dye Acid Red 18. The optimal doses of H₂O₂ and Fe⁰ were 60 and 50 mg/dm³, respectively at pH 3 and 15 minutes reaction time. Under the described conditions total visual discoloration was achieved. A very important factor was reaction time. Generally, the smaller dose of iron powder, the greater reaction time needed for visual discoloration. A strict linear correlation was observed between Fe⁰ amount in the range of 10-600 mg/dm³ and final pH. This suggests that the H₂O₂/Fe⁰ process has undoubted advantages in comparison with the classical Fenton reaction, because using excessive amounts of the iron powder could reach higher final pH in the H₂O₂/Fe⁰ process. Thus, smaller doses of base will be required for final neutralization of wastewater. It was also found that the dissolution time of iron powder at acidic conditions (before H₂O₂ was added) is an important parameter that influences the rate of discoloration. As the time of iron powder dissolution increases, the time needed for visual discoloration decreases.