During the decolorization of Orange II by 10 mg/L of nZVI for various initial pH values, the observed first order rate constant was inversely proportional to the initial pH, except for pH 2. The effect of pH was significant on the reduction of Orange II.
The decolorization efficiency of Orange II at pH 3 increased with an increase in the nZVI dosage. When the nZVI dosages were 5 and 10 mg/L, the decolorization efficiencies after 60 min were 30% and 53%, respectively. Once the nZVI dosage exceeded 20 mg/L, the decolorization efficiency reached a plateau above 95%. There was no obvious increase in the decolorization efficiency at nZVI dosages of 20, 40, 60, 80, and 100 mg/L. Therefore, based on the experimental conditions employed in this study, the optimum nZVI dosage for the decolorization of Orange II was 20 mg/L. Considering that the nZVI dosage was much lower than the microscale ZVI dosage, nZVI has great application potential in Orange II decolorization.