Catalytic wet peroxide oxidation of methyl orange using naturally-occurring South African ilmenite as a catalyst

Abstract

The introduction of large quantities of organic contaminants into effluents from industrial and agricultural processes has lead to the increasing demand for water reuse. The viability of using naturally-occurring South African ilmenite as a catalyst in the catalytic wet peroxide oxidation (CWPO) process, using methyl orange (MO) as a model compound, was investigated. Intial operating conditions ([MO] = 10 mg·L -1 , [H2O2] = 2.5 mM, ilmenite = 1,000 mg·L -1 , pH = 3.0, temperature = ±20 °C) lead to a complete decolourisation of methyl orange following 90 min of reaction time. Further research investigated the influence of pH and irradiation on the degradation of methyl orange. A pH of 2.5 was found to lead to the fastest degradation rate, this is because at pH values lower than 2.5 an •OH radical scavenging effect occurs and at pH levels above 2.5 dissolved Fe can precipitate. The degradation rate was found to be further enhanced in the presence of irradiation with complete decolourisation of methyl orange occurring after 75 min after reaction time in the presence of UVA and visible light and after 60 min reaction time in the presence of UVB irradiation. This can be attributed to the photo-reductive dissolution of Fe on the ilmenite surface. These results showed that ilmenite could be used as an efficient, cost-effective catalyst for the degradation of aromatic compounds, such as methyl orange, in the CWPO process. The rate of degradation could be further increased with a decrease to a pH of 2.5 in the presence of UVB irradiation.