[Degradation of methyl orange solution by microwave-assisted catalysis of H2O2 with chromium residue].

Heavy metal such as chromate compounds, together with unspent azo dyestuff, in effluent forms composite pollutants. The composite wastewater is persistent in color and nonbiodegradable. COD removal ratio and decolorization ratio of methyl orange solution were investigated by microwave -induced catalysis of H2O2 with chromium residue. Factors governing the degradation of methyl orange were experimentally studied including microwave power, microwave irradiation time, pH value, amount of chromium residue, and concentrations of H2O2 and methyl orange solution. Results indicated that some transition metal ions might be taken as catalysts for the purification of persistent organic pollutants in organic-heavy metal wastewater treatment, which can reduce the consumption of chemicals and lower the cost of wastewater purification. Chromium ions in residue and H2O2 could form Fenton-like reagent and produce hydroxyl to mineralize methyl orange. Microwave heating has both thermal and non-thermal effects, and can promote the mineralization rate of organic pollutants. Microwave can also enhance the utilization efficiency of H2O2 in the catalysis process and reduce the dosage of oxidant. The acidity is favorable for generation of hydroxyl for Fenton-like reagent. Employing chromate residue as catalyst in Fenton-like process, the decolorization ratio and COD removal ratio of aqueous MO at 1000 mg x L(-1) were 88% and 85%, respectively, under the following conditions: microwave frequency 2450 MHz, microwave power 700 W, microwave irradiation time 3 min, pH 3 and molar ratio of chromium to hydrogen peroxide 1:56.8.