Degradation Of Azo-dye Acid Red B In Aqueous Solution By Cast Iron Combined With Low Frequency Ultrasound

The toxic and the biorefractory organic compounds are the common kind of serious pollutants in water pollution and water quality nowadays,which is also a hot research focus in environmental science and environmental engineering.Azo dyes have an extensive application and wide colour spectrum.Because of the stability of azo dye,Standard Drainage of dye Waste Water is very hard by traditional water treatment.Since 1990s,the power-ultrasonic technology is a kind of novel water treatment technology which is applied to degrade the toxic and biorefractory organic compounds and get satisfying results.The Internal Electrolysis also have an extensive application in dye wastewater treatment and have better decolourization effect, decolourization efficiency of ARB should be improved further.The power-ultrasonic technology has the characteristics of the advanced oxidation processes,incineration and supercritical oxidation.The ultrasonic technology can be operated under mild reaction condition.The degradation rate is rapid,it can treat various kinds of waste water alone or with other water treatment technology.The water pollution situation and the danger to human beings from the toxic and the biorefractory organic compounds are discussed.The conventional water treatment methods in water treatment are reviewed,and the application of ultrasonic, internal electrolysis and ultrasonic-internal electrolysis technology to degrade the organic compounds are summarized.The paper aims to present its authors' investigation over the degradation of azo dye C.I.Acid Red B(ARB) by using cast iron in the absence and presence of low frequency ultrasound(59 kHz and 40 kHz).The feasibility of the above said combination was explored by analyzing the concentration of modeling wastewater containing azo dye Acid Red B.The results of our investigation reveal that,the degradation rate of ARB was very slow by means of the single low frequency ultrasound,whose removing rate was only 4.7%, after a 10 min reaction by low frequency ultrasound in weak acidic medium,while the removing rate of ARB can be 49.9%of ARB by cast iron after a 10 min reaction,it can then be made to rise over 90%by cast iron with low frequency ultrasound after 10 min reaction.The degradation of ARB dye wastewater was studied by single factor and orthogonal test in US/Fe system.The result showed that the major factors to impact the degradation of ARB were pH value＞temperature＞diameter of scrap iron＞reaction time.The optimum process conditions of reaction were decided:pH value was 6.0,reaction time was 8.0 min,temperature was 35℃,the diameter of scrap iron was 0.1-0.9mm.The removal of ARB amounted to 95.0%on this condition. Mineralization of ARB in this process was studied by UV-vis spectrum.We can see,ARB have azo bond and naphthalene ring.The structures of ARB were embodied on the UV-vis absorption spectra of their aqueous solutions.ARB has three absorbance peaks at 218 nm,317 nm and 515 nm.Extent of mineralization of ARB can be evaluated by measuring reduction of three absorbance peaks at 218 nm,317 nm and 515 nm and TOC removal.The reductions of three absorbance peaks were about 37.6%,46.8%and 97.5%,respectively.The TOC removal of ARB about 43.2%was observed after 20 min for ARB.A significant mineralization of ARB was observed.The degraded products of dye wastewater of ARB were analyzed by LC-MS technology.The kinetics of degradation reaction was analyzed,the model of kinetics was constructed and the parameters of kinetics quotation were estimated.The combination of low frequency ultrasound and cast iron shows a remarkable synergistic effect on the degradation of ARB,which proves to follow the first-order kinetics model. On the other hand,while the first-order rate constant of ARB degradation by cast iron was only 7.50×10^-2 min^-1,the degradation by US-Cast iron proved to be 2.04×10^-1 min^-1 and 2.54×10^-1 min^-1 under 175 W,59 kHz and 250 W,59 kHz ultrasound irradiation,respectively.Furthermore,a 2.72-fold increase in the reaction rate can be observed in the presence of 175 W,59 kHz ultrasonic irradiation as compared with that of absence of ultrasound.A 3.38-fold increase in the reaction rate was observed in the presence of 250 W,59 kHz ultrasonic irradiation compared with that of absence of ultrasound.Half times were shortened accordingly.It was thus found that for azo dye ARB,the rate of color decay was the first-order with respect to the visible absorption of the dye.The destruction of the naphthalene rings in azo dyes was slower than that of color.The process is easy to be operated,fast and feasible with a wide application foreground in the given engineering area.