Study On The Inner Electrolysis Process In Pretreatment Of Azo Dyeing Wastewater With Spongy Iron

With the rapid development of dyestuff industry, the environment pollution taken by dye wastewater has stepped up in the meanwhile. Azo dyes have high chromaticity, strong toxicity and difficulty to degrade. It has caused people‵s wide attention. Amiming at these problems , this article develop study on the inner electrolysis process in pretreatment of azo dyeing wastewater with spongy ironIn the present paper is systematically researched the removal effieiency and effects of azo dyes by sponge iron. The kineties of dyes removal by sponge iron was also analyzed. Through Scanning electron microscope,X-ray diffraction and ultraviolet scanning technology ,the surface characteristics and chemistry of sponge iron in reaction system and change of dyes molecular were analyzed. Next main conclusion was obtained.For this research ,five commonly used water-soluble azo dyes have been chosen for model wastewater dyes, which were treated by sponge iron internal eletrolysis. During the research various experimental parameters were then investigated such as time for internal electrolysis, particle size of sponge iron,pH, the concentration of the dye water,the temperature and also the mixing rate in order to find the optimum condition. Sponge iron has good effect on decolorization of dyes.when 3 gram of 1~3mm sponge iron, dye concentration 100mg/L, after 60min ,decoloration rate can reach 80%,where acid chrome black T reach 96%.The removal efficiency increased with the increasing of sponge iron addition and reaction temperature, low pH value and concentration of the dye water could accelerate the rate of dye removal. The smaller the sponge iron particles, the higher the surface area ,the faster the reaction rate. model dye wastewater was also used to degrade, the BOD5/COD of the wastewater was raised from 0.26 to 0.4 improving the bio-degrad ability of wastewater.Kinetics studies shows that the degradation of azo dyes fit the pseudo-first-order reactions.with increasing of acidity,mixing rate and iron surface area, the degradation rates increase. Like the amount of sponge iron shows a linear relationship between the reaction rate constant(kobs).The increases in the amount of sponge iron may result in the increase of kobs. High temperature also shows positive effects on kobs. According to the Arrehenius equation , active energy of each dye was obtained in this research. As the initial dye concentration increased, the kobs decreased, suggesting saturation of sponge iron surface reactive sites. The effect of both the mixing intensity and the initial dye concentration on the dye decolorization rate demonstrate that the sponge iron dye decolorization achieved in the present study is a surface-catalyzed, mass transfer-limited process. Base on these results, increase in reaction rate and the saving of production time can be achieved by the improvement of mass transport, higher reaction temperature and more sponge iron during the reduction of dyes.The mechanism of sponge iron internal eletrolysis has been further known through the study on the surface chemistry of sponge iron. SEM of sponge iron showed that thick claddings appeared on the surface of sponge iron, they could decrease the interstice rate of sponge iron and do harm to the decolorization efficiency ;XRD of sponge iron after reaction showed that some ferrous oxides and hydrates appeared on the surface of sponge iron. the breaking down of the azo bond and the formation of the products of the aromatic amine.