Study On Spent Liquor Of Dye Intermediate Crystallization By Heterogeneous Fenton Oxidation Technology

In recent years, textile dyes are hardly been photolysized, oxidized and biodegraded, and conventional wastewater treatment technologies find it difficult to cope with this kind of organic pollutions. Development of new economic treatment technology and method is impending. Fenton technology is a responsive, effective method which only required simple equipment and smooth reaction conditions. However, the main difficulties that narrow scope of applicable pH value and secondary pollution problem of sludge containing iron impeded the application of Fenton technology in industry.The spent liquor of H-acid and T-acid crystallization which are dye intermediates were used as model pollutants in this paper. The optimum experimental conditions, oxidation and reduction potential (ORP) values variation, pH values variation, iron ion mass concentration variation and kinetics of different heterogeneous Fenton reaction systems were investigated. By making a comparison of the treatment efficiencies among different reaction systems, this paper determined to choose the most economic and efficient catalyst.The main results are summarized as following:(1)By Fenton oxidation, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removals reached82%and50%at the optimal conditions, that is, H2O2concentration of140mmol·L-1, the molar ratio of H2O2to Fe2+of15:1and the initial pH value of2.0. The optimal operation conditions of Fe0-Fenton like reaction were pH value of1.6, H2O2concentration of140mmol·L-1and the Fe0dosage of0.50g·L-1. The corresponding COD and TOC removals were73%and47%, respectively. It was concluded that the catalytic performance and H2O2oxidant utilization efficiency of ferrous ions was superior to that of zero valence iron.(2)Relationship of the mathematic model on the initial COD value, ORPmax value during the reaction and H2O2doses as well as the relationship between initial COD value and the optimal H2O2doses were established by Fenton reaction for the spent liquor of H-acid crystallization with different concentrations. The results showed that the R2values of the mathematic relationships were above0.99, which showed good linear relationships. It obtained a stable result by using the controlled Fenton reagent calculated by mathematic model formulas for H-acid effluent, of which COD removals can remain above75%, and the doses of the oxidant were greatly reduced.(3)The catalytic activity sequence of the catalysts was:ilmenite>pyrite>ferrous ion>zero-valent iron; while the reaction rates were followed by zero-valent iron> ferrous ion> ilmenite≈pyrite. The initial pH value corresponding to the catalyst at the optimal conditions: pyrite, ferrous ion are3; ilmenite is5and zero-valent iron is2, respectively. Ilmenite and pyrite were insensitive to pH values variation, which had a wide pH applicable scope. It overcame the shortcomings of the traditional Fenton reaction.(4)The reusability and doses of ilmenite indicated that it can hardly been consumed and could be reused for many times of which TOC removals remains above72%. It overcame the shortcomings of the iron water residue and catalytic inferior reusability compared with conventional Fenton reaction. Meanwhile, it was convenient for large-scale applications.