Research On Catalytic Ozonation Of Cu-EDTA Wastewater By Supported Expanded Graphite

Catalytic ozone oxidation technology is a hot research topic which can efficiently mineralize refractory organics without secondary harm.In order to achieve efficient removal of Cu-EDTA wastewater,an ozone/catalyst system was established,catalysts carriers and supported expanded graphite catalysts were developed and optimized.By characterization tests,such as SEM,XRD,the microstructure,surface composition and crystal structure of catalysts were analysed;then a series of experimental factors for degradation of Cu-EDTA which have effect on the catalytic activity were investigated,at last,the reaction kinetics and reaction mechanism of catalytic degradation of Cu-EDTA were discussed.Expanded graphite?EG?was prepared by chemical oxidation method with natural graphite as raw material,ammonium nitrate as oxidant and perchloric acid as intercalation agent.Through orthogonal experiments and single factor experiments,the results of the optimum conditions were as follows:C?g?:ammonium nitrate?g?:perchloric acid?mL?=2.5:0.15:6,the reaction temperature was 50°C,the reaction time was 60 min,the expansion volume was 340 mL/g at 950°C.Magnesium oxide?MgO?was selected as the best catalytic active component.The preparation technology for MgO/EG catalyst was developed with 0.5 g EG,30%of the load mass fraction for EG mass,calcination temperature at 600°C,calcination time for 4 h.Characterization tests of SEM,XRD demonstrated that the prepared catalysts exist in the form of MgO crystal structure,and MgO were evenly dispersed on the surface of carriers.In ozone/catalyst system,the catalytic degradation reaction of Cu-EDTA occurred under the optimal process conditions,which were 0.6 g/L the initial concentration,3 of pH value,and 1 g/L of catalysts dosage,8 mg/L of ozone concentration,at room temperature.Copper ion(Cu²⁺)was completely removed,and the EDTA mineralization rate was73.25%after 90 min.It was found that the inorganic ions,such as Na⁺and SO₄^2-,have almost no effect on the degradation of Cu-EDTA.However there was a certain inhibitory effect on the reaction with CO₃^2-,Cl^-and PO₄^3-.Furthermore,the catalytic ozonation degradation of Cu-EDTA process was consistent with the quasi-first-order dynamics.The mechanism on the degradation of Cu-EDTA by MgO/EG catalysts was studied by using the radical inhibitor tert-butanol?TBA?.It was declared that TBA significantly inhibited the degradation of Cu-EDTA.Therefore,the Cu-EDTA degradation complies to·OH oxidation mechanism in the catalytic system.