Microwave Enhanced Iron Ore Tailings Fenton-like Process To Degrade Typical Organic Pollutants In Water

In recent years,the development of mineral causes a lot of tailings which brings not only the waste of resources but also the danger to people.Tailings contain a lot of resources and the tailings utilization has been the hot topic.The tailings have been already used as catalysts,adsorbents or auxiliary agents for the treatment of organic pollutants in water.The studies show that relevant technologies have good prospects and the relevant researchs have been arisen attention,but the investigation is still very limited.In addition,the extensive uses of dyes and antibiotics have caused serious pollution.The composition of dye wastewater is very complex,poor biodegradability and traditional wastewater treatment is ineffective to dye wastewater.Tetracycline antibiotics is one of the most widely used antibiotics,and its water pollution is more serious compared to other antibiotics.On the other hand,heterogeneous Fenton oxidation technology has increasingly been used to remove pollutants.The search of stable Fenton catalyst is one important anttrend in the Fenton catalysis.In addition,microwave assisted Fenton technique can improve the efficiency of Fenton oxidation degradation and has gradually become a hot topic.In this study,iron tailings was used as Fenton catalyst,and combined with microwave to degrade dye Acid Orange 7(A07)and tetracycline(TC).The factors affecting the degradation in the system detailedly studied.The degradation pathway was explored and the environmental security,economic and social evaluation of the proposed method was studied.The contents are as follows:(1)Iron tailings were characterized by XRD,XRF,XPS,BET and FT-IR.The results indicate that the tailings contain a variety of elements,and Fe,Si and Ca are the most abundant element.The iron tailing that contained highest amount of iron was characted by FT-IR and XPS characterization and the results show that the main component of the tailings is in the form of Fe oxides.Experimental results illustrate that the degradation rate of Fenton/microwave system is much greater than pure Fenton,Fenton/ultrasound system.(2)A07 could be quickly and effectively degraded by the microwave-assisted iron tailings Fenton system.After 3.5 min,TOC removal rate was 58.6%.The microwave power,catalyst dosage,concentration of H2O2 and the initial concentration of A07 were the factors to affect the degradation.The removal increased with the increase of microwave power and the amount of iron ore tailings.When pH and H2O2 concentration were 3.0 and 1.98 mmol/L,the removal was the highest.Meanwhile,·OH was presented to be the major species of degradation.The frontier orbital electron density of A07 was calculated by Guassian 03,and the value of FEDHOMO2+FEDLUMO2 of N11 and N12 were larger than that of other atoms.Hence,the tow atoms were possible to be attacked by·OH.Based on the GC-MS analysis,the pathway of the degradation was:the azo bonds of AO7 were firstly to be attacked by the·OH to form the intermediates with benzene and naphthalene ring.Then the intermediates were further oxidized to form CO2 and H2O.(3)The effects of microwave-assisted Fenton degradation of TC using iron ore tailings were observed.The result shows that TOC removal of TC with 6 min was 60%;The amount of iron ore tailings,concentration of H2O2,MW power,pH of solution and the initial concentration of TC have effects on the degradation;The degradation efficiency will increase with the rise of MW power,the concentration of H2O2 and the amount of iron ore tailings;·OH was the main species of the degradation of A07;The changes of H2O2 concentration in the experiment have been studied,the result shows that the degradation efficiency of TC obviously was higher than the degradation of H2O2,and TC was more easily react with·OH compared with H2O2;The frontier orbital electron density and bond energy values of TC were calculated by Gaussian 03;And analyses by GC-MS?HPLC-MS combined with the calculation have been applied to identify the degradation intermediates,and speculate the degradation route of microwave-assisted Fenton degradation of TC using iron ore tailings.(4)Microwave-assisted Fenton system with iron tailings could completely detoxify AO 7 solution;After the degradation,the toxic elements(Cr,Mn,As)contained in the tailings were not detected,and the precipitation of Cu and Pb was very little(both in ?g level),indicating that the established degradation system did not cause secondary pollution;In addition,iron tailings showed good stability in the Fenton reaction,but the content of Fe2O3 changed from the original 73.3%to 68.9%after using nine times;And with reusing iron tailings,no iron was dissolved into solution;After using nine times,XPS and XRD of the iron tailings had no significant difference with those before use;The established system had low costs and could treat waste-water with wastes,which demonstrated good environmental,economic and social benefits.