Synthesis Of Magnetic Sulfur-doped Fe-Cu-La Trimetal Oxides And Its Application In The Removal Of Arsenic And Chromium From Water

Arsenic and chromium,which are widely distributed in nature,are highly toxic.They not only cause serious harm to aquatic organisms,but also threaten people’s health and even life.Thus,it is imperative to expoilt an efficient approach to remove arsenic and chromium from aquoues solution.Adsorption is an economical and effective method for the removal of arsenic and chromium.In recent years,the development of composite adsorbents containing multi-metal oxides has attracted wide attention because of their obvious synergistic effect.Rare earth based adsorbents have excellent adsorption properties for oxoanions due to rich in hydroxyl groups on their surfaces.In particular,the oxide of lanthanum has been used in the study of water purification.However,due to the high dissolution of lanthanum oxide in water and the difficulty in separation from water,it is not feaisible for lanthanium oxides to be put into practical appilication in removing As and Cr.In this study,the magnetic Fe-Cu-La trimetal complex oxide(S-FeCuLaO)was synthesized by chemical coprecipitation method.The effects of initial pH and coexisting anions on the adsorption of As(Ⅲ),As(Ⅴ)and Cr(Ⅵ)by S-FeCuLaO were investigated in detail.The adsorption kinetics and thermodynamics were further studied by a series of batch experiments.The adsorbents before and after adsorption were characterized with scanning electron microscopy(SEM),Fourier infrared(FTIR),X-ray photoelectron spectroscopy(XPS)and so on.And a possible adsorption mechanism was proposed.The main research contents were as follows:S-FeCuLaO exhibited excellent adsorption properties for As(Ⅲ)and As(Ⅴ),and the removal efficiencies for As(Ⅲ)and As(Ⅴ)were high in a wide pH range(4-9).The adsorption process followed the Langmuir isothermal model and the pseudo-second-order kinetic equation.The maximum adsorption capacities of S-FeCuLaO for As(Ⅲ)and As(Ⅴ)were 181 mg/g and 250 mg/g,respectively,which were very close to the experimental values and much higher than thoes reported in the literature.The coexisting anions including CO32-,SO42-,NO3-,and Cl-excerted very weak effect on arsenic removal by S-FeCuLaO,while the presence of PO43-significantly inhibited the adsorption of arsenic via strong completion with arsenic for active adsorption sites on the surface of S-FeCuLaO.After regeneration for 12 h with 0.1 mol/L NaOH,the removal efficiencies of As(Ⅲ)and As(Ⅴ)(10 mg/L)by S-FeCuLaO still remained 100%after recycling for 3 times.The adsorption mechanism of As(Ⅲ)and As(Ⅴ)adsorption by S-FeCuLaO was revealed on the bais of the characterization of the adsorbents and the experimental results.Cu(I)on the surface of S-FeCuLaO reacted with the dissolved O2 in water to produce superoxide radicals(O2·-),which oxidized As(Ⅲ)to As(Ⅴ).Then As(Ⅴ)interacted with metal hydroxyl(-OH)on the surface of S-FeCuLaO and was further removed through cordination exchange,chemical adsorption and generating precipitation.The removal efficiency of Cr(Ⅵ)was greatly dependent on the solution pH and S-FeCuLaO displayed a very high adsorption efficiency for Cr(Ⅵ)in the initial pH range of 3-4.Pseudo-second-order equation could well describe the adsorption kinetic process of Cr(Ⅵ)removal with a high determination coefficient(R2>0.99).The adsorption process of Cr(Ⅵ)fitted well with the Langmuir isothermal model.The calculated maximum adsorption capacity of Cr(Ⅵ)was 158 mg/g,which was close to the experimental value and higher than those reported in the literature.The coexisting anions of PO43-,Cl-,NO3-and CO32-exhibited little influence on adsorption of Cr(Ⅵ).Hoverver,the removal of Cr(Ⅵ)was inhibited by the presence of SO42-due to outersphere complexation on the surface of S-FeCuLaO.After regeneration for 12 h with 0.1 mol/L NaOH,the removal efficiency of Cr(Ⅵ)(1020 μg/L)after five cycles still reached 100%.The results obtained in this study have demonstrated that S-FeCuLaO posesses an excellent performance in removing As(Ⅲ),As(Ⅴ)and Cr(Ⅵ),S-FeCuLaO can be used to remove high and low concentration As and Cr in wastewater and well water.These results can provide important theoretical basis and scientific guidance for the removal of pollutants in the water environment.