| In this paper,the cerium/ferric oxide composites were prepared by chemical co-precipitation method.The influencing factors such as iron concentration,cerium nitrate dosage,reaction temperature and reaction time were investigated by single factor and orthogonal experiment.And the material were characterized by XRD and Fourier transform infrared spectroscopy.The static adsorption test,kinetics and thermodynamics experiment and desorption experiment were carried out to study the removal efficiency of hexavalent chromium in waste water by cerium/iron oxide composites.The study showed that the cerium/ferric oxide composite has a higher adsorption capacity on hexavalent chromium wastewater.The main conclusions as follows:(1)The main factors determined by orthogonal experiment as follows:total concentration of iron salt>cerium addition>reaction time.The optimum preparation conditions were as follows:the iron salt concentration:0.6mol/L,the cerium nitrate dosage:0.1%,the reaction time:60min.(2)The composites showed higher crystallinity which analyzed by the XRD,and the cerium was doped in the form of the amorphous material on the material to form solid solution.The crystal grain size of cerium/iron oxide composites was 12.8 nm.The Fourier transform infrared spectroscopy showed that it was very important to the hydroxyl in the process of adsorption.(3)The results of static adsorption show that the removal rate of hexavalent chromium was 98.93%with the pH=2,Cerium/ferroferric oxide composite additive amount of 0.2 g,the initial concentration of hexavalent chromium of 20mg/L and the adsorption time of 15 min.At the pH<5,the adsorption effect of adsorbent on hexavalent chromium was the best.Increasing the initial concentration of Cr(VI),both the removal rate of hexavalent chromium and the adsorption capacity increased.And the dsorption rate was very fast,the removal rate of hexavalent chromium to maintain the basic adsorption balance after 15min.The SO42-has the greatest effect on the adsorption capacity,and the adsorption capacity decreased obviously in the coexisting system.(4)The second-order kinetic model can describe the process of adsorption of hexavalent chromium by composite materials.At the chromium concentration of 20 mg/L,the equilibrium adsorption capacity of 298K was 6.584mg/g,the equilibrium adsorption capacity of 308K was 6.64mg/g,the equilibrium adsorption capacity of 318K was 6.899mg/g.The activation energy was 3.7989 kJ/mol,and the adsorption process was mainly physical adsorption.(5)The results of adsorption thermodynamics showed that Freundlich adsorption isothermal model can well describe the isothermal adsorption of hexavalent chromium adsorbed by composite materials.The adsorption process belongs to preferential adsorption,and it's a spontaneous,endothermic process.The adsorption heat was 1.636kJ/mol,and the adsorption force was hydrogen bonding force.(6)The results of static saturated adsorption capacity showed that with adding chromium concentration of 20mg/L and different adsorbents(0.01,0.05,0.1,0.15,0.2,0.3g),the adsorbent static saturated adsorption capacity was 13.80 mg/g.(7)Adsorption and desorption experiments showed that using 0.01 mol/L sodium hydroxide to deal with adsorbent,the desorption rate was 80.64%.After three adsorption-desorption experiments,the removal rate of hexavalent chromium was 91%,which maintaining a high adsorption capacity.Cerium/erric oxide composite adsorption of hexavalent chromium was mainly electrostatic attraction adsorption,and the composite material can be recycled several times. |
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