Study On The Adsorption Of Cr(Ⅵ ) And Cd(Ⅱ) By Fe-Mn Oxides

Heavy metal pollution has a serious negative impact on the ecosystem and human health due to its toxicity,persistence and non-biodegradability.Among these heavy metal pollutions,Cr and Cd have strong mobility and are distributed in both water and soil.Among the many methods of heavy metal removal,the adsorption method was characterized by its operational simplicity and good treatment effect.As an effective absorbent,Fe-Mn oxides have received widespread attention thinks to their advantages of simple preparation,wide source of materials and low ecological impact.Therefore,in this experiment,Fe-Mn oxides adsorbents were prepared by co-precipitation method and studied by batch adsorption experiments on Cr（Ⅵ）and Cd（Ⅱ）The Fe-Mn oxides materials were characterized using TEM,XPS and XRD and fitted by four isothermal adsorption models,Langmuir,Freundich,D-R and Temkin,and four kinetic models,quasi primary,quasi secondary,internal diffusion and Elovich,which led to the following conclusions:（1）TEM characterization showed that the Fe-Mn oxide adsorbent showed granular dispersion and some agglomeration,The elemental composition of the adsorbent mainly included Fe,Mn and O;XRD analysis showed that the structure of the adsorbent was amorphous with low crystallinity.（2）The adsorption experiment of Cr（VI）by Fe-Mn oxide showed that the p H value was negatively correlated with the adsorption capacity of the material;The isothermal adsorption experiment showed that the adsorption test process of Cr（VI）by Fe-Mn oxide was the closest to the Langmuir adsorption model,and the maximum adsorption capacity of Cr（VI）was13.58 mg/g,the monolayer adsorption was dominant in the adsorption process;In the dynamic experiment,the pseudo-second-order dynamics best matches the test results,and the reaction rate constant k₂ was 7.57×10^-4 g/（mg·min）.The adsorption is mainly chemical adsorption.Humic acid 5 mg/g significantly affected the adsorption of Cr（VI）.（3）The adsorption experiment of Cd（Ⅱ）by Fe/Mn oxide showed that the p H value had little effect on the adsorption effect of Cd（II）;Based on the isothermal adsorption experiment,the adsorption of Cd（Ⅱ）by Fe-Mn oxides best matches to Langmuir adsorption model,The adsorption is mainly monolayer adsorption,and the maximum adsorption capacity of Cd（II）was 32.85 mg/g;The kinetic adsorption experiments showed that the experimental results were better fitted by pseudo-second-order kinetics,and the reaction rate constant k₂ was9.4871×10^-5 g/（mg·min）.The adsorption reaction was mainly chemical adsorption.（4）XPS showed that the iron-manganese oxide successfully adsorbed both Cr（VI）and Cd（II）,and the adsorption of Cd（II）relied mainly on Cd-O bonding,while the adsorption of Cr（VI）relied mainly on redox and electrostatic adsorption;It was concluded from the SPSS multiple linear regression model that the adsorption of Cr（VI）was most influenced by the p H of the solution,while the adsorption of Cd（II）was most influenced by the amount of adsorbent dosing.