| Selenium is an essential element to the human body,the lack of selenium will cause a variety of diseases. Meanwhile, the toxic effect range of selenium is very narrow, a higher concentration will produce toxic effects on the human body, such as the damage to the body's cells,or even threatening to our lifves. The mainly soluble existence form of Se in aqueous solution are selenate( Se O42-) and selenite(Se O32-), both of them are toxic and is easy to release into groundwater with a high level to cause environmental pollutions.Iron manganese ore has a good surface adsorption characteristics, because Fe and Mn are valence-variable matal elements. It has been shown that iron oxide,manganese oxide and Fe-Mn binary oxide can be used for the removal of heavy metal pollutants in sewage. The study of iron manganese ore as a adsorbent has theoretical significance to the environmental remediation. In this paper, the adsorption behavior of Se(IV) on iron manganese ore is studied.First of all, prepared iron manganese ore powder by ball milling and characterized the prepared powders. The results show that main composition of iron manganese ore are Fe2O3 and Mn O2, the BET-specific surface area is 33.9166 ±0.2523 m2/g, the medium particle size D50 is 0.432 um.Secondly, Studied effects of particle size of adsorbent, dosage of adsorbent, p H value,temperature, initial selenium concentration, ionic strength and coexisting ions on the Se(IV) adsorption by iron manganese ore. The adsorption isotherm model and adsorption kinetics were discussed. The surface chemical elements of iron manganese ore after adsorption were analysised through XPS test, the corresponding adsorption mechanism was discussed.(1) The smaller the particle size, the faster the removal rate. Within 72 hours, the initial concentration of selenium was 5.0, 10.0 and 20.0mg/L, the removal rate of Se(IV) by iron manganese ore was 88.65%, 56.23% and 38.54%.(2) In the experimental p H range, the adsorption rate of Se(IV) decreased with p H increased, adsorption optimum p H value range is 2.2~7.1.(3) The adsorption capacity of Se(IV) increased with the increase of the temperature, when the temperature rose to 60 oC, the adsorption capacity decreased slightly, but it is not significant.(4) The influence of ionic strength to the adsorption rate and adsorption capacity is slight, which indirectly inferred that iron manganese ore adsorb Se(IV) with specific coordination adsorption. The effect of CO32- has the most significant on adsorption, the Se(IV) romoval rate is 8%; The effect of NO3- on adsorption is minimum, the Se(IV) removal rate can be up to 97.02%.(5) The adsorption process is more in line with the quasi two stage dynamic model and Langmuir monolayer adsorption isotherm model, the maximum saturated adsorption capacity was 6.76mg/g.(6) The XPS analysis result shows that redox reactions did not occur through the Se(IV) adsorption, and Se(IV) is adsorbed in the form of an inner layer complex formed on the surface of the adsorbent.Finally,eight kinds of desorption agents was studied. Among them, Na OH and Na2CO3 are the best desorption agent, and best desorption effect of Na2CO3 concentration is 0.05mol/L. Under neutral condition, the adsorption of Se(IV) on iron manganese ore is very difficult to desorb,which means the adsorption effect of iron manganese ore is good.According to these studies, we can get a conclusion that iron manganese ore has the best function for the remove of the Se(IV) in aqueous solution, which provide a theoretical and practical basis for the further thorough understanding of the removal of Se(IV) by iron manganese ore. |
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