Research On Preparation Of Iron-doped Activated Carbon And Adsorption Of Arsenic(?) In Water

Arsenic?As?is a widely distributed element with high toxicity,which causes great harm to human's nervous system,respiratory system,cardiovascular system,etc.,and hinders animal development and plant growth.With the rapid development of industrialization,arsenic pollution in groundwater has become more and more serious,which is now a major environmental problem.Based on the development and utilization of environmental functional materials,a new iron-doped activated carbon?FGAC?adsorbent was prepared in this research,and the adsorption performance and mechanism of As???were fully discussed.The results indicated that the optimal preparation condition of iron-doped activated carbon was:first soak the granular activated carbon?GAC?for 24 h with 0.01 mol/L NaOH solution to prepare base-treated activated carbon?BGAC?;then infiltrate 1 g BGAC with 0.2 g FeSO₄·7H₂O and 0.8 mL NaClO at 35?;finally treat the material with 4-h freeze drying.The obtained FGAC had an iron content of 3.49%with numerous iron oxide clusters distributed unevenly in the pores,and the specific surface area and pore volume were 1083.86 m²/g and 0.232 cm³/g,respectively.The FTIR spectrum showed that the intensity of O-H peak was obviously enhanced after iron loading,which might be generated by the vibration of O-H of the doped iron oxide.The XRD pattern suggested that the loaded iron was mainly in an amorphous form,and the preparation process destroyed the original crystal structure of BGAC.As???could be well removed by FGAC in the pH range of 4¹0,,and the doped iron was nearly free of leaking.When the reaction proceeded to 1380 min,the adsorption amount of As???hardly changed,and the balanced adsorption capacity was0.9452 mg/g.When the temperature was raised from 25?to 45?,the uptake of As???increased a little.Both Ca²⁺and Mg²⁺promoted the adsorption of As???,but the promotion of Ca²⁺was somewhat stronger than that of Mg²⁺;NO₃^-and SO₄^2-had no influence on the adsorption performance of FGAC,while CO₃^2-,SiO₃^2-and PO₄^3-exhibited inhibition following the sequence PO₄^3->SiO₃^2->CO₃^2-;in the above ionic environment,the loaded iron manifested strong stability.NOM could prevent the adsorption of As???by FGAC,but the iron on it was able to resist the impact of NOM in water.The Lagergren pseudo-second-order equation was more suitable for describing the adsorption kinetics of As???by FGAC;the reaction rate was mainly controlled by external diffusion rather than internal diffusion;the adsorption process was divided into three stages,and the first and third stages were adsorption rate controlling steps.The Langmuir adsorption isotherm could better fit the adsorption thermodynamics,and the process was endothermic,entropy-increasing and spontaneous.The adsorption-desorption experiment showed that the desorption proportion of As???was not high,suggesting the difficulty of adsorbent regeneration.The bed volume at the point when the effluent concentration of As exceeded 10?g/L in the column test reached 3054,indicating that FGAC had excellent dynamic adsorption properties;meanwhile the doped iron remained fairly stable throughout the period.According to the characterization results of FGAC before and after adsorption,it could be further demonstrated that the adsorption mechanism included electrostatic interaction and complexation,and the complexation might occur among As???and several iron particles.Fe was mainly loaded on FGAC in the form of hydrated iron oxide,and Fe accepted electrons in the adsorption process;As was adsorbed on FGAC mainly in trivalent form.In the adsorption system only existed the weak oxidation of As???by DO,and other types of oxidation or catalytic oxidation were not observed.