Research On The Preparation Of Iron-coated Activated Carbon Adsorbent And Adsorption Mechanisms Of Arsenic

Arsenic is a widely distributed toxic element, the toxicity of which on humanhealthy shows in two aspects：acute toxicity and chronic toxicity caused by long-termaccumulation. Arsenic pollution has become a big environmental problem. To findnew environmental materials to adsorb As（Ⅴ） which are of high adsorption efficiencyand suitable for practical application, we prepared a high effective iron-coatedactivated carbon adsorbent（Fe-GAC）, studied its adsorption properties in removingarsenic, and discussed its adsorption mechanism.The results showed that the best preparation condition for Fe-GAC Weremodified GAC in0.5mol/L FeCl2solution oxidized by NaClO for24h and90℃aged.The loaded iron content is10.13mg/g. Fe-GAC had apparent pore structure, bigspecific surface area of330.765m²/g. Its surface attached to a lot of lamellar structure;FT-IR spectrum showed characteristic peak in1118cm^-1,890cm^-1and794cm^-1whichcorresponded to FeOOH; XRD spectrum analysis showed that loaded iron was mainlyin the form of amorphous type; XPS spectra analysis indicated that the iron Fe2pbinding energy belongs to the category of FeOOH, suggesting that loaded Fe ofFe-GAC mainly existed in the form of iron oxide hydrate.The reaction equilibrium required480minutes’ adsorption and the maximumAs（Ⅴ） adsorption capacity was3.14mg/g; In a wide range of the initial pH=3⁸, theAs （Ⅴ） removal rate achieved above90%, and under the neutral partial acid conditionthe adsorption effect of Fe-GAC was the best, at that moment As （Ⅴ） in anionicforms and adsorbent was positively charged. The As （Ⅴ） removal rate had beeninvestigated with three kinds of cation existing respectively, the promotion effect frombig to small was: calcium> magnesium ions>sodium magnesium ions; In coexistinganions，chlorine ion, fluorine ion,sulfate ion and nitrate ion, made no removal ratedifference; phosphoric ion, silicate ion and carbonate ion inhibited As （Ⅴ） adsorbedby Fe-GAC, and inhibition effect from big to small was: phosphate ion> carbonateion> silicate ion.The Lagergren secondary dynamics equation can well describe the adsorptiondynamics process which As absorbed by Fe-GAC, R2>0.99. Freundlich adsorptionisotherm fitted the adsorption dynamics process well when1/n value between0.1⁰.5,which means that the adsorption in solution can easily occur. Langmuir adsorptionisotherm fitting was better than that of the Freundlich adsorption isotherm with the R2=0.999. This adsorption reaction is a endothermic and spontaneous reaction,chemical adsorption plays a major role in the reaction,while physical adsorption playsa subsidiary role.The reaction rate is mainly controlled by liquid film diffusion. Using6%sodium hydroxide solution to desorb and regenerate the adsorbed Fe-GAC, theresults showed that the regeneration property of Fe-GAC was good.To contrast the pre-and post adsorption characterization of spectrums, it is furtherproved that the coated iron in Fe-GAC is loaded in the form of hydrated ferric oxideand the mechanism of As（Ⅴ） adsorption mainly is electrostatic adsorption andcoordination complexation, hydrated ferric oxide can react with arsenic acid radicalions to form hydrated ferric oxide coordinate complex.