Preparation Of Iron Modified Carbon-based Material And Its Adsorption For Cr(Ⅵ) In Water

Chromium （Cr（Ⅵ）） is a kind of heavy metal element with strong toxicity and lethality,and the problem of excessive Cr（Ⅵ）content in water can not be ignored.The adsorption method has been widely used in the treatment and remediation of Cr（Ⅵ）wastewater because of its advantages of environmental friendliness,wide sources,and low cost.In this study,two carbon-based materials,graphene oxide（GO）and coconut shell activated carbon（CC）are combined with chitosan（CS）by coprecipitation to synthesize GOCS and CSCC,and then Fe-modified graphene oxide/chitosan（α-Fe O（OH）/GOCS）and chitosan/coconut shell activated carbon（Fe/CSCC）materials are prepared with Fe Cl₃·6H₂O as a modifier.On this basis,static adsorption experiments and dynamic column experiments are designed to study the adsorption characteristics of Cr（Ⅵ）on materials,and the adsorption mechanism of Cr（Ⅵ）is revealed by combining the characterization of materials.The main conclusions are as follows:（1）The equilibrium adsorption capacity（Q_e） of α-FeO（OH）/GOCS for Cr（Ⅵ）increases with the increase of iron loading,initial concentration（C₀）,time（t）,and temperature（T）,and decreases with the increase of p H and solid-liquid ratio（m/v）.The Q_e value inhibition degree of anion and cation on Cr（Ⅵ）is SO₄^2->HPO₄^2->NO₃^->Cl^-and Ca²⁺>Mg²⁺>Mn²⁺.The adsorption of Cr（Ⅵ）accords with the quasi-second-order kinetics and is chemical adsorption.The best fitting of Langmuir and Sips models shows that Cr（Ⅵ）adsorption is monolayer adsorption on heterogeneous material,which belongs to spontaneous endothermic reaction.The maximum Q_e value of the Sips model is 62.96 mg/g at 45℃.Combined with the analysis of characterization results,the removal of Cr（Ⅵ）mainly includes the electrostatic and complexing action of Fe-OH and the reduction of C-OH.（2）The Q_e of Fe/CSCC to Cr（Ⅵ）increases with the increase of iron loading,C₀,t,and T,and decreases with the increase of p H and m/v values.The existence of SO₄^2-,HPO₄^2-and Ca²⁺decreased Q_e by 7.82,5.05,and 5.50 mg/g,respectively.The chemical adsorption process of Cr（Ⅵ）on Fe/CSCC is single-layer adsorption of heterogeneous material,and it is also a spontaneous endothermic reaction.The proper temperature increase is beneficial to adsorption.The maximum Q_e fitted by the Sips model is 60.47mg/g at 35℃.Combined with the characterization test results,it is considered that the removal mechanism of Cr（Ⅵ）mainly includes electrostatic attraction and complexation（related to-NH₃⁺and-COOH,respectively）and reduction of Fe-O.（3）In the static adsorption experiment,the adsorption performance ofα-Fe O（OH）/GOCS for Cr（Ⅵ）is better than that of Fe/CSCC.The Q_e of the former for Cr（Ⅵ）is 24.16 mg/g,and the removal efficiency is 97.69%.The latter is 23.71 mg/g and 97.25%.The column experiment results show that the dynamic adsorption capacity(Q_eq)of Fe/CSCC is 94.09 mg/g when the influent Cr（Ⅵ）concentration is 15 mg/L,which is 36.05 mg/g higher than that ofα-Fe O（OH）/GOCS.There is little difference in Q_eq between them at 25 mg/L and 45 mg/L.It is found that Fe/CSCC is more suitable for removing Cr（Ⅵ）with lower concentration.Both of them are suitable at higher concentrations.In the process of use,both materials will not cause secondary environmental pollution.