| Montmorillonite(MMT)is a kind of inorganic aluminosilicate mineral material,it has been widely used in industry owing to its abundance and cheapness.It has an advantage in removing the heavy metal ions as a result of high surface area,exchangeable interlayer cations and stable properties.The natural montmorillonite shows a low adsorption capacity to heavy metal ions,therefore,it is essential to study its modified methods and applications.Based on the previous studies about modifying the montmorillonite,in this article,hexadecyl pyridine bromide(CPB)and organic complexing agent ethylenediaminetetraa-cetic acid(EDTA)were used as modified agents,montmorillonite was modified to pr-epare the absorbents to chromium.Two system absorbents about CPB modified mont-morillonite CPB-MMT(CM),CPB and EDTA modified montmorillonite CPB-EDTA-M MT(CEM)were prepared respectively.Potassium dichromate was used to prepare the simulation wastewater which contains the chromium,the removal rate of Cr(VI)in the solution was taken as the evaluation index.The montmorillonite and adsorbent sampl-es were characterized by XRD,BET,FT-IR,SEM and Zeta potential techniques.The optimum preparation conditions were selected by studing different preparation conditio-ns on the quality and adsorption capacity of the adsorbents combining the characteriz-ation results.The absorption process conditions of CPB-EDTA-MMT absorbent were optimized.In the end,the adsorption isotherm and the adsorption kinetics were studied,the experinment and main conclusions are summerized as follows:The CPB-MMT adsorbent was prepared,the experinmental results revealed that the adsorbent CM-5 has the best adsorption capacity when the concentration of CPB was 5 g/L.Combining the result of characterization which concluded XRD,FT-IR,BET,SEM and Zeta potential,it showed that the layer spacing of montmorillonite was increased from 0.95 nm to 1.69 nm,the electric property had changed,the specific surface area was decreased owing to the blockage effect of the pore,the structure of the montmorillonite had not been changed yet.Therefore,the CPB had modified the montmorillonite successfully.In order to improve the adsorption capacity to metal cations,hexadecyl pyridine bromide and organic complexing agent ethylenediaminetetraacetic acid were simultaneously used to modify the montmorillonite,composite adsorbent CPB-EDTA-MMT were prepared,the optimized conditions to prepare adsorbent were:CPB and EDTA modified simultaneously,the solid-liquid ratio was 1.0%,the optimal ratio of nCPB/nEDTA was 1:1,the ultrasonic wave was 90 W.The removal rate of Cr(Ⅵ)counld reach 99.19%,the adsorption capacity was 11.91 mg/g,it increased 4.80 mg/g compared to the adsorbent CM-5.Combining the analysis of characterization which concluded XRD,FT-IR,BET,SEM and Zeta potential,the results revealed that CPB and EDTA had successfully modified the montmorillonite,the layer spacing of montmorillonite was increased from 1.69nm to 2.12nm,the specific surface area decreased to 10.690 m2/g,the pore volume and pore size of CPB-EDTA-MMT were decreased owing to the blockage effect.Appearance of alcoholic hydroxyl bending vibration revealed that the Cr(Ⅵ)was reduced to Cr(Ⅲ)by EDTA,the structure property of montmorillonite had not changed yet.Screening the adsorption condition of the best adsorbent CEM-1/1,the optimized adsorption process conditions were:the adsorption reaction temperature was room tem-perature,the dose of the adsorbent was 2.50 g/L,pH of the simulated chromium con-taining waste water was 6.0,the initial concentration of the simulated chromium cont-aining waste water was 50 mg/L.In the end,the experimental data of adsorbent CEM-1/1 was fitted by two kinds of common isothermal adsorption equation(Langmuir adsorption isotherm equation and the Freundlich adsorption isotherm equation),the results showed that the Langmuir adsorption modle could describe the adsorption process of Cr(Ⅵ)adsorbed on the composite adsorbent better(R2>0.999).The experimental data of adsorbent CEM-1/1 was also fitted by three kinds of dynamics equations(pseudo first order reaction kinetics equation,pseudo second order reaction kinetics equation and particle diffusion model),the results of the kinetics experinment demonstrated that pseudo second order reaction kinetics equation was fit for the adsorption process of Cr(Ⅵ)onto CPB-EDTA-MMT adsorbent,it showed the process of adsorption has chemical sorption.The experimental data of adsorbent CEM-1/1 was fitted by ntraparticle diffusion equation,it showed that the process of adsorption has two parts,the quick adsorption and the unsaturated adsorption,and the rate of the adsorption process was not intraparticle diffusion,but co-determined by the boundary layer diffusion and intrapaticle diffusion. |
