| The Ce/chitosan/fly ash composite adsorbent?Ce/CTS/FA?was prepared by the reaction of fly ash generated from the Inner Mongolia DaTang International Power Generation Co.,Ltd,chitosan and Ce?NO3?3·6H2O,and the effects of preparation conditions,such as the ratio of raw materials,the order of adding raw materials,stirring time and stirring temperature,on the properities of the adsorbents were investigated.The fly ash and Ce/CTS/FA composite adsorbent were analysed by SEM,EDS,FT-IR,XRD and the specific surface area and pore size to understand furtherly the adsorption mechanism.The Ce/CTS/FA composite adsorbent was used for the removal of direct blue 2B and direct sky blue 5B dyes from aqueous solution.The effects of various important factors on adsorption,the adsorption kinetics and thermodynamics were investigated,respectively.The detailed results are as follow:?1?Firstly,the chitosan/fly ash?CTS/FA?composite adsorbent was obtained by mixing fly ash with 2% chitosan acetic acid solution according to a certain mass ratio?m?FA?:m?CTS?=7.5:1?and stirring for 90 minutes at60?,then when the CTS/FA was mixed with cerium nitrate solution in a certain mass ratio?m?FA?:m?CTS?:m?Ce?=7.5:1:1?,dried at 110? and grinded through a 250 mesh sieve after stirring for 30 minutes at 60?,the Ce/CTS/FA composite adsorbent was obtained and has a good adsorption efficiency for direct blue 2B and direct sky blue 5B with the biggest adsorption capacity are 1134.01mg/g ? 619.53mg/g,respectively.?2?The fly ash and the Ce/CTS/FA composite adsorbent were analyzed by SEM,EDS,FT-IR,XRD and the specific surface area and pore size,the results show that undisturbed fly ash was dispersed spherical particles withsmooth surface and some irregular small particles.Compared with FA,the surface of Ce/CTS/FA was turned into crude,and it was collected among some spherical particles,some spherical particles and a few irregular particles,which made surface and pore size get samller slightly,and Ce and CTS have been loaded on FA successfully.?3?From the experiment results,the best adsorption conditions of Ce/CTS/FA composite adsorbent for the direct blue 2B and the direct blue 5B dyes are as follow: when the dosage of Ce/CTS/FA composite adsorbent is0.1g,the pH value of dyes solution is 2.0 and stirred for 90 minutes with oscillation frequency of 180r/min at room temperature,the adsorption efficiency is best,and the equilibrium adsorption capacities of the direct blue2 B dye and the direct sky blue 5B dye are 1134.01mg/g and 619.53mg/g.The adsorption process of Ce/CTS/FA composite adsorbent for the direct blue 2B and the direct sky blue 5B dyes at different temperatures?298328K?are fit with the pseudo-second-order kinetic equation,and they are extremely significant correlation,overwhile,the second-order kinetics rate constant k2 decreases with increasing temperature,which indicates that the adsorption process is exothermic.From the beginning of adsorption to 60 minutes,the adsorption process of two dyes on Ce/CTS/FA composite adsorbent are mainly controlled by intra-particle diffutsion,but also controlled by extra-particle diffutsion.The values of adsorption activation energies?Ea?obtained by Arrhenius equation are 2.81 kJ/mol for direct blue 2B and 3.14kJ/mol for direct sky blue 5B dyes,respectively.?4?The isothermal adsorption studies of two dyes on Ce/CTS/FA composite adsorbent indicates that the isothermal adsorption experimental data at different temperatures?298K,313 K,328K?,are more accord with Langmuir equation,and the fitting results is extremely significant correlation,the corresponding maximum saturated adsorption capacity at 25? are1111.11mg/g?direct blue 2B?and 625.00 mg/g?direct sky blue 5B?,the values of Langmuir adsorption coefficient b decrease for two direct dyes with increasing temperature,which illustrates that the adsorption process of thedirect blue 2B and the direct sky blue 5B dyes on Ce/CTS/FA composite adsorbent are both exothermic.The separation factor RL defined by Langmuir equation are from 0.0011 to 0.0025 for the direct blue 2B dyes and from0.0025 to 0.0083 for the direct sky blue 5B dye,illustrating the adsorption of two dyes on Ce/CTS/FA composite adsorbent are very easy.?5?From the adsorption thermodynamics results,the thermodynamics free energy change ?G for the direct blue 2B is in the range of-29.66-31.36kJ/mol,enthalpy change ?H is-12.97 kJ/mol,entropy change ?S is 0.057J/mol/K for the direct sky blue 5B,the value of thermodynamics free energy change ?G is in the ange of-28.50-29.80 kJ/mol,the value of enthalpy change ?H is-15.17 kJ/mol and the value of entropy change ?S is 0.044J/mol/K,illustrating the adsorption process of two dyes on Ce/CTS/FA composite adsorbent are spontaneous exothermic process and mainly finished by physical adsorption.The high-efficiency,low-cost,environmental-friendly and large adsorption capacity composite adsorbent,Ce/CTS/FA,was prepared by a simple method,which had a good adsorption efficiency for the direct blue 2B and the direct sky blue 5B dyes,and used successfully for the purification and the treament of dyes waste-water with high concentration. |
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