Preparation Of CTS/LCM/FA Composite And Its Adsorption For Direct Dyes From Aqueous Solution

The high-polluting characteristic dye waste water discharged from the printing and dyeing industry has always attracted the attention of environmental researchers.Fly ash?FA?is an industrial solid waste with adsorption function and has extensive application in water treatment.A novel composite material,CTS/LCM/FA composite was prepared by loading a small amount of Chitosan?CTS?and light calcined magnesia?LCM?on FA and applied to the adsorption of direct fast blue GL and direct fast black G.The CTS/LCM/FA composite and FA were characterized by SEM,XRD,FT-IR and UV-Vis DRS.Adsorption properties,adsorption kinetics and adsorption thermodynamics of CTS/LCM/FA were studied.At the same time,the regeneration performance of the CTS/LCM/FA was investigated.The main results are as follows:?1?CTS/LCM/FA composite was prepared using the simple solution reaction method.Optimized preparation conditions were studied.First,FA and 25mL CTS solution dissolved by 5%acetic acid solution?in according to the mass ratio 12.5:1 of FA to CTS?were mixed and stirred for 60min at room temperature.Second,powdery LCM was added to the mixture by the mass ratio of CTS:LCM:FA=1:4:12.5,and continued to be stirred for40min.The obtained object was further dried and ground over 250 mesh sieve and the CTS/LCM/FA composite was synthesized.The composite was used for removing two kind of direct dyes from aqueous solution.It is found that the adsorption performance of the CTS/LCM/FA for dyes is significantly better than those of FA,CTS,CTS/FA and LCM/FA.?2?The effects of some important factors such as initial concentration of direct dye,oscillation frequency and the solution pH value on dye adsorption onto CTS/LCM/FA were investigated.The optimum adsorption conditions were obtained.The adsorption capacity and removal rate of CTS/LCM/FA for 800mg/L direct fast blue GL were 180.4mg/g and 90.2%respectively at 25?and adsorbent dosage of 0.1g.The optimal adsorption condition to 600mg/L direct fast black G of CTS/LCM/FA were the dosage is 0.12g,the adsorption capacity and removal rate were 113.6mg/g and90.9%respectively.?3?Results of adsorption kinetics show that the adsorption processes of CTS/LCM/FA for two kinds of direct dye have fast adsorption rate at different temperatures?298K,313K and 328K?and adsorption can reach the basic equilibrium in 30min.The pseudo-second-order adsorption model can describe the adsorption process?R²?0.9998?well.The second-order kinetics rate constant k₂ increases with increasing temperature,indicating the endothermic property of the adsorption.The values of adsorption activation energy Ea of CTS/LCM/FA for the direct fast blue GL and direct fast black G are 27.32kJ/mol and 18.75kJ/mol,and the adsorption has physical adsorption characteristics.In addition,the fitting results of intra-particle diffusion model indicate that intra-particle diffusion is involved in the adsorption process but not the only rate-controlling step.?4?The results of isothermal adsorption studies of two direct dyes by CTS/LCM/FA show that the Langmuir model can well describe the adsorption behavior of direct fast blue GL and direct fast black G on CTS/LCM/FA?R²?0.9918?at different temperatures?298K,313K and328K?.The values of Langmuir adsorption coefficient b increase with increasing temperature.This indicates the endothermic property of the adsorption process.The separation factor R_L calculated by Langmuir equation are less than0.1,and the 1/n values obtained from the Freundlich model are between 0.1 and 0.5,illustrating that the adsorption of two acid dyes on CTS/LCM/FA is easy to occur.Dubinin-Radushkevich?D-R?model was used to investigate the adsorption behavior of direct dyes,and values of the average adsorption energy are in the range of 14.43²2.36kJ/mol at different temperatures,indicating that the adsorption has chemical adsorption characteristics.?5?Adsorption thermodynamic results show that the negative values of the free energy change?G,positive values of enthalpy change?H and entropy change?S for direct fast blue GL and direct fast black G adsorption on CTS/LCM/FA at different temperatures?298K,313K and328K?illustrate that the adsorption reactions of two dyes have spontaneous and endothermic nature.?6?The results of recycling performance show that the CTS/LCM/FA adsorbent saturated by direct fast blue GL and direct fast black G can be regenerated using NaOH solutions of 0.01mol/L and shaking 2h at room temperature and the first regeneration rate are 100%and 95.1%respectively.The adsorbent can be regenerated four and one times,respectively.?7?Combined with the characterization results of CTS/LCM/FA and FA,the adsorption mechanism was investigated.The CTS/LCM/FA composite adsorbent and FA were characterized by SEM,EDS,XRD,UV-Vis DRS and BET surface analysis.The results shows that CTS and LCM have been loaded on FA successfully,and the surface morphology of CTS/LCM/FA changes and its surface area and pore size is less than those of FA.Through analyzing change of the FT-IR and UV-Vis DRS before and after dyes adsorption on CTS/LCM/FA,the adsorption of the two direct dyes by CTS/LCM/FA has both physical and chemical adsorption characteristics.