The Study Of Adsorption Of Malachite Green And Auramine O Onto Lotus Leaf From Aqueous Solution

With the extensive application of the dye,the discharge of the coloured effluent will pose a threat to humans and the environment.To find a low-cost wastewater treatment technology has become the research hotspot.In this study,lotus leaf is used as a biosorbent for the removal of malachite green(MG)and auramine O(AO)from aqueous solutions.To identify the optimum adsorption conditions and explore the mechanism of adsorption,the adsorption potential of lotus leaf has been studied by batch adsorption technique and fixed-bed adsorption column experiments.The batch experiments were carried out under different conditions of contact time、dye solution pH、adsorbent dose、initial dye concentration、temperature and salt concentration.The optimum adsorbent dose was found to be lg/L.The optimum contact time for the removal of MG is7h and5h for AO;The temperature showed a positive effect on the removal process;The maximum adsorption capacity of lotus leaf for MG and AO were found to be125.3mg/g and134.3mg/g at316K and318K respectively.The commonly used isotherm models were employed to evaluate the adsorption behavior.The adsorption behavior for MG and AO were best described by the Koble-Corrigan and Redlich-Peterson isotherms.The activation energies for the adsorption of MG and AO were43.51kJ/mol and25.09kJ/mol,respectively.It indicated that the adsorption process of the two dyes were chemical adsorption-based.Thermodynamic parameters of AG were negative,AH and AS were positive,it indicated that the adsorption process was spontaneous and endothermic.The results of kinetics studies of adsorption indicated that Pseudo-second order model could better describe the adsorption process of lotus leaf for MG and AO,the Elovich model and the intraparticle diffusion model could also be used to describe the adsorption process,suggesting that the intraparticle diffusion and film diffusion control may control the adsorption process.In order to optimize the adsorption conditions of the lotus leaf for both dyes,the adsorption of MG and AO from water onto lotus leaf was also investigated using fixed beds adsorption column.The experiments were carried out to study the effects of bed height,feed flow rate and dye inlet concentration on the breakthrough characteristics of the adsorption process.It was found that the lower flow rate and higher lotus leaf bed height could be better performed by fixed beds experiments.The Bed Depth Service Time(BDST),Thomas and Yoon-Nelson models were applied to analyze the column experimental data.Thomas model was found to be suitable for describing the adsorption process at different conditions.Yoon-Nelson and BDST models can predict the breakthrough curves and the coefficients of correlation R2>0.9.The prepared lotus leaf was characterized by fourier transform infrared spectroscopy(FTIR)and scanning electron micro scope(SEM).The surface morphology of the lotus leaf can be seen from the characterization results.It will help us to better understand the adsorption mechanism of lotus leaf.The results of this research indicated lotus leaf may be considered as a natural and low cost biosorbent for elimination of malachite green and auramine O from aqueous solutions.It has laid a theoretical foundation for the industrial application.