The Study Of Adsorption Of Methylene Blue And Basic Fuchsin Onto Lotus Leaf From Aqueous Solution

Color wastewater discharged into water might cause various environmental problems. The low cost biomass material lotus leaf was firstly used as an adsorbent for the removal of cationic dye from aqueous solution. The dyes selected for the present study were methylene blue (MB) and basic fuchsin (BF). The potential of lotus leaf for the removal of MB and BF from aqueous solution was investigated. The batch and fixed-bed column experiments were discussed.The batch experiments were performed under various conditions including contact time, adsorbent dose, initial MB concentration, solution pH, salt ionic strength and temperature. The batch experiments indicated that 4 h was seen as the adsorption equilibrium time and adsorbent dose of 1 g/L was found to be the optimum concentration for the adsorption of methylene blue and basic fuchsin. The maximum monolayer adsorption capacity of lotus leaf for MB and BF were found to be 221.7 mg/g and 117.5 mg/g at 293 K, respectively. The influence of Ca2+ on removal of MB and BF were stronger than Na+. Higher temperature resulted in an increase in the amount of dyes adsorbed onto lotus leaf powder within the range of experimental temperatures. The Langmuir, Freundlich, Temkin, Koble-Corrigan and Redlich-Peterson isotherm models were employed to discuss the adsorption behavior of lotus leaf for MB and BF. The adsorption of MB onto lotus leaf follows the Langmuir and Temkin isotherm models well. Moreover, the adsorption of BF onto lotus leaf follows Langmuir, Freundlich, Redlich-Peterson isotherm models well. As temperatures were within the range of 293-313 K, the thermodynamic parametersΔG for adsorption of MB and BF onto lotus leaf were-25.67,-26.57,-27.74 kJ/mol and-24.28,-25.16,-27.28 kJ/mol, respectively. The results indicated the spontaneous nature and endothermic nature of the adsorption process of lotus leaf for MB and BF, and the increase in temperature was advantage to adsorb MB and BF. The kinetic studies for MB and BF adsorbed onto lotus leaf indicated that adsorption process followed the pseudo second-order mode, suggesting that the adsorption might be chemisorption process, and the boundary layer and intraparticle diffusion may control the adsorption process to some extent.In fixed-bed column experiments, the effects of flow rate, influent concentration and bed height on the breakthrough characteristics of adsorption for MB and BF were discussed. The Thomas and Yoon-Nelson were applied to the column experimental data to determine the characteristic parameters of the column adsorption, the results indicated that Thomas and Yoon-Nelson can describe the column adsorption process of MB and BF well. The bed-depth/service time (BDST) models can predicte the breakthrough time ang the saturated adsorption time, which were consistent with the experimental results.The characteristics of lotus leaf were studied using Brunauer-Emmett-Teller (BET), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential thermal analysis (DTA). The study of the characteristics of lotus leaf helped us to further understand the adsorption mechanism of MB and BF onto lotus leaf.The present study implied that lotus leaf was a promising candidate as low cost biosorbent for the removal of MB and BF from aqueous solution.