Abstract. Adsorption can be used as a cost effective and efficient technique for the removal of toxic heavy metals from wastewater. Waste materials with no further treatment such as orange barks from commercial oranges may act as adsorbent for the removal of lead. Batch kinetic and equilibrium experiments were conducted to study the effects of contact time, adsorbent dose, initial pH, particle size, initial concentration of lead and temperature. Three adsorption isotherm models namely, Langmuir, Freundlich and Dubinin-Radushkevich were used to analyse the equilibrium data. The Langmuir isotherm which provided the best correlation for Pb 2+ adsorption onto orange barks shows that the adsorption was favourable and the maximum adsorption capacity found was equal to 112.359 mg.g -1. Thermodynamic parameters were evaluated and the adsorption was exothermic. The equilibrium was achieved less than 30 min. The adsorption kinetic data was fitted with first and second order kinetic models. Finally it was concluded that the lead adsorption kinetic onto orange barks was well fitted by second order kinetic model rather than first order model. The results suggest that orange barks have high possibility to be used as effective and economical adsorbent for Pb 2+ removal.
In the present study, biomass fiber (Luffa cylindrica) has been successfully used as biosorbent for the removal of a cationic dye namely, methylene blue, from aqueous solution using a batch process. The characterization of the biosorbent was carried out by the infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The chemical composition has been established by the energy dispersive X-Ray spectroscopy (EDS). The effects of various parameters such as the contact time (0-160 min), solution pH (2-10), biosorbent dose (0.5-8 g L -1 ), particle size, initial MB concentration (20-300 mg L -1 ) and temperature (20-60°C) were optimized. The biosorption isotherms were investigated by the Langmuir, Freundlich, Dubinin-Radushkevich and Tempkin models. The data were well fitted with the Langmuir model, with a maximum biosorption capacity of 49.46 mg g -1 at 20°C. The kinetics data were analyzed by the pseudo-first-order and pseudo-second-order models. The mass transfer model in terms of interlayer diffusion was applied to examine the mechanisms of the rate-controlling step (R 2 = 0.9992-0.9999). The thermodynamic parameters: free energy (DG°= -5.428 to -3.364 kJ mol -1 ), enthalpy (DH°= -20.547 kJ mol -1 ) and entropy (DS°= -0.052 kJ mol -1 K -1 ) were determined over the temperatures range (20-60°C). The results indicate that Luffa cylindrica could be an interesting biomass of alternative material with respect to more costly adsorbents used nowadays for dye removal.
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