Preparation of novel biosorbents from various agricultural wastes for removal of some dyestuffs and heavy metals from aqueous solutions and their characterization

In this study, for the purpose of contributing to the literature, some domestic wastes such as parsley stalks, cucumber peels and watermelon seed hulls were used as novel biosorbents. Inorder to test the adsorption capabilities of the biosorbents, methylene blue (cationic), reactive black 5 (anionic), direct blue 71 (anionic), copper and lead that have different ionic characterswere used as adsorbates. To optimize the removal efficiencies, the effects of solution pH, biosorbent dose, adsorbate initial concentration, temperature and ionic strength were studied. Asreactive black 5 and direct blue 71 are anionic dyes, the biosorption of these dyes were too low. Hence, in order to enhance the adsorption of reactive black 5 and direct blue 71, the biosorbent surfaces were modified chemically. Kinetic and isotherm studies were carried out for modelling the adsorption kinetics and equilibrium. The kinetic data were evaluated using common kinetic models such as pseudo first order, pseudo second order and intraparticle diffusion models. Rate parameters and correlation coefficients were determined. Correlation coefficients were taken account of determining the kinetic model. Isotherm data were evaluated using Langmuir and Freundlich isotherm models and isotherm parameters and correlation coefficients were determined. Also, Langmuir constants and Van?t Hoff equation were used to calculate the thermodynamic parameters such as free enthalpy, enthalpy and entropy. In order to highlight the adsorption mechanism of the contaminants on the biosorbents, surface functional groups were determined by FTIR, surface morphologies were analyzed by SEM technique before and after adsorption. Also, point of zero charges were determined. In addition, desorption studies were carried out by water and different acid and bases for recovery of the contaminants. Experimental studies indicated that, the biosorbents used in this study could be used as low cost adsorbents for removal of cationic dyes and heavy metals such as copper and lead. Futhermore, the experimental studies pointed out that, in order to remove the anionic contaminants, the surfaces of the biosorbents must be modified.