Removal of copper(II) ions from aqueous solution by biosorption onto agricultural waste sugar beet pulp

Dried sugar beet pulp, an agricultural solid waste by-product, was used as an biosorbent for the removal of copper(II) from aqueous solution. A series of experiments were conducted in a batch system to assess the effect of the system variables, i.e. initial pH, temperature and initial metal ion concentration. The results indicated that at 250 mg l−1 initial copper(II) concentration dried sugar beet pulp exhibited the highest copper(II) uptake capacity of 28.5 mg g−1 at 25 °C and at an initial pH value of 4.0. The equilibrium data were analyzed using the Freundlich, Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models depending on temperature. The Langmuir model was found to best describe the data in the concentration and temperature ranges studied. Simple mass transfer and kinetic models were applied to the experimental data to examine the mechanisms of biosorption and potential rate-controlling steps such as external mass transfer, intraparticle diffusion and biosorption process. It was found that the intraparticle diffusion played an important role in the biosorption mechanisms of copper(II), and biosorption kinetics followed pseudo first- and pseudo second-order kinetic models rather than the saturation type kinetic model for all temperatures studied. The activation energy of biosorption (EA) was determined as −58.47 kJ mol−1 using the Arrhenius equation. Using the thermodynamic equilibrium coefficients obtained at different temperatures, the thermodynamic constants of biosorption (ΔG°, ΔH° and ΔS°) were also evaluated.