Analysis of temperature-dependent biosorption of Cu2+ ions on sunflower hulls: Kinetics, equilibrium and mechanism of the process

The waste material originating from food industry, i.e. sunflower hulls was used for the biosorption of heavy metal ions (Cu2+) from aqueous solutions. A series of kinetic and equilibrium experiments has been conducted at various temperatures (20-55 degrees C). The results of the kinetics have been presented in the form of various models based on the order of reaction or diffusion. Equilibrium experimental points have been described by means of four isotherms. The sorbent showed the maximum sorptive capacity amounting to 57.14 mg g(-1) at 30 degrees C and pH 5.0. The analysis of the results yielded by the experiments shows that binding of Cu2+ ions is a complex and multi-stage process. While copper ions are bound, the ions of light metals, such as Na, K, Mg, Ca, are released. The analysis of the thermodynamic parameters showed that the process is spontaneous, feasible and endothermic within the set temperature range (20-50 degrees C). The application of a temperature higher than 50 degrees C negatively affects the sorptive capacity, which may be put down to the damage caused to the structure of the biosorbent. (C) 2012 Elsevier B.V. All rights reserved.