Predictions of binary sorption isotherms for the sorption of heavy metals by pine bark using single isotherm data

The adsorption of three heavy metal ions by pine bark was studied. The study was divided into two parts; single component adsorption of the metals Cu²⁺, Cd²⁺ and Ni²⁺ and bisolute adsorption of the three binary systems Cu²⁺-Cd²⁺, Cu²⁺-Ni²⁺ and Cd²⁺-Ni²⁺. Extended Langmuir model, extended Freundlich model, Sips model and ideal adsorption solution theory (IAST) models were used to predict the equiblibrium uptake for Cu²⁺, Cd²⁺ and Ni²⁺ in the binary diluted solutions using the single adsorption constants. The experimental data of single isotherm adsorption process were found to follow Langmuir isotherm model with less accuracy than Freundlich and Sips models. Whereas, the predictions of bisolute adsorption isotherms of the mentioned three systems, Cu²⁺-Cd²⁺, Cu²⁺-Ni²⁺ and Cd²⁺-Ni²⁺, showed good agreement with experimental data when using Extended-Langmuir, Extended-Freundlich and IAST. However, the only good fit of the Sips model was with the Cu²⁺-Cd²⁺ system. (C) 2000 Published by Elsevier Science Ltd.