Application of composite adsorbents prepared from waste PS and PET for removal of Cr and Cu ions from wastewater

In this study, waste polystyrene and polyethylene terephthalate were used to prepare efficient adsorbents by incorporating with bentonite clay and biochar, for removal of Cr and Cu ions from wastewater. In waste polymers as matrix, biochar and bentonite clay were incorporated as fillers in different compositional ratios to prepare biochar/bentonite/waste polystyrene (wPS/C/Bt) and biochar/bentonite/waste polyethylene terephthalate (wPET/C/Bt) composites. The composites were characterized by SEM, specific surface area analysis and FTIR analysis. The optimum conditions for maximum adsorption of Cr6+ and Cu2+ ions from aqueous solution on the wPS/C/Bt and wPET/C/Bt composites were found to be: pH 3 for Cr6+ and pH 6 for Cu2+, contact time of 90 min, temperature 60 degrees C, adsorbent dose of 0.20 g and Cr6+ and Cu2+ ions concentration of 30 mg/L. The concentration of Cr6+ and Cu2+ ions was determined by atomic absorption spectrophotometer and the adsorption efficiencies of the composites were calculated under optimal condition. Results shown that maximum removal of Cr6+ and Cu2+ ions from aqueous medium attained over wPS/C/Bt adsorbent was 77.56% and 79.80%, respectively, while that of wPET/C/Bt adsorbent was 90.10% and 86.30%, respectively. Adsorption kinetics was studied using different kinetics models, the results were also evaluated by applying various adsorption isotherm models. Kinetic study shows that the adsorption of Cr and Cu ions follows pseudo-second-order kinetics. The experimental data best fitted to both the Langmuir and Freundlich isotherm model. The values of thermodynamic parameters such as entropy (Delta S degrees), Gibbs free energy (Delta G degrees) and enthalpy (Delta H degrees) show that the adsorption process is feasible, spontaneous and endothermic in nature. This investigation demonstrated that the novel composite wPET/C/Bt has a large potential for the removal of Cr6+ and Cu2+ ions from industrial wastewater.