Adsorptive removal of Cu 2+ and direct sky blue 5B from aqueous solutions by acid treated tea waste—application of response surface methodology

Abstract

A low-cost adsorbent, tea waste was activated by nitric acid and adsorption of Cu 2+ and direct sky blue 5B from aqueous solution was investigated. Response surface methodology (RSM) was used to study the adsorption process. The RSM results showed that temperature and concentration are major factors to modelling Cu 2+ and direct sky blue 5B adsorption, respectively. Higher temperature has a positive effect on the adsorption of Cu 2+ and direct sky blue 5B. Under the same temperature, the adsorption capacity was increased along with the concentration till maximum is attained both for Cu 2+ and direct sky blue 5B. The optimum condition of the RSM for Cu 2+ was determined as following: pH 4.5, 45°C, concentration of 1.5 × 10 –2 mol/L; for direct sky blue 5B, the optimal condition were pH 6.0, 25°C, 1.5 × 10 –2 mol/L. The equilibrium data during adsorption were modeled to Langmuir and Freundlich isotherms for Cu 2+ . For direct sky blue 5B, the equilibrium data were well presented by Freundlich isotherms. The maximum adsorption capacities were determined at 59.88 mg/g for Cu 2+ , 58.27 mg/g for direct sky blue 5B. The kinetic data fit to pseudo-second-order equation well with correlation coefficients larger than 0.99. The results strongly support that tea waste can be used as an economic and excellent adsorbent for the removal of Cu 2+ and direct sky blue 5B from contaminated water.