Application of the biochar derived from orange peel for effective biosorption of copper and cadmium in batch studies: isotherm models and kinetic studies

Abstract

Orange peel biochar (OPb) was used as an adsorbent to investigate its potential in the removal of copper (Cu2+) and cadmium (Cd2+). The adsorption data were modeled using different isotherm models and reaction kinetics after optimizing reaction parameters such as solution pH, equilibrium contact time, OPb dose, and initial metal concentrations. Scanning electron microscopy images showed porous and irregular surfaces in OPb prior to the sorption process. Energy dispersive X-ray results depicted successful adsorption of the metal ions. An equilibrium time of 30 min was estimated for low initial metal ion concentrations (25–50 mg L−1). Metal adsorption and removal efficiency increased with an increase in the initial solution pH from 2.5 to 5.5. The adsorption capacity increased as the initial metal concentration varied from 25 to 200 mg L−1; the removal efficiency decreased from 99% to about 41% and 52% for Cu2+ and Cd2+, respectively. A decrease in adsorption capacity with an increase in metal removal efficiency was observed by increasing the OPb dose from 0.2 to 1.4 g. Langmuir and Temkin isotherm models best fit the adsorption data for Cu2+ and Cd2+, with a coefficient of determination (R2) value of 0.85. Other isotherm models fit the adsorption data in the following order: Temkin > D-R > Halsey and Freundlich > H-J and Halsey > D-R > Langmuir > Freundlich > H-J, respectively. The chemisorptive nature of OPb for the adsorption of both ions was suggested based on R2 values close to unity (1.0) in a pseudo-second-order kinetic model.