Removal of Cd(II) from aqueous solution by exploring the biosorption characteristics of gaozaban (Onosma bracteatum)

Onosma bracteatum biomass showed excellent sorption in removing toxic Cd(II) from aqueous solution. Various parameters such as effect of pH, contact time, temperature, and initial concentration were investigated using batch process to optimize conditions for maximum sorption. It was found that optimum sorption occurred at pH 3.8. The experimental data were modeled by Langmuir, Freundlich and Dubinin–Radhuskevic (D−R) isotherm models and the Langmuir isotherm model was found to be best fit at all temperatures. The mean sorption free energy derived from the D−R equation was 10.67 kJ mol−1. The kinetic studies indicated that pseudo-second-order model was better obeyed. The activation energy (Ea) calculated from Arrhenius equation was 87.530 kJ mol−1. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were also calculated and it was found that sorption of Cd(II) was endothermic. The breakthrough and exhaustive capacities were 46.2 and 99.0 mg g−1, respectively.