Batch studies on adsorptive removal of Co ions by CoTreat® in acidic media

The kinetics of Co ions sorption on CoTreat® was investigated in the 5–40 mg/L concentration range at a bulk temperature of 30 °C in HNO3 (pH 2.6). A pseudo-second order kinetic model best describes the sorption kinetics at low Co ion concentrations, while a pseudo-first order kinetic model was the best fit at higher concentrations. The equilibrium data were examined using the three models, viz. the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherms. The Langmuir and the D–R isotherms were the best fits to data from which the monolayer sorption capacity (Q0) and mean sorption energy (E) can be determined. The estimated values of Q0 and E were calculated to be 3.20 mg/g and 8.45 kJ/mol respectively at 30 °C. The thermodynamic parameters ∆H° and ∆S° were determined to be + 32.52 kJ/mol and 0.19 kJ/(mol K) in the temperature range 30–60 °C respectively, yielding negative values of the Gibbs free energy (∆G°), indicating the spontaneous nature of the process. The competitive sorption study of Co, Ce, Ru, Sb and Sr ions revealed that the CoTreat® exchanger can effectively remove all the elements concurrently.