Abstract
This study evaluated the potential use of the D301 anion exchange resin for separating molybdate and tungstate ions from standard solutions.It was found that tungstate sorption reaches 90% of its equilibrium capacity within 5 minutes, whereas for molybdate, this level is reached after 35 minutes.The sorption kinetics of molybdate follow the pseudo-second-order model, whereas the behavior of tungstate can be described by both the pseudo-first-order and pseudo-second-order models.The resin was saturated with molybdate ions at an initial concentration of 1 g Mo/L, while for tungstate, this value was five times higher, i.e., 5 g W/L.At saturation, the maximum sorption capacity was 85 ± 5 mg Mo/g (0.89 ± 0.05 mmol Mo/g) for molybdate and 364 ± 9 mg W/g (1.98 ± 0.05 mmol W/g) for tungstate.The Langmuir and Redlich-Peterson adsorption isotherm models indicate a uniform adsorption process of molybdate.On the other hand, the Sips adsorption isotherm model explains a heterogeneous pathway with a low affinity for the tungstate adsorption process.The Gibbs free energy calculated from the isotherms was -18.7 kJ/mol Mo for molybdate and -7.4 kJ/mol W for tungstate.The sorption of molybdate is endothermic with a positive entropy change, whereas the sorption of tungstate is exothermic with a negative entropy change.