An application for nonlinear heterogeneity-based isotherm models in characterization of niobium sorption on clay rocks and granite

Abstract The nonlinear heterogeneous adsorption behaviors of niobium (Nb) on clay rocks (bentonite and argillite) and granite in synthetic groundwater and seawater systems were evaluated by adsorption experiments, applying two heterogeneity-based isotherm models: the Langmuir–Freundlich (LF) and generalized-Freundlich (GF) models. According to the root mean square error (RMSE) between the experimental results and numerical simulation, the two heterogeneous sorption models (LF and GF), which correspond to a different heterogenous constant ( β ), were more adequate than Langmuir models for characterizing the Nb adsorption mechanism. The fitting results demonstrated that the sorption of Nb on granite, bentonite, and argillite exhibited a different adsorption affinity spectrum as a result of the heterogeneous mineral surface. Consequently, the Nb sorption capacity of bentonite and argillite was higher than that of granite and was estimated at 9.24E-01 mmol/g for bentonite, 8.44E-01 mmol/g for argillite, and 2.33E-02 mol/kg for granite.