Mercury removal with titanosilicate ETS-4: Batch experiments and modelling

Crystalline microporous titanosilicates have been recently recognized by their interesting adsorption properties and ion-exchange capability, as well as relatively easy catalytic activation. The aim of this work is to evaluate the ability of titanosilicate ETS-4 to uptake Hg2+ from aqueous solutions, assessing their potential as decontaminating agents for waters, and model the ion-exchange process.Batch stirred tank experiments were carried out by contacting a fixed volume of solution with known masses of ETS-4 in order to study the equilibrium and the kinetics of this unit operation. The evolution of Hg2+ concentration along with time was obtained by sampling and measuring solution concentration by cold vapour fluorescence atomic spectroscopy.With respect to equilibrium, Freundlich isotherm provides good representation in the range of experimental conditions studied.A mathematical model based on the Nernst–Planck approach was developed to describe the ion-exchange process. The model combines both intraparticle and film resistances to mass transport, and involves three parameters: the self-diffusivities of Hg2+ and Na+, and the convection mass transfer coefficient. The resulting ordinary differential equations have been solved numerically using the method of lines and integrated by the finite-differences method. The deviations found are remarkably small, AAD = 2.69% for 47 data points, laying well inside the experimental accuracy (5–8%). The predictive capability of the model has been also tested, using the parameters correlated in this work to simulate data from literature; the good results obtained confirmed that feature of the model (AAD = 6.78%).