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Abstract: The present study reports the assembly and operation of a fixed bed using the microporous titanosilicate ETS-4 as sorbent. Sorption–desorption cycles were carried out on an ETS-4 fixed-bed, for the removal of Hg2+ from contaminated water. The sorption capacity of the ETS-4 in the column in two consecutive cycles remained constant (33.6 and 33.3mgg−1, respectively); however due to certain difficulties encountered during ETS-4 packaging and operation mode, breakthrough curves corresponding to these cycles showed dissimilar patterns. A concentration gradient of an EDTA-Na2 solution (0.05–0.25M) was efficient for bed regeneration, achieving an elution efficiency of 98%. The elution curve had an asymmetrical shape, the concentration peak was attained in less than 5min, and the concentration factor was 920. Four kinetic models, namely Thomas, Bohart–Adams, Clark and Yoon–Nelson, were applied to predict the breakthrough curves and to estimate the characteristic parameters of the column, which are the basis for the process design at a real scale. The operation of an ETS-4 fixed-bed for the treatment of Hg2+ contaminated waters was shown to be feasible, despite some limitations mainly related with its loose packing. [Copyright &y& Elsevier]

Abstract: The synthetic microporous titanosilicate material ETS-4 has been used for the removal of Hg2+ and Cd2+ from water. Batch stirred experiments were carried out to study the equilibrium and the kinetics of the removal of Hg2+ and Cd2+ from water. It has been demonstrated that ETS-4 has a great affinity for both these metal cations even when their initial concentrations are low. The uptake rates for both Hg2+ and Cd2+ were well described by the pseudo-second order model which constants confirmed that the kinetics of the removal of Cd2+ is faster than that of Hg2+. However, at the equilibrium, ETS-4 has a higher capacity to remove Hg2+ than Cd2+. Adsorption isotherms for both Hg2+ and Cd2+ were well fitted to Langmuir isotherm and the corresponding monolayer capacities of ETS-4 are 0.43 and 0.24µmol mg-1, respectively, which are quite consistent with those predicted by the pseudo-second order kinetic equation. Hence, the contribution of this work is to support the use of this material for the removal of Hg2+ and Cd2+ from water. [Copyright &y& Elsevier]

Abstract: Batch stirred tank experiments were carried out to study the application of ETS-4 microporous titanosilicate for Hg2+ ions removal from aqueous solution. The effect of operational conditions was assessed and it was proved that Hg2+ uptake (%) increases with increasing contact time, increasing ETS-4 mass and decreasing initial Hg2+ concentration. It was confirmed that stirring rate does not affect the Hg2+ removal by ETS-4 as long as it is high enough to break the diffusion resistance. Two simplified models, the pseudo first-order and the pseudo second-order equations, were used to describe the kinetics of the sorption process and better fittings were obtained by the last one. The Bt versus t plots indicated that film diffusion is the rate-limiting step of the removal of Hg2+ by ETS-4. Langmuir, Freundlich and Dubinin–Radushkevich isotherm equations fitted quite well the equilibrium data and the Langmuir maximum capacity of ETS-4 was found to be 246mgg−1 at 21°C. [Copyright &y& Elsevier]

Abstract: 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%). [Copyright &y& Elsevier]