Patrícia F. Lito

Removal of Anionic Pollutants from Waters and Wastewaters and Materials Perspective for Their Selective Sorption

The presence of some anionic species, such as nitrate, nitrite, chloride, sulfide, fluoride, and cyanide, in water supplies may represent a serious environmental problem. In this work, the main sources and harmful effects of their bioaccumulation on living organisms are reviewed, as well as the most adopted technologies for their uptake. The major advantages and disadvantages of each methodology are also listed. In general, ion-exchange has been elucidated as the most suitable removal process. In view of that the most promising materials used to remove anionic pollutants from aqueous solutions are highlighted in this review. In particular, the major efforts towards the development of low-cost and easily available effective sorbents for water decontamination are covered. For instance, natural waste solid materials and derivatives have emerged as promising low-cost exchangers for selective anions uptake. Besides, a number of structural modifications including the introduction of more suitable surface functional groups or compensation species into the sorbent matrix have been investigated in order to enhance sorbents selectivity and capacity for anionic pollutants. The influence of speciation and removal conditions is also focused.

Ion Exchange Equilibria and Kinetics

The accurate modelling of equilibrium and kinetics of ion exchange is fundamental for economic and safe design of industrial units, particularly to carry out the delicate scale-up studies and simulations.

Metal Recovery, Separation and/or Pre-concentration

Metals are essential for the existence of life. Due to their chemical, physical, electrical and mechanical properties, they found a large number of applications, their use being intrinsically associated with the development of society. Besides their natural occurrence in the ecosystem, the application of metallic compounds in several industrial and agricultural sectors gives an inevitable rise to their release and dispersion into the environment. Accordingly, metallic ions must be separated from water and industrial water or effluents prior to final discharge whenever toxic or radioactive, or recovered in the case of valuable and precious species.

Universal model for accurate calculation of tracer diffusion coefficients in gas, liquid and supercritical systems

In this work it is presented a new model for accurate calculation of binary diffusivities (D12) of solutes infinitely diluted in gas, liquid and supercritical solvents. It is based on a Lennard-Jones (LJ) model, and contains two parameters: the molecular diameter of the solvent and a diffusion activation energy. The model is universal since it is applicable to polar, weakly polar, and non-polar solutes and/or solvents, over wide ranges of temperature and density. Its validation was accomplished with the largest database ever compiled, namely 487 systems with 8293 points totally, covering polar (180 systems/2335 points) and non-polar or weakly polar (307 systems/5958 points) mixtures, for which the average errors were 2.65% and 2.97%, respectively. With regard to the physical states of the systems, the average deviations achieved were 1.56% for gaseous (73 systems/1036 points), 2.90% for supercritical (173 systems/4398 points), and 2.92% for liquid (241 systems/2859 points). Furthermore, the model exhibited excellent prediction ability. Ten expressions from the literature were adopted for comparison, but provided worse results or were not applicable to polar systems. A spreadsheet for D12 calculation is provided online for users in Supplementary Data.

Kinetic Modeling of Pure and Multicomponent Gas Permeation Through Microporous Membranes: Diffusion Mechanisms and Influence of Isotherm Type

The main transport mechanisms involved in pure and multicomponent gas permeation through real microporous membranes are reviewed in this article. They include viscous flow, Knudsen diffusion, bulk diffusion (in mixtures), surface diffusion, and activated gaseous diffusion. The individual contribution of each mechanism may be discriminated from permeation experiments, and can be used to detect the occurrence of defects in the membrane structure. In the case of multicomponent mixtures, the milestone theory of Maxwell–Stefan can be advantageously applied to model the transfer mechanisms embodied. The separation of mixtures can be predicted from data measured for pure gases; here, computer simulations may provide relevant information concerning the loading influence upon diffusivities. With respect to surface diffusion, equilibrium plays a major role in the process, which requires accurate isotherms to compute the corresponding Maxwell–Stefan thermodynamic factors. New single/multicomponent factors are derived here for the first time for Freundlich, Dual-site Langmuir, and Dual-site Langmuir–Freundlich isotherms. The influence of loading upon the surface diffusivities is also addressed, and the most significant theories and approaches adopted to model the phenomenon are discussed.

Modelling ion exchange kinetics in zeolyte-type materials using Maxwell-Stefan approach

AbstractIn this essay, the Maxwell-Stefan (MS) formalism was adopted to model the removal of cadmium(II) and mercury(II) ions from aqueous solutions using microporous titanosilicate ETS-4. The embodied transport mechanism is surface diffusion, since the small pore diameters of such zeolite-type materials imply that counter ions never escape from the force field of the matrix co-ions, mainly owing to the strong and long range electrostatic interactions. The parameters of the global model are the MS diffusivities of ion–ion and ion–solid pairs, and a convective mass transfer coefficient. The average absolute relative deviations (AARD) achieved for Cd2+/Na+/ETS-4 and Hg2+/Na+/ETS-4 systems were only 3.47 and 7.34%, respectively. The model calculates concentration profiles and their evolution along time under transient regime, being able to represent the initial steep branches of removal curves and subsequent transition to equilibrium, where kinetic curves are frequently very difficult to fit. The well-known ...

Maxwell–Stefan based modelling of ion exchange systems containing common species (Cd2+, Na+) and distinct sorbents (ETS-4, ETS-10)

Cadmium(II) is a toxic hazardous cation, whose presence in the environment causes great concern because of its bioaccumulation in organisms and bioamplification along food chain. Hence, the removal of cadmium compounds from industrial waters and wastewaters is particularly essential, which requires intensive experimental and modelling studies to deal with the problem. In this work, the ion exchange of Cd2+ ions from aqueous solution using microporous titanosilicates (ETS-4 and ETS-10) has been modelled using adapted Maxwell–Stefan equations for the ions transport inside the sorbent particles. The fundamentals of the Maxwell–Stefan equations along with correlations for the convective mass transfer coefficients have been used with advantage to reduce the number of model parameters. In the whole, the model was able to represent successfully the kinetic behaviour of 11 independent and very distinct curves of both studied systems (Cd2+/Na+/ETS-4 and Cd2+/Na+/ETS-10). The predictive capability of the model has been also shown, since several uptake curves were accurately predicted with parameters fitted previously to different sets of experimental data.

Comparison between Maxwell-Stefan and Nernst-Planck Equations to Describe Ion Exchange in Microporous Materials

Two models comprising external and intraparticle mass transfer resistances developed to describe ion exchange in microporous materials are compared. Maxwell-Stefan and Nernst-Planck equations account for both concentration and electric potential gradients. However, under certain conditions, Maxwell-Stefan approach can be more advantageous particularly due to taking into account ion-ion and ion-solid interactions separately. The models were tested and compared with data available in the literature, namely batch experiments on cadmium (II) removal from aqueous solution using ETS-4 microporous titanosilicate. Calculated results reveal both models provide good and similar representations as well as fine predictive capability. Therefore, under the conditions investigated, both models can be successfully applied to describe intraparticle ionic transport.