Studies in separation engineering have been focused on the following areas: i) cyclic adsorptive separations for purifying amino acid solutions; ii) integration of ion-exchange and nanofiltration for separating and recovering valuable metals from industrial effluents; iii) separation of macromolecules by ultrafiltration and ii) dioxide sequestration through the carbonation process using magnesium silicate minerals.
Adsorptive Processes (adsorption/ion-exchange). Experimental work has been performed with the objective to gather basic information useful for the design of industrial fixed bed systems. The experimental methodologies include the determination of equilibrium isotherms for adsorbents and resins pre-selected and kinetic studies for evaluating the dynamic behavior of the processes in column tests. A rigorous mathematical model which takes into account axial dispersed plug flow, external and intraparticle mass transfer resistances, as well as non-constant selectivity coefficient data, has been successfully applied to simulate the experimental breakthrough curves. The application of ion-exchange resins for the recovery of trivalent chromium from electroplating effluents and amino acid separations have been extensively investigated. Parametric pumping separation technique, where the bed is exposed to alternate adsorbing and nonadsorbing conditions determined by the pH change synchronized to changes in flow direction, has been addressed for separating two amino acids with similar isoelectric points (phenylalanine and Tyrosine).
Membranes Technologies (ultrafiltration/nanofiltration). The modeling of mass transfer phenomena in binary separations using ultrafiltration (UF) membranes has been addressed with a modified Maxwell-Stefan model. This approach is essential for the efficient design and optimization of UF processes applied in food and biotechnology industries. Nanofiltration (NF) membranes have been employed for the treatment of the concentrated waste (chromic acid solution) coming from the column regeneration allowing thus to permeate the acid for reuse in other regenerations steps and to recover the chromium in the retentate stream. NF experiments are performed in a laboratory cross flow filtration system with a flat membrane operating in batch mode. The effect of operating variables (the transmembrane pressure, cross-flow velocity, feed solution concentration, feed solution pH and temperature) on the retention factor of the membrane has been investigated. A Donnan steric partitioning pore and dielectric exclusion model based on the extended Nernst–Planck equation has been useful for describing experimental rejections of the ionic species in solution.
Hybrid separation techniques. The integration of ion-exchange and nanofiltration processes has been investigated for separating and recovering valuable metals from industrial effluents. This approach results in synergetic effects that supported by methodologies using a well-balanced experimental design and simulation and/or modelling tools enables to achieve better recovery efficiencies. Future research studies will be focused on the integration of ion-exchange and membrane processes for sea water desalination and recovery of proteins from the by-products produced in the whey manufacture. The integration of separation methods, namely solvent extraction and ion-exchange will be also assessed in the case of the treating of spent batteries.
Carbon dioxide sequestration by mineral carbonation has been developed in cooperation with Åbo Akademi University, in Finland. Experimental work involving the extraction of magnesium from silicate rocks (serpentinite) with ammonium sulfate have been carried out under proper conditions. Portuguese serpentinite rocks were tested and the results compared with those previously obtained with Finish minerals. Future work in this field will be directed to maximize the conversion of CO2 to carbonate and minimize energy consumption of the overall process using Aspen Software.