Durch den Zusatz von Tensiden kann die Extraktion deutlich beeinflusst werden. Für Tensidkonzentration geringfügig oberhalb der kritischen Mizellbildungskonzentration steigt die Stofftransportrate durch die Bildung inverser Mizellen und eines dadurch verursachten mizellaren Zinkextraktionsmechanismus. Anhand von Extraktionsgleichgewichten und Stoffaustauschuntersuchungen wird die Beeinflussung der Zinkextraktion mit dem Kationenaustauscher Di(2‐ethylhexyl)phosphorsäure (D2EHPA) unter Zugabe des Tensids Cetyltrimethylamoniumbromid (CTAB) aufgezeigt und phänomenologisch erläutert.
Measurements of the interfacial tension as a fundamental component of mass transfer modelling in process engineeringThe interfacial tension is a material parameter describing the interface between two fluid phases. It is also a changing physical value in mass transfer processes beyond equilibrium.Thus, the measurement of change in interfacial tension characterizes adsorption and mass transfer processes at liquid-liquid interfaces. The units of a pendant drop tensiometer can represent a mini mass transfer cell.
Different mass transfer models were evaluated on the basis of zinc extraction with the liquid ion exchanger di(2-ethylhexyl)phosphoric acid. Comparison of the models showed that the film model inadequately describes the time dependence of zinc concentration in aqueous solution. The best match of the measured timeconcentration profiles was achieved by adapting the film-penetration model. Studies were carried out in a stirred cell with a planar interface stabilized by the mixing conditions. Under the chosen experimental conditions mass transfer was limited by zinc transfer in the aqueous phase. The mass transfer equations of each model were solved analytically using empirical correlations for the modeling parameters.
The addition of surfactants can influence extraction processes. In cases where the surfactant concentration is above the critical micelle concentration, the mass transfer rate increases due to the formation of inverse micelles and, thus, through the mechanism of micellar extraction of zinc. The influence of the added surfactant cetyltrimethylammonium bromide on zinc extraction with the cation exchanger di(2-ethylhexyl)phosphoric acid was analyzed based on extraction equilibrium and mass transfer experiments. The observed experimental results are explained phenomenologically.
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