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Die Vergroserung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 – 10 μm) stellt eine erhebliche Herausforderung fur die Forschung dar. Ein moglicher Prozessansatz zur Verbesserung des Sortierergebnisses ist die Flussig/Flussig-Flotation. In dieser Studie werden Aussagen bezuglich Anwendbarkeit und Prozessverhalten dieses Ansatzes in Abhangigkeit von ausgewahlten Prozessparametern an verschiedenen Modellpartikelsystemen prasentiert. Increasing the range of application of separation processes to effectively separate ultrafine particles (0.1 – 10 μm) represents a significant research challenge. A possible process approach to enhance the separation result is two-liquid flotation. In this investigation, conclusions regarding the applicability and the process behavior of this approach are presented for different model particle systems with respect to selected process parameters.

The focus of this research is a new type of particle extraction process for the transfer of magnetite nanoparticles from an aqueous to an immiscible organic phase, directly through the liquid-liquid phase boundary in a drop column. The particle extraction process comprises several advantages such as a minimum amount of stabilizing surfactant, no exposure of the particles to a gas atmosphere and with it the avoidance of sintering by capillary forces and a high particle concentration in the receiving phase as well. The study presents experimental results of the characterization of the process environment and the transfer behavior in a drop column. The solution of surfactant in the continuous phase has been investigated during a particle-free phase transfer experiment including the measurements of the total organic carbon (TOC) content and analysis of the size of the stabilized droplets using the laser diffraction spectroscopy. The determination of the transfer fluxes, the mass flows as well as the yield of transferred magnetite by ICP-OES measurements provide information on the impact of interaction of the elementary processes at the phase boundary. Furthermore, the transfer kinetics of the process is described and compared with calculated theoretical values resulting from a kinetic approach.

Because of the large surface area of colloids interface effects are dominant in contrast to volume effects. The study presents experimental results of the direct transfer of magnetite nanoparticles from an aqueous to a non-miscible organic phase. The starting point is a water-based colloid that is synthesized through a precipitation reaction. The transfer is based on the adsorption of surfactants onto the particle surface at the liquid–liquid interface. While penetrating the liquid–liquid interface, the particles are covered with surfactants and a partial de-agglomeration is initiated. The intention is to produce a stable organic colloid, which has important applications in industry. The optimized process parameters for the successful phase transfer process, the adsorption reactions at the liquid–liquid interface and the stabilization of primary particles in the organic phase are demonstrated.

The fatty acid stabilization of magnetite nanoparticles is important for a broad field of studies and applications. In numerous previous studies TGA analyses are applied to investigate these compounds and draw conclusions such as magnetite concentration and surface grafting densities of the chemisorbed molecules. There are however deviations in interpretation of the analysis results. In the presented work we contribute to the discussion on the inert gas decomposition of the fatty acid ricinoleic acid adsorbed on the surface of magnetite nanoparticles with a priori knowledge of magnetite concentration. We report on impacts of autoxidation of the fatty acid as well as significant reduction of magnetite from carbonaceous residues. The findings are based on subsequent gas analysis with FTIR coupled to the TG device. We show how stoichiometric calculations on the reduction in the temperature range of 600–900 °C let conclude that the residues are most probably from the chemisorbed fatty acid molecules. Only the physically adsorbed fatty acid molecules have decomposed or detached before 600 °C. In context to the investigations on chemically adsorbed fatty acid on magnetite we compare the decomposition of pristine fatty acid and fatty acid physically adsorbed on a high surface area SiO 2 nanopowder. Three distinct steps of decomposition which have often been reported before are found and accounted.

The emphasis of the study presented is on a new process of particle extraction to transfer magnetite nanoparticles from an aqueous into an immiscible organic phase directly through the liquid-liquid interface. For the production of high-quality organosols, stabilized colloidal and functionalized particles are required in a liquid organic phase. The mechanism of phase transfer is initiated by adsorption and chemical binding of surfactants (fatty acids) at the particle surface. The resulting physico-chemical dispersion of the hydrophobically modified particles leads to the formation of the stabilized organic colloid, or organosol. The aim here is to demonstrate the entire chain of the transfer process in a continuous miniplant, which comprises particle synthesis, conditioning, and transfer, and which uses a drop column for extraction and as a transfer device. Based on the investigation of the governing principles and the material parameters, the results obtained for the transfer kinetics in the individual contact devices (centrifuge, single-drop column, and drop column for different operations) are used for the dimensioning of the entire process chain.