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Flotation processes are essential processes for resource separation, the monitoring of which can save vast amounts of water and energy. To control them, it is necessary to measure the phase fractions present in the froth. Currently, no suitable measurement method exists that can be easily integrated into the existing process and has a penetration depth of more than 5 cm. Therefore, in this paper we present a measurement system for determining the liquid distribution in foam using ultrasound. To counteract the strong attenuating effect of the foam on the ultrasound, we use low-frequency probes with a center frequency of 135 kHz. Electrodes determine an integral liquid fraction by conductivity measurement. Within a liquid range of 0.17 x 10(exp −2) to 0.82 x 10(exp −2), the measurement system was first calibrated for a penetration depth of 9.2 cm and validated by simultaneous neutron imaging. An absolute and relative measurement uncertainty of 0.23 x 10(exp −2) and 42.5% was the respective result. A resolution of 7.5mm in the axial, 13mm in lateral direction and 1 Hz in time were obtained. In a dynamic inhomogeneous case, the measurement system was additionally validated for a use case. This investigation represents a first step towards process optimization in flotation processes. more...

Flotation is a separation process in which hydrophobic particles inside a liquid bath attach to uprising bubbles, which subsequently form a froth layer on the liquid surface. This froth phase, which consist of foam with particles, has a large impact on the transport of separated materials and therefore the overall process efficiency. Despite the importance for process control, a notable lack of suitable techniques for on-line characterization of the froth’s properties such as the liquid fraction or particle content can be found. An potential approach to gain information on the different phase fractions in froth is the application of low-frequency ultrasound measurement techniques. In this contribution an overflowing froth containing varying mass fractions of Quartz particles and liquid is analyzed using combined optical and ultrasonic measurements. The measured intensity of the ultrasonic reflections sent from above the froth’s surface correlate to the fraction of solids inside the froth (Figure 1). Therefore it is shown, that current optical froth characterization techniques can be improved by incorporating ultrasonic measurements, which can be seen as a first step towards advanced process control in industrial flotation processes. more...

Flotation is an important process in liquid-solid and solid-solid separation, whereby desired solids in suspensions are recovered by their attachment to gas bubbles. Monitoring the process is essential for increased grade of quality and reduced water consumption. However, in situ measurements of the froth’s phases (liquid, air, particles) or volume flow, which is easily integrable in industrial process are not available. In this paper, we propose an instrumentation with ultrasound transducers of center frequency of 135 kHz and electrodes to measure the liquid fraction distribution in foam and froth with high spatio-temporal resolution of 6.65 mm (axial), 13 mm (lateral) and 1 Hz. The measurement system was calibrated in homogeneous, steady foam by an integral conductivity measurement. A backscatter model was applied to reduce the effect of ultrasound shadowing and enhance quantitative liquid fraction estimates. The measurement was validated by neutron radiography. An averaged absolute and relative measurement uncertainty of 0.17 ·10 −2 and 35.1 % for 1 s and 0.08 ·10 −2 and 17.2 % for 100 s measurement was achieved respectively. As an additional validation six cases of inhomogeneous and dynamic liquid fraction distributions were investigated qualitatively. We were able to determine the liquid fraction in froth in a spatially and temporally resolved manner with a penetration depth of 9.2 cm. This investigation distinguished between two of the three froth phases within the analyzed range. However, only processes with low liquid fraction (≤ 0.83 ·10 −2 ) can be monitored. This work be considered a a first step towards in situ monitoring of froth flotation processes. more...

Der Einsatz moderner Meßtechnik kann einen wesentlichen Beitrag für den ressourceneffizienten Betrieb von Anlagen für die Schaumflotation leisten. Insbesondere die Kenntnis der Stoffzusammensetzung des überströmenden Schaums kann hilfreich für die optimierte Echtzeit-Steuerung des Flotationsprozesses sein. Aufgrund der komplexen und lichtundurchlässigen Struktur der Schaumphase existieren zum heutigen Zeitpunkt allerdings nur wenige Möglichkeiten die Schaumzusammensetzung in Echtzeit und im Volumen zu bestimmen. Zusätzliche Anforderungen an die Robustheit des Maßsystems entstehen aus den rauhen Umgebungsbedingungen in industriellen Anwendungen. more...

We present a hybrid algorithm for the simulation of vicinal surface growth which combines a lattice gas Ising model with a phase-field model. The molecular behavior of individual adatoms is resolved by the kinetic Monte-Carlo (KMC) generated dynamics of the anisotropic Ising model. The microstructure dynamics on the vicinal surface are calculated using the phase-field method. Therefore adsorption processes on two different scales are described. In addition to step-flow growth the hybrid algorithm describes nucleation processes on the terraces which lead to an epitaxial layer-by-layer growth controlled by temperature and by deposition rate. The method is faster than pure KMC simulation and can take into account the stochastic processes in a comparable way. more...

Editorial - Materials have become an ever more important factor in most advanced technologies. It was no coincidence when the former State Secretary Christoph Matschie stated, at the opening of WING (Materials Innovations for Industry and Society initiated by the German Ministry for Education and Research), that nearly any new product is based on the improvement of an engineered material. This comes along with a constant quest for new materials, improved performance and decreased development costs. This quest is particularly strong for high-wage countries in the global market situation. Thus there is a steadily growing importance of systematic materials development supported by computer simulation methods in tailoring new materials for more and more specific demands for a wide range of applications from everyday household goods to opto-electronics and even further to medicine. In this context the tailoring of materials interfaces, respectively that of corresponding condensed matter systems, often used as model systems for the first ones, plays a particularly important role. The reason for this is that a material’s functional properties are to a large extent determined by its inner and outer interfaces. Prominent examples are corrosion-resistant surfaces of household goods, or likewise inert surfaces of prostheses engineered for medical applications. During materials processing the inner and outer interfaces of such functional materials evolve driven by the complex interplay of all the physical and chemical mechanisms contributing to interface energetics, interface kinetics and interface dynamics. Essentially, this opens a multiscale problem ranging from the quantum mechanical to the continuum scale. more...

The Burton-Cabrera-Frank (BCF) model describes the structural evolution of vicinal surfaces in terms of an incoming particle flux and concentration-dependent desorption and surface diffusion terms. A continuum formulation of the BCF scheme given by a phase-field implementation for the moving-boundary problem yields the long-term evolution of the step structure during a step-flow growth mode. A particle-based Ising-type approach with a Metropolis-Monte-Carlo kinetics additionally provides nucleation processes in a temperature-controlled manner and on a shorter time and length scale. We have integrated both approaches in a hybrid algorithm, which describes adsorption, nucleation, and structure evolution processes at solid-liquid and solid-gas interfaces on both time and length scales. The short term nucleation is resolved by the Monte-Carlo generated dynamics of an anisotropic Ising model, whose interaction parameters stem from first-principles calculations. The long-term microstructure dynamics is calculated by the phase-field method. Several growth modes are distinguished: In addition to step-flow growth the nucleation processes on the terraces can lead to roughening or an epitaxial layer-by-layer growth controlled by temperature and by flux. more...

The Burton-Cabrera-Frank (BCF) model describes the structural evolution of vicinal surfaces in terms of an incoming particle flux and concentration-dependent desorption and surface diffusion terms. A continuum formulation of the BCF scheme given by a phase-field implementation for the moving-boundary problem yields the long-term evolution of the step structure during a step-flow growth mode. Phenomena like step bunching or meandering are well covered by such an approach, but the nucleation of additional structures is not. A particle-based Ising-type approach with a Metropolis-Monte-Carlo kinetics provides such nucleation processes in a temperature-controlled manner and on a shorter time and length scale. We have integrated both approaches in a hybrid algorithm, which describes adsorption, nucleation, and structure evolution processes at solid-liquid and solid-gas interfaces on both time and length scales. The short-term nucleation from individual adatoms or molecules is resolved by the Monte-Carlo generated dynamics of an anisotropic Ising model, whose interaction parameters stem from first-principles calculations. The long-term microstructure dynamics on the vicinal surface is calculated using the phase-field method. Several growth modes are distinguished by the present scheme: In addition to step-flow growth the nucleation processes on the terraces can lead to roughening or an epitaxial layer-by-layer growth controlled by temperature and by flux. This hybrid algorithm has been applied to the decoration of structured crystalline surfaces with optically active molecules and to the coverage of glass surfaces with inhibitor molecules, which suppress glass corrosion. more...

A hybrid scheme is developed to describe vicinal surface growth during epitaxy on two different time and length scales. For this purpose this algorithm combines two modules based on a continuum and an atomistic approach. The continuum module is realized by a phase-field-model which traces back to the Burton-Cabrera-Frank theory, the atomistic module is based on the anisotropic Ising model which is mapped onto a lattice-gas model. The latter provides thermal density fluctuations resulting in adatom clustering. With increasing temperature the probability for island nucleation on the terraces decreases according to1-p where p is an Arrhenius-type activation probability which prevents clusters from becoming islands. Within this framework it is possible to find the transition from a rough surface at low temperatures to an evenly stepped surface at high temperatures where slight step meandering is observed. Furthermore two competing mechanisms of step bunching are investigated within this algorithm: alternating anisotropic diffusion and different Ehrlich-Schwoebel barriers at the step edges. Step bunching is found on two different time and length scales. more...

Eine Kombination aus einem kontinuumstheoretischen Phasenfeld-Ansatz fuer das Burton-Cabrera-Frank-Modell und einem teilchenbasierten Metropolis-Monte-Carlo-Verfahren erlaubt es, die Bedeckung strukturierter Oberflaechen mit Teilchen (Molekuelen) und die zeitliche Evolution der Bedeckung bzw. der Oberflaechenkonzentration in Abhaengigkeit von der Temperatur zu studieren. Phasenfeldschritte zur zeitlichen Entwicklung der Oberflaechenstruktur und Monte-Carlo-Schritte zur Ausbildung und zum Reifen von Clustern werden abwechselnd ausgefuehrt. Die Grundgroessen der BCF-Theorie (Teilchen-Fluss, Desorption, Diffusion) werden als Randbedingungen in die Monte-Carlo-Schritte uebernommen. Da die Wechselwirkung der Monte-Carlo-Teilchen untereinander, mit der Oberflaeche und speziell mit Stufenkanten (Schwoebel-Barriere) kurzreichweitig ist, koennen auch umgekehrt die lokalen Konzentrationen und Phasenfeld-Werte aus der MC-Teilchen-Verteilung berechnet werden. Eine systematische Variation der Wechselwirkungsparameter ermoeglichte es, neben den Kontinuums- und Teilchen-dominierten Regimes auch Strukturbildungen zu simulieren, die erst durch das Zusammenwirken beider Ansaetze moeglich sind. more...