A Hybrid Device for Enhancing Flotation of Fine Particles by Combining Micro-Bubbles with Conventional Bubbles

Flotation in the mining industry is a very significant separation technique. It is known that fine and ultra-fine particles are difficult to float, leading to losses of valuable minerals, mainly due to their low collision efficiency with bubbles. Flotation of fine particles can be enhanced either by increasing the apparent particle size or by decreasing the bubble size. Literature review reveals that electroflotation resulted in higher recoveries of ultrafine particles as compared with dispersed-air flotation, because electrolytic bubbles are smaller in size. To this end, the best practical approach is to combine conventional air bubbles and micro-bubbles from water electrolysis. Therefore, the design, fabrication, and operation of a bench-scale micro-bubble generator through water electrolysis is proposed. Moreover, this electrolysis unit is adapted in a mechanical Denver-type flotation cell. The resulting hybrid flotation device is capable of producing bubbles within a wide range of diameters. The significance of this process is that micro-bubbles, attached tothe surface of fine particles, facilitate the attachment of conventional-sized bubbles and subsequently increase the flotation recovery of particles. Experimental flotation results so far on the hybrid device indicate the enhancement of fine particle recovery by approximately 10% with the addition of micro-bubbles.

Ice Multiplication by Fragmentation during Quasi-Spherical Freezing of Raindrops: A Theoretical Investigation

Ice multiplication by fragmentation during collision–freezing of supercooled rain or drizzle is investigated. A zero–dimensional dynamical system describes the time evolution of number densities of supercooled drops and ice crystals in a mixed–phase cloud. The characteristic time–scale for this collision–freezing ice fragmentation is controlled by the collision efficiency, the number of ice fragments per freezing event, and the available number concentration of supercooled drops. The rate of the process is proportional to the number of supercooled drops available. Thus, ice may multiply extensively, even when the fragmentation number per freezing event is relatively small. The ratio of total numbers of ice particles to those from the first ice, namely the ‘ice–enhancement factor’, is controlled both by the number of fragments per freezing event and the available number concentration of supercooled drops in a similar manner. Especially, when ice fragmentation by freezing of supercooled drops is considered in isolation, the number of originally–existing supercooled drops multiplied by the fragmentation number per freezing event yields the eventual number of ice crystals. When supercooled drops are continuously generated by coalescence, ice crystals from freezing fragmentation also continuously increase asymptotically at a rate equal to the generation rate of supercooled drops multiplied by the fragmentation number per freezing event. All these results are expressed by simple analytical forms, thanks to the simplicity of the theoretical model. These parameters can practically be used as a means for characterizing observed mixed–phase clouds.

Formation of Oil-Particle-Aggregates: Numerical Model Formulation and Calibration

When oil spills occur in turbid waters, the oil droplets and mineral grains can combine to form oil-particle aggregates (OPAs). The formation of OPAs impacts the vertical transport of both the oil and the mineral grains; especially increasing deposition of oil to the seabed. Though the coastal oceans can be very turbid, to date, few numerical ocean models have accounted for aggregation processes that form OPAs. However, interactions between oil and mineral aggregates may be represented using techniques developed to account for sediment aggregation. As part of Consortium for Simulation of Oil Microbial Interactions in the Ocean (CSOMIO), we modified an existing, population dynamics-based sediment flocculation model to develop OPAMOD, a module that accounts for the formation of OPAs. A zero-dimensional model using OPAMOD is shown to be capable of reproducing the size distribution of aggregates from existing laboratory experimental results. Also using the zero-dimensional model, sensitivity tests were performed on two model parameters, the fractal dimension and collision efficiency. Results showed that fractal dimension played a role in the OPA size distribution by influencing the effective particle density, which modified the number concentration of flocs for a given mass concentration. However, the modeled particle characteristics and oil sequestration were relatively insensitive to collision efficiency. To explore OPA formation for an outer continental shelf site, two simulations were conducted using a one-dimensional (vertical) implementation of the model. One scenario had high sediment concentration near the seabed to mimic storm-induced resuspension. The other scenario represented river plume sediment delivery by having high sediment concentration in surface waters. Results showed that OPA formation was sensitive to the vertical distribution of suspended sediment, with the river plume scenario creating more OPA, and sequestering more oil within OPA than the storm resuspension scenario. OPAMOD was developed within the Coupled Ocean-Atmosphere-Wave-and-Sediment Transport (COAWST) modeling system, therefore the methods and parameterizations from this study are transferrable to a three-dimensional coupled oil-sediment-microbial model developed by CSOMIO within the COAWST framework.

Understanding the coagulation mechanism and floc properties induced by Fe(VI) and FeCl3: population balance modeling

Coagulation kinetics and floc properties are of great fundamental and practical importance in the field of water treatment. To investigate the performance of Fe(VI) and Fe(III) salt on particle coagulation, Malvern Mastersizer 2000 was employed to continuously and simultaneously monitor the kaolin floc size and structure change, and population balance modeling was used to investigate the coagulation mechanism. The results show dosage increase had positive effect on collision efficiency and floc strength and negative effect on restructure rate. Low shear rate resulted in higher collision efficiency and stronger floc. Low water temperature had a pronounced detrimental effect on coagulation kinetics. Temperature increase showed the most significant positive effect on collision efficiency, floc strength and restructure rate. The optimum pH zone for the coagulation was found to be between 6 and 8. Further pH increase lowered the collision efficiency and floc strength and increased the restructure rate. FeCl3 resulted in a larger ratio of the mass to volume of kaolin flocs (compactness) than those induced by ferrate.

Feasibility Evaluation on Single-Collector Collision Model to Separate Microplastics in Micro Bubble Flotation Process

Objectives:The single collector collision (SCC) model is a model that predicts the separation efficiency of particles based on the collision efficiency between microbubbles and particles in the particle separation process. In order to remove micro-plastics (MPs) particles, which have recently been known to be harmful, we tried to analyze the impact and separation efficiency of MPs based on the SCC model and evaluate its application feasibility.Methods:Based on the SCC model, the collision efficiency prediction for MPs particle removal was simulated and the separation efficiency was evaluated. In addition, a series of flotation experiments were conducted using a flotation device that injects microbubbles to remove MPs particles suspended in water, and the experimental results and predicted values were compared.Results and Discussion:Using the SCC model, the collision efficiency according to the size distribution of MPs particles was not significantly different from that of typical particles (clay, kaolin) in water. Based on this collision efficiency, the maximum removal efficiency of MPs particles separated from the water body is predicted to reach about 90%. On the other hand, the initial collision-adhesion coefficient () of the MPs particles based on the SCC model was 0.03 to 0.1, showing a slight difference from the clay particles having the range of 0.3 to 0.4. The flotation separation efficiency of the MPs particles evaluated and predicted by applying this initial collision-adhesion coefficient showed a range similar to the measured value. In addition, the particle separation efficiency according to the increase of the measured bubble volume concentration to improve the particle separation efficiency also showed a pattern similar to the predicted value.Conclusions:In the flotation process, the initial collision-adhesion efficiency of the MPs particles predicted by the SCC model was lower than that of the kaolin particles. Based on the simple and simple model SCC theory, it was confirmed that it can be applied to the flotation separation analysis of MPs particles.

Active prevention of snow accumulation on cameras of autonomous vehicles

Accumulation of atmospheric icing, particularly wet snow, on the visual sensors/navigators of autonomous vehicles (AVs) increases the possibility of accidents by obstructing the lenses of the sensors. Here, two navigator designs were suggested that use airflow across the lens surfaces of the AVs to prevent snow accumulation on them. The impact of airflow intensity across the lens, wind velocity (relative velocity of wind with respect to vehicle), and liquid water content of snow on prevention of snow accumulation on the lenses of the AVs was explored experimentally. Here, artificial snow grains were formed using a novel snow gun and their average sizes at low liquid water content (LWC of ≈ 8%) and high liquid water content (LWC of ≈ 28%) were measured to study the impact of grain sizes on snow accumulation on camera lenses. The effects of wind velocity, snow density, and diameter of the snow grains on their trajectory in the testing section were also studied numerically. The results indicated that the snow grains with higher velocity, density, or diameter possessed higher inertia forces and were more prone to collide with the navigator, increasing collision efficiency of snow grains. We realized that the airflow across the lens effectively prevented snow accumulation on the lens at vehicle/wind velocities of up to 20 mph. The proposed designs actively reduced the snow accumulation on the camera lens, promising to be applied in future AVs. Graphic abstract