Bubble generation, flotation

The bubble size in these cells tends to be the smallest (10 to 50 Im) as compared to the dissolved-air and dispersed-air flotation systems. Also, very httle turbulence is created by the bubble formation. Accordingly, this method is attractive for the separation of small particles and fragile floes. To date, electroflotation has been applied to effluent treatment and sludge thickening. However, because of their bubble generation capacity, these units are found to be economically attractive for small installations in the flow-rate range of 10 to 20 mVh. Electroflotation is not expected to be suitable for potable water treatment because of the possible heavy metal contamination that can arise due to the dissolution of the electrodes. 

Grainger-Allen, T. J. N. Bubble generation in froth flotation machines. Trans. IMMVo 79, C15-22. 1970. 

Hydrodynamic cavitation provides a practical method for in situ generation of tiny bubbles in flotation systems. Although cavitation phenomena in flotation have been considered since the beginning of commercial applications, intentionally applying... 

All the aforementioned process terms can simply be called foam separation. It is important to note that although any type of technique can be used for bubble generation in a foam separation system, the most common bubble generation technique for a foam separation system is dispersed air flotation, which is also known as induced air flotation. 

Again, any type of technique can be used for generating gas bubbles in a nonfoaming adsorptive bubble separation system. The most effective bubble generation techniques for a nonfoaming system are dissolved air flotation and electrolytic flotation. The following are the process descriptions of selected nonfoaming processes. 

Air bubbles were generated through electroflotation. This procedure allowed easy control of bubble generation and thus of the air-solids parameter which is crucial for flotation processes. Furthermore, because electroflotation bubbles have a very small diameter, this parameter will no longer be ratecontrolling. 

If a exceeds this value, a decrease of bubble size will only decrease the collision efficiency. Large bubbles with the size of the order of a 0.5mm are obtained in usual pneumatic dispersions formed in flotation machines. It is much more diflflcult to obtain bubbles 10 to 50 times smaller, which can be achieved by using completely different methods of bubble generation, electroflotation and air-dissolved flotation. Since a decrease of bubble dimensions is connected with substantial complication and a rise in price of the technology, it is necessary to forecast sufficiently accurately the required size of bubbles as a function of surfactant... 

If the polydispersity of bubbles generated in air-dissolved flotation or electroflotation is high, there is no need for additional introduction of centimicron bubbles. Optimal flow of two-stage flotation corresponds to the maximum attainable degree of monodispersity of bubbles. In this case the ratio between volume fractions of micro- and macrobubbles and collision efficiencies of the processes of particle capture by small bubbles and bubble coagulation must be such that the particle capture process outweighs the process of coalescence. 

Carrying out flotation in a flotation machine by adding air (or gas). Hydrophobic particles adhere to air bubbles generated in the machine, float to the slurry sitrface, and are collected as a froth fraction, while the hydrophilic particles remain in the cell and discharge as a cell (sink) fraction. 

In the past a large variety of flotation ceU designs were used. All cells have to ensure bubble generation, collision of the ink particles with the bubbles, transport of the ink-bubble aggregate to the suspension surface, and foam removal. 

Nonselective flotation is used for process water clarification in the water loops (see Chapter 5). The objective is to dispose of aU the undesired water components which cannot be removed by mechanical separation, such as anionic trash, fines, or microstickies. These components would negatively affect the production process and/or the product quality. As flotation is based on bubbles generated by de-... 

In a couple of particular papers, the application of LD particle sizer to measure the size distribution of micro-bubbles are mentioned. Couto et al. [44] performed micro-bubble size distribution measurements by the laser diffraction technique. It was concluded that the size distribution of micro-bubbles generated for the dissolved air flotation process could be assessed on a fast and reliable way by the application of the laser diffraction technique. The micro-bubble size distribution was measured by the Mastersizer 2000 SM equipment from Malvern Instruments, UK. The instrument specifications state that analysis in the particle range from 0.1 to 2000 ttm is possible, and the data interpretation computations could either be performed by use of the... 

Wastewater can be treated by several physical processes. In some cases, simple density separation and sedimentation can be used to remove water-immiscible liquids and solids. Filtration is frequently required, and flotation by gas bubbles generated on particle surfaces may be useful. Wastewater solutes can be concentrated by evaporation, distillation, and membrane processes, including reverse osmosis, hyperfiltration, and ultrafiltration. Organic constituents can be removed by solvent extraction, air stripping, or steam stripping. 

Flotation. Flotation is a gravity separation process which exploits differences in the surface properties of particles. Gas bubbles are generated in a liquid and become attached to solid particles or immiscible liquid droplets, causing the particles or droplets to rise to the surface. This is used to separate mixtures of solid-solid particles and liquid-liquid mixtures of finely divided immiscible droplets. It is an important technique in mineral processing, where it is used to separate different types of ore. 

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