Liquid-solid flotation techniques

This method has been employed to measure the critical wetting surface tensions of particles of sulfur, silver iodide, methylated glass beads, quartz, paraffin-wax-coated coal, and surfactant-coated pyrite. Generally. Fuerstenau and coworkers [106-115] found that the film flotation technique is sensitive to the surface hydrophobicity and the heterogeneity of the particles. It was found that particle size, particle shape, particle density, film flotation time, and the nature of the wetting liquids have negligible effects on the results of film flotation. But the liquid and the solid particles used in the experiments must not have any chemical interactions. 

Liquid waste streams with a high-suspended solids content can be cleaned up by solids removal in clarifiers, thickeners, and liquid cyclones and by accelerated settling by inclined Chevron settlers or the like [73]. For waste streams with very finely divided solids in suspension (i.e., less than about 100 pm) dissolved air flotation techniques have been shown to be more efficient than methods employing sedimentation. Final dewatering of the sludges obtained may be carried out on a continuous filter or a centrifuge. The clarified water product can be accepted for more potential options of reuse or final disposal options than untreated water, and the separated solids may be burned or discarded to landfill, as appropriate [74]. 

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. 

Flotation is an important technique in mineral processing, where it is used to separate different types of ores. When used to separate solid-solid mixtures, the material is ground to a particle size small enough to liberate particles of the chemical species to be recovered. The mixture of solid particles is then dispersed in the flotation medium, which is usually water. The mixture is then fed to a flotation cell, as illustrated in Figure 8.12a. Here, gas is also fed to the cell where gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid particles are collected from the surface by an overflow weir or mechanical scraper. The separation of the solid particles depends on the different species having different surface properties such that one species is preferentially attached to the bubbles. A number of chemicals can be added to the flotation medium to meet the various requirements of the flotation process ... 

On this subject notice that, possibly combined with various heating methods, several physical effects may be considered which allow free flotation of solid and even liquid matter. Materials may be levitated for instance by a jet of gas, by intense sound waves or by beams of laser light. Conductors levitate in strong radiofrequency fields, charged particles in alternating electric fields, magnets above superconductors or vice versa. A review on levitation in physics with the description of several techniques and their principles and applications was made by Brandt (1989). 

Solid-liquid separation by flotation may be achieved by gravity alone or induced by dissolved-air or vacuum techniques. The mechanisms and driving forces are similar to those found in sedimentation, but the separation rate and solids concentration can be greater in some cases. 

Flotation. This method is used to remove suspended organic and inorganic solids from waste streams or slurries. This technique is basically a physical process in which solutions carrying suspended particles are agitated with the stream of air bubbles or a mechanical agitator. A froth forms at the surface of the liquid or slurry, which is then removed by skimmers or scrapers. Individual or combinations of similar materials may be removed by this method from wastewater streams. 

According to the collection procedure for the enriched gas-liquid and/or gas-solid interfaces, adsorptive bubble separation processes or techniques can also be divided into two large categories (a) foam separation, which involves the production of foam in the process, and (b) nonfoaming adsorptive bubble separation, which involves no production of foam. Foam separation can be further subdivide into foam fractionation and flotation. Nonfoaming adsorptive bubble separation, however, can be further subdivided into bubble fractionation, solvent sublation, and noirfoaming flotation. Lemlich (84) and Wang (1,75) provided the definitions of these technical terms in their books. 

In general, flocculants are used in solid-liquid separation processes such as thickening and filtration. Inorganic salts are also used sometimes to aggregate fine particles. Flocculation technique has been developed further for special applications of selective flocculation, selective dispersion and agglomeration flotation. 

Flotation, not floatation, is the term used to describe the use of a gas to cause selected solid particles to rise to the surface from a mixture of particles suspended in a liquid. A newer term, adsubble, has been proposed, and may eventually win out. Parts of the two chapters in this section are not flotation in the strictest sense in that one technique does not separate solid particles, and the other does not use a gas, yet all four techniques are closely related. 

In this section we present a brief account of the most recently published smdies and techniques concerning the solid-liquid interface involving silica and related materials. Interactions between solutions and solid surfaces play an important role in several processes such as ore flotation, colloidal stabilization, oil recovery, soil pollution and so on [105]. 

Flotation. The use of ak or gas bubbles to separate mineral particles by preferential attachment and subsequent flotation has been a feature of the mineral processing industry for many decades, but the application of the principle to solid-liquid separations is of more recent origin. The techniques have similarities but differences. In mineral flotation it is more common to use chemicals to enhance the collection of the particles and the stability of the ffoth and to produce the bubbles by beating air into the suspension, but in solid liquid separation it is more usual to dissolve air into the liquid under pressure, allowing the gas to expand out of solution under the lower pressure of the separation chamber, producing bubbles for the preflocculated particles to collect on without the need for further chemical addition. 

Flotation is a technique to separate finely dispersed solid particles based on different surface wettabilities. The principle of flotation is illustrated in Figure 8.11. Air bubbles are blown through a slurry of solid particles dispersed in a liquid. In the case of an aqueous liquid, the more hydrophobic particles attach to the air bubbles that pass through the liquid and arrive in the froth, leaving the hydrophilic particles behind in the bulk liquid. 

A comprehensive overview of preconcentration techniques for uranium (VI) and thorium (IV) prior to analysis was published (Prasada Rao et al. 2006). The multitude of off-line techniques that were reviewed includes liquid-liquid extraction, liquid membranes, ion exchange, extraction chromatography, flotation, absorptive electrochemical accumulation, solid-phase extraction (SPE), and ion imprinting polymers. In addition, online preconcentration methods for uranium, thorium, and mixtures of the two are also briefly surveyed. This overview includes over 100 references and is a good source for finding a suitable preconcentration technique with regard to the enrichment factor, retention and sorption capacity, method validation, and types of real samples. The review article focused on samples in which the uranium was already in solution so that digestion procedures for solid samples were not discussed (Prasada Rao et al. 2006). 

Considering the aforementioned reasons, the necessity of metal ion removal from liquid effluents becomes evident. The conventional technique applied for effluent treatment containing metal ions consists of increasing the pH by adding calcium oxide or another chemical. The metal ion is precipitated as an insoluble hydroxide and removed by flotation or sedimentation, concentrated, and disposed of in special class landfills, which represents an important cost for the treatment process. The main drawback of this technique is the high and irreversible consumption of chemicals and the fact that the problem is only transferred from the liquid to the solid phase [7]. 

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