Flotation separation processes

A flotation separation process, in which particles or droplets become attached to gas bubbles that are injected (sparged) into the flotation medium. Also termed induced gas flotation . Example the froth flotation of bitumen. See also Froth Flotation. 

Table 14.14. Mineral flotation separation processes involving the use of cationic surfactants ...

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 or froth flotation is a physicochemical property-based separation process. It is widely utilised in the area of mineral processing also known as ore dressing and mineral beneftciation for mineral concentration. In addition to the mining and metallurgical industries, flotation also finds appHcations in sewage treatment, water purification, bitumen recovery from tar sands, and coal desulfurization. Nearly one biUion tons of ore are treated by this process aimuaHy in the world. Phosphate rock, precious metals, lead, zinc, copper, molybdenum, and tin-containing ores as well as coal are treated routinely by this process some flotation plants treat 200,000 tons of ore per day (see Mineral recovery and processing). Various aspects of flotation theory and practice have been treated in books and reviews (1 9). 

The raw ROM (run of mine) ore is reduced in size from boulders of up to 100 cm in diameter to about 0.5 cm using jaw cmshers as weU as cone, gyratory, or roU-type equipment. The cmshed product is further pulverized using rod mills and ball mills, bringing particle sizes to finer than about 65 mesh (230 p.m). These size reduction (qv) procedures are collectively known as comminution processes. Their primary objective is to generate mineral grains that are discrete and Hberated from one another (11). Liberation is essential for the exploitation of individual mineral properties in the separation process. At the same time, particles at such fine sizes can be more readily buoyed to the top of the flotation ceU by air bubbles that adhere to them. 

Flotation reagents are used in the froth flotation process to (/) enhance hydrophobicity, (2) control selectivity, (J) enhance recovery and grade, and (4) affect the velocity (kinetics) of the separation process. These chemicals are classified based on utili2ation collector, frother, auxiUary reagent, or based on reagent chemistry polar, nonpolar, and anionic, cationic, nonionic, and amphoteric. The active groups of the reagent molecules are typically carboxylates, xanthates, sulfates or sulfonates, and ammonium salts. 

Gravity concentration, ie, the separation of ore from gangue based on the differences in specific gravities, using jigs, heavy—medium separators, or spiral concentrators for example, is appHcable for lead ores. However, the predominant beneficiation technique used in modem plants is the bubble or froth flotation (qv) process (4,5). 

A development in the 1960s was that of on-line elemental analysis of slurries using x-ray fluorescence. These have become the industry standard. Both in-stream probes and centralized analyzers are available. The latter is used in large-scale operations. The success of the analyzer depends on how representative the sample is and how accurate the caUbration standards are. Neutron activation analyzers are also available (45,51). These are especially suitable for light element analysis. On-stream analyzers are used extensively in base metal flotation plants as well as in coal plants for ash analysis. Although elemental analysis provides important data, it does not provide information on mineral composition which is most cmcial for all separation processes. Devices that can give mineral composition are under development. 

Scrubbing andDesliming. Sylvinite ores in North America contain 1—6 wt % water-insoluble clays. A significant portion of these clays is less than 0.002 mm in diameter. If not removed or controUed in some manner, clay bodies that are dispersed in the flotation solution, ie, brine saturated with KCl and NaCl, absorb the amine coUector, which is added to effect flotation separation, and the coUector is rendered ineffective. Clay is the most troublesome impurity encountered in the processing of sylvinite ore. 

Foam Production This is important in froth-flotation separations in the manufac ture of cellular elastomers, plastics, and glass and in certain special apphcations (e.g., food products, fire extinguishers). Unwanted foam can occur in process columns, in agitated vessels, and in reactors in which a gaseous product is formed it must be avoided, destroyed, or controlled. Berkman and Egloff (Emulsions and Foams, Reinhold, New York, 1941, pp. 112-152) have mentioned that foam is produced only in systems possessing the proper combination of interfacial tension, viscosity, volatihty, and concentration of solute or suspended solids. From the standpoint of gas comminution, foam production requires the creation of small biibbles in a hquid capable of sustaining foam. 

The area of interest covered by this paper is limited to processes in which chemical conversion occurs, as in the processes noted above. Gas-liquid-particle processes in which a gaseous phase is created by the chemical reaction between a liquid and a solid (for example, the production of acetylene by the reaction between water and carbide) are excluded from the review. Also excluded are physical separation processes, such as flotation by gas-liquid-particle operation. Gas absorption in packed beds, another gas-liquid-particle operation, is not treated explicitly, although certain results for this operation must necessarily be referred to. 

It may finally be pointed out that certain separation processes in addition to packed-bed gas absorption are gas-liquid-particle operations. Examples are flotation and a special type of fluidized crystallization process (Z2). 

Copper, Cu, is unreactive enough for some to be found as the metal, but most is produced from its sulfides, particularly the ore cbalcopyrite, CuFeS2 (Fig. 16.10). The crushed and ground ore is separated from excess rock by froth flotation, a process that depends on the ability of sulfide ores to be wetted by oils but not by water. In this process, the powdered ore is combined with oil, water, and detergents (Fig. 16.1 l). Then air is blown through the mixture the oil-coated sulfide mineral floats to the surface with the froth, and the unwanted copper-poor residue, which is called gangue, sinks to the bottom. 

Separation Techniques, Academic, New York, 1972 Lemhch, Adsub-ble Methods, in li (ed.). Recent Developments in Separation Science, vol. 1, CRC Press, Cleveland, 1972, chap. 5 Grieves, Chem. Eng. J., 9, 93 (1975) Valdes-Krieg King, and Sephton, Sep. Purif Methods, 6,221 (1977) Clarke and Wilson, Foam Flotation, Marcel Deldcer, New York, 1983 and Wilson and Clarke, Bubble and Foam Separations in Waste Treatment, in Rousseau (ed.). Handbook of Separation Processes, Wiley, New York, 1987. 

An earlier section which dealt with mineral separation included flotation among the category of concentration separation processes. The introduction of flotation was one of the major milestones in the history of mineral processing. There exist variations (natural or artificially created) in the surface properties of mineral particles, and the technique of flotation is based on the utilization of these differences. The actual specific gravity of the mineral particle plays little or no part in the separation. 

Krofta, M. and Wang, L.K., Flotation and Related Adsorptive Bubble Separation Processes, Lenox Institute of Water Technology, Lenox, MA, Report No. LIR-0681/1, 150pp., June 1981. 

Flotation is a gravity separation process that exploits the 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... 

Liquid-solid distributions are involved in ion-exchange and other adsorption-based separation processes, separation processes based on crystallization or precipitation, flotation processes for ore dressing, and smelting processes. 

Flotation is a solid-liquid separation process, that transfers solids to the liquid surface through attachment of gas bubbles to solid particles. Flotation processes are used in the processing of crushed ores, whereby a desired mineral is separated from the gangue or non-mineral containing material. Various applications in solid separation processes are also in use in waste treatment. 

The proposal was fatally flawed by failing to address some of the most critical elements of soil washing. Soil washing is essentially a hydraulic flotation process which removes the fines from the soil. Depending upon the soil, that can account for between 5% and 15% of the volume processed. The process is strictly one of density settling and stokes law is followed in the separation process. What you wind up with is a clean and sterile soil because the organic materials in the soil have a density of between 1.2 and about 2.0 and the clays, and some of the silts, because of their particle size are removed from the soil. In the case of Belarus soils, this also removed about 60%-80% of the fine radioactive materials, but that was not the problem. The problem was one of scale and residuals. 

Grinding is essential for the liberation of sulphide minerals in order to achieve effective flotation. The grinding process, however, may also have a various effects on the flotation separation because of the galvanic interactions among the grinding media and the different minerals due to the high redox activity of sulphide mineral and iron media as well as thio-reagents. 

This is an innovative separation process for removal of suspended solids and oil and grease by flotation followed by skimming. It requires very short RT (less than 30 minutes), and can achieve 90-99% removal efficiency [15,18]. 

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