Flotation of minerals

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

Alkali metal xanthates are prepared in high yield from reaction of amyl alcohols with alkah metal hydroxide and carbon disulfide (39—42). The xanthates are useful as collectors in the flotation of minerals and have minor uses in vulcani2ation of mbber and as herbicides (39,41). 

The chemical and biological effects of ultrasound were first reported by Loomis more than 50 years ago (4). Within fifteen years of the Loomis papers, widespread industrial applications of ultrasound included welding, soldering, dispersion, emulsification, disinfection, refining, cleaning, extraction, flotation of minerals and the degassing of liquids (5),(6). The use of ultrasound within the chemical community, however, was sporadic. With the recent advent of inexpensive and reliable sources of ultrasound, there has been a resurgence of interest in the chemical applications of ultrasound. 

Figure 22.4 Effect of sodium alkyl sulphate on flotation of minerals from pegmatite ores at a pH of 1.4.

FIGURE 5.13 Flotation of mineral particles as aided by air bubbles. 

The flotation of minerals is based on different attachment forces of hydrophobized and hydrophilic mineral particles to a gas bubble. Hydrophobized mineral particles adher to gas bubbles and are carried to the surface of the mineral dispersion where they form a froth layer. A mineral is hydrophobized by the adsorption of a suitable surfactant on the surface of the mineral component to be flotated. The hydrophobicity of a mineral particle depends on the degree of occupation of its surface by surfactant molecules and their polar-apolar orientation in the adsorption layer. In a number of papers the relationship was analyzed between the adsorption density of the surfactant at the mineral-water interface and the flotability. However, most interpretations of adsorption and flotation measurements concern surfactant concentrations under their CMC. 

Chelating agents that can form insoluble, hydrophobic chelates on the surface of minerals are potential collectors for the selective flotation of minerals.3 4 As early as 1927, Vivian5 reported the use of cupferron, a well-known analytical reagent, as a collector for the flotation of cassiterite (Sn02). Since then, there have been a number of reports on the use of chelating agents in flotation. 

Foams and emulsions may also be encountered simultaneously [114]. Figure 1.5 shows an example of an aqueous foam with oil droplets residing in its Plateau borders (see Section 5.6.7). In addition to containing gas, an aqueous phase, and an oleic phase, foams can also contain dispersed solid particles. Oil-assisted flotation of mineral particles provides one example (Chapter 10). Oil-sand flotation of bitumen provides another (Chapter 11). In the case of oil-sands flotation, an emulsion of oil dispersed in water is created and then further separated by a flotation process, the products of which are bituminous froths that may be either air (and water) dispersed in oil (from primary flotation) or air (and oil) dispersed in water (from secondary flotation). In either case, the froths must be broken and de-aerated before the bitumen can be upgraded to synthetic crude oil. (See Section 11.3.2). 

Emulsion flotation is analogous to carrier flotation. Here, small-sized particles become attached to the surfaces of oil droplets (the carrier droplets). The carrier droplets attach to the air bubbles and the combined aggregates of small desired particles, carrier droplets, and air bubbles float to form the froth. An example is the emulsion flotation of submicrometre-sized diamond particles with isooctane. Emulsion flotation has also been applied to the flotation of minerals that are not readily wetted by water, such as graphite, sulfur, molybdenite, and coal [623]. Some oils used in emulsion flotation include mixed cresols (cresylic acid), pine oil, aliphatic alcohols, kerosene, fuel oil, and gas oil [623], A related use of a second, immiscible liquid to aid in particle separation is in agglomeration flocculation (see Section 5.6.4). 

THE PREFERENTIAL FLOTATION OF MINERALS AN APPLICATION OF THE MIXED POTENTIAL CONCEPT... 

The rest of the chapter has been devoted to special topics and in materials science there are many possibilities. Those selected include the mechanism of the flotation of minerals in which the addition of a certain organic to the solution causes a specific mineral to become hydrophobic so that it is exposed to air bubbles, the bubbles stick to it and buoy the mineral up to the surface, leaving unwanted minerals on the bottom of the tank. It turns out that the mechanism of this phenomenon involves a mixed-potential concept in which the anodic oxidation of the organic collector, often a xanthate, allows it to form a hydrophobic film upon a semiconducting sulfide or oxide, but only if there is a partner reaction of oxygen reduction. This continues until there is almost full coverage with the dixanthate, and the surface is thereby made water-repelling. 

Suggested industrial uses of carbohydrate xanthates, apart from the cellulose Viscose process, include the flotation of minerals and the production of plastics. Two patents by Brown and his associate claim an effective purification of both iron ore and silvinite ore by froth-flotation processes employing, for example, sodium starch xanthate, pine oil, and a suitable amine. Silberstein obtained plastic masses from mixtures of sodium dextrin xanthate with urea, formaldehyde, or glyceritol. Starch xanthate has been suggested as a dispersing, wetting, and adhesive ma-... 

In the case of long chain surfactants used as collectors, a signiflcant correlation between their adsorption in the form of aggregates and flotation of minerals with them was established in the 1960 s by Somasundaran et al. (1964). Somasundaran et al. (1976, 1985) developed the relevant dissociation and aggregation equilibria for flotation reagents in the solution as well as at the mineral-solution interface. Importantly, the ion-molecule complexes phenomenon was proposed later by Somasundaran (1976), Hanna and Somasundaran (1976) to account for the flotation maximum exhibited at certain pH values by hydrolyzable surfactants. 

Weakly acidic fatty acids such as oleic acid undergo dissociation to form ions (R ) at high pH values and neutral molecules (RH) at low pH values. In the intermediate pH region, the ions and neutral molecules can associate to form iono-molecular complexes (Kulkarni and Somasundaran, 1980). As the collector concentration is increased, miceUization or precipitation of the collector will occur. In addition, collector species can undergo associative interactions to form other aggregates such as dimers (R ) (Somasundaran and Anantha-padmanabhan, 1979b). Since the surface activities of these species will vary from those of each other, flotation of minerals with these collectors can also be expected to be dependent upon pH and such solution conditions. 

A. M. Gandin and P. Malozemoff, Recovery by Flotation of Mineral Particles of Colloidal Size,... 

Solutions on Froth Flotation of Minerals, J. Colloid Interface Sci., 47, 290 (1974). 

Flotation properties of pen [land ite are not well understood notability is in between chalcopyriie and pyrrhotite Naturally flolable since Mo S is sob, it can coat other minarals and thus enhance gengne dotation Quartz is the gangee Tor other minerals it can be floated easily wilh amines during the flotation of minerals sodium silicate can be used to depress quartz... 

Calcium cyanide is used for the extraction of gold and silver from their ores, in the froth flotation of minerals, as a fumigant, and as a rodenticide. 

Miranda and Berglund [79] used a food grade polymer, (hydroxypropyl)methyl cellulose (HPMC), and ammonium sulfate as additives for the recovery of recombinant a-amylase by flotation. The enzyme was removed from the liquid phase by partition to a salted-out HPMC phase and the enzyme-containing polymer floes were recovered by flotation. This system behaved in a manner similar to the flotation of mineral systems. The problem with this technique is the cost of the polymer and the separation of the enzyme from the polymer phase. Both of them complicate the process and increase the separation cost In general, for protein recovery and separation, especially in the pharmaceutical industry, it is not proper to add chemicals to the feed, because they have to be removed from the product completely and this separation causes problems and additive costs. 

Typical diameters of bubbles formed by these different methods are given in Fig. 1.2. The usual range is 200 (tm to 3 mm. In CSTR reactors the bubble diameter is usually 2 to 2.5 mm for froth flotation of minerals, 1 mm for foam fractionation the diameter is in the range 0.8-1 mm for DAF, the bubbles nucleate on particulates, their diameter is usually 70-90 pm. 

NFPA Health 3, Flammability 0, Reactivity 1 Uses Fumigant for greenhouses, flour mills, grain, seed, citrus trees under tents for control of scale insects rodenticide to leach gold and silver ores in froth flotation of minerals in mfg. of stainless steel mfg. of other cyanides Calcium cyclamate CAS 139-06-0 INS952... 

Fuerstenau, D. W. and Herrera-Urbina, R.. Adsorption of cationic surfactants and the flotation of minerals, in Cationic Surfactants Physical Chemistry, Rubingh, D. N. and Holland, P. M. (Eds), Surfactant Science Series, Vol. 37, Marcel Dekker, New York, 1991, pp. 407-447. 

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