Flotation froth

The process of froth flotation for the separation of minerals exploits the fact that either minerals differ naturally in their degree of wettability by surfactant solutions or their surface properties can be modified by adsorption. When air is blown through a suspension of finely ground ore in an appropriate surfactant solution, those particles which have the relevant surface properties become 

In emulsions the dispersed phase and the dispersion medium arc both fluids. The commonest examples arc those in which the two phases are oil and an aqueous medium. They may be of two distincL types a dispersion of fine oil droplets in an aqueous medium, an oU-in-waler (O/YV) emulsion, or of aqueous droplets in oil, a waler-in-ail (YV/O) emulsion. In some special cases a biconlinuous emulsion may he formed in which one phase forms a continuous network in the other. Recently, dilute pas-in-liquid emulsions (dispersions of fine gits bubbles in liquid) have been shown to exist in solutions of gas at high pressure in liquids (for example in carbonated drinks), from this point of view also an aerosol of liquid droplets may be regarded as a dilute liquid-ingas emulsion. 

Whether or not an O/W or W/O emulsion is formed depends on a number of factors. If the ratio of the amounts of the two phases (the ratio of phase volumes) is very low, the phase present in the lower amount is often the disperse phase if the phase volumes are roughly equal, other factors determine which type of emulsion is formed. It is usually possible to identify the type of emulsion by-examining the effect of diluting it with one of the phases. Thus on adding water to an O/W emulsion the emulsion is diluted. On the other hand, on adding oil the added oil forms a separate layer. That milk may be diluted with water shows that it is an O/W emulsion, while mayonnaise, a W/O emulsion, can be blended with additional oil. 

As already discussed in earlier chapters, the formation of an emulsion, which involves an increase in interfacial area between the two phases, is accompanied by an increase in free energy. The case of formation of an emulsion may be measured by the amount of work needed for its formation the lower the inlerfacial tension the less work is needed and the more readily the emulsion is formed. The addition of emulsifying agents which adsorb at the interface and lower the interfacial tension is therefore usually 

Emulsions, like foams, can also be stabilised by finely divided solids, provided the properties of the solid/liquid/liquid interface are appropriately adjusted. These properties may also determine whether an O/W or a W/O emulsion is formed. For example, shaking water and benzene together with finely divided calcium carbonate yields a benzene-in-water emulsion. On the other hand, if the calcium carbonate is made hydrophobic by treatment with oleic acid solution, a water-in-benzene emulsion results. 

Finely divided solids or immiscible liquids can be made to adhere to gas bubbles and then can be removed from the main liquid. Affinity of a solid for an air bubble can be enhanced with surfactants which adhere to the surface of the solid and make it nonwetting. The main application of froth flotation is to the separation of valuable minerals from gangue. Ores of Cu, Zn, Mo, Pb, and Ni are among those commercially preconcentrated in this way. Reagent requirements of each ore are unique and are established by test. A 

Promoters or collectors give the mineral the water-repellent coating that will adhere to an air bubble. Frothers enhance the formation and stability of the air bubbles. Other additives are used to control the pFI, to prevent unwanted substances from floating, or to control formation of slimes that may interfere with selectivity. 

Polyether Polyphenylene oxide General Electric IS00 84 77 0.1 max. 54 C 

Inorganic membranes Glass hollow fiber Glass hollow fiber Graphite, oxidized Schott A Gen. Westinchouse (Union Carbide Comp.) SO 98 80 120 41 0.5 0.5  

Total residence time in a bank of cells may range from 4 to 14 min. A table of approximate capacities of several makes of flotation cells for a pulp with 33% solids of specific gravity = 3 is given in the Chemical Engineers Handbook (McGraw-Hill, New York, 1984, p. 21.49) on an average, an 8-cell bank with 4-min holdup has a capacity of about 1.5 tons solid/(hr) (cuft of cell) and a power requirement of about 0.6HP/(cuft of cell). 

Polyurea Cthyleneimlne toluylene diIsocyanate NS 100 ultrathln wound module North Star Res. Inst. (Usiv. Oil Prod.) 500 99.6 70 3.5 pH 2-12 

Dynamically formed membranes Zr02/po1yacryi ic acid Polyacryllc acid Oak Ridge Nat. Lab. UNIV. Oil Prod (Gulf) 5000 2000 90 80 70 102 0.3 0.3  

This chapter reviews the adsorption of thiols at metal and metal sulfide surfaces. The motivation for studying these systems derives from the interaction of this interesting group of organic compounds with native metal and sulfide mineral surfaces being the key chemical step in the separation and concentration of such minerals from their ores by froth flotation. A number of different species can be formed by the interaction of thiols with metals and sulfides, the identity of the adsorbate depending on the particular thiol and mineral, the adsorption conditions, and the extent of reaction. This review focuses on the chemisorbed species formed in these systems. The concept of chemisorption is one of the formation of chemical bonds between the thiol and atoms in the mineral surface without removal of component atoms from their positions in the metal or metal sulfide lattice. 

The froth flotation process involves crushing the ore to liberate separate grains of the various valuable minerals and gangue components, pulping the ore particles with water, and then selectively rendering hydrophobic the surface of the mineral of interest through the addition of an organic 

Modem Aspects of Electrochemistry, Number 29, edited by John O M. Bockris et al. Plenum Press, New York, 19%. 

The flotation process was developed in Australia at the turn of the century to treat the primary sulfidic silver/lead/zinc ore at Broken Hill, New South Wales, following the mining of the overlying secondary ore. Oxidation to form the secondary zone had resulted in a concentration of silver and lead, and this section of the ore body could be smelted directly. The underlying sulfide zone, which comprised the bulk of the resource, was less amenable to treatment in the smelters of that era, and a method was required to recover the zinc values if the potentiality of the primary ore was to be realized. Many approaches were pursued to solve the sulfide problem before selective flotation was developed. The flotation process was then rapidly adopted by mining companies throughout the world. 

Materials mined from the Earth s crust are usually highly heterogeneous mixtures of amorphous and crystalline solid phases. Crushing and grinding operations are employed to liberate individual pure grains in the 10-50 pm size range. One of the most widely used (10 tons per 

The common gangue material quartz (silica) is naturally hydrophilic and can be easily separated in this way from hydrophobic materials such as talc, molybdenite, metal sulphides and some types of coal. Minerals which are hydrophilic can usually be made hydrophobic by adding surfactant (referred to as an activator ) to the solution which selectively adsorbs on the required grains. For example, cationic surfactants (e.g. CTAB) will adsorb onto most negatively charged surfaces whereas anionic surfactants (e.g. SDS) will not. Optimum flotation conditions are usually obtained by experiment using a model test cell called a Hallimond tube . In addition to activator compounds, frothers which are also surfactants are added to stabilize the foam produced at the top of the flotation chamber. Mixtures of non-ionic and ionic surfactant molecules make the best frothers. As examples of the remarkable efficiency of the process, only 45 g of collector and 35 g of frother are required to float 1 ton of quartz and only 30 g of collector will separate 3 tons of sulphide ore. 

Surfactant molecules will adsorb onto a wide range of solid substrates from aqueous solution. The amount and type of adsorption depends 

In the case of adsorption from solution, the surfactant layers are in equilibrium with the solution and will de-sorb on dilution. However, it would be very useful to produce adsorbed layers in both air and water, which will remain adsorbed. This can be achieved using the Langmuir-Blodgett deposition technique. The technique is based on the observation that if a surfactant, which is insoluble in water, is dissolved in a volatile, non-aqueous solvent and then spread on water, an insoluble monolayer of orientated surfactant molecules will remain at the air/solution interface. The effect of the spreading surfactant and its surface film pressure can be dramatically demonstrated by spreading hydrophobic talc powder on a clean water surface and then placing a 

The first description of a Langmuir trough appears to have been given by Langmuir in Journal of the American Chemical Society (1848). 

For systems with a narrow range of both density differences and particle size. Density ratio 1-1.3 particle diameter usually 20-50 pm although occasionally the diameter could be as large as 200 pm. Feed concentration of target solid 0.5%. 

Condition the solids to alter the wettability of the mineral and the gangue. The fundamental surface wettability for sulfide ores is different from oxides, silicates and salt-type minerals. pFJ is a critical variable. 

Typical conditioning chemical additions include collector about 0.01-0.1 kg/Mg solids, frother about 0.01-0.05 kg/Mg solids, activator about 1-4 kg/Mg solids, depressant about 0.02-2 kg/Mg solids. 

Allow 6 min contact for conditioning. Air 1-1.5 m /m. Bubble size about 1000 pm. Flotation rate constant is 0.2-1 min sink rate constant is 0.005 min  

Flotation cells working volume = 80% of nominal cell volume. 

---

F. F. Apian and D. W. Fuerstenau, in Froth Flotation, D. W. Fuerstenau, ed., American Institute of Mining and Metallurgical Engineering, New York, 1962. 

Fig. XIII-4. Schematic diagram of a froth flotation cell. Note the mineralized bubble shown in the inset. [Reprinted with permission from P. Somasumdaran, Interfacial ChemisUy of Particulate Flotation. AIChE Symp. Sen, 71(150), 2 (1975) (Ref. 58). Reproduced by permission of the American Institute of Chemical Engineers.]...

In other surfactant uses, dodecanol—tetradecanol is employed to prepare porous concrete (39), stearyl alcohol is used to make a polymer concrete (40), and lauryl alcohol is utilized for froth flotation of ores (41). A foamed composition of hexadecanol is used for textile printing (42) and a foamed composition of octadecanol is used for coating polymers (43). On the other hand, foam is controUed by detergent range alcohols in appHcations by lauryl alcohol in steel cleaning (44), by octadecanol in a detergent composition (45), and by eicosanol—docosanol in various systems (46). 

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). 

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. 

Table 6. Organic Auxiliary Reagents Used in Froth Flotation Technology...

It is possible to analy2e froth flotation as a probabiUty process, ie. 

B. Yarar, in S. H. Castro andj. Alvare2, eds.. Froth Flotation, Elsevier, Amsterdam, the Netherlands, 1988, p. 41. 

Froth flotation (qv) is a significant use of foam for physical separations. It is used to separate the more precious minerals from the waste rock extracted from mines. This method reHes on the different wetting properties typical for the different extracts. Usually, the waste rock is preferentially wet by water, whereas the more valuable minerals are typically hydrophobic. Thus the mixture of the two powders are immersed in water containing foam promoters. Also added are modifiers which help ensure that the surface of the waste rock is hydrophilic. Upon formation of a foam by bubbling air and by agitation, the waste rock remains in the water while the minerals go to the surface of the bubbles, and are entrapped in the foam. The foam rises, bringing... 

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). 

The fine mica fraction is deslimed over 0.875—0.147-mm (80—100-mesh) Trommel screens or hydrocylcones, or is separated with hydrosi2ers. The deslimed pulp (<0.589 mm (—28 mesh)) of mica, feldspar, and quart2 is then fed to a froth flotation circuit where these materials are separated from each other either by floating in an acid circuit with rosin amine and sulfuric acid (2.5—4.0 pH), or an alkaline circuit (7.5—9.0 pH) with tall oil amine, goulac, rosin amine acetate, and caustic soda (see Eig. 2). 

Froth Flotation. Froth flotation (qv) of potassium chloride from sylvinite ores accounts for ca 80% of the potassium chloride produced in North America and about 50% of the potassium chloride in Europe and the CIS. Fractional crystallisation and heavy-media processing account for the remaining amounts produced. Froth flotation has been described (6,16,17). 

Mining. Numerous patents have advocated the use of alkanolamines in mining appHcations. Triethanolarnine has been used as a depressent in the flotation of copper (164), in the electrotwinning of gold (165), and as an aid in the froth flotation of nickel ores. Phosphate ore flotation has been improved through the use of a fatty acid condensate with ethanolamine (166). Beneficiation of tin ore has been accompHshed using fatty acid alkanolamides (167). 

---