Mineral frothers

Flotation is commonly employed for beneficiation of minerals. Frothers are added to the vigorously agitated mixture. Air bubbles attach to the collector-mineral particles, which then rise and are removed along with the froth or foam. The valuable components are separated from the waste or gangue by preferential floating of one of the components to the top while the other sinks to the bottom. 

Table 4. Examples of Flotation Frothers Widely Utilized in the Minerals Industry...

The pH of the pulp to the flotation cells is carefliUy controlled by the addition of lime, which optimizes the action of all reagents and is used to depress pyrite. A frother, such as pine oil or a long-chain alcohol, is added to produce the froth, an important part of the flotation process. The ore minerals, coated with an oily collected layer, are hydrophobic and collect on the air bubbles the desired minerals float while the gangue sinks. Typical collectors are xanthates, dithiophosphates, or xanthate derivatives, whereas typical depressants are calcium or sodium cyanide [143-33-9] NaCN, andlime. 

The frother should not in itself be a strong collector, especially of minerals meant for drowning. It should work in the presence of the other reagents necessary for flotation. The frothers must be soluble in water to some extent otherwise they would be distributed very unevenly in an aqueous solution, with the result that their surface activity would not be fully effective or exploited. There are three main groups of reagents employed by the mineral industry as frothers (Figure 2.24) these different groups include aliphatic alcohols (me-... 

Flotation of sulfide minerals is a popular topic in the literature dealing with flotation. It displays well the application of the different flotation reagents such as frothers, collectors, depressants, and activators. 

Frothing Agents are intended to stabilize the particle (mineral)-air mixture (foam) at the surface of the flotation tank. Alkyl or amyl alcohols in the C5 to C12 range are typical frothers. They lower ysv which is beneficial to the stability of the foam to some extent collectors and frothers may counteract in their effects so that compromise conditions must be selected. 

The type and addition of frother are found to have a pronounced effect on the collectorless floatability of chalcopyrite (Heyes and Trahar, 1977). The recovery of collectorless flotation of chalcopyrite is much higher using PPG40 than amyl alcohol. The effects of several frothers on the collectorless flotation of some minerals have been tested and the results are presented in Table 10.1. It further provides the evidence that the type of frother produces a markable influence on collectorless flotation of sulphide minerals. The frothers with lower surface tension are more effective in enhancing the recovery of collectorless flotation of sulphide minerals. 

Table 10.1 Influence of frother on the collectorless flotation of the sulphide minerals (Wang etal., 1991a,b,c,d)...

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. 

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. 

Frothers are chemicals whose molecules contain both a polar and a nonpolar group. The purpose of a froth is to carry mineral-laden bubbles lor a period of lime until the froth can be removed from the flotation machine for recovery of ils mineral content. Typical frothing chemicals are alcohols, cresylic acids, eucalyptus oils, camphor oils, and pine oils, all of which are slightly soluble in water. Soluble frolhers in common use include alkyl ethers and phenyl ethers of propylene and polypropylene glycols. 

Concretion mass of mineral matter found in rock of a composition different from its own and produced by deposition from aqueous solution in the rock. Conditioning agents all chemicals that enhance the performance of collectors or frothers (ASTM D-5114). 

Froth flotation is an application of foams that is used to separate mineral components from each other based on their having different surface properties, typically their wettability and surface electrical charge. For example, froth flotation is the classic process used to separate copper from lead ore. The process involves having hydrophobic particles attach to gas bubbles which rise through a turbulent suspension to create a surface foam called a froth. Figure 10.2 shows an illustration of a mechanical flotation cell. This is the classic flotation device [53,91,625], First, the flotation feed particles are well dispersed into a particle suspension. Together with chemical flotation aids, such as collectors and frothers, this constitutes what is called the flotation pulp. In a mechanical flotation cell, air is fed in the form of fine bubbles and introduced near the impeller (see Figure 10.2). In addition to mechanical flotation cells, there are also pneumatic cells and cyclone flotation cells. Pneumatic... 

For flotation to be most effective, reagents such as oil (collector) and surfactant (frother) must be added to the aqueous coal slurry. The collector adsorbs on the coal surface and makes it more hydrophobic, while the surfactant facilitates production of a stable froth. According to Leonard (26), the optimum coal sizes for froth flotation are between 50 and 140 mesh (0.3 and 0.106 mm). While conventional froth flotation will successfully remove minerals from coal, it has limited effect on the pyrite content, as pyrite tends to float almost as well as coal. Because of this, researchers have been looking for better ways to remove pyrite from coal. In addition, as previously mentioned, it is necessary to grind coal to very fine sizes in order to sufficiently liberate the mineral matter and pyritic sulfur. But, at these very fine sizes,... 

K. Hadler, Z. Aktas, and J. J. Cilliers, The effects of frother and collector distribution on flotation performance. Minerals Engineering 18(2) (2005). 

Oils,—These are of two kinds the collectors which have high affinities for sulphides and the frothers. Hard-wood creosote is the standard collective oil but owing to its expense other wood-, coal-, and oil-distillate products are substituted for it either entirely or in part, coal tar being a favorite. On silver minerals... 

If a bubble carrying air-avid mineral particles reaches the surface of the flotation unit and then bursts, the raised mineral particles will sink again. Bubble stability is maximized by addition of a foam stabilizer or frother, which assists in generating a sufficiently stable foam layer on the flotation unit to enable the foam plus associated mineral to be skimmed from the water phase. The frother also puts an oily phase on the surface of each bubble as it forms, which helps the mineral-gangue differentiation function of the collector. Typical frothers are oily materials of no more than slight water solubility such as pine oil (a mixture of terpenes) or a long chain (C5 or higher) alcohol such as 1-pentanol, and are used at the rate of 20-45 g/tonne of ore. 

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. pH is a critical variable. Typical conditioning chemical additions include collector about 0.01 to 0.1 kg/Mg solids frother about 0.01 to 0.5 kg/Mg solids activator about 1 to 4 kg/Mg solids depressant about 0.02 to 2 kg/Mg solids. Allow 6-min contact for conditioning. Bubble size about 1000 pm. Flotation rate constant is 0.2 to 1 min sink rate constant is 0.005 min-. Flotation cells mechanical cell for fast float, sequential separation, and relatively coarse particle diameter 1.6 to 2.4 kW/m cell volnme. Pneumatic cell for relatively dilute feed concentrations and smaller particle diameters. Air blower 0.5 kW/m cell volume. Typical solids throughput 0.4 to 0.8 kg/s m feed concentration 10 to 40% w/w. Air escape velocity 0.02 m/s. Float times 6 to 20 min. Feed concentration to rongher or scavenger 30% w/w to cleaner 10% w/w. 

Frothers The purpose of a frothing agent is to produce air bubbles in the floatation cell, which must then remain intact until they are skimmed off to collect the floated mineral particles. If the collector cannot act as a frothing agent on its own, then additional agents are added, such as pine oil, polyglycols, and cresylic acid. 

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