Collective flotation

On the basis of the function it performs, the flotation process can be divided into two categories (i) bulk and (ii) selective. The process is called bulk or collective flotation when it accomplishes the separation of several valuable components from the gangue minerals. In selective flotation, one valuable component is separated from several others. This selectivity could be accomplished by either using collectors selective with respect to a particular mineral or by differential flotation wherein two or more mineral concentrates are recovered consecutively from the same feed by using modifiers. 

A schematic flowsheet for molybdenum recovery from porphyry coppers is shown in Figure 2.34. Here the important role is played by flotation. The first stage involves collective flotation of copper and molybdenum. The floated product is upgraded through two or three cleaning flotations. Finally, molybdenum is recovered by depressing copper values. In order to depress a mineral, some kind of oxidation should be implied on its surface, or re-... 

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. Gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid partices 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 are added to the flotation medium to meet the various requirements of the flotation process ... 

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

Collagen [9007-34-5] Collagen [9059-25-0] Collagenase [9001-12-1] Collective marks CoUectorless flotation Collector reagents Collectors... 

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. 

The processes that occur in a typical flotation cell are schematically shown in Figure 5 and consist of agitation, particle—bubble coUision and attachment, flotation of particle—bubble aggregates, collection of aggregates in a froth layer at the top of the cell, removal of mineral-laden froth as concentrate, and flow of the nonfloating fraction as tailings slurry. 

Interaction of Solids With Flotation Reagents. For flotation to occur with the aid of reagents, such compounds must adsorb at the sohd—hquid interface unless the soHd to be floated is naturally hydrophobic. In this latter case only depression can be attempted by the use of additional ions or depressants that hinder bubble—particle adhesion. Frothers (typically long-chain alcohols) and/or modifying agents such as hydrocarbon oils can, however, be used to enhance the collection of naturally hydrophobic soflds such as M0S2, talc, or plastics. 

If equation 7 holds, then the soHd is exclusively in the aqueous phase equation 8 defines the condition at which the soHd resides in the oil phase whereas if equation 9 is satisfied then the soHd collects at the water—oil interfacial region. Figure 16 is the flow sheet of a bench-scale study that demonstrates the concept of two-Hquid flotation (40). 

Piggyba.ckFlota.tlon, This process has also been called carrier flotation. The principle is based on the flotation of fine particles adhering to others by mutual coagulation. Thus when one is floated the other, which is usually more difficult to float, is also collected. 

Flotation. The slurry of ground ore leaving the grinding circuit may be separated from part of the water in thickeners or may go directly to the flotation cells. The latter are rectangular tanks into which air is injected or drawn via impellers. Flotation is based on producing a water-repellent chemical film on the exposed sulfide minerals in the ground ore. The sulfide minerals collect on the surface of the air bubbles and rise to the top of the flotation cell, where they can be removed from the froth. The froth overflows the cells in collector troughs called launders. 

Flotation reagents are selected to produce a stable froth and adjust the affinity of target minerals to collect in the froth. Other reagents depress the collection of minerals in the froth. The froth containing the copper minerals overflows into collection launders. 

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. 

Molybdenite [1309-56 ] M0S2, normally floats with the copper sulfides. Therefore, the copper concentrate from the cleaner cells frequently has to be separated from molybdenite in a separate flotation circuit before the copper concentrate goes to the smelter. Gold, silver, selenium, and tellurium are collected with the copper concentrate. 

Mixed liberated particles can be separated from each other by flotation if there are sufficient differences in their wettability. The flotation process operates by preparing a water suspension of a mixture of relatively fine-sized particles (smaller than 150 micrometers) and by contacting the suspension with a swarm of air bubbles of air in a suitably designed process vessel. Particles that are readily wetted by water (hydrcmhiric) tend to remain in suspension, and those particles not wetted by water (hydrophobic) tend to be attached to air bubbles, levitate (float) to the top of the process vessel, and collect in a froth layer. Thus, differences in the surface chemical properties of the solids are the basis for separation by flotation. 

In contrast to vacuum flotation, dissolved-air flotation units can be operated on a continuous basis by the application of pressure. This consists of pressurizing and aerating the process stream and introducing it into the flotation vessel that is maintained at the atmospheric pressure. The reduction of pressure results in the formation of fine air bubbles and the collection of fine particulates to be floated and removed as sludge. 

To recover barite from drilling muds, a direct flotation without prior dewatering and washing of the drilling muds has been described [809]. An alkyl-phosphate is used as a collecting and frothing reagent. 

Scrubbing with liquid (usually water) can enhance the collection of particles when separating gas-solid mixtures. Flotation is a gravity separation process that 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. 

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