Flotation of Metal Ores

This reduces the requirement for costly decolouriser additives. 

For glass fibre production, the number and size of acid insoluble refractory particles (mainly grains of silica sand) are of particular importance as they can cause breakages of the fibres as they are drawn out to the required diameter. 

Slaked lime is sometimes blended with the kaolin and ball clays used in the production of whiteware pottery. It helps to bind the materials and also increases the whiteness of the fired product [32.4]. 

The fluxing and glass-forming properties of lime are exploited in various formulations for vitreous enamel. 

While most calcium aluminate cements are produced from limestone and alumina (see section 9.5), high purity, refractory-grade material is made by at least one producer using ground quicklime as the source of calcium. The quicklime and alumina are blended and fed to a rotary kiln, where they sinter and melt at over 1500 °C. The molten calcium aluminate (about 70 % AI2O3 and 28 % CaO) is cooled in a rotating cylinder to produce a clinker, which is subsequently ground to substantially less than 90 pm [32.6]. 

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Table 8 summarizes domestic consumption by use for amyl alcohols. About 55% of the total 1-pentanol and 2-methyl-1-butanol production is used for zinc diamyldithiophosphate lubrication oil additives (150) as important corrosion inhibitors and antiwear additives. Amyl xanthate salts are useful as frothers in the flotation of metal ores because of their low water solubiUty and miscibility with phenoHcs and natural oils. Potassium amyl xanthate, a collector in flotation of copper, lead, and zinc ores, is no longer produced in the United States, but imports from Germany and Yugoslavia were 910 —1100 t in 1989 (150). 

Rather than reiterating what is well known about flotation of gold, PGMs and oxide minerals, emphasis has been placed on the separation methods which are not so effective when using conventional treatment processes. These difficult separation methods are largely attributed to problems with selectivity between valuable minerals and gangue minerals, especially in the flotation of oxide ores and base metal oxides, such as copper, lead and zinc oxide ores. 

A characteristic property of organophosphorus compounds with P=0 or P=S bonds is their ability to form complexes. This was the basis for the industrial use of these substances as flotation agents in nonferrous metallurgy. Dibutyl- and dicresyldithiophosphates proved efficient collectors of sulfide or sulfidised nonferrous metals during the flotation of oxide ores. 

Promoters or collectors provide the substances to be separated with a water-repellent air-avid coating that will adhere to air bubbles. Typical collectors for flotation of metallic sulfides and native metals are dithiophosphates and xanthates. Fatty acids and their soaps, petroleum sulfonates, and sulfonated fatty acids are widely used as collectors in flotation of fluorspar, iron ore, phosphate rock, and others. Fuel oil and kerosene are used as collectors for coal, graphite, sulfur, and molybdenite. Cationic collectors such as fatty amines and amine salts are widely used for separation of quartz, potash, and silicate minerals. 

V. A. Glembotski and E. A. Anfimova, Flotation of Oxidized Ores of Non-Ferrous Metals, Nedra, Moscow, 1966 (in Russian). 

Flotation is the single most important method of mineral processing and is widely used for the concentration of metal ores, industrial minerals, and coals. Several investigations were carried out during the last century, and the flotation literature was immense, particularly on selective collectors and their interaction mechanisms on sulfide, oxide, and silicate minerals. However, it is often difficult... 

Lower grades, such as sulfate pine oil are used for the flotation of metallic sulfide ores, including copper, zinc, nickel, iron, and lead. In textiles, the most important property of pine oil is its ability to reduce surface tension and interfacial tension between fiber and solution. Pine oil allows ingredients in wet-processing baths to get into fibers and to work immediately. Also, because of its bacteriocidal activity, it is used in almost all wet processing of cotton, silk, rayon, and woollen goods. Pine oil production has declined as a result of the decrease in the amount of pine oil used in cleaner and disinfectant products. The pine oil content of those products has dropped from 70-90% to 10-30% (182). 

Sulfide collectors ia geaeral show Htfle affinity for nonsulfide minerals, thus separation of one sulfide from another becomes the main issue. The nonsulfide collectors are in general less selective and this is accentuated by the large similarities in surface properties between the various nonsulfide minerals (42). Some examples of sulfide flotation are copper sulfides flotation from siUceous gangue sequential flotation of sulfides of copper, lead, and zinc from complex and massive sulfide ores and flotation recovery of extremely small (a few ppm) amounts of precious metals. Examples of nonsulfide flotation include separation of sylvite, KCl, from haUte, NaCl, which are two soluble minerals having similar properties selective flocculation—flotation separation of iron oxides from siUca separation of feldspar from siUca, siUcates, and oxides phosphate rock separation from siUca and carbonates and coal flotation. 

In mineral technology, sulfur dioxide and sulfites are used as flotation depressants for sulfide ores. In electrowinning of copper from leach solutions from ores containing iron, sulfur dioxide prereduces ferric to ferrous ions to improve current efficiency and copper cathode quaHty. Sulfur dioxide also initiates precipitation of metallic selenium from selenous acid, a by-product of copper metallurgy (326). 

The reaction of chloroformates with sodium xanthates results in the formation of alkyl xanthogen formates that are useful as flotation agents in extraction of metals from their ores (48). 

When the ore contains a large amount of clay minerals, these form difficult to separate slimes, which hinder the recovery of the minerals (see Clays). The tailing from the scavenger cells can be cycloned to remove the slimes before the coarse material is floated in a tailings retreatment plant. The flotation product from the rougher cells of this plant can be reground and cleaned. This additional treatment of the tailings from the main copper flotation plant may improve the recovery of metal values by 1—3%. 

The isolation of zinc, over 90% of which is from sulfide ores, depends on conventional physical concentration of the ore by sedimentation or flotation techniques. This is followed by roasting to produce the oxides the SO2 which is generated is used to produce sulfuric acid. The ZnO is then either treated electrolytically or smelted with coke. In the former case the zinc is leached from the crude ZnO with dil H2SO4, at which point cadmium is precipitated by the addition of zinc dust. The ZnS04 solution is then electrolysed and the metal deposited — in a state of 99.95% purity — on to aluminium cathodes. 

If the ore consists of separate grains containing the desired material, it can be separated from undesired minerals by physical methods such as flotation, sedimentation, or magnetic separation. For metals this step can lead to 80 to 95 percent concentration of the value of the ore. Ceramic raw materials such as sand and clay can often be found pure enough in nature so that no concentration is needed. 

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. 

The metallic or semi-metallic character of many common sulfides implies the significance of electrochemical factors in the study of their oxidation, which is relevant to environmental, energy, and metallurgical issues, e.g., in connection with the direct electrochemical conversion of sulfide ores to metals, the pressure leaching of ore materials, or flotation processes. 

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