Mineral separations, properties

An earlier section which dealt with mineral separation included flotation among the category of concentration separation processes. The introduction of flotation was one of the major milestones in the history of mineral processing. There exist variations (natural or artificially created) in the surface properties of mineral particles, and the technique of flotation is based on the utilization of these differences. The actual specific gravity of the mineral particle plays little or no part in the separation. 

Provided that the physical properties of the minerals contained in the particulate ore are significantly different, the particles of distinct mineralogical compositions can be separated physically to achieve a mineral separation. Particles that consist predominantly of valuable mineral(s) will report to the concentrate under the influence of the exploited physical force, but will dilute... 

Prior to the 1960s, mineral compositions were determined either by wet chemical analyses of mineral separates or by reference to an extensive database of the optical properties of... 

The conventional approach to asphalt analysis has been to extract the bitumen with an organic solvent and then to characterize bitumen and minerals separately. Sulfur content and melting point are commonly measured properties of bitumen. Minerals are generally screened and then subjected to simple quantitative tests. Measurement of weight loss on ignition helps to distinguish between calcium carbonate, which loses... 

Of prime importance to gaining detailed knowledge of the behavior of minerals in a coal during various stages of combustion or other use are the abundance and composition of each mineral phase in the coal. The behavior of minerals and the derived ash depends primarily on the properties of the minerals in the coal, rather than on the concentration of the metal oxides in the ash, as is commonly reported. Few analyses of individual minerals separated from coal are available (30, 22). This is due to the extreme difficulty of separating the different minerals from coal in sufficient quantity for separate analysis. At present the best available estimates of the compositions of minerals in coal are the well known stoichiometric formulas (Table II). 

New methods to improve the separation properties of the organomontmorillonites can also be proposed. For example, it was shown in Section 4 that the introduction of Cs+ cations into the exchange complex of layer silicates, followed by the modification of the mineral by long-chain organic cations, results in the development of surface micropores on side faces of the adsorbent particles. This, in turn, leads to the increase of the adsorption sites, where the chromatographic separation of hydrocarbons takes place. 

The effective enrichment of ores and minerals by flotation, including the possibility of separating materials with similar chemical properties, is achieved by employing a variety of different surfactants which selectively hydrophobize the surface of minerals that undergo flotation, and hydrophilize the surface of those that do not (or the other way around). Due to the relatively small surface area of the minerals treated, the consumption of surfactant-based flotation aids can be as low as 100 grams per tonne, which allows one to use rather complex and expensive surfactants in fine tuning the surface properties of the minerals separated. 

In this case, the crucial data appears to require higher precision than the " °Ar- Ar technique was capable of when the problem was first attacked. Using mineral separates, instead of whole rock samples (Pb-Pb and 1-Xe), was the other key step. Although " °Ar- Ar experiments are capable of the required precision, whether any minerals within the meteorites will have remained closed systems for the entire 4.5 Ga remains to be seen. If so, the logical next step is to use mineral separates so that the extensive terrestrially-derived database on diffusion properties can be used to define closure temperatures (McDougall and Harrison 1999). 

Qian Y, Sturchio NC, Chiarello RP, Lyman PF Lee T-L, Bedzyk MJ (1994) Lattice location of trace elements within minerals and at their surfaces with X-ray standing waves. Science 265 1555-1557 Rajh T, Nedeljkovic JM, Chen LX, Poluektov O, Thumauer MC (1999) Improving optical and charge separation properties of nanocrystalline 2 by surface modification with vitamin C. J Phys Chem ... 

It is weU known that the selective adsorption of surfactants at the solid-water interface imparts hydrophobicity to the surface of the solid. The relative hydrophobicity of the solid surface is responsible for various macroscopic properties observed experimentally. For example, in mineral separation, the hydrophobicity of the solid surface leads to selective bubble-particle attachment, which accounts for the selective flotation of minerals in large scale industrial plants. The relative measure of mineral surface hydrophobicity is usually quantified in terms of contact angle measurements and flotation experiments (Fuerstenau 1957, 1970, 2000 Fuerstenau and Herrera-Urbina 1989 Fuerstenau and Pradip 2005 Pradip 1988). Molecular-modeling tools can be successfully employed to compute the interaction energies and contact angle on both virgin and surfactant-covered mineral surfaces. The relative flotation efficacy of different surfactants can thus be related to their molecular structure and properties. 

Flotation. Flotation is a gravity separation process which 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. This is used to separate mixtures of solid-solid particles and liquid-liquid mixtures of finely divided immiscible droplets. It is an important technique in mineral processing, where it is used to separate different types of ore. 

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). 

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. 

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... 

Although the size separation/classification methods are adequate in some cases to produce a final saleable mineral product, in a vast majority of cases these produce Httle separation of valuable minerals from gangue. Minerals can be separated from one another based on both physical and chemical properties (Fig. 8). Physical properties utilized in concentration include specific gravity, magnetic susceptibility, electrical conductivity, color, surface reflectance, and radioactivity level. Among the chemical properties, those of particle surfaces have been exploited in physico-chemical concentration methods such as flotation and flocculation. The main objective of concentration is to separate the valuable minerals into a small, concentrated mass which can be treated further to produce final mineral products. In some cases, these methods also produce a saleable product, especially in the case of industrial minerals. 

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. 

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