Hydrophobic minerals

Surface properties such as the absorptional ability and the wettability of minerals are again of significant technical importance. On the wettability scale, as for example, minerals are classified as hydrophilic minerals (which are easily wetted by water) and hydrophobic minerals (which are not wetted by water). Hydrophobicity is very helpful in obtaining enrichment of ores by flotation. 

Hydrophobic mineral particles Hydrophilic mineral particles... 

Bubbles with some of them attached with hydrophobic mineral particles shown in the rising mode. Hydrophilic mineral particles with minority presence of hydrophobic mineral particles (those lost chance for contact with bubbles) and bubbles attached with hydrophobic mineral particles (those got mechanically driven along with hydrophilic particles) shown in the descending mode. (B) Froth flotation air bubbles carry nonwetted particles upwards, while wetted mineral particles drown. 

Pyrrhotite is a relatively slow floating mineral, especially monoclinic pyrrhotite, which is usually present in these ore types. The floatability of pyrrhotite also decreases when using certain hydrophobic mineral depressants, such as guars and dextrins. The flotation of pyrrhotite may improve with small additions of copper sulphate (CuS04). 

Kartio, I. J., Basilio, C. I., Yoon, R. H., 1996. An XPS study of sphalerite activation by copper. In R. Woods, F. Doyle, P. E. Richardson (eds.), Electrochemistry in Mineral and Metal Processing IV. The Electro-Chemical Society, 25 - 34 Kelebek, S., 1987. Wetting behaviow, polar characteristics and flotation of inherently hydrophobic minerals. Trans. MM, Sec. C, 96 103 - 107... 

When rocks in a crushed state are dispersed in water with suitable surfactants (also called collectors in industry) to give stable bubbles an aeration, hydrophobic minerals will be floated to the surface by the attachment of bubbles, while the hydrophilic mineral particles will settle to the bottom. The preferential adsorption of the collector molecules on a mineral makes it hydrophobic. 

In water the wetted solid is termed hydrophilic , whereas the non-wetted solid is hydrophobic . Naturally hydrophobic minerals, such as some types of coal, talc and molybdenite are easily separated from the unwanted hydrophilic quartz sand (referred to as gangue ). However, surfactants and oils are usually added as collectors . These compounds adsorb onto the hydrophilic mineral surface and make it hydrophobic. 

The flotation of minerals is based on different attachment forces of hydrophobized and hydrophilic mineral particles to a gas bubble. Hydrophobized mineral particles adher to gas bubbles and are carried to the surface of the mineral dispersion where they form a froth layer. A mineral is hydrophobized by the adsorption of a suitable surfactant on the surface of the mineral component to be flotated. The hydrophobicity of a mineral particle depends on the degree of occupation of its surface by surfactant molecules and their polar-apolar orientation in the adsorption layer. In a number of papers the relationship was analyzed between the adsorption density of the surfactant at the mineral-water interface and the flotability. However, most interpretations of adsorption and flotation measurements concern surfactant concentrations under their CMC. 

Flotation of Naturally Hydrophobic Minerals. Flotation response of naturally hydrophobic minerals correlates very well with elec-trokinetic measurements. Figure 3 shows that the flotation of coal correlates well with zeta potential of demineralized coal (5.). The flotation rate is maximum where the zeta potential is zero and it decreases with increase in the magnitude of the zeta potential. Similar observations were made earlier by Chander and Fuerstenau (6 ) for the flotation of molybdenite. The decrease in flotation rate with increase in zeta potential is because of the electrical double layer repulsion between the charged particle and the air bubble. 

Scalping flotation is where a first flotation step is practised in order to remove a minor, hydrophobic mineral. This mineral could be one that is valuable, such as MoS2 in a Cu-Mo ore [91], or one that is unwanted, such as talc. 

Mineral flotation is a method for selective separation of mineral components out of polymineral dispersions of ground ores in water (ca. 5-35 vol.% of the solid) by using dispersed gas (usually air) bubbles. The method consists in the different adhesion of hydrophobized and hydrophilic mineral particles to an air bubble. Hydrophobized mineral particles adhere to the air bubble and are carried out as a specifically lighter aggregate to the surface of the mineral dispersion where they form a foam (froth) layer. This foam, called concentrate, is mechanically removed (Fig. 1A). A mineral is hydrophobized by adsorption of a suitable surface-active compound (surfactant, collector) on the surface of the mineral component to be flotated. All other nonhydrophobized particles remain dispersed in the mixture (Fig. IB). 

A collector is required to have at least two essential properties, namely adsorption on desired mineral particles and hydrophobization of their surfaces. Except for non-polar oils that are used sometimes as collectors for such naturally hydrophobic minerals like coal, the most common collector molecules possess minerophilic and hydrophobic portions in... 

This phenomenon can be explained in terms of the variation kinetics of the electrical resistance of systems with punctured films (Fig. 2.59b). In contrast to non-plasticized films, for which R diminishes with time, the resistance of the plasticized samples increases as a result of, firstly, incrementing oil content in the film, and secondly, filling of the puncture hole in the film with a hydrophobic mineral oil through S3meresis [72]. 

The above descriptions show the monomeric structures of starch, dextrin, cellulose, and guar gum. In reality, these polysaccharides can be extracted from different sources and the chain length and configuration, molecular weights, and the contents of impurities may vary considerably. Generally, starches have been used mainly as flocculants or flotation depressants for iron oxide minerals and phosphate minerals while the associated silica is floated. Dextrin has been mainly tested as depressants for inherently hydrophobic minerals such as talc, molybdenite, and coal [96]. Applications of polysaccharides in other mineral systems, both in the laboratory and in commercial processes, have also been frequently reported. As can be seen, the polysaccharides have been used or tested as selective depressants in practically all types of mineral systems, ranging from oxides, sulfides, salt-type, and inherently hydrophobic minerals. 

RH Yoon, D Guzonas, BS Aksoy. Processing of hydrophobic minerals and fine coal. Proceedings of the First UBC-McGill Bi-Annual International Symposium, Vancouver, 1995, pp 277-289. 

Froth flotation separation of minerals requires the mineral of interest to have a hydrophobic surface while the other minerals present in the pulp (a mixture of 25% m/m powdered ore with water) are hydrophilic [361, 362]. The particles of the hydrophobic mineral can be captured by the gas bubbles and raised to the pulp surface where they are collected to the froth. Flotability of the mineral depends not only on the amount of adsorbed hydrophobizing reagent (the collector), which in most cases does not exceed a monolayer, but also on the form in which it is adsorbed [361, 363]. 

Flotation equipment consists of a series of agitated tanks through which the mineral pulp flows and into which air is dispersed as a stream of fine bubbles. A froth is formed on the surface, containing the hydrophobic mineral particles, and is skimmed off into a trough where it collapses and flows into a collection tank. 

Ore dressing Chemicals, often containing sulfur, are added to the crushed ore dispersed in by flotation water. The chemicals are adsorbed on the surface of the valuable mineral grains and make them hydrophobic. When air is blown into the suspension the air bubbles stick to the hydrophobic mineral-grain surfaces and they float to the surface. The gangue grains stay on the bottom of the container. 

In this chapter, the use of MD simulations in examining the solution chemistry and interfacial phenomena of selected flotation systems common to mineral processing are examined, including soluble salt minerals, phyllosilicate minerals, oxide minerals, and natural hydrophobic minerals. These initial MD simulation results are discussed in terms of their significance in the understanding of flotation technology for the separation and recovery of mineral resources. 

Naturally hydrophobic minerals are minerals of the surfaces which are of sufficiently low polarity that they are not well wetted by water. A selected list of naturally hydrophobic minerals is presented in Table 4.8 (Zettlemoyer 1969). In some instances, recovery of these minerals is desired, but in... 

Composition and Contact Angle of Selected Naturally Hydrophobic Minerals... 

Naturally hydrophobic minerals such as graphite and talc are common gangue minerals found in sulfide ores and are difficult to separate due to their tendency to float together with valuable sulfide minerals. Despite the relatively successful use of the polysaccharide group of chemicals (e.g., dextrin, guar gum, and carboxymethyl cellulose) as flotation depressants for these naturally hydrophobic minerals, the nature of the adsorption processes remains in debate. Consequently, the adsorption of amphipathic solutes at naturally hydrophobic minerals such as coal and graphite, talc, and sulfur is of interest to many researchers, and a substantial amount of research has been discussed. 

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