Hydrophilic minerals

Clearly, it is important that there be a large contact angle at the solid particle-solution-air interface. Some minerals, such as graphite and sulfur, are naturally hydrophobic, but even with these it has been advantageous to add materials to the system that will adsorb to give a hydrophobic film on the solid surface. (Effects can be complicated—sulfur notability oscillates with the number of preadsoibed monolayers of hydrocarbons such as n-heptane [76].) The use of surface modifiers or collectors is, of course, essential in the case of naturally hydrophilic minerals such as silica. 

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. 

Suitable collectors can render hydrophilic minerals such as silicas or hydroxides hydrophobic. An ideal collector is a substance that attaches with the help of a functional group to the solid (mineral) surface often by ligand exchange or electrostatic interaction, and exposes hydrophobic groups toward the water. Thus, amphi-patic substances (see Chapter 4.5), such as alkyl compounds with C to C18 chains are widely used with carboxylates, or amine polar heads. Surfactants that form hemicelles on the surface are also suitable. For sulfide minerals mercaptanes, monothiocarbonates and dithiophosphates are used as collectors. Xanthates or their oxidation products, dixanthogen (R - O - C - S -)2 are used as collectors for... 

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. 

Often the minerals we want to float are hydrophilic, and surfactants (called collectors ) are added, which, at a specific concentration, adsorb onto the particle surface, making it hydrophobic and hence floatable. In a mixture of hydrophilic minerals, optimum flotation will occur where one of the minerals adsorbs collector but the others do not. 

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. 

The problems in bonding polymers to hydrophilic mineral surfaces were discussed and a theory of adhesion in which silane coupling agents provide a bond at the interphase was proposed by Plueddemann in 1974 [3]. However, silane coupling agents specifically designed to impart hydrophilicity to mineral surfaces have been proposed only recently [34], A trimethoxysilyl-terminated poly( /V-... 

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). 

Formation of organic inclusions, i.e. petroleum inclusions as opposed to water inclusions in hydrophilic minerals, poses several interesting questions as to how one may get the oil into the necessary intimate contact with the liphophobe water wetted mineral. 

The specific immersion wetting enthalpies of kaolinite, illite, and their organo-philic derivatives were investigated in methanol and benzene in our earlier publications [35,37,38]. These data reveal that the heat of immersion in methanol is the highest in the case of the dialyzed hydrophilic mineral, and with increasing surface modification its value decreases. The comparison of immersion wetting enthalpies relative to unit mass of the adsorbent is justified only when the specific surface area of the adsorbent is constant. It is also known, on the other hand, that the value of liquid sorption capacity, is a function of surface modification 02 = where 2flm,2 is the hydrophobic surface area and a is the total... 

In a laboratory experiment (Adamson and Gast, 1997), one may use the following recipe. To a 1% sodium bicarbonate solution, one can add a few grams of sand. Then if one adds some acetic acid (or vinegar), the bubbles of CO2 produced cling to the sand particles and thus make these float on the surface. It must be mentioned that in wastewater treatments, the flotation method is one of the most important procedures. When rocks in crushed state are dispersed in water with suitable surfactants (also called collectors in industry) to give stable bubbles on aeration, hydrophobic minerals will float to the surface due to 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. Xanthates (alkyl-O-CSj) have been used for flotation of lead and copper. 

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