Flotation Reagent

Flotation Reagent

 

any one of various chemical substances that govern and regulate most flotation processes. The introduction of flotation reagents into the liquid phase of the pulp and subsequent adsorption along the liquid-gas and solid-liquid interfaces create conditions for the selective flotation of specific mineral particles. There are three principal types of flotation reagents: collectors, regulating agents, and frothing agents.

Collectors are organic substances that impart hydrophobicity to mineral particles to be floated, which makes possible the attachment of the particles to gas bubbles. The molecules of a collector are generally composed of two parts: (1) a hydrocarbon (nonpolar) and carboxyl group and (2) an amino-acid group and another (polar) chemically active group affixed to the mineral surface. Collectors are classified as nonionogenic and ionogenic according to their ability to dissociate into ions in an aqueous medium. Nonionogenic collectors are virtually insoluble in water and usually include nonpolar, hydrocarbon liquids, such as kerosine and petroleum oils. Ionogenic collectors dissociate in water into an anion and cation and, depending on the type of hydrophobic ion, are divided into anion collectors (for example, xanthogenates, Aerofloats, fatty acids and their salts, alkyl sulfates) and cation collectors (for example, higher aliphatic amines and their salts, quaternary ammonium bases).

The chemisorptive attachment of the collector to specific elements of the surface of mineral particles determines the selectivity of flotation. The hydrocarbon part of the collector molecule, which has an extremely weak attraction for water molecules, inhibits the hydration of the mineral surface, that is, the formation of a stable layer of water molecules. The addition of nonpolar liquids, such as oils and kerosine, to the pulp increases hydrophobicity. Sometimes a combination of various collectors is used for a more complete separation of the necessary minerals. The flotation of sulfide minerals, for example, galena, chalcopyrite, and sphalerite, most often involves the use of water-soluble salts of xanthic or dithiophosphoric acid, that is, xanthogenates or dithiophosphates. Nonsulfide minerals, such as apatite, fluorite, and natural phosphates, are usually floated with various fatty acids and their salts, for example, sodium oléate and sulfonic acid salts. The use of alkylhydroxamic acids and their salts appears promising. Reagents that are poorly soluble in water and that adhere to particles in the form of droplets are used in the flotation of naturally hydrophobic minerals, such as coal and native sulfur.

Regulating agents are used to increase the selectivity of collector adherence to the surface of specific minerals, increase the strength of the adherence, reduce the amount of collector used, and impart optimum stability to the mineralized froth. When a regulating agent acts directly on a mineral surface, making possible better adherence of the collector to the mineral and activating flotation, it is called an activator. For example, the addition of sodium sulfate sulfidizes the surface of oxidized nonferrous metal minerals and permits the adherence of xanthogenate molecules to the mineral. Copper sulfate exhibits an activating effect on the flotation of sphalerite. A regulating agent that inhibits the interaction of the mineral with the collector is called a depressor. For example, waterglass prevents the anchoring of soaps on silicate minerals and depresses flotation; lime and cyanides depress the flotation of pyrite. In addition to activators and depressors, there are regulating agents that maintain a specific alkalinity and acidity in the medium (pH regulators). Regulating agents that peptize micron-sized particles (fine slurry)—for example, sodium silicate—and reduce their adverse effect on flotation are called peptizers and are most often inorganic compounds; organic regulating agents, for example, carboxymethyl cellulose, are seldom used.

Frothing agents increase the stability of the mineralized froth and facilitate the dispersion of air in the pulp and the formation of the minutest possible bubbles. Such agents are usually organic surfactants, the molecules of which have a polar and nonpolar group and are adsorbed along the surface of the gas-liquid interface, thereby reducing surface tension. The polar groups are transformed into water, as a result of which the air bubbles are surrounded by stable hydrated envelopes, which prevent their coalescence. Various industrial alcohols and their mixtures and pyridine bases are used as frothing agents. Certain collectors, such as soaps and amines, exhibit a frothing effect.

The action of flotation reagents depends on several factors, including the natural composition of the mineral surface, the alkalinity and acidity of the medium, and pulp temperature (for fatty acids and their salts). The amounts of flotation reagents used vary from several grams to several kilograms per ton of material treated. Several different reagents introduced in a given sequence are used during flotation. Usually one or several regulating agents are added to the pulp first, then a collector, and subsequently a frothing agent. Optimum contact time for the pulp and each reagent is maintained. In many cases, the action of reagents is complex, and their classification given here is arbitrary.

REFERENCES

See references under and CONCENTRATION OF MINERALS.

V. I. KLASSEN [27–1494–3 ]

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