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Classification of Flotation Reagents

Reagents are the most important part of the flotation process. In the early stage of thedevelopment of the flotation process, the major advances were due to better flotationreagents. In developing a treatment process, much time, energy and attention is spent onthe selection of reagents to give the most effective separation and concentration results. Incommercial plants, the control of reagent additions is the most important part of the flota-tion strategy.

Modern classification of the reagents is based on the function of a particular reagent. Onthis basis, reagents are divided into collectors, frothers, regulators and depressants. Severalthousands of chemicals were either tested or suggested as flotation reagents. Nowadays,there are only a few hundred of these reagents that are extensively used in flotation.

Collectors are a fairly large group of organic chemical compounds, which differ inchemical composition and function. The basic purpose of the collector is to selectivelyform a hydrophobic layer on a given mineral surface in the flotation pulp and thus provideconditions for attachment of the hydrophobic particles to air bubbles and recovery of suchparticles in the froth product.

According to the ability of collectors to dissociate in water, they can be divided into dis-tinct groups. Ionizing collectors consist of heteropolar organic molecules. Depending onthe resulting charge, the collector assumes the character of a cation or anion. Anionic col-lectors are further classified into oxhydryl and sulfhydryl collectors on the basis of theirsolidophilic property.

Cationic collectors are chemical compounds in which the hydrocarbon radical is pro-tonized. These reagents are amines from which the primary amines are the most importantflotation collectors (i.e. R-NH2).

Non-ionizing collectors are also divided into two groups. The members of the first groupare the reagents containing bivalent sulfur. The second group contain non-polar hydrocar-bon oils.

Frothers are heteropolar surface-active compounds that lower the surface tension ofwater and have the ability to adsorb on the air bubble–water interface. Their presence inthe liquid phase increases the film strength of the air bubbles, thus providing betterattachment of hydrophobic particles to the bubbles. Surface tension also affects the sizeof the air bubbles. The effectiveness of some of the frothers is very much dependent on pulp pH. Their performance is optimum when frother is in the molecular form.

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For example, cresol at high pH is converted into an ionized compound, which does notact as a frother:

Quinoline in acid pH forms ions, which have poor frothing properties:

On the basis of the effectiveness of frothers at different pH values (i.e. the pH at whichthe frother is most effective), they can be divided into: acidic, when frothing ability isreduced with an increase in pH from acid to alkaline and neutral, when the performanceof the frother does not depend on pH value of the pulp.

The acidic frothers are chemicals that belong to two basic groups: phenols (cresol,xylenol) and alkylsulfonates (surfactants).

The most important group of frothers is the neutral type of frothers. These frothers aredivided into the following groups: cyclic alcohols, aliphatic alcohols, alkoxy paraffins andglycols.

Regulators: Activators, depressants and pH regulators are often referred to in the litera-ture as modifiers or regulators of the flotation process. The main purpose of these reagentsis to modify the action of the collector on mineral surfaces and as a consequence governthe selectivity of the flotation process. In the presence of regulators, the collector onlyadsorbs on particles that are targeted for recovery.

In some cases, a regulator reacts directly with the mineral surface (copper sulfate withsphalerite) and provides conditions for interaction of this mineral with the collector. Thesereagents are known as activators. Some regulators may reduce conditions for hydropho-bization of a particular mineral with the collector, or they can make the surfacehydrophilic. These reagents are called depressants. Both activators and depressants can beeither inorganic or organic compounds.

The third group of modifiers is pH regulators. The purpose of these is to regulate theionic composition of the pulp by changing the concentration of the hydrogen ion in thepulp. Consequently, this results in improvement in collector interaction with the selectedmineral and reduces collector interaction with undesirable minerals. The pH regulators canalso be depressants at the same time (e.g. lime and some organic acids).

N+ HCl

N

H

+

Cl−

CH3

OH

CH3

O Na+

−

+ NaOH

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This classification of regulators is very arbitrary. For example, regulators under certainconditions act as depressants and under other conditions as activators. Other importantgroups of reagents, which cannot be included in any group of regulators, are dispersantsbecause of the multiplicity of functions that they can fulfill. Dispersants added to a pulpcontaining slimes or clay act as a cleansing medium and can improve the rate of flotationof particular minerals and reduce excessive collector consumption.

Flocculants are natural or synthetic polymers with different polar groups. Normally,they have molecular weights ranging from 20,000 to several millions, and they can be elec-trolytes and non-electrolytes. On the basis of the way they dissociate in water, flocculantscan be loosely classified into the following groups:

(a) Anionic polyelectrolytes dissociate in water into complex polymer anions and simple cations (Na�, NH4

�, K�, etc).(b) Cationic polyelectrolytes dissociate into polymer cations and anions (Cl�, SO4

�,CH3COO�).

(c) Amphoteric polyelectrolytes are polymers that contain both anionic and cationicgroups.

(d) Non-ionic polymers contain polar groups without attached an anion or cation.

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