Flotation reagent- Depressants, Deactivators, Dispersants and Flocculants

In mineral processing plant,a number of organic and inorganic reagents are used in flotation and auxiliary processes to achieve separation, including collectors, frothers, extenders, activators, depressants, deactivators, flocculants, and dispersants. Collectors, frothers, and extenders are surfactants added to impart hydrophobicity to the minerals and to make selective adsorption of the collector possible or to eliminate interference to flotation by various dissolved or colloidal species. We discuss Depressants, Deactivators, Dispersants and Flocculants this article.

Depressants

Depressants retard or inhibit flotation of a desired solid. The action of a depressing agent is often a result of its adsorption on the particle surface, which preempts the collector from adsorbing and masks the adsorbed collector from the bulk solution so that the particle does not exhibit a hydrophobic exterior. For example, multivalent ions, such as phosphate, can prevent oleate adsorption on apatite because of charge reversal by the phosphate species. Multivalent ions can also act by depleting the collector through precipitation; that is, calcium can depress flotation of apatite by removing oleate from the solution as calcium oleate precipitate. Other chemicals used as depressants include silicates, chromates, dichromates, and aluminum salts. Organics are also used as depressants. Common examples include starch, tannin, quebracho, and dextrin. These massive molecules probably act by adsorbing on the mineral surface, sometimes even with the collector species, and then masking the collectors’ hydrophobic tails with their own large size.

Deactivators

Deactivators are chemicals that react with activators to form inert species, thus preventing flotation.

For example, activation of sphalerite with copper using xanthate as a collector is prevented by adding cyanide, which complexes with copper.

Dispersants and Flocculants

Flotation is often hampered by the presence of fine particles called slimes, which can coat the coarser mineral particles and consume excessive amounts of reagents because of their large specific surface areas. When slimes are a problem, chemicals such as silicates, phosphates, and carbonates are usually added to disperse them. Some of these chemicals also influence flotation, because they can complex with deleterious chemical species. Oxalic acid, tartaric acid, and ethylenediaminetetraacetic acid (EDTA) are often used for this purpose.

Systems for beneficiation and effluent treatment often deal with fines by flocculation using polymers. The polymers used include starch and its derivatives, polyacrylamides, and polyethylene oxide. Polymers flocculate particles into larger aggregates (flocs) by forming bridges between them. Adsorption of polymers on the mineral particles is attributed to hydrogen bonding between functional groups, such as OH and –NH2 and surface –OH on the mineral particles, or chemical or electrostatic bonding between polymer functional groups and surface sites. In addition to the mineral and polymer properties, the extent of flocculation also depends on variables such as mode of polymer addition, dosage, and agitation. Polymers that can selectively adsorb on mineral fines are used also to selectively flocculate them, followed by separation of the flocs from gangue using elutriation or flotation. For example, starch is used to selectively flocculate hematite from fine taconite ore, which is then separated by floating the coarse quartz using amine. Another example is hydroxamated polyacrylamide, which is strongly adsorbed on iron oxide in “red mud” effluents from the Bayer process. Polymers added for flocculation should not interfere with downstream processes such as flotation, filtration, or effluent treatment. Note also that many low-molecular-weight polymers can act as dispersants.

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Sinonine technology team