Flotation reagent-Frothers, Extenders,and Activators

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 Frothers, Extenders,and Activators this article.

Frothers

The bubbles that rise to the top of the flotation cell must not break until they are skimmed off to collect the floated particles. To produce the desired stability of the froth that forms in the cell, nonionic surfactants such as monohydroxylated cresols are usually added unless the collector itself can act as a frother. When long-chained collectors such as oleic acid are used, they will adsorb also at the bubble surface in sufficient amounts to achieve an elastic surface and stable bubbles. However, when short-chained chemicals such as ethyl xanthate are used as collectors, additional reagents must be added for froth stability. Table 1 lists some commonly used frothers.

Along with the benefits of froth stability, frother species can co-adsorb with the collector on the particle. Also, the frother on the bubble surface can migrate to the particle–gas interface during the time of contact to arrive at the desired equilibrium adsorption density at that interface on the solidbubble contact perimeter. Such migration and co-adsorption of the frother can anchor the bubble onto the particle and cause it to adhere as desired.

In addition to frothers and collectors, nonionic and nonpolar surface-active agents are used in many flotation schemes simply to enhance the hydrophobicity of the particles and the resultant flotation recovery. Kerosene and fuel oils are used in the flotation of phosphates and coal, for example. These reagents are thought to act by forming a multilayer coating on the already partly hydrophobic surfaces.

They can also act like frothers by co-adsorbing with collectors. Intensive agitation is required in some cases to disperse and “smear” these reagents onto particle surfaces.

Activators

Many minerals do not adsorb collectors, so they do not float unless special reagents are added to activate adsorption. For example, oleate will not float quartz on its own, but flotation will occur when calcium salts are added to the pulp at high values of pH where hydrolysis of Ca2+ has occurred. Similarly, copper sulfate acts as an activator for the flotation of sphalerite using xanthate as a collector at relatively low concentration. An activator normally acts by adsorbing on the mineral, providing sites for adsorption of the collector species. Copper ion exchanges for zinc ion of the mineral surface, and the sphalerite particle then behaves in flotation like a copper sulfide particle.

Multivalent ions can adsorb on oppositely charged particles and reverse their zeta potential, causing adsorption of collectors that have a charge of the same sign as that of the mineral. An example is sulfate activation of alumina.

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Sinoninetechnology team