Conditioning for Flotation
The surface chemical changes necessary for froth flotation require varying degrees of agitation and, in some cases even more intensive treatment by scrubbing and attritioning. Heating may be also used. The process are always heterogeneous with the mineral surface one component, and the variability arising from the physical state of the other components, and
the intensity and duration of the agitational requirements. The reactants used in pretreatment can be completely soluble, partially insoluble solids or liquids, completely insoluble oils, and gases. The specific types of interactions, ordered approximately according to the intensity of agitation required, are as follows: reactions with soluble reagents, reactions with partially soluble precipitates and emulsions, desorbing flotation reagents of one type before retreatment with other types, altering nonselective collector distributions already on surfaces to obtain selectivity, and removal of preexisting foreign minerals films. Soluble reagents such as xanthates, soluble salts, inorganic depressants and pH adjusters, have almost negligible separate agitational requirements. Once the reagents solutions are mixed with the following flotation feed pulp, the reaction time requirements are usually measured in brief minutes. The slow step in the process being the diffusion of the reagent through the stationary layer at the mineral solution interface. No specific equipment such as a conditioning tank is necessary with soluble reagents added directly to grinding mills, launders, distributors or to flotation cells. Conditioning with insoluble reagents or partly insoluble precipitates or emulsions is a frequent requirement; in most cases specific conditioning equipment is used. A common example is the activation of zinc sulphides with CuSO4, usually carried out at pH values
near 10 and with collector present. This result in immediate precipitation of Cu +2 both by combination with OH- and SO4=, and by collector, and often in oxidation of the collector to an insoluble form. In spite of this, the agitation times and intensities are moderate. Typical figures are 5 to 10 minutes with commercial conditioners.
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