Polymeric flocculants selection

Flotation is certainly the major separation method based on the surface chemistry of mineral particles. It is, however, not the only method. Selective flocculation and agglomeration may be mentioned as other methods used commercially to a limited extent. The former is for hematite, while the latter is for coal and finely divided metallic oxide minerals. Both processes use the same principles as described for flotation to obtain selectivity. In selective flocculation, polymeric flocculants are used. The flocculants selectively adsorb on the hematite, and the hematite floes form and settle readily. Thereby separation from the sili-... 

A novel technique for separating ultrafine pyrite particles (minus 1 0 micrometers) from coal fines has been conceptually developed and tested. The technique involves the use of a selective polymeric dispersant for pyrite, while flocculating coal particles with a polymeric flocculant. The suspended pyrite can then be removed from the flocculated coal fines which settle preferentially by gravity. 

The process of selective flocculation is used for solid-solid separations (i.e. to separate a desired component from a mixture of particles). The process involves the selective adsorption of a polymeric flocculant on the desired component, resulting in the formation of agglomerates known as floes, and the separation of such aggregates from particles of other component(s) in the dispersed phase. The competition between different surfaces for the flocculant has to be controlled in order to achieve adsorption on the targeted compo-nent(s). The floes are separated from the suspension either by sedimentation/elutriation or floc-flotation. In order to improve the concentrate grade, if possible, the floes may be subjected to further washing. 

The number of antiflocculants suitable to stabilize emulsions is limited and the effect is less distinct compared with polymeric particles. Selection of an anti-flocculant requires consideration of net charge increa.se, effects of pH shift, and toxicological acceptance (38). 

The principal consideration in selecting an appropriate soluble polymeric component for the steric barrier is that it should be freely soluble in the dispersion medium to be usedo This had been recognised empirically for some years before Napper (4) undertook quantitative studies which showed that sterically stabilised latexes flocculated at or around the theta point for the soliible polymer in the dispersion medium. Later studies have shown that both upper and lower critical flocculation temperatures may occur in organic solventso... 

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