Mineral floe flotation

Very finely divided minerals may be difficult to purify by flotation since the particles may a ere to larger, undesired minerals—or vice versa, the fines may be an impurity to be removed. The latter is the case with Ii02 (anatase) impurity in kaolin clay [87]. In carrier flotation, a coarser, separable mineral is added that will selectively pick up the fines [88,89]. The added mineral may be in the form of a floe (ferric hydroxide), and the process is called adsorbing colloid flotation [90]. The fines may be aggregated to reduce their loss, as in the addition of oil to agglomerate coal fines [91]. 

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-... 

To obtain a suitable concentrate, the flocculated particles must be separated from the suspension. The usual method is sedimentation of the floes combined with elutriation of the dispersed particles. Flotation of the flocculated particles is a possible method to achieve that separation. The effect of polymers used as flocculants on the flotation of a few minerals has received... 

Water soluble polymers serve widely as flocculants, particularly in the water treatment, paper making, and minerals industries. The objective generally is to destabilize dispersions and cause large, strong, and compact floes to form quickly. The floes are often removed subsequently by sedimentation or flotation. Polymers perform efficiently without introducing the salt needed to... 

Miranda and Berglund [79] used a food grade polymer, (hydroxypropyl)methyl cellulose (HPMC), and ammonium sulfate as additives for the recovery of recombinant a-amylase by flotation. The enzyme was removed from the liquid phase by partition to a salted-out HPMC phase and the enzyme-containing polymer floes were recovered by flotation. This system behaved in a manner similar to the flotation of mineral systems. The problem with this technique is the cost of the polymer and the separation of the enzyme from the polymer phase. Both of them complicate the process and increase the separation cost In general, for protein recovery and separation, especially in the pharmaceutical industry, it is not proper to add chemicals to the feed, because they have to be removed from the product completely and this separation causes problems and additive costs. 

Flocculated slurries are encountered in flotation cells circuits, thickeners, and various processes in mineral extraction plants. With the formation of floes, the slurry may develop an internal structure. This structure may develop properties leading to a non Newtonian flow, shear thinning behavior (pseudoplastic), and sometimes thixotropic time dependent behavior. When shear stresses are applied to the slurry, the floe sizes may shrirrk and be come less capable of entrapping the carrier slurry. At higher shear stresses, the floes may shrink to the size of particles, and the flow may lose its non Newtonian behavior. 

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