Selective flotation process

Figure 10.8 Illustration of a selective flotation process for the separation of heavy metal sulfides such as Cu-Mo, Cu-Ni, or Ni-Co-Cu, from unwanted gangue minerals, and from each other. From Leja [91]. Copyright 1982, Plenum Press.

The reduction of sulfur is one of the principal benefits of the froth flotation process. Of the two types of sulfur in coal (i.e., inorganic and organic), only the inorganic sulfur (mainly represented by pyrite) can be separated fi om coal by physical methods. The floatability of coal-pyrite is, however, somewhat different fi om that of ore-pyrite, and its separation from coal presents a difiicult problem. The research based on the behavior of ore-pyrite in the flotation process— namely, its poor flotability under alkaline conditions—did not result in a development of a coal-pyrite selective flotation process. The two-stage reverse flotation process proved to be much more successful. In... 

The first commercial flotation process was used at Broken Hill, Australia in 1902. By 1910, a process had been developed to make a collective concentrate from lead-zinc ore and the first selective flotation process was patented in 1912. 

Flotation reagents are used in the froth flotation process to (/) enhance hydrophobicity, (2) control selectivity, (J) enhance recovery and grade, and (4) affect the velocity (kinetics) of the separation process. These chemicals are classified based on utili2ation collector, frother, auxiUary reagent, or based on reagent chemistry polar, nonpolar, and anionic, cationic, nonionic, and amphoteric. The active groups of the reagent molecules are typically carboxylates, xanthates, sulfates or sulfonates, and ammonium salts. 

On the basis of the function it performs, the flotation process can be divided into two categories (i) bulk and (ii) selective. The process is called bulk or collective flotation when it accomplishes the separation of several valuable components from the gangue minerals. In selective flotation, one valuable component is separated from several others. This selectivity could be accomplished by either using collectors selective with respect to a particular mineral or by differential flotation wherein two or more mineral concentrates are recovered consecutively from the same feed by using modifiers. 

Conox A process for beneficiating sulfide ores by selective flotation. Developed and offered by Lurgi. 

The treatment process and flotation properties of pyrochlore are very much dependent on the gangue composition of the ore. The selective flotation of pyrochlore from carbonatite ore is not possible since calcite and dolomite have similar flotation properties as pyrochlore. In addition, in the presence of carbonates, the stable pH required for flotation of pyrochlore (i.e. 5.0-5.5) cannot be maintained. 

This multi-step, one-pot process was taken further by integration of a third supported reagent for the sequential preparation of 3,5-diphenylpyrazole (Scheme 2.17). Following the previously established procedure, acetophenone was deprotonated and acylated to afford the 1,3-dicarbonyl species. This intermediate was easily separated from the spent polymers by filtration and passed without isolation into a suspension of the resin bound hydrazine salt (9), affording the desired pyrazole in 91% yield. In a subsequent publication, the authors reported that the depleted polymeric reagents from the first step of the conversion (i.e. (7) and (8)) were recovered and separated via a selective flotation procedure, enabhng them to... 

The flotation process is applied on a large scale in the concentration of a wide variety of the ores of copper, lead, zinc, cobalt, nickel, tin, molybdenum, antimony, etc., which can be in the form of oxides, silicates, sulfides, or carbonates. It is also used to concentrate the so-called non-metallic minerals that are required in the chemical industry, such as CaF2, BaS04, sulfur, Ca3(P03)2, coal, etc. Flotation relies upon the selective conversion of water-wetted (hydrophilic) solids to non-wetted (hydrophobic) ones. This enables the latter to be separated if they are allowed to contact air bubbles in a flotation froth. If the surface of the solids to be floated does not possess the requisite hydrophobic characteristic, it must be made to acquire the required hydrophobicity by the interaction with, and adsorption of, specific chemical compounds known as collectors. In separations from complex mineral mixtures, additions of various modifying agents may be required, such as depressants, which help to keep selected minerals hydrophilic, or activators, which are used to reinforce the action of the collector. Each of these functions will be discussed in relation to the coordination chemistry involved in the interactions between the mineral surface and the chemical compound. 

Again, any type of technique can be used for generating gas bubbles in a nonfoaming adsorptive bubble separation system. The most effective bubble generation techniques for a nonfoaming system are dissolved air flotation and electrolytic flotation. The following are the process descriptions of selected nonfoaming processes. 

Interaction between two surfactants in aqueous solution producing synergism in foaming and decreased adsorption onto solid surfaces has been used to advantage in the separation of minerals. An alkyl sulfosuccinate-POE nonionic mixture that shows synergism in foaming and whose interaction results in decreased adsorption onto scheelite and calcite surfaces produced enhanced selectivity and recovery of scheelite by the flotation process (von Rybinski, 1986). 

Various types of flotation agents are used for selective hydrophobization of minerals in froth flotation. Oleic acid is the most common collector used commercially in the flotation processes of salt-type mineral because of its low cost and availability. In the case of complex ores containing similar constituent minerals such as calcium carbonate and calcium phosphate, the selectivity of flotation using oleate as a collector is usually poor and the reagent consumption is generally high (Lawver et al., 1982 Hanna and Somasundaran, 1976). In order to achieve improvements in the separation, it is helpful to identify various interactions between the dissolved mineral species and the oleate species. These interactions are discussed below. 

The general relationships described above are not specific to a certain system. However, given the need for optimal separation of valuable particles from the associated gangue, the colloid and surface chemistries that are involved may be quite complex. As in the flotation process, selective agglomeration by immiscible liquids depends strongly on the relative wettability of surfaces, and the same fundamentals of surface chemistry apply to the conditioning of particles to yield the required affinity for the wetting liquid. 

The properties of water as a washing agent and a solvent can be enhanced with additives. Several types of additives include (i) surfactants that improve the wettability of the soil components and improve the solubility of lipophilic impurities (ii) complex-ing agents which convert heavy metals and their insoluble compounds into water-soluble compounds (iii) flotation agents (collectors and foamers), which convert certain insoluble substances into a separable phase and (iv) acids or bases for pH control which is necessary for the stability of compounds and for the selectivity of the flotation processes (Venghaus and Werther 1998 Wilichowski 2001). 

Selectivity of the flotation process is determined by both selective hydrophobisation of mineral particles and conditions of their aggregation, stability and conditions of destruction of three-phase flotation foams. 

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