Mineral flotation, selective

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. 

Dichmann, T. K. Finch, J. A. The role of copper ions in sphalerite—pyrite flotation selectivity. Miner. Eng. 2001, 14, 217-225. 

Lead is produced commercially from its principal ore, galena (PbS). The ore is associated with sulfides of several metals including iron, copper, zinc, silver, bismuth, arsenic, antimony and tin. The ore is crushed and ground. It then is selectively separated from gangue and other valuable minerals by one or more processes that include gravity separation and flotation. Selective... 

The recovery of valuable minerals and metals requires several stages of sequential processing operations. The mined ore must be crushed and ground to fine sizes prior to treatment by such bene-ficiation processes as heavy-medium separation, tabling, magnetic separation, electrostatic separation, flotation, selective flocculation, etc. Since most of these processes are carried out in aqueous media, solid-liquid separations by such operations as thickening and filtration are an integral part of the benefici-... 

Mineral flotation is a method for selective separation of mineral components out of polymineral dispersions of ground ores in water (ca. 5-35 vol.% of the solid) by using dispersed gas (usually air) bubbles. The method consists in the different adhesion of hydrophobized and hydrophilic mineral particles to an air bubble. Hydrophobized mineral particles adhere to the air bubble and are carried out as a specifically lighter aggregate to the surface of the mineral dispersion where they form a foam (froth) layer. This foam, called concentrate, is mechanically removed (Fig. 1A). A mineral is hydrophobized by adsorption of a suitable surface-active compound (surfactant, collector) on the surface of the mineral component to be flotated. All other nonhydrophobized particles remain dispersed in the mixture (Fig. IB). 

In achieving solid-solid separation in mineral beneficiation, selective coatings of water insoluble or sparingly soluble reagents are required in electronic ore sorting, froth flotation, and emulsion flotation operations. 

It is evident from this discussion that dissolution equilibria of sparingly soluble minerals can play a major role in determining the surface properties of mineral particles. Selective hydrophobization of such particles using surfactants is the key to flotation separation. 

The so-called chelating collectors, such as hydroxamic acids, continue to be studied by flotation specialists. The flotation selectivity of minerals partly soluble in the flotation pulp has been studied, at bench scale, in [159]. It has been shown that optimum results are achieved, when the mineral to be floated is the most soluble in the system and the chelate formed with the cation on the surface is most stable. 

The predominant perception regarding the use of polysaccharides in mineral flotation is that their adsorption is non-selective primarily resulting from hydrogen bonding and that their functions are unpredictable. The applicability of the polysaccharides in such a wide range of mineral systems, however, seems to indicate that this general perception is probably oversimplified and incorrect. In... 

Selective flotation of apatite from dolomite was predicted by single mineral tests In the pH range of 7 to 10, and of dolomite from apatite at pH of about 5, with 4 X 10 kmol/m of sodium oleate collector. Once again, mixed mineral (50 50) tests did not yield the selectivity predicted on the basis of the single mineral flotation studies. 

Mixed Mineral Flotation Tests. Flotation of 88 12 apatite-dolomite mixtures was conducted to verify the selectivity predicted on the basis of single mineral experiments. Results presented in Table II demonstrate that at dodecylamine concentration of 1.6 X10" kmol/m apatite can be selectively recovered from the mixture leaving dolomite In the sink fraction. 

It is clear from the above data that addition of sodium chloride results in selective flotation of apatite from its mixture with dolomite using dodecylamine as the collector at pH 6.3. Single mineral flotation results at pH 6.7 indicated that more apatite floats in the presence of salt than without it. On the other hand, addition of sodium chloride had no significant effect on dolomite flotation,. 

Dolomite flotation below its iep (pH 5.3) is about 20% indicating the presence of weak specific interactions in addition to the coulombic attraction. The heat of reaction of dodecylamine with phosphate and carbonate anions (-15.1 and -3.3 kj/mol for apatite and dolomite, respectively) determined by Soto and Iwasaki , supports this hypothesis. The heat of reaction measurements indicate that the collector would adsorb preferentially on apatite than dolomite when both the minerals are present. Addition of sodium chloride decreases the magnitude of negative zeta potential, thus reducing the adsorption of the cationic collector and enhancing the selectivity In the mixed mineral flotation. 

Thiambutosine was firstly used in mineral flotation in 1921. In general, thiambu-tosine is used in the presence of xanthate or aerofloat. It performs good selectivity, especially toward galena containing silver and silver sulfide ore. It is usually applied for the separation of Cu-Pb-Zn-Fe multi-metal sulfide ore. 

Surfactants can be used to selectively alter wettability. For example, in mineral flotation surfactant can be added to adsorb on metal ore particles increasing the contact angle, so they attach to gas bubbles. The surfactant is chosen so that it will not adsorb much on sihcates, so the latter do not attach to gas bubbles. The surfactant may also stabihze a foam containing the desired particles, thereby facilitating their recovery as a particle-rich froth that can be skimmed. Flotation processes thus involve careful modification of surface tension and wettability. 

This study presents a procedure for the design or improvement of mineral flotation circuits, based on a mathematical programming model with disjunctive equations. The procedure is characterized by 1. The development of hierarchized superstructures, such that the first level represents certain separation tasks. The second level represents circuits of equipment needed to carry out the tasks. 2. A MILP mathematical model is developed which includes the selection of equipment, first principles, and operational conditions. 3. The objective function is the maximization of profits. Examples are included to demonstrate the advantages of the procedure. 

Froth flotation is a complex three phase physico-chemical process which is used in mineral processing industry to separate selectively fine valuable minerals from gangue. The importance of the mineral froth flotation process to the economy of the whole industrial world is important. As costs has increased in mining industry and ore grades and metal prices decreased, role of mineral flotation has become even more important. The flotation process depends among many other factors on control of the pulp aeration, agitation intensity, residence time of bubbles in pulp, pulp density, bubble and particle size and interaction and pulp chemistry. 

The 1930s saw the development of theories to elucidate collector-mineral interaction and to explain the selectivity for sulfide mineral flotation of thiol collectors such as the xanthates. Three propositions were put forward, and each was promoted and defended by its proponents with considerable vigor and intensity. 

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]. 

Collectors Fitting into Fattice Cavities. Lattice site fitting of collectors at sohd walls has been invoked as a means of explaining the selective behavior of amines (cationic coUectors) as reagents in the flotation-separation of soluble salt minerals such as KCl and NaCl (22). 

Other Interaction Processes. The selectivity of flotation reagents in a pulp and their functions depend on their interactions with the mineral phases to be separated, but other physicochemical and hydrodynamic processes also play roles. AH adsorption—desorption phenomena occur at the sohd—hquid interfacial region. Surface processes that influence such adsorptions include activation and depression. Activators and depressants are auxiUary reagents. 

Activators enhance the adsorption of collectors, eg, Ca " in the fatty acid flotation of siUcates at high pH or Cu " in the flotation of sphalerite, ZnS, by sulfohydryl collectors. Depressants, on the other hand, have the opposite effect they hinder the flotation of certain minerals, thus improving selectivity. For example, high pH as well as high sulfide ion concentrations can hinder the flotation of sulfide minerals such as galena (PbS) in the presence of xanthates (ROCSS ). Hence, for a given fixed collector concentration there is a fixed critical pH that defines the transition between flotation and no flotation. This is the basis of the Barsky relationship which can be expressed as [X ]j[OH ] = constant, where [A ] is the xanthate ion concentration in the pulp and [Oi/ ] is the hydroxyl ion concentration indicated by the pH. Similar relationships can be written for sulfide ion, cyanide, or thiocyanate, which act as typical depressants in sulfide flotation systems. 

The basic flow sheet for the flotation-concentration of nonsulfide minerals is essentially the same as that for treating sulfides but the family of reagents used is different. The reagents utilized for nonsulfide mineral concentrations by flotation are usually fatty acids or their salts (RCOOH, RCOOM), sulfonates (RSO M), sulfates (RSO M), where M is usually Na or K, and R represents a linear, branched, or cycHc hydrocarbon chain and amines [R2N(R)3]A where R and R are hydrocarbon chains and A is an anion such as Cl or Br . Collectors for most nonsulfides can be selected on the basis of their isoelectric points. Thus at pH > pH p cationic surfactants are suitable collectors whereas at lower pH values anion-type collectors are selected as illustrated in Figure 10 (28). Figure 13 shows an iron ore flotation flow sheet as a representative of high volume oxide flotation practice. 

Depressants are reagents that selectively prevent the reaction between a coUector and a mineral, thus preventing its flotation. For example, sodium cyanide [143-33-9] depresses sphalerite [12169-28-7] (zinc sulfide) and pyrite [1309-36-0] (iron sulfide) but not galena. It thus enhances selective flotation of the galena. 

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