Molybdenite flotation

The functional group ia collectors for nonsulfide minerals is characterized by the presence of either a N (amines) or an O (carboxyUc acids, sulfonates, etc) as the donor atoms. In addition to these, straight hydrocarbons, such as fuel oil, diesel, kerosene, etc, are also used extensively either as auxiUary or secondary collectors, or as primary collectors for coal and molybdenite flotation. The chain length of the hydrocarbon group is generally short (2—8 C) for the sulfide collectors, and long (10—20 C) for nonsulfide collectors, because sulfides are generally more hydrophobic than most nonsulfide minerals (10). 

Molybdenite flotation from copper/molybdenum concentrates by ozone conditioning results in relatively pure copper-free molybdenum. The process including multi-step ozone flotation proves to be a technical and economical profitable method [141],... 

Before scmbbing procedures were estabUshed for copper ore, most of the rhenium was lost as the volatile (Re202). A small portion, perhaps 10%, was retained in flue dust, which was processed to give the metal. A commercial flotation (qv) process for the recovery of the molybdenite by-product is available that permits a high recovery of molybdenum and rhenium. This process is used at the Caridad copper mine in Mexico. 

Molybdenite [1309-56 ] M0S2, normally floats with the copper sulfides. Therefore, the copper concentrate from the cleaner cells frequently has to be separated from molybdenite in a separate flotation circuit before the copper concentrate goes to the smelter. Gold, silver, selenium, and tellurium are collected with the copper concentrate. 

Drawing reference to the flotation practice of molybdenite, it may in the first instance be pointed out that production of molybdenite by flotation results from the processing of primary molybdenum ores and copper porphyry ores in which molybdenite is recovered as a byproduct. This by-product accounts for about one-third of the total molybdenum production in the western world. 

Fuerstenau (1980) found that sulphide minerals are naturally floatable in the absence of oxygen. Yoon (1981) ever attributed the natural floatability of some sulphide minerals to their very low solubility. Finkelstein et al. (1975) considered that the natural floatability of sulphide minerals are due to the formation of elemental sulphur and related to the thickness of formation of elemental sulphur at the surface. Some authors reported that the hydrophobic entity in collectorless flotation of sulphide minerals were the metal-deficient poly sulphide (Buckley et al., 1985). No matter whichever mechanism, investigators increasingly concluded that most sulphide minerals are not naturally floatable and floated only under some suitable redox environment. Some authors considered that the natural floatability of sulphide minerals was restricted to some special sulphide minerals such as molybdenite, stibnite, orpiment etc. owing to the effects of crystal structure and the collectorless floatability of most sulphide minerals could be classified into self-induced and sulphur-induced floatability (Trahar, 1984 Heyes and Trahar, 1984 Hayes et al., 1987 Wang et al., 1991b, c Hu et al, 2000). 

The inherent hydrophobicity once thought to be typical of sulphides (Ravitz and Porter, 1933) is now thought to be restricted to sulphides such as molybdenite (Chander et al., 1975) and other minerals or compound with special structural feature (Gaudin et al, 1957b). Common commercial sulphide minerals, which are needed to recover in flotation, are normally composed of anion (S ) and heavy metal ions such as Cu, Cu, Pb, Zn, Hg, Sb, Bi transitive metal ion such as Fe, Co, Ni and noble and rare metal ions such as Ag, Au, Mo. On the basis of structural pattern or mode of linkage of the atoms or polyhedral imits in space, Povarennyk (1972) introduced a crystallochemical classification of sulphide minerals, which have six major patterns as shown in Table 1.1. 

Heyes and Trahar (1984) leached pyrite with cyclohexane and compared the extract with a sulphur-containing solution of cyclohexane in a UV spectra photometer as shown in Fig. 1.4, indicating that sulphur was present at the mineral surface. Therefore, the inherent hydrophobicity and natural floatability once thought to be typical of sulphides is now thought to be restricted to sulphides such as molybdenite and other minerals or compound with special structural features. The collectorless floatability that most sulphide minerals showed came from the self-induced or sulphur-induced flotation at certain pulp potential range and certain conditions. 

Molybdenum is recovered primarily from its sulfide ore, molybdenite, M0S2. It also is produced, although to a much lesser extent, from the tungsten ore wulfenite, which yields lead molybdate, PbMo04. The first phase of the recovery process generally involves concentration of the ore, because ore coming from the mine is very lean and usually contains less than one percent molybdenum. Molybdenite at first is concentrated by flotation which concentrates the M0S2 over 90%. If wulfenite is used as a source material, concentration is usually done by hydrauhc methods. 

The common gangue material quartz (silica) is naturally hydrophilic and can be easily separated in this way from hydrophobic materials such as talc, molybdenite, metal sulphides and some types of coal. Minerals which are hydrophilic can usually be made hydrophobic by adding surfactant (referred to as an activator ) to the solution which selectively adsorbs on the required grains. For example, cationic surfactants (e.g. CTAB) will adsorb onto most negatively charged surfaces whereas anionic surfactants (e.g. SDS) will not. Optimum flotation conditions are usually obtained by experiment using a model test cell called a Hallimond tube . In addition to activator compounds, frothers which are also surfactants are added to stabilize the foam produced at the top of the flotation chamber. Mixtures of non-ionic and ionic surfactant molecules make the best frothers. As examples of the remarkable efficiency of the process, only 45 g of collector and 35 g of frother are required to float 1 ton of quartz and only 30 g of collector will separate 3 tons of sulphide ore. 

Flotation of Naturally Hydrophobic Minerals. Flotation response of naturally hydrophobic minerals correlates very well with elec-trokinetic measurements. Figure 3 shows that the flotation of coal correlates well with zeta potential of demineralized coal (5.). The flotation rate is maximum where the zeta potential is zero and it decreases with increase in the magnitude of the zeta potential. Similar observations were made earlier by Chander and Fuerstenau (6 ) for the flotation of molybdenite. The decrease in flotation rate with increase in zeta potential is because of the electrical double layer repulsion between the charged particle and the air bubble. 

Emulsion flotation is analogous to carrier flotation. Here, small-sized particles become attached to the surfaces of oil droplets (the carrier droplets). The carrier droplets attach to the air bubbles and the combined aggregates of small desired particles, carrier droplets, and air bubbles float to form the froth. An example is the emulsion flotation of submicrometre-sized diamond particles with isooctane. Emulsion flotation has also been applied to the flotation of minerals that are not readily wetted by water, such as graphite, sulfur, molybdenite, and coal [623]. Some oils used in emulsion flotation include mixed cresols (cresylic acid), pine oil, aliphatic alcohols, kerosene, fuel oil, and gas oil [623], A related use of a second, immiscible liquid to aid in particle separation is in agglomeration flocculation (see Section 5.6.4). 

Molybdenite is separated by crushing and liquid flotation from the felspar and quartzite which constitute the bulk of the ore. The molybdenite is finely dispersed in the ore, and most of it is ciosely associated with quartz in very fine... 

The bulk of the concentrate separated from molybdenite ore by flotation is further processed to produce molybdenum. A typical extraction and purification procedure is outlined in Figure 2.1. The concentrate is roasted to convert the moiybdenum disulphide to molybdic oxide. The product is called roasted concentrate, and about 30% is marketed as Technical Oxide, mainly for alloy manufacture. A typical range of compositions is shown in Table 2.6. 

Promoters or collectors provide the substances to be separated with a water-repellent air-avid coating that will adhere to air bubbles. Typical collectors for flotation of metallic sulfides and native metals are dithiophosphates and xanthates. Fatty acids and their soaps, petroleum sulfonates, and sulfonated fatty acids are widely used as collectors in flotation of fluorspar, iron ore, phosphate rock, and others. Fuel oil and kerosene are used as collectors for coal, graphite, sulfur, and molybdenite. Cationic collectors such as fatty amines and amine salts are widely used for separation of quartz, potash, and silicate minerals. 

Various starches have been used in industry for depressing talc, mica, natural sulfur, carbon gangue and sulfide minerals, and especially for depressing oxidized iron minerals in the reverse flotation of iron ore and the separation of Cu-Mo in the copper-molybdenite sulfide flotation. 

Selective flotation of fluorite and barite is usually very difficult using water glass and tannic acid. However, good separation of these minerals has been achieved with the use of lignosulfonate [18]. Lignosulfonate can also selectively depress molybdenite and some rare earth metal minerals. In the reverse flotation of hematite and quartz, lignosulfonate has been used as a depressant of hematite. 

The above descriptions show the monomeric structures of starch, dextrin, cellulose, and guar gum. In reality, these polysaccharides can be extracted from different sources and the chain length and configuration, molecular weights, and the contents of impurities may vary considerably. Generally, starches have been used mainly as flocculants or flotation depressants for iron oxide minerals and phosphate minerals while the associated silica is floated. Dextrin has been mainly tested as depressants for inherently hydrophobic minerals such as talc, molybdenite, and coal [96]. Applications of polysaccharides in other mineral systems, both in the laboratory and in commercial processes, have also been frequently reported. As can be seen, the polysaccharides have been used or tested as selective depressants in practically all types of mineral systems, ranging from oxides, sulfides, salt-type, and inherently hydrophobic minerals. 

The raw ore is pulverized using a series of crushers and rotating ball and/or rod mills to fine particles. This liberates the molybdenite from its host rock. The product is then beneficiated by flotation separation, subsequent regrinding, and reflotation to increase the molybdenite content of the new concentrate stream by steadily removing the unwanted material. The final concentrate may contain 70-90% molybdenite. An acidic leach may be employed to dissolve copper and lead impurities, if required. A schematic of the production of molybdenum compounds including M0S2 can be found in Ref. [13]. 

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