Talc flotation

Fuerstenau, D. W, and Huang, R 2003. Interfacial phenomena involved in talc flotation and depression. XKII International Mineral Processing Congress. South African Instimte of Mining and Metallurgy in Marshalltown, Cape Town, South Africa. 1034. 

Interaction of Solids With Flotation Reagents. For flotation to occur with the aid of reagents, such compounds must adsorb at the sohd—hquid interface unless the soHd to be floated is naturally hydrophobic. In this latter case only depression can be attempted by the use of additional ions or depressants that hinder bubble—particle adhesion. Frothers (typically long-chain alcohols) and/or modifying agents such as hydrocarbon oils can, however, be used to enhance the collection of naturally hydrophobic soflds such as M0S2, talc, or plastics. 

There is some beneficiation of talc by froth flotation (qv), practiced especially on ultramafic-type deposits. In this process (Fig. 2), talc is milled to its hberation size (—100 mesh (ca 0.15 mm)) using ball mills or ring-type roUer mills and then slurried at 10—30% in water. Flotation is done in conventional multistage float cells using methyl amyl alcohol as a frother. Typically two to four stages are required to upgrade the ore from 50—70% talc to 90—98%. The product is filtered and then flash-dried and milled to a final product. 

In conventional chemical pulping systems, micronized talc is used for pitch control. The mechanism is not well understood, but talc does adsorb on the pitch and detackify it, preventing it from agglomerating and attaching on equipment. In de-inking talc is used both to enhance ink removal in conventional screening/centrifugation methods and as a carrier in flotation systems. 

A U.S. Bureau of Mines survey covering 202 froth flotation plants in the United States showed that 198 million tons of material were treated by flotation in 1960 to recover 20 million tons of concentrates which contained approximately 1 billion in recoverable products. Most of the worlds copper, lead, zinc, molybdenum, and nickel are produced from ores that are concentrated first by flotation. In addition, flotation is commonly used for the recoveiy of fine coal and for the concentration of a wide range of mineral commodities including fluorspar, barite, glass sand, iron oxide, pyrite, manganese ore, clay, feldspar, mica, sponumene, bastnaesite, calcite, garnet, kyanite, and talc. 

Most of the current commercial operations that treat PGM from sulphide-dominated deposits are located in South Africa (Morensky Reef), Stillwater mines (Montana, USA) and Lac des Hies (Ontario, Canada). From a processing point of view, most of these ore types contain hydrophobic gangue minerals, including talc, which has a negative effect on PGM recoveries. Other major factor that affects flotation recovery of PGM is the presence of a variety of sulphide minerals, including pyrrhotite, pentlandite, chalcopyrite, violarite and pyrite, where... 

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. 

Scalping flotation is where a first flotation step is practised in order to remove a minor, hydrophobic mineral. This mineral could be one that is valuable, such as MoS2 in a Cu-Mo ore [91], or one that is unwanted, such as talc. 

Naturally occurring talc is mined and pulverized before being subjected to flotation processes to remove various impurities such as asbestos (tremolite) carbon dolomite iron oxide and various other magnesium and carbonate minerals. Following this process, the talc is finely powdered, treated with dilute hydrochloric acid, washed with water, and then dried. The processing variables of agglomerated talc strongly influence its physical characteristics. " ... 

Natural talc in usually contaminated with accessory minerals, mainly magnesite and minerals containing iron oxides. The contaminated raw materials are treated by flotation and magnetic separation. Ceramic manufacture requires low contents of Fc203 and CaO (each below 1.5%) and the highest possible MgO content. The composition of natural talc is shown in Table 8,... 

In general, flotation separation relies on the attachment of properly prepared mineral surfaces to air bubbles in water. Surfaces which are easily wetted by water, such as ordinary ground rock, are not attracted to bubbles and thus sink. Elemental sulfur, graphite (and other forms of elemental carbon, such as the pigment in printers inks), and talc (minerals with layer lattice type structures) have hydrophobic surfaces, which are attracted to the surface of an air bubble and, if small enough, may be lifted to the surface of the water and separated from the water as a froth layer. 

Solvents can be eliminated from some reactions by running them in ball mills.57 Methyl methacrylate can be polymerized in a vibratory ball mill using a talc catalyst.58 Ball mills are feasible for reactions on a commercial scale. Huge mills are used by the mining industry in grinding ores before flotation. If the mill is used repeatedly to make the same product, the problem of cleaning it out between runs is eliminated. It is also possible to use an inert liquid diluent in the milling, so that the product can be recovered as a slurry. The preferred diluent would be water if it is inert for the reaction in question. 

With non-polar minerals such as talc, mica and coal, the particle surfaces can interact with the non-polar portion of the molecules by van der Waals force. In this case, hydrocarbon portions can function as mineralophilic groups. Except in the case of depressants or some flocculants, the non-polar portions of long hydrocarbon chains in flotation agents possess only the framework formed from C-H groups with linking to polar hydrophilic and minerophilic groups [4]. 

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. 

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. 

Sulfonated lignin is used in the mining industry to refine ore by ore flotation. The lignosulfonates depress the entrainment of minerals such as calcite, barite, and talc and produce a higher metal content extract fiom the ore (167). 

The talc/magnesite variety of ores are derived from serpentinite hosts and are typically found in Vermont, Quebec, and Finland. This type of ore is macrocrystalline in nature and composed of approximately 45-65% talc by weight, with the remainder of the ore made up of magnesite (magnesium carbonate). In some low-cost applications, such as automotive underhood, these ores are coarsely ground and used as is. These ores are also frequently beneficiated to 93-99 wt% talc by flotation. Because talc is hydrophobic, it is easy to float with surfactants. The talc floats on an aqueous bubble, whereas the co-mineral impurities sink in the water phase. 

Some talcs may be subjected to beneficiation by froth flotation. The talc is ground, dispersed in water, subjected to froth flotation in which the talc may be floated from the impurities or vice versa using a surfactant, selective for the appropriate surface, to transfer it to a foam and effect separation. The talc may then be subjected to grinding, classification or both to achieve the desired particle size distribution. 

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