Flotation principles

It is considered relevant to begin this presentation on flotation principles by drawing a reference to Figure 2.22 which quite comprehensively presents a summary of general classification of mineral processing separation methods. Present attention is focused on the... 

Vilan A, Cahen D (2002) Soft contact deposition onto molecularly modified GaAs. Thin metal film flotation principles and electrical effects. Adv Funct Mater 12 795-807... 

Trahar, W.J., 1983. The influence of pulp potential in sulfide flotation, principles of mineral flotation, The Wark Symposium, Aust. Inst. Min. Metall. Adlaide, Austalia, p. 117. 

Several books on flotation principles and reagents have been published, however, for further improvement of current minerals processing performance and for the treatment and recovery of refractory and nontraditional mineral and energy resources, scientists need to develop new reagents and innovative processes. 

K. L. Sutherland and I. W. Wark, Principles of Flotation, Australian Institute of Mining and Technology, Inc., Melbourne, 1955. 

The KDF Filter. The KDP filter (Pig. 23) (Amafilter, Holland) is based on the same principle as disk filters. It was developed for the treatment of mineral raw materials, like coal flotation concentrates or cement slurries, and can produce a filter cake of low moisture content at very high capacities, up... 

Other Applications. There are a variety of flotation processes employing the principles described. 

Piggyba.ckFlota.tlon, This process has also been called carrier flotation. The principle is based on the flotation of fine particles adhering to others by mutual coagulation. Thus when one is floated the other, which is usually more difficult to float, is also collected. 

The KEN-FLOTE column (11) is one of several column flotation processes based on a countercurrent principle. The feed slurry containing reagents is iatroduced iato the column just below the froth zone. Air is iujected at the bottom of the column via an air sparger. Wash water is sprayed within the froth zone to reject the entrained impurities from the froth. Test results on this column iadicate that a 6% ash product coal having a combustible-recovery of 75—80% can be obtained. A 70—80% pyrite reduction is also claimed. Figure 2 shows the operation of such a column. 

Two types of floater aozzles are curreafly ia use and they are based on two different principles. The Bernoulli principle is used ia the airfoil flotatioa aozzles, ia which the air flows from the aozzle parallel to the web and the high velocities create a reduced pressure, which attracts the web while keeping the web from touching the nozzles. The Coanda effect is used to create a flotation nozzle when the air is focused and thus a pressure pad is created to support the web as shown ia Figure 19. 

Particle-Bubble Attachment. In the above, principles leading to creation of desired hydrophobicity/hydrophihcity of the particles has been discussed. The next step is to create conditions for particle-bubble contact, attachment, and their removal, which is simply described as a combination of three stochastic events with which are associated the probability of particle-bubble colhsion, probabihty of attachment, and probability of retention of attachment. The first term is controlled by the hydrodynamic conditions prevaihng in the flotation unit. The second is determined by the surface forces. The third is dependent on the s irvival of the laden bubble by liq ud t irbulence and impacts by the other suspended particles. A detailed description of the hydrodynamic and other physical aspects of flotation is found in the monograph by Schulze (19 ). 

Overflow at the rate of 2700 m (713,000 gal) per day from a zinc-concentrate thickener is treated by ion flotation, precipitate flotation, and untrafine-particle flotation [Nagahama, Can. Min. Metall. Bull., 67, 79 (1974)]. In precipitate flotation only the surface of the particles need be coated with collector. Therefore, in principle less collector is required than for the equivalent removal of ions by foam fractionation or ion flotation. 

Vrablik, E. R. Fundamental principles of dissolved air flotation of industrial wastes. Industrial Waste Conference Proceedings. 14th, 1959, Purdue University, Ann Arbor, USA, 743-779. 

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-... 

Its unique compact and efficient design is made possible by the use of the principle of zero velocity eliminating internal water turbulence (see below). The flocculated water thus stands still in the flotation tank for optimum clarification. The unit is complete with automatic backwash filter in which dirty backwash water is recycled back to the unit inlet for reprocessing. The average waste flow from the process is less than 1.0% of the incoming raw water. 

In Section 27.2, the principles of a DAF unit and the entire improved activated sludge wastewater treatment system are disclosed in detail. The economic use of secondary flotation in the improved system requires only a relatively inexpensive high-rate DAF cell that is commercially available. The consulting engineers should understand such principles for the selection of an appropriate DAF unit and for the optimization of the entire improved wastewater treatment system. 

All DAFs are similar to each other in terms of theory, principles, design, operation, and secondary flotation performance. The authors select the circular DAF process equipment manufactured by KEC for the purpose of feasibility studies. The users should contact more than one major DAF and DAFF manufacturers for appropriate pilot plant demonstrations and cost comparisons. Rectangular DAF and DAFF clarifiers are as good as circular DAF and DAFF clarifiers. 

The following sections describe the operational procedures and the principles and special features of some selected major flotation components. 

The unique, compact and efficient design of a circular DAF cell is made possible by using the principle of zero velocity. As mentioned earlier, the influent distribution duct moves backward with the same velocity as the forward incoming water. The zero velocity quiescent state in the flotation chamber is thus created ideally for flotation. 

Each of the sulphide minerals, which are PGM carriers (i.e. pyrrhotite, pyrite, pentlan-dite, etc.) have different flotation properties under some flotation conditions. The selectivity between sulphide minerals and gangue minerals is relatively poor in principle, and in the majority of cases, a hydrophobic gangue depressant has to be used. 

On this subject notice that, possibly combined with various heating methods, several physical effects may be considered which allow free flotation of solid and even liquid matter. Materials may be levitated for instance by a jet of gas, by intense sound waves or by beams of laser light. Conductors levitate in strong radiofrequency fields, charged particles in alternating electric fields, magnets above superconductors or vice versa. A review on levitation in physics with the description of several techniques and their principles and applications was made by Brandt (1989). 

In the 2nd period ranging from the 1930s to the 1950s, basic research on flotation was conducted widely in order to understand the principles of the flotation process. Taggart and co-workers (1930, 1945) proposed a chemical reaction hypothesis, based on which the flotation of sulphide minerals was explained by the solubility product of the metal-collector salts involved. It was plausible at that time that the floatability of copper, lead, and zinc sulphide minerals using xanthate as a collector decreased in the order of increase of the solubility product of their metal xanthate (Karkovsky, 1957). Sutherland and Wark (1955) paid attention to the fact that this model was not always consistent with the established values of the solubility products of the species involved. They believed that the interaction of thio-collectors with sulphides should be considered as adsorption and proposed a mechanism of competitive adsorption between xanthate and hydroxide ions, which explained the Barsky empirical relationship between the upper pH limit of flotation and collector concentration. Gaudin (1957) concurred with Wark s explanation of this phenomenon. Du Rietz... 

Although there have been a lot of investigations on the interactions of sulphide minerals with thio-collectors in terms of the mixed potential principle, there are still much controversy about the products formed on a sulphide mineral in the presence of a collector in different conditions. In the following sections, the effects of potential on the flotation and formation of surface products of many kinds of sulphide minerals will be introduced based on the results of flotation, electrochemical measurement, surface analyses and thermodynamic calculations. 

Abstract In this chapter, the depression mechanism of five kinds of depressants is introduced respectively. The principle of depression by hydroxyl ion and hydrosulphide is explained which regulates the pH to make the given mineral float or not. And so the critical pH for certain minerals is determined. Thereafter, the depression by cyanide and hydrogen peroxide is narrated respectively which are that for cyanide the formation of metal cyanide complex results in depression of minerals while for hydrogen peroxide the decomposition of xanthate salts gives rise to the inhibitation of flotation. Lastly, the depression by the thio-organic such as polyhydroxyl and poly carboxylic xanthate is accounted for in detail including die flotation behavior, effect of pulp potential, adsorption mechanism and structure-property relation. 

It is well known that the flotation of sulphides is an electrochemical process, and the adsorption of collectors on the surface of mineral results from the electrons transfer between the mineral surface and the oxidation-reduction composition in the pulp. According to the electrochemical principles and the semiconductor energy band theories, we know that this kind of electron transfer process is decided by electronic structure of the mineral surface and oxidation-reduction activity of the reagent. In this chapter, the flotation mechanism and electron transferring mechanism between a mineral and a reagent will be discussed in the light of the quantum chemistry calculation and the density fimction theory (DFT) as tools. 

Sun Shuiyu, Wang Dianzuo, Li Baidan, 1992. Principle of collectorless flotation of sulphides and design of separation schemes. Nonferrous Metals (Bimonthly), 6 4-8 (in Chinese)... 

Sutherland, K. L. and Wark, I. W., 1955. Principles of flotation. Austral-asian Inst. Min. Metall., Melboure, 489 - 499... 

Method Density gradient. Rate-zonal. The rate-zonal method is one of six addressed by SpinPro. The other methods are differential, differential-flotation, discontinuous, isopycnic, and 2-step isopycnic. These methods differ dramatically in their set up, principles of operation, and expected results. The rate-zonal method is described here briefly so that the recommendations to follow can be appreciated. Prior to the run in a rate-zonal method, a gradient material is introduced to the rotor tubes in steps of increasing density from the top to the bottom of the tube. The sample to be separated is layered, as a thin band, on the top of the gradient. As the run begins, each component in the sample moves toward the bottom of the tube. Some components sediment faster than others. This fact is the basis for the separation. If the run parameters are appropriate, the components will form separate bands within the gradient. At the conclusion of the run, the band representing the component of interest can be removed from the tube. 

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