Differential flotation

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. 

Ravitz, S. F. and Potter, R. R., 1933. Oxygen-free flotation I flotation of galena in absence of oxygen. Am. Inst. Min. Metall. Eng., Tech. Publ., No.513 Rey, M. and Formanek, V., 1960. Some fiictors affecting the selectivity in the differential flotation of lead-zinc ores in the presence of oxidized lead mineral. Proc. 5 Int. Min. Proc. Congr., Inst. Mining and Met., London, 343 - 352... 

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. 

Rath R. K., Subramanian S. 1999. Adsorption, electrokinetic and differential flotation studies on sphalerite and galena using dextrin. Int 1. Miner. Process. 57. 265-283. 

This table shows how the physical loss of values into tailings from differential flotation rises steeply as the complexity of the mineral matrix increases. The second column shows a fairly uniform level of unpaid-for values in concentrates for the ores of the Zn-Pb-Ag type. It is much lower for the copper ores as the standard rate to payment for copper in concentrates is substantially higher than it is for zinc. The combined losses (third column) rise to formidable amounts for the more complex ores. 

The physical limitations of differential flotation cause the losses and, as the data collected show, the recoveries are getting worse. From this data bank, alternative ways by which the treatment of the sulphides might be improved were reviewed and the possible methods are discussed below. 

Despite the enormous effort put into improving flotation, it is clear that the trend is for concentrates to become less and less clean or recoveries have to be lowered to meet smelter specifications. One might particularly note that the separation of pyrite from other sulphides is an ever-pressing need as iron disposal by smelters has become a more environmentally sensitive issue. Differential flotation relies on a scientific paradox. In ores of volcanogenic origin the sulphide mass has formed in a combination of chemical and thermal reactions. In liberation and flotation the aim is to unravel what nature has raveled by purely physical means. 

The capital for a production plant was estimated excluding the site acquisition cost. The total cost will, of course, vary somewhat from location to location but it was clear that it would be less than for an equivalent operation using present day technology (e.g., differential flotation followed by separate and distant smelting and refining of clean zinc, lead and copper concentrates). The standard plants would be replaced with a bulk concentrator, a single smelter and refineries. The capital cost comparison is not quite so... 

Differential flotation can be achieved when only specific minerals are floated. This is done by the use of additives to the pulp to depress or promote the collection of particular mineral surfaces. The particular response of minerals contained in an ore will differ widely, and hence there is a considerable variation in flotation practices from one plant to another. The general approach, however, is to first float copper and depress the other base metal sulfides, then float lead and finally zinc. The aim is generally to depress pyrite, but this can be difficult and it is often the major diluent in lead and zinc concentrates. 

Two main operational variables that differentiate the flotation of finely dispersed coUoids and precipitates in water treatment from the flotation of minerals is the need for quiescent pulp conditions (low turbulence) and the need for very fine bubble sizes in the former. This is accompHshed by the use of electroflotation and dissolved air flotation instead of mechanically generated bubbles which is common in mineral flotation practice. Electroflotation is a technique where fine gas bubbles (hydrogen and oxygen) are generated in the pulp by the appHcation of electricity to electrodes. These very fine bubbles are more suited to the flotation of very fine particles encountered in water treatment. Its industrial usage is not widespread. Dissolved air flotation is similar to vacuum flotation. Air-saturated slurries are subjected to vacuum for the generation of bubbles. The process finds limited appHcation in water treatment and in paper pulp effluent purification. The need to mn it batchwise renders it less versatile. 

Further hydrolysis of the carbon disulfide and the trithiocarbonate produces hydrogen sulfide, etc (33). In another study of the decomposition of sodium ethyl xanthate [140-90-9] in flotation solutions, eleven components of breakdown were studied. The dependence of concentration of those components vs time was examined by solving a set of differential equations (34). 

Some of the phenomena of differentiation of silicate rocks are probably to be treated as results of simple crystallization backed up by the effects of gravity in causing sinking or flotation of crystals. This is the only method of differentiation that has been experimentally proven, but the separation of two or more liquid phases, and perhaps other phenomena also, may take part in this little-known process. 

In on effort to establish the mechanism of coal flotation and thus establish the basis for an anthracite lithotype separation, some physical and chemical parameters for anthracite lithotype differentiation were determined. The electrokinetic properties were determined by streaming potential methods. Results indicated a difference in the characteristics of the lithotypes. Other physical and chemical analyses of the lithotypes were mode to establish parameters for further differentiation. Electron-microprobe x-ray, x-ray diffraction, x-ray fluorescent, infrared, and density analyses were made. Chemical analyses included proximate, ultimate, and sulfur measurements. The classification system used was a modification of the Stopes system for classifying lithotypes for humic coals. 

Wadsworth and coworkers (13, 14) have found considerable evidence for surface polarization in double-beam infrared spectroscopy. Not only do new differential peaks due to adsorption appear in the spectrograms but also the bands due entirely to the adsorbent are frequently appreciably shifted by adsorption. This occurred, for example, in calcium fluorite treated with oleic acid, in samples of bentonites taken from aqueous solutions of different pH, and in various minerals treated by flotation collectors. In fact, it is more the rule than the exception that the spectrograms of finely divided solids dispersed in the KI or KBr window exhibit distortion due to adsorption, whether adsorption occurs at the solid-aqueous solution or at the solid-vapor interface. For example, Eyring and Wadsworth (13) found that two (differential) peaks were produced by adsorption on willemite either from the vapor or aqueous solution of hexanethiol. These peaks were due to the influence of adsorption of the hexanethiol on the Si-O bands of the willemite and occurred at about 9.2 and 12.3 microns. 

For separations below 80-mesh size and for slime separation and particularly for pilot-table work following flotation the Deister slimer table shown in Fig. 8 is very satisfactory. Owing to its extremely powerful differential motion it requires very rigid foundations, concrete being the preferable material for this purpose. 

Potassium chloride as a component in fertilizers is specified in terms of its K2O equivalent. On this basis, 100% pure potassium chloride is equated to 63.18% K2O equivalent. The approximately 96% pure potassium chloride product of the flotation separation is thus equivalent to 60.7% K2O (see Chap. 9). Chemical grades correspond to the once-crystallized, soluble product of about 99.5% KCl, and 99.95% KCl, which is the Refined, twice crystallized material. The price differential, 60-62.4% K2O equivalent at 108-112 US /tonne, and 99.95% KCl at 115-137 US /tonne (1995 prices [30]) is sufficient to cover the cost of the additional processing for Chemical grade potash. 

Froth flotation is used to raise the low mineral concentrations in ores to concentrations that can be more economically processed. A concentration of 25-30% is suitable for economical smelting of copper. The froth flotation technique was originally developed in about 1910 to raise the copper concentrations of the strip-mined ores of Bingham Canyon, near Salt Lake City [9], and was further perfected for the differential separation of lead, zinc, and iron sulfides at Trail, B.C., at about the same time [10]. Flotation technologies are now widely used for separations such as the beneficiation of low grade Florida phosphate ores from 30-40% to 60-70% concentrations of calcium phosphate (BPL), and the separation of about 98% potassium chloride from sylvinite, a natural mixture of potassium and sodium chlorides. It is also used for bitumen separation from tar sand, removal of slate from coal, and removal of ink from repulped paper stock preparatory to the manufacture of recycled paper stock. More details of these separations are discussed in the relevant chapters. 

If a bubble carrying air-avid mineral particles reaches the surface of the flotation unit and then bursts, the raised mineral particles will sink again. Bubble stability is maximized by addition of a foam stabilizer or frother, which assists in generating a sufficiently stable foam layer on the flotation unit to enable the foam plus associated mineral to be skimmed from the water phase. The frother also puts an oily phase on the surface of each bubble as it forms, which helps the mineral-gangue differentiation function of the collector. Typical frothers are oily materials of no more than slight water solubility such as pine oil (a mixture of terpenes) or a long chain (C5 or higher) alcohol such as 1-pentanol, and are used at the rate of 20-45 g/tonne of ore. 

---