Flotation procedure

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

If flour or meal has become contaminated with storage insects after milling, the insect parts or larvae may be removed for identification by sieving or by a flotation procedure, but perhaps only excrement remains in the sample. This is about the same color as the material upon which the insects have fed and has generally the same appearance macroscopically. By means of the fluorescent light, however, pellets may be rendered more readily visible. If such flour is treated with clove oil, the pellets stand out distinctly and may be readily counted. 

This is very similar to the flotation procedure described under basic physical treatments. In the case of foam fractionation, not only are the pollutants raised to the surface where they can be skimmed off, but a froth, like beer foam, is produced in which the pollutants become concentrated. The key to the process is the adsorption of the pollutants onto the surface-active agents that cause the froth to form. Sometimes a surfactant is added so that non-surface-active components can be removed. 

This multi-step, one-pot process was taken further by integration of a third supported reagent for the sequential preparation of 3,5-diphenylpyrazole (Scheme 2.17). Following the previously established procedure, acetophenone was deprotonated and acylated to afford the 1,3-dicarbonyl species. This intermediate was easily separated from the spent polymers by filtration and passed without isolation into a suspension of the resin bound hydrazine salt (9), affording the desired pyrazole in 91% yield. In a subsequent publication, the authors reported that the depleted polymeric reagents from the first step of the conversion (i.e. (7) and (8)) were recovered and separated via a selective flotation procedure, enabhng them to... 

The reasonably well-established dithiophosphate complexes are listed in Table 1. Complexes alleged to be involved in colorimetric analytical methods, solvent extraction and flotation procedures are generally omitted unless they have also been characterized in the solid state. 

To fully understand the physical-chemical basis of flotation in these systems so that new flotation procedures might be developed to make other appropriate mineral separations, extensive research in applied surface chemistry is required. 

Another important application is water suspensions of charged colloids in the form of ore particles such as silica and silicate. These systems can be destabilized by addition of surfactants followed by a separation of the ore by froth flotation procedure. This is of great importance for the mineral industry, while it permits large-scale and economic processing of crushed ores, where the desired mineral is separated from the non-mineral containing... 

FIGURE S.3. Simplified flow sheet of a combined gravity-flotation procedure as applied at Canada Tungsten Mining Corporation (before closing down) [S.l]. 

For many purposes it is simpler to use the flotation procedure in which the sample is made to float in a liquid of the same density. The density of the liquid may then be determined according to known methods with an aerometer. One can use aqueous zinc chloride or magnesium chloride solutions as the liquids. With densities below 1 g/cm, methanol-water mixtures are useful. 

Surfactants find a variety uses in analytical processes. One is the formation of micelles (or microemulsions) which can provide protective environments for analytes or reagents which may enhance stability, or luminescence intensity, for example, or allow reagents to act in conditions not normally accessible to them. They also find application in sample pretreatment including flotation procedures, electro-analytical measurements (e.g. suppression of polaro-graphic maxima) and flow systems. 

The raw ROM (run of mine) ore is reduced in size from boulders of up to 100 cm in diameter to about 0.5 cm using jaw cmshers as weU as cone, gyratory, or roU-type equipment. The cmshed product is further pulverized using rod mills and ball mills, bringing particle sizes to finer than about 65 mesh (230 p.m). These size reduction (qv) procedures are collectively known as comminution processes. Their primary objective is to generate mineral grains that are discrete and Hberated from one another (11). Liberation is essential for the exploitation of individual mineral properties in the separation process. At the same time, particles at such fine sizes can be more readily buoyed to the top of the flotation ceU by air bubbles that adhere to them. 

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. 

Different extraction-spectrophotometric procedures were proposed for the P(V) and As(V) determination as ionic associates (lA) of polyoxometalates with basic dyes. Main disadvantage is difficulty in separation of reagent excess. Flotation, centrifugation or extraction does not allow to create sufficiently sensitive procedures due to worsening of reproducibility. 

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

Sheather sugar flotation is recommended for the concentration of Cryptosporidium cysts. Although these oocysts will concentrate when the Formalin-ethyl acetate or zinc sulfate technique is used, they are more readily detected with the Sheather sugar flotation, for they stand out sharply from the background in this solution of high specific gravity. This procedure may be performed on unfixed or Formalin-fixed feces. The procedure for Sheather sugar flotation is outlined below. 

Haywood and Riley [14] have described a spectrophotometric method for the determination of arsenic in seawater. Adsorption colloid flotation has been employed to separate phosphate and arsenate from seawater [15]. These two anions, in 500 ml filtered seawater, are brought to the surface in less than 5 min, by use of ferric hydroxide (added as 0.1 M FeC 2 ml) as collector, at pH 4, in the presence of sodium dodecyl sulfate [added as 0.05% ethanolic solution (4 ml)] and a stream of nitrogen (15 ml/minutes). The foam is then removed and phosphate and arsenate are determined spectrophotometrically [16]. Recoveries of arsenate and arsenite exceeding 90% were obtained by this procedure. 

Ferric hydroxide coprecipitation techniques are lengthy, two days being needed for a complete precipitation. To speed up this analysis, Tzeng and Zeitlin [595] studied the applicability of an intrinsically rapid technique, namely adsorption colloid flotation. This separation procedure uses a surfactant-collector-inert gas system, in which a charged surface-inactive species is adsorbed on a hydrophobic colloid collector of opposite charge. The colloid with the adsorbed species is floated to the surface with a suitable surfactant and inert gas, and the foam layer is removed manually for analysis by a methylene blue spectrometric procedure. The advantages of the method include a rapid separation, simple equipment, and excellent recoveries. Tzeng and Zeitlin [595] used the floation unit that was devised by Kim and Zeitlin [517]. 

In a laboratory experiment (Adamson and Gast, 1997), the following recipe may be used. To a 1% sodium bicarbonate solution, add a few grams of sand. Further, some acetic acid (or vinegar) will cause the bubbles of C02 produced to cling to the sand particles and thus make these float to the surface. It must be mentioned that, in wastewater treatment, the flotation method is one of the most important procedures. 

---