Mineral flotation, correlation

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. 

The mixed-potential model demonstrated the importance of electrode potential in flotation systems. The mixed potential or rest potential of an electrode provides information to determine the identity of the reactions that take place at the mineral surface and the rates of these processes. One approach is to compare the measured rest potential with equilibrium potential for various processes derived from thermodynamic data. Allison et al. (1971,1972) considered that a necessary condition for the electrochemical formation of dithiolate at the mineral surface is that the measmed mixed potential arising from the reduction of oxygen and the oxidation of this collector at the surface must be anodic to the equilibrium potential for the thio ion/dithiolate couple. They correlated the rest potential of a range of sulphide minerals in different thio-collector solutions with the products extracted from the surface as shown in Table 1.2 and 1.3. It can be seen from these Tables that only those minerals exhibiting rest potential in excess of the thio ion/disulphide couple formed dithiolate as a major reaction product. Those minerals which had a rest potential below this value formed the metal collector compoimds, except covellite on which dixanthogen was formed even though the measured rest potential was below the reversible potential. Allison et al. (1972) attributed the behavior to the decomposition of cupric xanthate. 

Despite the conflicting evidence, Heyes and Trahar (1984) believe there is sufficient evidence to confirm the presence of sulphur on mineral surface. They leached the surface of floated pyrrhotite from a typical test with cyclohexane and have examined the leach solution in a UV spectrophotometer. They found that sulphur could be extracted from the surface of pyrrhotite, which had been floated in the absence of collector. As can be seen from Fig. 2.26, the spectrum from the leached pyrrhotite was compared with the spectrum of sulphur dissolved in cyclohexane indicating that sulphur was present at the siuface. Kelebek and Smith (1989) used UV spectrophotometer to determine sulphur in the ethanol extract from the surface of floated galena and chalcopyrite showing that the amount of sulphur on the minerals can be correlated with their flotation rate which was found to be first order within the critical surface tension range. 

There is significant agreement between the lower potential boundary of the flotation region and the potential at which the anodic ciurent begins in a potential sweep. The amoimt of extracted sulphur on the sulphide minerals can be correlated with their collectorless flotation behaviors. The higher the concentration of surface sulphur, the faster the collectorless flotation rate and thus the higher the recovery. 

Kelebek, S. and Smith, G. W., 1989. Collectorless flotation of galena and chalcopyrite correlation between flotation rate and the amount of extracted sulfur. Miner. Metall. Process, 6(3) 123 -129... 

In the case of long chain surfactants used as collectors, a signiflcant correlation between their adsorption in the form of aggregates and flotation of minerals with them was established in the 1960 s by Somasundaran et al. (1964). Somasundaran et al. (1976, 1985) developed the relevant dissociation and aggregation equilibria for flotation reagents in the solution as well as at the mineral-solution interface. Importantly, the ion-molecule complexes phenomenon was proposed later by Somasundaran (1976), Hanna and Somasundaran (1976) to account for the flotation maximum exhibited at certain pH values by hydrolyzable surfactants. 

Correlation of oleate adsorption and flotation maximum at about pH 7.5 for a variety of minerals and high abstraction (adsorption + surface precipitation) below this pH with the species distribution diagram (Fig. 4.9) suggests that the role of acid-soap dimer and precipitated oleic acid can be significant in controlling the adsorption and resultant flotation behavior. 

Two cells used in the laboratory for studying the physical chemistry of flotation process are the Hal-limond cell and Fuerstenau cell. Tests can be conducted in these cells under controlled chemical conditions. Tests in a Hallimond tube cell, shown schematically in Fig. 16.2-2, require only about I g of the mineral and do not require the use of a frother. Rigorous control of flotation time, gas flow, and citation that have been made possible by recent modiflcations enable one to conduct tests with a reproducibility of 1%. Also, application of the results obtained using the Hallimond tube cell has been demonstrated recently by correlating such results with those obtained using conventional laboratoiy large-scale cells. ... 

Van der Westhuizen AP, Deglon DA. (2008) Solids suspension in a pilot-scale mechanical flotation cell a critical impeller speed correlation. Miner. Eng., 21 621-629. 

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