Flotation measurement

The flotation of minerals is based on different attachment forces of hydrophobized and hydrophilic mineral particles to a gas bubble. Hydrophobized mineral particles adher to gas bubbles and are carried to the surface of the mineral dispersion where they form a froth layer. A mineral is hydrophobized by the adsorption of a suitable surfactant on the surface of the mineral component to be flotated. The hydrophobicity of a mineral particle depends on the degree of occupation of its surface by surfactant molecules and their polar-apolar orientation in the adsorption layer. In a number of papers the relationship was analyzed between the adsorption density of the surfactant at the mineral-water interface and the flotability. However, most interpretations of adsorption and flotation measurements concern surfactant concentrations under their CMC. 

A decrease in flotability is characterized by an increase in polarity of the adsorption layer of both surfactants due to the formation of a second adsorption layer with polar groups of the surfactant orientated toward the bulk phase, up to the CMC. The analysis of the flotation measurements was carried out on the basis of kinetic data for the shortest constant... 

Thanks are due to Miss. U. Wamsler from this department for her technical assistance with the flotation measurements. 

Figure 20.18. Correlations of surface force measurements with flotation measurements on the same surfactant system (157), reproduced with permission from Steinkop Publishers...

The flotation of mica has been correlated to the adhesion force measured from surface force (SFA—see Section VI-4) experiments although, to these authors, it is clear that dynamic effects prevent an absolute comparison [69, 70],... 

Density. Density of LLDPE is measured by flotation in density gradient columns according to ASTM D1505-85. The most often used Hquid system is 2-propanol—water, which provides a density range of 0.79—1.00 g/cm. This technique is simple but requires over 50 hours for a precise measurement. The correlation between density (d) and crystallinity (CR) is given hy Ijd = CRj + (1 — Ci ) / d, where the density of the crystalline phase, ify, is 1.00 g/cm and the density of the amorphous phase, is 0.852—0.862 g/cm. Ultrasonic methods (Tecrad Company) and soHd-state nmr methods (Auburn International, Rheometrics) have been developed for crystallinity and density measurements of LLDPE resins both in pelletized and granular forms. 

The principal experimental method used to measure the density of a solid is determination of the mass of liquid displaced by a known mass of solid. It is essential that the solid have no appreciable solubility in the liquid, that all occluded air be removed from the solid and that the density of the displacement fluid be less than that of the solid lest the solid float. Densities of crystalline solids also can be determined from the dimensions of the unit cell. Davis and Koch discuss other methods for measuring the density of liquids and solids such as hydrostatic weighing of a buoy and flotation methods. 

The aeration requirements of the deep shaft (vertical shaft bioreactor using flotation technology) are provided by two, 100 hp rotary screw compressors rated at a pressure of 7 kg/m2 (100 psig). Dissolved oxygen (DO) levels of 4 mg/L are maintained in the head tank, and during the startup phase of the plant a DO meter measured a dissolved oxygen concentration of 25 mg/L at the shaft bottom. 

MOSH/MOAH Flotation free printing inks All measures papermaking... 

The three most common ways of obtaining true density measurements are gas pycnometry (gas displacement), liquid displacement, and flotation in a liquid. These three techniques have been compared based on accuracy, ease of use, and instrumentation [63], and the results are summarized in Table 4. Gas pycnometry will be discussed in this section because of its wide use and ease of operation. 

Single crystal x-ray diffraction studies showed that the crystals of halcinonide recrystallized from tz-propyl alcohol-water azeotrope (79 22) are orthorhombic and belong to the gpace group P2 2 2, with unit ell constants of a = 10.007 A, = 11.875 A ana Q = 19.460 A. Density is 1.330 gm/cm2 3, as measured by flotation in a hexane-carbon tetrachloride gradient. The molecular weight calculated from the unit cell volume and density is 461 daltons (theoretical is 455 daltons). 

Many processes involving carbonates - ubiquitous minerals in natural systems -are controlled by their surface properties. In particular, flotation studies on calcite have revealed the presence of a pH-variable charge and of a point of zero charge (Somasundaran and Agar, 1967). Furthermore, electrokinetic measurements have shown that Ca2+ is a charge (potential) determining cation of calcite. (Thompson and Pownall, 1989). 

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. 

This book systematically summarizes the researches on electrochemistry of sulphide flotation in our group. The various electrochemical measurements, especially electrochemical corrosive method, electrochemical equilibrium calculations, surface analysis and semiconductor energy band theory, practically, molecular orbital theory, have been used in our studies and introduced in this book. The collectorless and collector-induced flotation behavior of sulphide minerals and the mechanism in various flotation systems have been discussed. The electrochemical corrosive mechanism, mechano-electrochemical behavior and the molecular orbital approach of flotation of sulphide minerals will provide much new information to the researchers in this area. The example of electrochemical flotation separation of sulphide ores listed in this book will demonstrate the good future of flotation electrochemistry of sulphide minerals in industrial applications. 

Nevertheless the potential to be monitored in flotation system would be the mineral potential, not the solution potential. The electrode constracted from the mineral being concentrated should be the most appropriate electrode for f h measurements because the relevant is established at the mineral/solution interface (Woods, 1991). 

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. 

Because of the strong hydrolysis property of antimony salt, it is very difficult to prepare antimony xanthate salt to obtain its IR spectrums. Therefore, the formation of antimony xanthate is difficult to be identified by the UV and FTIR analysis, which has been determined by using XPS. Finally, it can be concluded that the interaction mechanism between ethyl xanthate and jamesonite are attributed to the formation of lead and antimony xanthate on the surface in the light of flotation results, voltammogram measurement, UV and FTIR as well as XPS analyses. 

In 0.1 mol/L KNO3 solution, pH is adjusted to 9.98 by NaOH, Ca(OH)2 and N32C03 respectively. Electrochemical impedance spectroscopy (EIS) of jamesonite electrode in 0.1 mol/L KNO3 solution with different pH adjusting was measured and the results are given in Fig. 5.11. Because i NaOH > cacoH. Q= l (oR), then Cd(Ca(OH)2)< Cd(NaOH). It suggests that Ca(OH) has stronger tendency to adsorb onto jamesonite surface than OH . Ca(OH)2 is a more efficient depressant than NaOH in the flotation of sulphide minerals. 

At the same pH made by different pH modifiers, the different flotation response of one sulphide mineral may arise from its effect on the potential of this mineral electrode. The change of potential of mineral electrodes with time at pH= 12 modified by NaOH and Ca(OH)2 is measured and demonstrated in Fig. 10.5. It follows that a mineral electrode potential increases faster with the time at pH= 12 modified by sodium hydroxide and changes a little at the same pH modified by calcium hydroxide. When pH is adjusted by NaOH, the electrode potential of galena, sphalerite and p5oite increase rapidly, respectively, from -30, -12, and 70 mV at the initial stage to -10, 10, and 110 mV after 50 min. When pH is modified by lime, the electrode potential of galena, sphalerite and pyrite... 

In addition, the flotation rate of galena in the OPCF process is much faster than that in the traditional through the measurement of galena recovery of each cell as shown in Fig. 10.19. The Pb recovery is more than 90% only through 4 flotation cells operation and Zn recovery reaches to 87% only through 12 flotation cells operation in OPCF. But for the traditional process, 8 flotation cells are needed to reach 90% Pb recovery and 20 flotation cells are needed to reach 87% Zn recovery. 

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