Density separation techniques

Green River oil shale, obtained from the Mahogany zone of the C-a tract in Rio Blanco County, Colorado, was crushed to nominal 15 cm topsize and separated by standard density separation techniques (13,14) into nominal grades of 104, 129, and 184 liters per tonne (L/t). Each grade fraction was then further size-reduced to finer than 10 mesh and screened into different mesh size samples. The 100 to 200 mesh shale from each grade was used in the current experiments. Several experiments were also conducted using samples of Eastern U.S. shale obtained from Lewis County, Kentucky. 

The silicate species occur in coal chiefly as separate strata and large particle inclusions, and this mode of occurrence is termed the "adventitious" mineral matter. Figure la shows a typical sample of the adventitious silicate mineral particles, density separated from pulverized coal. The density separation technique does not remove the small silicate particles, chiefly alumino-silicate species, the "inherent" mineral matter, in the coal substance (Figure lb). 

Coal desulfurization can be achieved on a commercial scale by means of physical or physicochemical methods which generally use the principal of density separation techniques or other techniques that exploit the surface properties of coals and minerals. For example, the methods exploit the difference in properties that exist between the various forms of pyritic sulfur (pyrite and/or marcasite, FeS2, and occasionally including galena, PbS) and the organic matrix of the coal. 

Figure 9.6 Schematic representation of the process by which compatibilization and density separation techniques can be used to recover over 99% of the plastics used in the manufacture of a minivan door [87],...

Any difference in physical properties of the individual solids can be used as the basis for separation. Differences in density size, shape, color, and electrical and magnetic properties are used in successful commercial separation processes. An important factor in determining the techniques that can be prac tically applied is the particle-size range of the mixture. A convenient guide to the application of different solid-solid separation techniques in relation to the particle-size range is presented in Fig. 19-1, which is a modification of an original illustration by Roberts et al. 

In general, when sepiarating two liquids, they must be immiscible and have different spiecific gravities before a separation technique-such as oil/water separation-would be effective. In the case of finely dispersed liquids or finely dispersed solids, if the dispersed material is below one micron in particle size, centrifuging should be considered. The use of centrifugal force on the differing densities of the material can facilitate the separation technique. 

Most of the methods used for collected and concentrating gold exploit its relatively high density (19.30 g/mL) -a physical property. However, that fact that gold is chemical inactive - a chemical property - allows gold to exist in nature as the pure metal, so its density can be used in separation techniques, like panning. 

Density gradient centrifugation is used to separate macromolecules that differ only slightly in size or density. Two techniques are commonly used. 

Cadmium acetate is used in the pottery and porcelain industry for producing iridescent effects the borotungstate forms an aqueous solution of high density when concentrated (d = 3.28), useful in die mechanical separation of minerals and in density gradient techniques the bromide, like the zinc salt, is used in photography, process engraving and lithography. 

ED appears to be an inefficient method to recover free citric acid because of its low electric conductivity (Novalic et al., 1995). As it is converted into the monovalent (at pH ca. 3), divalent (at pH ca. 5), or trivalent (at pH about 7) citrate anion, there is a significant increase in the electric conductivity (%), the latter increasing from 0.95 to 2.18 and to 3.9 S/m, respectively, in the case of an aqueous solution containing 50 kg/m3 of citric acid equivalent (Moresi and Sappino, 1998). By increasing the pH from 3 to 7, e reduced about eight times, the solute flux (JB) practically doubled, while the overall water transport (/w) increased 3-4 times. The latter partly counterbalanced the greater effectiveness of the electrodialytic concentration of citric acid at pH 7 with respect to that at pH 3. Table XV presents a summary of the effect of current density ( j) on the main performance indicators of the electrodialytic recovery of the monovalent, divalent, or trivalent ionic fractions of citric acid (Moresi and Sappino, 1998). All the mean values or empirical correlations of the earlier indicators were useful to evaluate the economic feasibility of this separation technique (Moresi and Sappino, 2000). 

Work is now underway to separate these various resinite types using density gradient techniques and to chemically characterize the separated resinite fractions. 

There have been a large number of electron spin resonance (ESR) studies of coal and coal products,(1J but a microscopic interpretation of the resulting data has been hampered by the chemical heterogeneity of the coal samples examined. While several surveys of specially selected macerals have appeared, 3), the recent evolution of maceral separation techniques - now allows detailed ESR observations to be made on coals systematically fractionated in which coal rank, maceral type, and maceral density are simultaneously distinguished. The present report surveys the behavior of a variety of ESR properties of carbon radicals in exinite, vitrinite, and inertinite macerals in a variety of coals of different rank. These data... 

Physical cleaning of various coals by oil agglomeration reduced levels of As, Cr, Pb, Mn, Mo, Ni, and V by 50-80%, while levels of some other trace elements were reduced by lesser amounts (20). Oil agglomeration appeared to be more effective at removing trace elements than the wet concentrating table or float/sink density separations. This may be related to an increase in the liberation of mineral matter associated with grinding to produce the relatively fine particle sizes required in the oil agglomeration technique. 

In addition, improved separation of fine particles has resulted from recent advances in density-based separation techniques. This includes the development of several new water-only devices, such as various concentrating spirals, the Kelsey Jig, the Multi-Gravity... 

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