Minerals sink-float techniques

The chemical extraction procedure used to preferentially disassociate carbonate and silicate minerals is described elsewhere in this Symposium Series (12), and, thus, will be described only briefly here. The separation scheme is outlined in Figure 1. Initially, a bitumen-free oil shale is isolated by exhaustive Soxhlet extraction with a methanol/benzene mixture. A portion of the bitumen-free shale oil is then treated with HC1 to produce a carbonate-, bitumen-free oil shale. Following Soxhlet extraction with benzene/methanol to remove carbonate-associated bitunens, a portion of the carbonate-, bitumen-free oil shale is then extracted with HF/HC1 to produce a silicate-, carbonate-, bitumen-free shale. This shale is also Soxhlet extracted to remove silicate-associated bitumens. Finally, a portion of the silicate-, carbonate-, bitumen-free shale is separated by density into three fractions by sink/float techniques using both 15 wt% ZnCl2 in distilled water and pure distilled water as immersion bath media. 

The mineral matter in the coke was extremely difficult to identify because it was finely disseminated throughout. X-ray diffraction techniques were used to gain some insight into the mineral content of the coke. In order to obtain x-ray diffraction patterns of the mineral matter, the interference of carbon had to be reduced to a minimum this was accomplished by grinding the coke to —200 mesh, sink-floating it in a 2.30-specific gravity liquid, and centrifuging. 

A method has been developed, utilizing sink float procedures, which calculates the H/C and N/C ratios in raw shales. In addition the technique eliminates the need for acid extraction to obtain kerogen and also estimates the H and N content of the mineral matrix. 

G. Dodbiba, N. Haruki, A. Shibayama, T. Miyazaki, and T. Fujita, Combination of Sink-float Separation and Flotation Technique for Puriflcation of Shredded PET-bottle from PE or PP Flakes , Int. J. Mineral Processing 65, 11-29 (2002). 

Solids of different densities can be separated by immersing them in a fluid of intermediate density. The heavier solids sink to the bottom and the lighter float to the surface. Water suspensions of fine particles are often used as the dense liquid (heavy-medium). The technique is used extensively for the benefication (concentration) of mineral ores. 

Two bituminous coals of moderate ash content were chosen for this paper to illustrate this method of determining coal-mineral association. The first sample was an Upper Freeport coal with 1.3% moisture, 9.88% ash, and 1.56% total sulfur. The second sample was an Indiana No. 3 coal having 10.5% moisture, 7.35% ash, and 4.26% total sulfur. Both coals had been precleaned at a coarse particle size, ground to minus 325 mesh (44 ym), and then separate samples were cleaned by float-sink and by froth flotation techniques, as described elsewhere [5]. Analyses of the feed coals are included in Table I. 

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. 

The AIA-SEM technique has been used in Ames Laboratory to study the effect of grinding on the liberation of mineral matter from fine coal and its subsequent removal during cleaning. Several series of coals have been characterized by this technique in recent years, thus demonstrating its usefulness. In this work, the AIA-SEM technique was applied to determine the coal mineral character before and after cleaning by a float-sink technique. 

In addition to its chanical properties, the efficient use of a coal also requires a knowledge of its physical properties, such as its density (which is dependent on a combination of rank and mineral matter content), hardness, and grindability (both related to coal composition and rank). Other properties include its abrasion index (derived mainly from coarse-grained quartz) and the particle size distribution. Float-sink testing may also be included with the analysis process. This involves separating the (crushed) coal into different density fractions as a basis for assessing its response to coal preparation processes. Float-sink techniques may also be used to provide a coal sample that represents the expected end product of a preparation plant, in order to assess the quality of the coal that will actually be sold or used rather than the in situ or ROM material represented by an untreated (raw) coal sample. 

One other technique for the investigation of trace elements in coal applies the float-sink principle in which comminuted coal can be separated into several specific gravity fractions by flotation in mixtures of liquids such as perchloroethylene and naphtha a liquid such as bromoform (CHBrj) can also be employed for further subfractionation. This procedure can virtually be employed as a fractionation technique to remove significant proportions of the mineral matter from coal without resorting to the use of heat. 

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