Spiral concentration separation

Gravity concentration, ie, the separation of ore from gangue based on the differences in specific gravities, using jigs, heavy—medium separators, or spiral concentrators for example, is appHcable for lead ores. However, the predominant beneficiation technique used in modem plants is the bubble or froth flotation (qv) process (4,5). 

Principle of Operation Spiral concentration of ores and industrial materials is based primarily on the specific-gravity differentials of the materials to be separated. The shape facdor of the feed material is also important, and utilization of reagentized feed can change the apparent specific gravity of component minerals by forced attachment of air bubbles to mineral floes. The best known spiral-type concentrator is the Humphreys spiral concentrator, which first proved its commercial feasibihty in 1943. In that year an Oregon plant successfully... 

The Humphreys spiral concentrator is a spirally shaped channel or launder with a modified semicircular cross section, as illustrated in Fig. 19-30. The standard spiral consists of five complete turns, but three-turn units are used in some instances when an unusually rapid and clean separation takes place, as in second-stage or cleaner spirals. There is a drop of 0.34 m (13.5 in)/turn as the flowing pulp progresses from the top to the bottom of the spiral. One spiral concentrator occupies about 0.37 m" (4 ft") of floor space and about 2.1 m (7 ft) of headroom measured from feed to discharge box. The optimum particle-size range of feed particles for spirals is about 10 to 200 mesh (2 to 0.074 mm). 

Although the spiral concentrator is mechanically a veiy simple piece of equipment, the separating ac tion taking place is complex. It involves centrifugal force, rric tion against the spiral surface, gravity, and the drag of the water. 

Gravimetric separation systems. These include jigs, shaking tables, Humphrey-type spiral concentrators, and so on. 

Figure 8.27. FEM-images of the oscillating CO-oxidation reaction on Pt ( (1 0 0) (E.T. Latkin, V. I. Elokhin, V. V. Gorodetskii, Spiral concentration waves in the Monte Carlo model of CO oxidation over Pd(l 1 0) caused by synchronisation via COads diffusion between separate parts of catalytic surface. Chemical Engineering Journal, 91 (2003) 123).

Gas separation Hollow-fibre for high-volume applications with low-flux, low-selectivity membranes in which concentration polarisation is easily controlled (nitrogen from air) Spiral-wound when fluxes are higher, feed gases more contaminated, and concentration polarisation a problem (natural gas separations, vapour permeation). 

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