Spiral concentrators

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. 

Maintenance The only moving parts in spiral concentrators are those in the pumps that supply the feed and recirculate intermediate products. However, there are sometimes minor maintenance problems associated with the spiral trough itself. Some ores contain sharp particles of veiy abrasive minerals. The presence of these minerals in some ore causes rapid formation of deep grooves in the surface of cast-iron spirals. Wear grooves can be patched with a variety of plastic and metallic cements. Most spirals presently in service are made of cast iron with molded and vulcanized liners. These liners have successfully solved most wear problems. 

A typical summaiy of an approximate range of spiral concentration plant direct costs is given in Table 19-11. 

TABLE 19-11 Approximate Range of Direct Costs for Spiral Concentration... 

B) spiral diameter versus application (C) a view of the spiral concentrator. 

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

Fig. 5. Photographs of spiral concentrator showing overall view and detail of trough. Source Outokumpu (2003).

Basic Requirements for Spiral Concentration Minerals or materials of different specific gravity can usually be concentrated on spirals if the heavy particles do not exceed 10 mesh (2 mm) or are not finer than 200 mesh (0.074 mm). The size of the low-specific-gravity component is not critical when the values to be recovered are in the heavier-particle fraction. In this case the size of the light particles may range from 4 mesh (4.76 mm) to zero. The quantity of locked grain components (referred to as middlings in the mineral industry) that are present in a given pulp can be critical because this material is fre-... 

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