Spiral Separator
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The term spiral separator can refer to either a device for separating
slurry A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...
components by
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
(''wet spiral separators''), or for a device for sorting particles by shape (''dry spiral separators'').


Wet spiral separators

Spiral separators of the wet type, also called spiral concentrators, are devices to separate solid components in a slurry, based upon a combination of the solid particle density as well as the particle's hydrodynamic properties (e.g. drag). The device consists of a tower, around which is wound a
sluice A sluice ( ) is a water channel containing a sluice gate, a type of lock to manage the water flow and water level. There are various types of sluice gates, including flap sluice gates and fan gates. Different depths are calculated when design s ...
, from which slots or channels are placed in the base of the sluice to extract solid particles that have come out of
suspension Suspension or suspended may refer to: Science and engineering * Car suspension * Cell suspension or suspension culture, in biology * Guarded suspension, a software design pattern in concurrent programming suspending a method call and the calling ...
. As larger and heavier particles sink to the bottom of the sluice faster and experience more drag from the bottom, they travel slower, and so move towards the center of the spiral. Conversely, light particles stay towards the outside of the spiral, with the water, and quickly reach the bottom. At the bottom, a "cut" is made with a set of adjustable bars, channels, or slots, separating the low and high density parts.


Efficiency

Typical spiral concentrators will use a slurry from about 20%-40% solids by weight, with a particle size somewhere between 0.75—1.5mm (17-340 mesh), though somewhat larger particle sizes are sometimes used. The spiral separator is less efficient at the particle sizes of 0.1—0.074mm however. For efficient separation, the density difference between the heavy minerals and the light minerals in the feedstock should be at least 1 g/cm3; and because the separation is dependent upon size and density, spiral separators are most effective at purifying
ore Ore is natural rock or sediment that contains one or more valuable minerals, typically including metals, concentrated above background levels, and that is economically viable to mine and process. The grade of ore refers to the concentration ...
if its particles are of uniform size and shape. A spiral separator may process a couple tons per hour of ore, per flight, and multiple flights may be stacked in the same space as one, to improve capacity. Many things can be done to improve the separation efficiency, including: * changing the rate of material feed *changing the grain size of the material *changing the slurry mass percentage *adjusting the cutter bar positions *running the output of one spiral separator (often, a third, intermediate, cut) through a second. *adding washwater inlets along the length of the spiral, to aid in separating light minerals *adding multiple outlets along the length, to improve the ability of the spiral to remove heavy contaminants *adding ridges on the sluice at an angle to the direction of flow.


Dry spiral separators

Dry spiral separators, capable of distinguishing round particles from nonrounds, are used to sort the feed by shape. The device consists of a tower, around which is wound an inwardly inclined flight. A catchment funnel is placed around this inner flight. Round particles roll at a higher speed than other objects, and so are flung off the inner flight and into the collection funnel. Shapes which are not round enough are collected at the bottom of the flight. Separators of this type may be used for removing
weed A weed is a plant considered undesirable in a particular situation, growing where it conflicts with human preferences, needs, or goals.Harlan, J. R., & deWet, J. M. (1965). Some thoughts about weeds. ''Economic botany'', ''19''(1), 16-24. Pla ...
seeds from the intended harvest, or to remove deformed
lead shot Shot is a collective term for small spheres or pellets, often made of lead. These have been projected from slings since ancient times and were the original projectiles for shotguns and are still fired primarily from shotguns and grenade launch ...
.


See also

*
Sieve A sieve (), fine mesh strainer, or sift is a tool used for separating wanted elements from unwanted material or for controlling the particle size distribution of a sample, using a screen such as a woven mesh or net or perforated sheet m ...
*
Screw conveyor A screw conveyor or auger conveyor is a mechanism that uses a rotating helical screw (simple machine), screw blade, called a "''flighting''", usually within a tube, to move liquid or granular materials. They are used in many bulk handling in ...
* Cyclone (separator) *
Mineral processing Mineral processing is the process of separating commercially valuable minerals from their ores in the field of extractive metallurgy. Depending on the processes used in each instance, it is often referred to as ore dressing or ore milling. Be ...
*
Mechanical screening Mechanical screening, often just called screening, is the practice of taking granulated or crushed ore material and separating it into multiple grades by particle size. This practice occurs in a variety of industries such as mining and minera ...


References


Further reading

*{{Cite patent , inventor-last = Wright , inventor-first =Douglas , publication-date =7. Jul. 1978 , issue-date =19. Feb. 1980 , title = Spiral Separators , country-code =US , description = Design of a take-off point for the extraction of dense material separated from a helical spiral separator. , patent-number =922804


External links


Screw Conveyor
separator Chemical equipment Separation processes