The term spiral separator can refer to either a device for separating slurry

Slurry

A slurry is, in general, a thick suspension of solids in a liquid.-Examples of slurries:Examples of slurries include:* Lahars* A mixture of water and cement to form concrete* A mixture of water, gelling agent, and oxidizers used as an explosive...

 components by density

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

, or for a device for sorting particles by shape. Here, these are termed wet and dry spiral separators, respectively.

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

Drag

- In science and technology :* Drag , the force which resists motion of an object through a fluid* Drag equation, a mathematical equation used in analyzing the magnitude of drag caused by fluid flow...

). The device consists of a tower, around which is wound a sluice

Sluice

A sluice is a water channel that is controlled at its head by a gate . For example, a millrace is a sluice that channels water toward a water mill...

, from which slots or channels are placed in the base of the sluice to extract solid particles that have come out of suspension.

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. 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

Typical spiral concentrators will use a slurry from about 20%-40% solids by weight, with a particle size somewhere between 1.5-.075mm (17-340 mesh), though somewhat larger particle sizes are sometimes used. For good 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

An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

 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.

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

Weed

A weed in a general sense is a plant that is considered by the user of the term to be a nuisance, and normally applied to unwanted plants in human-controlled settings, especially farm fields and gardens, but also lawns, parks, woods, and other areas. More specifically, the term is often used to...

 seeds from the intended harvest, or to remove deformed lead shot

Lead shot

Lead shot is a collective term for small balls of lead. These were the original projectiles for muskets and early rifles, but today lead shot is fired primarily from shotguns. It is also used for a variety of other purposes...

.

See also

• Cyclone (separator)
• Sieve
  Sieve
  A sieve, or sifter, separates wanted elements from unwanted material using a woven screen such as a mesh or net. However, in cooking, especially with flour, a sifter is used to aerate the substance, among other things. A strainer is a type of sieve typically used to separate a solid from a liquid...
  
  
• Mineral processing
• Mechanical screening
  Mechanical screening
  Mechanical screening, often just called screening, is the practice of taking granulated ore material and separating it into multiple grades by particle size....