Classifying – separating – and assorting solids – Stratifiers – With liquid treatment
Patent
1984-12-07
1986-07-01
Lutter, Frank W.
Classifying, separating, and assorting solids
Stratifiers
With liquid treatment
B03B 552
Patent
active
045978611
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to spiral separators. Spiral separators are used extensively for the wet gravity separation of solids according to their specific gravities. For examples, spiral separators are used in separation of various kinds of mineral sands from silica sands, and in cleaning crushed coal by the removal of ash or other impurities. An example of such a spiral separator is described in pending Australian patent application No. 55205/80.
BACKGROUND ART
Separators of the kind under discussion have a helical trough or sluice which has an inner wall and an outer wall connected by a floor. In use, a pulp or slurry containing species to be separated is fed to the trough. The species in the slurry are sorted according to size and specific gravity with the largest and/or heaviest species moving to one side of the stream and the finer and/or lighter species being distributed in layers from the bed of the stream upwardly and from the inside of the curve outwardly and with water piling up on the outside of the bend. When the gravitational force is greater than the centrifugal force the largest and/or heaviest species are concentrated in a band near the inner wall ("concentrate band") and/or the finer and lighter species move towards the outer wall forming a band of depleted concentrate ("depleted band"). A splitter is arranged to remove the concentrate band via a take-off opening and the separation may be repeated on the depleted band.
DISCLOSURE OF THE INVENTION
While spirals of this general type have proved highly valuable, problems do arise in their operation in practice. Firstly, it has been observed that when the lighter and finer species (for example silica sand or other gangue) of the slurry has a very fine particle size, comparable with the particle size of the more dense material to be separated, some of the lighter species will move inwardly toward the inner wall of the spiral with the concentrate of the more dense species even though there is a very great difference in their respective specific gravities. In separating a mineral concentrate from silica sand, the presence of the silica sand can be observed as a band or layer which at least partially overlies the concentrate. This overlying depleted band or layer adversely affects the yield and/or grade of the concentrate which can be recovered from the slurry.
Secondly, a recent trend has been to operate such spirals without the addition of wash water as the pulp flows down the spirals. It has been observed that, with spirals having a large pitch and/or floors with a relatively large inclination to the horizontal in the trough longitudinal direction, the water in the pulp rapidly moves outwardly towards the outer walls of the spiral under centrifugal action and the remaining concentrate and gangue in the pulp quickly become sluggish as they flow down the spirals.
It is an object of the present invention to provide a method of, and apparatus for, overcoming or at least ameleorating those disadvantages and which in preferred embodiments improves the yield and/or grade of the concentrate obtainable from a spiral separator.
Methods according to the invention achieve the first object by the step of diverting the overlying remainder band or layer outwardly from the underlying concentrate at a location upstream of a concentrate take-off.
In a preferred embodiment a slurry deflector is situated inwardly of the remainder band. The shape of the deflector and the velocity of the slurry are selected so that a "bow wave" is produced which urges the overlying band outwards. The deflection means will also serve to fan out the width of the concentrate band in addition to diverting the overlying remainder band outwards relative thereto, the widened concentrate band facilitating setting by an operator of take-off splitters to obtain optimum grade and/or yield.
It is another object of the invention to provide a method of and apparatus for repulping the remainder band with water to maintain the flow of the tailings down the spiral and to enable
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Lithgow Thomas M.
Lutter Frank W.
Mineral Deposits Limited
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