Tablingaassfg

8/11/2019 Tablingaassfg

1/8

[Shaking/Slanting of table is used to

separate large bulk of samples. Such

orientation of table separates the bulkmineral samples into light and heavy-

mineral fractions provided that there is

a marked difference in the density of

the minerals. This process is known

as..]

Tabling

A Form of Gravity Concentration

P r e s e n t e d b y :269/11AMIT ABHINAV

317/11CHANDRASHEKHAR

440/11ABHISHEK KUMAR


2/8

Gravity separation techniques have been in use in the mineral sands industry for decades; from the Reichert

cone to Wilfley tables, Wright sluices and the Kelsey Jig, all attempting that elusive perfect gravity

separation.

Gravity concentration methods separates minerals of different specific gravity by their relative movement in

response to gravity and the resistance to motion offered by a viscous fluid, such as water or air.

It is essential for effective separation that a marked density difference exists between the mineral and the

gangue. Some idea of the type of separation possible can be gained from the concentration criterion.

Where:

Dh : Specific gravity of the heavy mineral Df : Specific gravity of the fluid

Dl : Specific gravity of the Light Mineral

In very general terms, when the quotient is

greater than 2.5 the gravity separation is relatively easy

below about 1.25 gravity concentration is not generally commercially feasible.

The motion of a particle in a fluid is dependent not only on its specific gravity, but also on its size; larger

particles will be affected more than smaller ones. The efficiency of gravity processes therefore increases

with particle size, and the particles should be sufficiently coarse to move in accordance with Newtons law

Particles (which are so small that their movement is dominated mainly by surface friction) respond

relatively poorly to commercial high capacity gravity methods.

Many different machines have been designed and built in the past to affect separation of minerals by

gravity and they are continuously reviewed. Many gravity devices have become obsolete,

Some of the equipments that is used in modern mills are:

Jigging:In the jig the separation of minerals of different specific gravity is accomplished in a bedwhich is rendered fluid by a pulsating current of water so as to produce stratification. Essentially it

consists of an open tank, filled with a fluid, with horizontal or slightly inclined jig 'screen' near the top upon

which the particles are supported, and through which the fluid flows in alternating directions.


3/8

Screening: Screening is generally carried out on relatively coarse material, as the efficiency

decreases rapidly with fineness. Screening is the process of separating particles size and fine

screening typically refers to separation in the rage of 10mm to 38 microns (400 mesh). Fine

screening, wet or dry, is normally accomplished with high frequency, low amplitude, vibrating

screening machines with either elliptical or straight-line motion.

.

Classifiers:In it mixtures of minerals are separated into two or more minerals on the basis of the

velocity with which the grain falls through the fluid. Classifiers consist essentially of a sorting column in

which a fluid is rising at a uniform rate. Particles introduced into the sorting column either sink or rise

according to whether their terminal velocities are greater or lesser than the upward velocity of the fluid. Thesorting column therefore separates the feed into two products, an overflow consisting of particles with

terminal velocities lesser than the velocity of the fluid and an underflow or spigot product of particles with

terminal velocities greater than the rising velocity.


4/8

Heavy Medium Separator (HMS): In it heavy liquid of suitable density are used, so that those

minerals lighter than the liquid float, while those denser than it sinks.

Tabling: In it shaking of table is used to separate minerals into light and heavy fractions.

Disadvantage of Gravity Separation:One of the most important aspects of gravity circuit operations is correct water-balance within the

plant. Almost all gravity concentrators have an optimum feed pulp-density, and relatively little deviation

from this density causes a rapid decline in efficiency.

Conclusion

In practice, close size control of feeds to gravity processes is required in order to reduce the size

effect and make the relatively motion of the particles specific gravity dependent.


5/8

Accurate pulp-density control is therefore essential, and this is most important on the raw feed.

Now keeping in mind the disadvantages of Gravity Separation and the key points of conclusion, let us

explore the depths and different aspects of one of its process (as assigned by our Geology & Mineral

Beneficiation Professor Dr. Ranjit) Tabling.

Tabling:In it a shaking table is used to separate large bulk samples. The shaking table separates the bulk

mineral samples into light and heavy-mineral fractions provided that there is a marked difference in the

density of the minerals.

H istory of Tabli ng:From the washing operation of the ancients, it was only a step to the use (but not the understanding)

of a combination of washing force of streams with the force of gravity to segregate mineral particles of

different specific gravities. Ruins of the works at the famous silver mines in Atticahave yielded stonetables set as a slant; these were used by Atheniansfor the concentration of the fines from the Argentiferous

lead ores of Laurium. The mineral separation plant commenced operation in 1977. Heavy mineral

concentrates (HMC) from the mining plants were treated on wet high intensity magnets (WHIMS) to

recover limonite for the smelting process. And from there the actual application of the usage of gravity of

the minerals for their separation is started. Water was allowed to flow down the slope of the table, and it

carried away the lighter and the finer particles; at the same time the heavier particles settled on the table.

After a certain length of time, the valuable sediments were scraped from the table, and the operation was

repeated as often as necessary on either the concentrated product or the waste. This was the beginning of

Tabling, a form of gravity concentration.

Types of Tabl ing process:

As the tabling process commences different ways were invented to use this method common of which is

wilfley table. Thus the varieties of tabling process are

a)Wil fl ey Table

Wilfley Tables are designed to wet gravity-based separation of minerals and other granular

materials, table that separates heavy mineral particles from lighter gangue by means of longitudinal

riffles impeding the downward flow and a horizontal reciprocating motion carrying the heavy

particles off the end of the table.

The principle behind this wilfley shaking table is that the shaking action of the table causes the

grains to be arranged according to their density; after on heavy minerals move towards the end of the

table, and light minerals towards the slope side of the table.


6/8

The Wilfley shaking table is used to separate large bulk samples (several tons of kg). The shaking

table separates the sieved sand samples into light and heavy-mineral fractions provided that there is a

marked difference in the density of the minerals. Slurry of sediment and water moves across the table

and is caught and forms pools behind the longitudinal riffles. The longitudinal shaking action of the

table deck causes the grains to be arranged according to their density. When the deck is accelerated

in the forward direction, the minerals will move ahead during the forward stroke. At the end of the

stroke, the direction of the motion of the table is reversed. Due to the large inertia heavy minerals

tend to move more effectively to the end of the table, while the light minerals tend to follow more

effectively the direction of the backward stroke. The water flow forces the light minerals to move

slowly across the riffles down the small slope of the table.

b)Air Tabling

Air tabling is a dry gravity method. The air table is mainly comprised of a hopper, a vibrating feeder, a

porous deck powered by an eccentric drive to impart the longitudinal vibration and an electric fan located

below the porous deck to generate the upward airflow. It consists of three compartments separated with the

splitters being positioned by preliminary visual assessments. The flat trapezoidal deck, constructed of wood

and porous material, is fitted with a perforated plate with circular openings (opening area portion being

11.8%) and with a series of riffles of 7 mm height arranged in parallel to the direction of longitudinal

vibration. The diameter of openings (0.06 mm) is smaller than the size of the smallest particle in the

mixture, disallowing particles passing through. In operation, the feed is fed onto the deck, creating a uniform

bed of material. The longitudinal vibration of the deck and the upward airflow spread and expand the entire

bed of materials. This causes high-density particles to settle on the deck and contact its surface, while thelow-density ones to float on top of the bed. The high-density particles are then vibrated uphill along the end

slope towards the higher side. At the end of each forward stroke of vibration, the motion of the porous deck

is sharply reversed, but the high-density particles continue to move forward during most of the backward


7/8

stroke due to their built-up momentum. The vibration proceeds until they flow off the deck at its higher end,

entering the right-hand compartment of the collecting bin. On the other hand the low-density particles which

remain fluidized drift downhill in the direction of the decks inclination due to gravitational pull, and flow

off the deck at its lower end. The low-density particles are then collected at the left-hand compartment of the

collecting bin.

I nf luence of tabli ng in mineral beneficiation:

There are many applications where the shaking tables are of particular value of particular value and

cannot ne equaled for economical and efficient performance. They are effective in processing precious and

base metal, rare metal and non-metallic minerals. The benefits of Shaking Tables / Tabling process is that it

has good high-grades sorting rate, high efficiency, and easy operation and maintenance, easy strokeadjustment.


8/8

www.jaw-breakers.com/T112.html

en.wikipedia.org/wiki/Mineral_processing

www.britannica.com/EBchecked/topic/303843/jigging

en.wikipedia.org/wiki/Mechanical_screening

www.ranjit.rds.net.in

Documents

Tablingaassfg