Friday, April 14, 2017

Wilfley Table

Aim of the Experiment: Concentration of ore with the help of Wilfley Table.

Apparatus required: Laboratory model Wilfley Table.

Theory: The shaking or Wilfiey table consist of a substantially plane surface (the deck), inclined slightly from the horizontal and shaken with an asymmetrical motion in the direction of the long axis. Asymmetrical motion means, the stroke of the table is faster in one direction and slower in opposite direction. Usually the back- stroke is faster compared to forward stoke. The wash water flows over the table at right-angle to the direction of jog. Longitudinal cleats or riffles are fixed on the table surface in the direction of the table movement.

The feed is introduced through the feed box at the upper corner of the table. As the feed hits the deck, it is fanned out by combination of differential motion transversely flowing water. The jolts cause the heavier particles to work down of form the bottom layer and travel in the through formed by the riffles.

The lighter gangue materials are thrown into suspension and discharge over the edge of the table opposite the feed box by the flowing wash water. The heavier minerals finally arrange themselves on
the smooth unrifled proportion of the table when they encounter the full force of the wash water. The middlings are selected in that corner of the table which is intermediate between concentrate and tailing.

The reciprocating (to and fro) speed of the riffle table is usually 200-300 strokes/ minutes with amplitude of 12-15mm. the coarser feed requires larger stroke length.

Constructional Features of Wilfley Table:

The Wilfley laboratory table was equipped with a conventional twelve-inch by thirty-inch riffled deck and a standard Wilfley head motion. The total concentration area of the deck was 360 square inches.
Special treatment of cleats or riffles is required as they constitute part off the consumables items in the working of wilfley table which required frequent replacement. The cleats are usually made up wood with a maximum height of 1 cm and maximum width of 1 cm. the riffles are tapered from one end toanother. They are so placed that they form channels of around 1 cm width and 1 cm deep which
trappers to zero depth at the opposite end. All the cleats end along a diagonal line imagined on the Wilflely table which approximately divides the total surface area of the table in the ratio of 2:1. This
means 2/3 of the total surface area of the table is cleated and rest 1/3 portion is unriffled.

The surface of the wilfley is lined with rubber or linoleum to restrict the wear of the wooden table surface and also increase roughness or friction. Riffles along with linoleum lining the capacity of the table.

Working Principle Wilfley Table:

The points of the compass are used for clarity in describing the operation of the Wilfley shaking table. The feed is screened to <3mm and fed into a small hopper above the north-east corner of the shaking table, where it is mixed with clean water. The resulting slurry is introduced to the north-east corner of the shaking table and begins to spread southwards as a thin film. The feed fan outs towards the edge of the table, allowing the operator to see exactly what is happening, and to decide where to subdivide the fan into distinct streams each dominated by a particular mineral. The shaking motion has a slow westward stroke and rapid return eastward stroke – often with a bump. This induces settled particles to crawl in a juddering manner westward along the table with the thin film of slurry. The shaking is usually very rapid with a frequency of 4 to 5.5 strokes per second. The shaking displacement is usually half to one inch to-and-fro. A set of low riffles aligned east-west guide the heavies ever westward to fall off the south-west corner of the table into a hopper as a continuous discharge. Meanwhile, a spray bar introduces clean ‘wash water’ along the north edge of the table, sending a thin film of clean water southward to encounter the riffles and the westward flowing slurry. The wash water mixes with the slurry and overrides the riffles taking the lighter particles with it to spill over the southern edge as a continuous discharge of tailings.

Characteristics of Shaking table operation

1. Under idealized conditions particles segregate into four groups:-

a. Light- large

b. Large- heavy

c. Small- light

d. Small- heavy

2. The angle of inclination of shaking table depends on the minerals handled. Tonnage handled

depends on:-

a. Size of the feed.

b. Whether the operation is roughing or cleaning. c. The difference in Sp. Gs., between the mineral that are to be separated.

d. Average specific gravity of the mineral to be treated.

3. Capacity of the wilfley table

It varies with table size and many other associated factors. But in general a table size of 4ftx 2ft has a capacity as high as 200 tons/ 24hrs.
4. Cost of operation
a. Power 0.5-0.8kw/hrs.
b. Repairing cost of the cleats & deck as and when required.

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