CONCENTRATION | GRAVITY SEPARATION

Concentration

The sorting operation along with gravity concentration has become a very important method of concentration or even the mode of this. This is by the two ways :

● If the valuable constituents of the crushed ore in one size range and the waste in other size range.
● The settling can be crowded enough for stratification to occur, when both valuable mineral and waste have similarsized as per the theory of hinder settling.
● In this case the lower stratum consist of heavier minerals and the upper stratum consist of lighter minerals.

Gravity Separation :
Gravity separation
Gravity separation

The basic principle involved in this gravity separation concentration process is the float and sink using a fluid whose specific gravity is in between the specific gravity of the two mixed up mineral practice in the crushed ore. Since all the mineral are heavier than water, water is not a suitable fluid medium for practising float and sink method of separation.

Separation Circuit :

A simple heavy media separation circuit consist of the :
1. A separating vessel in which heavy suspension is kept with a provision for introducing the feed with drawing the product continuously.

2. Means to clean the product, recover the media and recirculate the media to the vessel.
Specific industrial processes using separation :
Three different process have developed untill now
1. Lessing process.
2. Bertrand process
3. Du pont (nagel voort) process.

JIGGING

It us one of the most ancient method of ore concentration, the three physical factors
1. Hinderd settling classification.
2. Differential acceleration at the beginning of the fall.
3. Consolidation trickling at the end of the fall.

Jigging Cycle :
Jigging process
Gold jiging

Short fall are to be realized in jig for stratification to occur. This is obtained by pulsion and suction of water or any fluid through a bed of ground ores, held on a perforated gread. A complete cycle of suction and pulsion is known as jigging cycle.
Jigging Characteristics :

1. Jigging ratio :
This is defined as the ratio of diameter of the jigging particles. This varies enormously with the duration of fall.

2. Rate of stratification :
The distance gained per second by one type of particle over another. The gain us nil if the time of settling is infinitely smaller or infinitely large. Rate of gain for fine heavy is less then the rate of gain for coarse. So large number of settling periods are required.

Construction and Working of Jigging :

1. It is essentially a water filled box in which a bed of mineral grains is support on a perforated.
Jigging cycle graph
Jigging graph
2. Jigs are usually made up of wood or other materials. In place of one compartment there may be several compartment connected in series.
3. The talling of one compartment work as feed to the next compartment. The jigging amplitude is max in the first cell and least in the last cell.
Add caption
4. When water is pulsed through the screen the particles brought in to suspension in water and are allowed to settle under hindered settling condition modified greatly by differential acceleration.
Types of Jigs : This is two type 1. Hand jig, 2. Mechanical jig.

Advantage of Jigs :

1. It is primarily used to concentrate coarse minerals.
2. Mainly used in coal washing and also to beneficial non magnetic iron ores.
3. Jigs are cheap to operate and substantially full roof and offers an easy access for inspection.

Limitations :

1. Inspire for sulphide ores.
2. Requires large amount of water.
3. Finer cannot be treated in jigs and can be operated on ores that are too coarse for complete liberation.
4. Jigs do not provide a complete solution to any mineral benification.

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