Gravity Concentration By Jigs Engineering Essay

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Gravity concentration methods separate minerals of different specific gravity. They are used to treat a great variaty of materials [ranging from Au ( sp. gr. 19.3 ) to coal ( sp. gr. 1.3 ) ]. Gravity concentration methods remained, however the main concentrating methods for iron , tungsten, tin ores and coal. This methods are usually preferred to flotation due to its low cost . Minerals liberated at sizes above flotation range may be concentrated even more economically using gravity methods (also cause efficient dewatering due to decreased surface area.). The main principles of appliying this method is different size and shape of minerals having different specific gravity. This method can be applied at the range of 7.5 - 1.3. And, the advantages of this method are its simplicity, having high capacity and low cost. In order to apply gravity concentration method concentration criteria ( cc ) shoud be at optimum range.

CC = dh - df

dl - df

CC >2.5 ( 74 micron )

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CC <1.25 HMS depending on the liberation size it can be

CC = 2.5-1.75 ( 150 micron ) applied easly

CC =1.75 -1.50 ( 1.7 micron)

CC = 1.5 - 1.25 ( 6mm )

Jigging is a kind of gravity concentration method. This method seperates minerals of different specific gravity by their relative movement in response to gravity and ore or more other forces the latter often being the resistance to motion offered by a viscous fluid, such as water or air. The jig is normally used to concentrate relatively coarse material. Good separation is possible if the feed is closely sized (e.g. 3 - 10) and if the sp. gr. difference is large. Many large jig circuits are still operated in the coal, cassiteriite, tungsten, gold, barytes and iron-ore industries. Jigs have a relatively high unit capacity and can achieve good recovery of values down to 150 µm and acceptable recoveries often down to 75 µm. (High proportions of fines interfere with performance.).

Jigging is the stratification of minerals of different sp. gr. The separation is accomplished in a bed which is rendered fluid by a pulsating current of water so as to produce stratification. The aim is to dilate the bed of material being treated and to control the dilation so that the heavier, small particles penetrate the interstices of the bed and the larger high sp gr particles fall under a condition probably similar to hindered settling. On the pulsion stroke, the bed is normally lifted as a mass , the bottom particles falling first until the whole bed is loosened. On the suction stroke, it then closes slowly again and this is repeated at every stroke; the frequency varying between 55 - 330 cycle / min. The fine particles tend to pass through the interstices after the large ones have become immobile. The motion can be obtained either by using a fixed sieve jig and pulsating the water, or by employing a moving sieve in a simple hand- jig.

Jigs can be divided into two groups. One of them is Mineral Jigs ( 16mm - 100 micron ) This jigs is seperated into two groups: Harz and Denuer. And, another one is Coal Jigs

( 25mm - 150 mm). This jigs is also seperated into two groups. These are Baum and Batac.

Mechanism:

Jigging operations

Terminal velocity: As the object keeps on accelerating downwards, the drag produced is increased. At a particular speed, the drag force produced will be equal to the downward force, mostly the weight (mg), of the object. Eventually, it plummets at a constant speed called terminal velocity. Terminal velocity varies directly with the ratio of drag to mass. More drag means slower terminal velocity. Increased mass means higher terminal velocity. An object moving downwards at greater than terminal velocity (for example because it was affected by a force downward or it fell from a thinner part of the atmosphere or it changed shape) will slow until it reaches terminal velocity.

Free settling: An object that sinks in a fluid because of just gravity is said to be free falling.

Hindered settling: When the proportion of solids in the pulp increases hindered settling occurs. In this situation particles move slower under the affect of crowded pulp.

Objectives

To demonstrate the effect of the ragging layer

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To see the effect of operating parameters of jıgs

To demonstrate the stratification process

To observe the difference in the rate of stratification as a function of the value of the concentratin criterion

Experimental

Materials:

Quartz

Chromite

Equipment:

Multi compartment piston type laboratory jig with a screen of 3 mm aperture, and 200 gr of stainless steel balls of 4 mm diameter as ragging material

Crushed heavy mineral in the size of - 3mm + 5mm (Chromite)

Crushed light mineral in the size of - 3mm + 5mm (Quartz)

Procedure:

By using of the batch laboratory jig;

a mixture of one heavy mineral ,one light mineral a bed of stainless steel balls as ragging material was ready on only one of the jig screen.

Fill up the jig with hutch water

Start the jig and observe the rate of stratification of mixture components

Collect the light product that lows over the discharge weir.

Discussion

Batac Jigs;

BATAC Jigs are applied in coal beneficiation plants as well as in ore and slag upgrading processes. For coal preparation BATAC Jigs are used for destoning and thus for the precipitation of the inorganic sulfur. For ore and slag processing, among other applications, BATAC Jigs are used for the pre-concentration of the feed material. Cut-points in the range of 1.3 kg/dm³ to 7.85 kg/dm³ are adjustable.

There is one decisive difference between a BATAC Jig and a Baum Jig: the water current is not generated in an air chamber mounted adjacent to the screen plate but in air chambers underneath the jig bed. These air chambers are intermittently supplied with compressed air by an electronically controlled valve or flap valve system (pulse generator). The air is intermittently discharged from the system at atmospheric pressure after completion of the upward stroke. Motion is imparted to the water inside the jig as a function of the pressure generated inside the air chambers. Moreover, make-up water is added at the lowest location of every jigging chamber to intensify the upward current and to dampen the downward current. The feed is stratified according to its density by the pulsating motion of the water when preparing coal, e.g., in refuse, middlings and clean coal.

The heavy fraction of the stratified raw material is sensed by floats in accordance with the product qualities required. The system provides for controlled withdrawal of the heavy fraction over a discharge device. Jigs of great widths are equipped with independently operating discharge devices fitted with separate sensor systems and hydraulic units. This configuration ensures optimal product qualities over the entire jig width even material distribution is non-uniform.

Distincitve Features

In order to attain highest efficiencies, all modern under-bed pulsated BATAC Jigs are equipped with:

a centre air chamber for each compartment for stable operation and uniform stroke distribution,

PLC-based jig controllers for all jig functions, inter-operable with all established process automation systems,

independently working discharge devices, each equipped with separate hydraulic drive systems,

ultrasonic sensor technology for highest discharge precision,

large open-area jig decks with excellent durability, customized for each application.

Baum Jigs;

A Baum Jig for gravitational enrichment of minerals, particularly hard co in which a screen deck is transversely located to the axis of the jig. Air chambers are made of plates as cut-outs of a cylindrical surface. The axes of symmetry are deflected from the perpendicular by an angle of 5° to 15° in the direction of the mineral to be enriched. The chambers are provided with asymmetric guide vanes adjustable in the horizontal direction. The side walls of a water cistern possess at the height of the screen decks, horizontal off-sets outside the cistern. Spring-loaded protection plates are provided in the off-set supports. The lower edge of one wall of each chamber is shaped as a conduit of back water provided from the bottom with a deflectable arched diaphragm.

In comparison with known jigs, a great engineering and design similarity enables a prefabrication of parts in a wide range, thus shortening production time.

2) For example; Centrifugal jigs

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An example of a centrifugal jig is the Kelsey jig, manufactured by RocheMT. This incorporates the pulsing action, water injection and the use of a ragging medium and internal screen of a conventional, but in addition centrifugal spinning motion to enhance the gravity separation. This enables sand sized minerals of fairly similar SG as well as fine minerals to be separated more efficiently. Because of the additional processes used the Kelsey jig is significantly more expensive and complex to operate and maintain. The feed to a Kelsey jig must be screened at a size less than the internal screen to avoid pegging, and the tailings must be screened in order to recover ragging as oversize. In order to maintain operational and mechanical efficiency the Kelsey jig must have the internal screen cleaned daily and some of the moving parts checked and greased. This can now be done automatically, but the feed must still be stopped. The Kelsey jig is offered in two models: the J1300 and J1800, the latter having greater capacity.

Operating variables include:

Hutch water flow

Spin rate

Pulsation frequency

Pulsation stroke length

Ragging SG, size and shape

Bed depth

Concentrate orifice diameter

Internal screen aperture size

Feed rate and density ( typically 20 to 25 tph at 40% solids for a J1300 although throughput is dictated principally by concentrate rate)

3) Gold mining equipment diaphragm jig : industry type

Specifications

Gold mining equipment diaphragm jig

Smelting slag metal recycling ,High recover

large capacity of treatment, continuous works

Mining equipment diaphragm jig

1.Structure of side way action diaphragm jig, it is also called up way action diaphragm jig. The double compartments side way action diaphragm jig is composed of two jigging chambers connected with each other with certain difference. The structure of each chamber is the same, which consists of framework, driving and moving mechanism, jigging chamber and pyramid bottom box.

2.The working process of double compartments side way action diaphragm jig. Crude ore is fed to jigging chamber from the 1st feed launder, the diaphragm produces vertical alternating current under the action of eccentric link meachnism, which makes the ores separate as their density, the principle is the same as abovemetioned.

Illustrate:

Diaphragm jig belongs to double rooms under the single plug-fuse type. It makes use of water as medium, and separates according to the proportion of the gangue minerals (density). It is the beneficiation equipment.

Superiority:  jig machine does the sine wave motion. It has the advantage of high recover, large capacity of treatment, continuous work .

UseWidely used in processing tungsten, tin, antimony, mercury, alluvial gold deposits, manganese ore, barites, fluorite, lapis lazuli, ore, pyrite, limonite and ore dressing and hematite etc all kinds of smelting slag metal recycling. As this machine is a small size, so it can used as test machine in lab.

Conclusion

Jigs are easy operated devices with high efficiency and applicability. Many parameters should be considered in use of jigs to get the best result. It has some advantages over other concentration devices. First, it is simple to operate. Second, it requires less labour and floor space. Moreover, it has a low maintenance cost. Furthermore its energy consumption is considerably low as it works only with a pump to pulsate water. Jigs can be used to achieve a good recovery in particle size below 150 µm. It can be said that although its construction is very simple, it has many actions at work affect seperation of minerals of different gravities. And also, its mechanism is very simple to seperate the minerals with different specific gravities.