Jigging mineral processing

2.3.1 Jigging Principle Jigging is a gravity separation method for separating minerals in a vertically flowing water stream with varying speeds. The equipment used is called a jig. The space inside the jig for separating minerals is called the jigging chamber, which contains fixed or moving screens. The former is called a fixed screen, and the latter a moving screen. During operation, the material to be separated forms a layer on the screen, called a bed, and water flows through the screen periodically. When the water flow rises, the bed detaches from the screen surface and loosens. Mineral particles of different densities undergo relative transfer under the action of static pressure difference and settling velocity difference; heavier minerals enter the lower layer, and lighter minerals move to the upper layer. When the water flow descends, the bed gradually compacts, and finer heavy mineral particles can continue to pass through the gaps in the bed to enter the lower layer, replenishing and recovering heavy minerals. This process is called suction. This process is repeated until the light and heavy minerals are separated. The concentrate and tailings are then discharged separately (as shown in Figure 2-5).

Jigging is a simple and cost-effective method for processing coarse, medium, and even fine-grained ores. It is widely used in placer deposits containing precious and rare metals such as gold, tantalum, niobium, titanium, and zirconium. Its main disadvantages are high water consumption, the need for graded feeding when processing metal ores, and relatively low separation efficiency when processing fine-grained ores. The maximum particle size range for processed metal ores is 50–0.1 mm, with a suitable feed particle size range of 20–0.2 mm.

2.3.2 Jigs Jigs can be classified according to the raw materials processed, the sorting medium, whether the screen plates are movable, the moving parts driving the water flow, the type of transmission mechanism, the feed particle size, the type of cycle curve, and the surface shape of the jigging chamber. Based on the raw materials processed, they are divided into mining jigs and coal jigs. Based on the sorting medium, they are divided into hydraulic jigs and pneumatic jigs. Based on whether the screen plates are movable, they are divided into fixed-screen jigs and moving-screen jigs. Based on the moving parts driving the water flow, they can be divided into piston jigs, diaphragm jigs, hydraulically agitated jigs, and compressed air jigs. Diaphragm jigs are mainly used when processing metal ores. Diaphragm jigs can be further classified according to the position of the diaphragm into side-moving diaphragm jigs, bottom-moving diaphragm jigs, and side-moving diaphragm jigs (as shown in Figure 2-6).

A                             B                                 c

D                                    E

Figure 2-6 Schematic diagram of diaphragm jig classification

a— Side-moving diaphragm jig; b— Downward-moving diaphragm jig with movable cone bottom;

c— Downward-moving internal diaphragm jig; d— Side-moving external diaphragm jig; e— Side-moving internal diaphragm jig

2.3.2.1 Side-Mounted Diaphragm Jig

Its structure is shown in Figure 2-7. The diaphragm is located beside the jigging chamber. It is modeled after the Denver jig from the United States and is also known as a Denver-type jig. The machine contains two jigging chambers connected in series, each with a screen size of 450 mm × 300 mm. The diaphragm is driven by an eccentric linkage mechanism, which consists of two eccentric discs. Adjusting their relative positions allows the stroke to vary within the range of 0–25 mm. Two stroke rates are available: 329 and 420 strokes/minute. The water flow follows a sinusoidal periodic motion. It has a strong suction effect, requiring frequent replenishment of large amounts of underflow water from the side wall. It is suitable for processing various metal ores, gold-bearing and rare metal placer deposits. The maximum feed particle size is 12-18 mm, the lower limit of the recovery particle size is 0.2 mm, the processing capacity of each unit is 1-5 tons/hour, and the water consumption of a single unit is 5-15 cubic meters/hour.

Figure 2-7 Side-Moving Diaphragm Jig: 1—Eccentric Mechanism; 2—Diaphragm

2.3.2.2 Down-acting Diaphragm Jig Its drive diaphragm is located below the jigging chamber. Main types include down-acting conical diaphragm jigs, reciprocating jigs, rectangular sawtooth wave jigs, hydraulic circular jigs, and Carri motor jigs. The down-acting conical diaphragm jig is the most widely used in my country, and its structural diagram is shown in Figure 2-8.

Figure 2-8 Schematic diagram of a bottom-moving conical diaphragm jig

1—Transmission device; 2—Diaphragm; 3—Screen surface; 4—Frame

The bottom-moving conical diaphragm jig, also known as the Pan American Placer or MexaHoop jig, consists of two tandem square jig chambers, each with a circular vibrating cone bottom, connected to the machine housing by a diaphragm ring. The vibrating cone bottom is supported on a vibrating frame. One end of the vibrating frame is connected to a transmission eccentric disc via a spring plate. When the eccentric disc rotates, the cone bottom vibrates up and down. The eccentric disc has a double eccentric structure with a total eccentricity of 0–26 mm. Three strokes per minute are achieved by changing the pulley: 256, 300, and 350 rpm. In my country, this type of jig is used to process tungsten, tin, sulfide ores, and gold-bearing ores, with the concentrate discharged using a through-screen discharge method. The maximum feed particle size is 18 mm, but in practical applications it does not exceed 10 mm, and the minimum recoverable particle size is 0.1 mm.

The structure of the compound vibrating jig (called the Wemco-Remer jig in the US) is similar to that of the down-acting cone jig. It consists of two jig chambers connected in series, with an eccentric disc driving the frame to swing, thereby pushing the cone buckets on it to vibrate alternately up and down. The difference is that it has two sets of eccentric drive mechanisms, one for high-stroke, small-stroke operation and the other for low-stroke, large-stroke operation. Both act together on the swinging frame to produce compound vibrations in the cone buckets.

The rectangular sawtooth wave jig and the trapezoidal sawtooth wave jig have similar structures, the difference being that the former consists of two square jig chambers connected in series, while the latter consists of two horizontally trapezoidal jig chambers connected in series. Cams and springs drive the cone bucket diaphragms to move simultaneously through a crossbeam, and the displacement curve of the water flow is sawtooth wave shaped. The former is mainly used for the beneficiation of gold-bearing placer ore, while the latter is used for processing cassiterite and sulfide ores. 2.3.2.3 Circular Jig Its horizontal cross-section is circular, and it uses a mechanical-hydraulic transmission system. A rotating rake is installed at the top of the jigging chamber, hence it is also called a hydraulic circular jig. It is often installed on gold or tin dredgers for separating placer gold or tin ore. An improved circular jig is called the MTE radial jig (MTE company, Netherlands), commonly available in three-chamber 90° jig, six-chamber 180° jig, and nine-chamber 270° jig. The diaphragm below the jigging chamber is driven by the piston rod of the driven cylinder. The travel distance-time curve of the driven cylinder piston is controlled by a rotating cam that drives the piston rod of the driving cylinder. The radius of each point on the outer edge of the cam, if continuously expanded according to the rotation angle, presents a sawtooth waveform. Therefore, the jigging cycle curve of the water flow is a rectangular waveform, while the displacement curve is a sawtooth waveform. This cycle curve has the characteristic of rapid water rise and slow water fall. The downward velocity of the water flow is close to the settling velocity of the bed, reducing the impact of hydrodynamics on stratification, improving sorting efficiency, and reducing the amount of underfill water.

The working principle of the mechanical-hydraulic system is shown in Figure 2-9. When the moving cone descends, the kinetic energy of the water, ore, and moving cone in the jigging chamber is absorbed by the accumulator and converted into potential energy. When the diaphragm rises again, the potential energy is released to do work, driving the diaphragm to move. This energy can be repeatedly utilized, resulting in good energy-saving effects.

Figure 2-9 Working Principle Diagram of Mechanical-Hydraulic System

1—Accumulator; 2—Driven Cylinder; 3—Diaphragm Cone; 4—Cam; 5—Driven Cylinder

The DYTA and PYTA type circular jigs developed in my country use a speed-regulating motor and a pulley to drive the cam, respectively. The entire circle consists of 12 trapezoidal jig chambers with a diameter of 7750 mm. They process placer gold ore, with most feed particles smaller than 15 mm, allowing for unclassified feeding. The processing capacity is 280 tons/hour, and the gold recovery rate can reach 98%.

2.3.2.4 Side-Mounted Diaphragm Jig

The diaphragm is located on the underside wall or partition wall of the jig chamber. Rectangular side-moved diaphragm jigs, large-particle jigs, Yuba-type jigs, single-row and double-row trapezoidal jigs, etc., all belong to this type of jig.

The diaphragm of a rectangular side-driven diaphragm jig is mounted on the outside of the casing below the screen plate and is driven by an eccentric linkage mechanism. The jigging chamber has a rectangular horizontal cross-section and comes in single-row double-chamber and double-row four-chamber structures. The structure of the double-row four-chamber 2LTC-79/4 jig is shown in Figure 2-10. It is also available for processing coarse-grained (12-3 mm) and fine-grained (3-0 mm) ore. In the former, the undersize heavy products are discharged centrally, while in the latter, the heavy products are discharged individually from each chamber. This machine has a wide adjustable diaphragm stroke range, steplessly changing from 0 to 50 mm. The stroke rate is adjusted by changing pulleys of different diameters. It is commonly used for processing iron, manganese, tungsten, tin, and gold-bearing ores.

The structure of a large-particle jig is shown in Figure 2-11. The main model developed in my country is the Am-30, which can process coarse-grained ore. Its structure and transmission method are similar to those of a typical side-driven diaphragm jig. However, its diaphragm has a large stroke, with a maximum stroke of 50 mm and a maximum feed particle size of 30 mm. The concentrate is discharged using an over-screen discharge method, with a V-shaped discharge valve at the end of the screen plate.

Figure 2-10700×900 Rectangular Side-Moving Diaphragm Jig Structure Diagram

1—Feed trough; 2—Junior chassis; 3—Motor; 4—Intermediate shaft; 5—Screen plate; 6—Actuating diaphragm; 7—Transmission device

The jig is controlled by a V-shaped plate. Heavy products pass through the bottom edge of the V-shaped plate and are discharged via a weir. Lighter products move along both sides of the V-shaped plate and then pass over the baffles. Under coarse-grained conditions, the surrounding rock and gangue are separated, and the heavy products are further crushed and separated. Under a few conditions, concentrate can be obtained directly.

Figure 2-11 Structure of Am-30 Large-Particle Jig

1—Frame; 2—Box; 3—Drum; 4—Transmission Box; 5—Underscreen Discharge Device;

6—V-Shaped Separating Baffle; 7—Motor; 8—Screen Plate

The diaphragm of the YIba type jig is mounted on the end walls of the feed and discharge ends, with the slurry flow direction perpendicular to the diaphragm. Some diaphragms are mounted on the side walls of the casing. There are single-row double-chamber and double-row four-chamber types, mainly used for separating placer gold ore.

The horizontal cross-section of the jigging chamber of the trapezoidal jig increases from the feed end to the discharge end, and the screen surface is a continuous trapezoid. There are various forms; the earliest in my country was the eight-chamber double-row trapezoidal jig, which is widely used. Its structure is shown in Figure 2-12. An eccentric linkage mechanism is used to drive the movement of the diaphragm on the side wall. Its specifications are expressed as single chamber length × (feed end width ~ discharge end width). The largest model is 2LTC-610%T, with specifications of 900 mm × (600～1000) mm, a maximum feed particle size of 10～13 mm, and an effective recovery particle size of 5～0.075 mm.

Figure 2-12 Schematic diagram of an eight-chamber double-row trapezoidal jig

1 — Feed trough; 2 — Front agitator; 3 — Transmission box; 4 — Motor;

5 — Screen frame; 6 — Rear agitator; 7 — Jigging chamber; 8 — Agitator diaphragm; 9 — Screen plate

The industrial-type jig is a three-chamber single-row side-acting diaphragm jig developed in my country, with specifications of 1100 mm × (750～1050) mm. Its characteristic is that the diaphragm is driven by a 6-S type shaking table head. The water flow characteristics are asymmetrical motion with a large upward velocity and a small downward velocity, resulting in a short stroke and a small adjustable range. It is suitable for processing fine-grained ores (-3 mm).

2.3.2.5 Hydraulic agitator jig

Its characteristic is that it uses a valve to intermittently agitate the rising water flow, and no other transmission mechanism is installed inside the machine. Its structure is shown in Figure 2-13. Pressurized water (30-250 kPa) enters below the valve through a pipe, pushing the valve upwards. The water then flows into the jigging chamber, agitating and separating the bed. As the water flows rapidly below the valve, the pressure decreases, and the valve closes under spring action. The water pressure then rises again, reopening the valve, thus creating a jigging cycle with only upward water flow. Because there is no downward water flow, the bed is highly dispersed, allowing for large throughput, but only coarse, heavy products can be recovered. This type of jig was used relatively early and is mainly used for processing vein gold ore. It is installed in a closed-circuit grinding cycle to recover coarse gold or other single heavy minerals to prevent over-grinding.

Figure 2-13 Hydraulic Jig

1—Screen plate; 2—Grid screen; 3—Main water pipe; 4—Rubber diaphragm; 5—Spring; 6—Valve valve; 7—Inlet pipe

2.3.2.6 Moving screen jig

Its characteristic is that it uses the vibration of the screen plate to loosen the bed and achieve stratification. The earliest moving screen jig was a manual barrel wash. The ore was loaded into the screen frame, placed in a water bucket, and the screen frame was manually vibrated to loosen and stratify the ore, removing the lighter and heavier products layer by layer.

The structure of the LTD1625 hydraulic moving screen jig developed in my country is shown in Figure 2-14. The two side walls of the moving screen frame extend about twice the length of the screen surface and are fixed at the end with pins. The other end is connected to the piston rod of the hydraulic cylinder above the screen plate, driving the screen frame to move. During operation, the raw ore is fed to one end of the screen surface, loosened and stratified by vibration, and simultaneously moved along the screen surface towards the discharge end. Heavy minerals from the lower layer are discharged onto one side of the elevator wheel via the discharge wheel, while light minerals cross the overflow weir and enter the other side of the elevator wheel. As the elevator wheel rotates, they are discharged separately into light and heavy product chutes, and then transported out by belt conveyor. Fine ore falling through the screen into the bottom of the tank is pumped to the thickener using a sand pump. Overflow water is recycled, and sediment is mixed into the concentrate. The screen area reaches 4 m², with a processing capacity of 80–100 tons/hour, and a feed particle size of 130–15 mm.

Figure 2-14 Schematic diagram of LTD1625 hydraulic moving screen jig

1—Water supply pipe; 2—Hall effect reversing switch; 3—Hydraulic piston cylinder; 4—Discharge wheel hydraulic motor;

5—Lifting wheel; 6—Waste rock discharge chute; 7—Ore discharge chute; 8—Moving screen; 9—Discharge wheel; 10—Overflow trough; 11—Chassis; 12—Frame

2.3.3 Jigging Process

Jig beneficiation usually uses water as the medium, and air is used as the medium only under special conditions; this is called pneumatic jigging. The time required for water to complete one cycle through the screen is called the jigging cycle. The maximum distance the water flows up and down in the jigging chamber is called the stroke of the water flow, and the number of cycles completed by the water flow per minute is called the stroke or frequency. To prevent the bed from becoming too dense in the later stages of water flow and to adjust the intensity of suction, water needs to be added under the screen; this is called under-screen water. The main factors affecting jigging separation efficiency are ore properties, feed rate, stroke, stroke frequency, and undersize water volume. The highest separation efficiency can only be achieved by optimizing these process parameters through experiments based on the ore properties. Generally, when processing coarse-grained ore, a thick bed, large stroke, and small stroke frequency are required, with a throughput of approximately 8–10 tons per unit area (m²·hour) and water consumption (feed water and undersize water) of 6–8 m³/(ton·hour). When processing fine-grained ore, the process parameters are reversed: a thin bed, small stroke, and large stroke frequency should be used, reducing the throughput to 3–4 tons per unit area (m²·hour) and water consumption to 4–6 m³/(ton·hour).