shaking table mineral processing

2.4.1 Shaking Table Mineral Processing Principle

Shaking table mineral processing is a gravity separation method that utilizes an inclined bed surface with asymmetrical reciprocating motion for inclined flow separation. Figure 2-15 shows a schematic diagram of the shaking table structure, which mainly consists of a transmission mechanism, a bed surface, and a frame. The bed surface has a wear-resistant layer (raw lacquer ash, rubber, etc.) and slopes downwards from the feed side to the tailings side in the transverse direction, with an inclination angle not exceeding 10°. The bed surface slopes upwards from the feed end to the concentrate end in the longitudinal direction, with an inclination angle of 1°~2°. Bed strips (or grooves) are arranged longitudinally on the bed surface. The height of the bed strips (or the depth of the grooves) gradually decreases (or becomes shallower) from the feed end to the concentrate end, and tapers along one or two inclined lines. The bed surface is supported or suspended by the frame and driven by the transmission mechanism to perform asymmetrical reciprocating motion. The material to be selected is mixed with water to a concentration of 25%–30% and fed into the feed trough, the length of which is 1/3–1/4 of the bed surface length. Flushing water is fed into the bed surface through a flushing trough along the upper edge, the length of which is approximately 2/3–3/4 of the total bed surface length. Common transmission devices (commonly known as the headstock) include eccentric toggle-plate rocking mechanisms, cam-lever rocking mechanisms, and eccentric spring rocking mechanisms.

Figure 2-15 Typical Shaking Table Layout

1—Transmission Device; 2—Feed End; 3—Feed Trough; 4—Water Flushing Trough; 5—Concentrate End; 6—Bed Surface; 7—Frame

The separation of ore on the bed surface includes two processes: loosening and stratifying the material, and separating mineral particles according to density and particle size. After the ore enters the feed trough, it flows by gravity to the bed surface. The loosening and stratification of mineral particles on the bed surface are mainly achieved by the vibration force of the asymmetrical reciprocating motion of the bed surface and the flushing force of the water flow. The height and position of the mineral particles in the bed grooves are different; the vibration force and flushing force they experience are also different. The upper layer of mineral particles is subject to a greater flushing force from the water flow, while the lower layer of mineral particles is subject to a greater frictional force from the bed surface. As the water flows laterally along the bed surface, it continuously crosses the bed strips or grooves, creating a small hydraulic jump each time it crosses a strip or groove (as shown in Figure 2-16). The vortices generated by the hydraulic jumps form an upflow at the edge of the lower bed strips along the water flow path and a downflow inside the grooves. These upflows and downflows continuously loosen, compact, and resuspend the upper particle group, causing denser particles to move to the lower layer and less dense particles to move to the upper layer. Below the vortex zone, the loosening of the particle group is mainly achieved through the asymmetric reciprocating motion of the bed surface, creating a velocity difference between layers of particles at different heights. This causes the particles to tumble and compress each other, pushing the bed layer to expand and loosen. The asymmetric reciprocating motion of the bed surface also leads to segregation and stratification, allowing denser finer particles to settle to the bottom layer through the gaps between the particles. The final result of loose stratification is that coarse and light mineral particles are located on the top layer, followed by fine and light mineral particles, then coarse and heavy mineral particles; the bottom layer consists of fine and heavy mineral particles.

Figure 2-16 Schematic diagram of particle stratification within the bed grooves. The zoning and transport of particles mainly rely on the mechanical forces generated by the transverse slurry flow and the asymmetric reciprocating motion of the bed surface. The resultant force of these two forces determines the direction of particle movement. The transverse slurry flow covers the entire bed surface, exerting dynamic pressure on the particles as it flows along the surface. This dynamic pressure increases with the increase of the water flow velocity. The water flow velocity varies with the bed height, being higher in the upper layer and lower in the lower layer. The greater the dynamic pressure on the particles, the greater their velocity. Therefore, the transverse velocity of the upper layer particles is greater; at the same height, larger particles have a greater velocity than smaller particles, and lower-density particles have a greater transverse velocity than higher-density particles. This difference in transverse velocity becomes more pronounced after stratification as particles of different densities and sizes are located at different bed heights. The asymmetric reciprocating motion of the bed surface causes longitudinal transport of the particles. When mineral particles accelerate along with the bed surface, they generate inertial forces. When the acceleration of the bed surface is large enough that the inertial force of the mineral particles exceeds the friction between the particles and the bed surface, the particles begin to move forward relative to the bed surface. The inertial acceleration at which the mineral particles begin to move relative to the bed surface is called the critical acceleration. On the same bed surface, the inertial force of denser mineral particles is greater than that of less dense particles, and the inertial force of the bottom layer particles is greater than that of the top layer particles. Therefore, heavier mineral particles, especially those at the bottom, will be propelled forward by the bed surface more quickly, while the lighter particles at the top exhibit a more pronounced swaying motion, ultimately giving the denser, finer mineral particles at the bottom a greater longitudinal velocity. Mineral particles move both laterally and longitudinally on the bed surface, and the final direction of their motion is determined by the vector sum of these two motions (as shown in Figure 2-17).

Figure 2-17 Schematic diagram of the separation of mineral particles with different properties on the bed surface

The angle between the longitudinal axis of the bed surface is called the deviation angle (β), and its tangent is:

In the formula, Vy and Vx are respectively the average lateral and longitudinal velocities of the mineral particles. The larger the β value, the more the mineral particles move towards the tailings side; the smaller the β value, the more the mineral particles move towards the concentrate side. Coarse particles of light minerals have the largest deviation angle, fine particles of heavy minerals have the smallest deviation angle, and the deviation angles of fine particles of light minerals and coarse particles of heavy minerals are in between. Therefore, a zoning of particle groups according to mineral density and particle size is formed on the bed surface. Appropriate interception can yield products of different densities and some intermediate products.

Shaking table beneficiation has a high enrichment ratio; a single separation can yield the final concentrate and final tailings, and one or more middlings can be collected as required. Different particle sizes of ore have different requirements for the operating parameters of the shaking table. To obtain better separation indicators, a classifier (box) is often used before the ore enters the beneficiation process to separate it into several particle sizes, which are then fed into the corresponding shaking tables for separation. Its main disadvantages are low processing capacity, high number of units required, and large footprint. Shaking tables are widely used in the beneficiation of gold-bearing ores.

2.4.2 Shaking Tables Shaking tables are classified into three types according to their application: coarse sand shaking tables (mineral particles larger than 0.5 mm), fine sand shaking tables (mineral particles 0.5–0.074 mm), and slime shaking tables (mineral particles 0.074–0.037 mm). Classification can also be based on structural factors such as the headstock mechanism, table shape, support method, and number of table layers; however, a unified classification standard has not yet been established. The structural types of various shaking tables are listed in Table 2-2.

Table 2-2 Structural Types of Various Shaking Tables

Generally, they are named after equipment characteristics, model, or the surname of the developer. In my country, the most commonly used are Yunnan Tin shaking tables, 6-S shaking tables, spring-type shaking tables, and suspended multi-layer shaking tables; a few use suspended-surface shaking tables. Abroad, the most commonly used are Wilfley type shaking tables, Holman type shaking tables, Plat-O type shaking tables, and Deister type shaking tables. They were widely promoted in ore roughing and coal preparation after the 1970s.

Multi-layer suspended shaking tables with multi-eccentric inertial gear transmission are also widely used. Some countries have also developed new types of shaking table heads and configured them as multi-layer units.

2.4.2.1 Yunnan Tin Shaking Table

Its characteristic is that the headstock of the table is driven by a cam lever type. It was manufactured by Yunnan Tin Company in my country, based on the Soviet Union’s CC-2 shaking table, and its structure is similar to the American Plat-O type shaking table. There are three types of shaking tables: coarse sand, fine sand, and slime. They are used for the separation of metallic ores. Coarse sand and fine sand shaking tables process ores with a diameter of 3–0.074 mm, while slime shaking tables process slime with a diameter of 0.074–0.026 mm.

The structure of the cam-lever type headstock is shown in Figure 2-18. Its asymmetry criterion E₁ has a relatively small adjustment range, while its E₂ value has a wider adjustment range. The bed surface is stepped along the longitudinal direction (connected by a longitudinal slope and a stepped plane), which allows the upper light minerals to be washed away by water flow during the climbing process, improving concentrate quality. Early bed surfaces were made of wood, with a lacquer ash composed of raw lacquer and calcined gypsum as the surface material; now, some bed surfaces are made of fiberglass. The bed surface uses a sliding support (as shown in Figure 2-19).

Figure 2-18 Cam Lever Mechanism Headstock

1—Pull rod; 2—Adjusting screw; 3—Sliding head; 4—Large pulley; 5—Eccentric shaft;

6—Roller; 7—Eccentric shaft of a platform; 8—Rocking arm (platform); 9—Connecting rod (clamp);

10—Crank lever (rocker arm); 11—Rocking arm shaft; 12—Machine cover; 13—Connecting fork

The resistance is relatively large. Turning the handwheel pushes the wedge block to adjust the bed surface slope, raising or lowering one side of the bed surface, thus changing the longitudinal slope. However, this method of adjusting the slope alters the axis position of the headstock pull rod.

Figure 2-19 Schematic diagram of sliding support and wedge block slope adjustment mechanism

1—Slope adjustment handwheel; 2—Slope adjustment rod; 3—Slider; 4—Slider seat; 5—Slope adjustment wedge block; 6—Shaking table surface

2.4.2.2 6-S Shaking Table

Its characteristics include an eccentric linkage headstock and a rocker-supported table surface, also known as the Hengyang-type shaking table, originally manufactured by Hengyang Mining Machinery Factory. It is similar to the A. Wilfley shaking table in the United States. It is mainly used for separating non-ferrous metal ores such as tungsten and tin. It is suitable for processing sands larger than 0.075 mm and can also process slime.

The structure of the eccentric linkage headstock is shown in Figure 2-20. Its asymmetry criterion E₁ has a large adjustment range. The table support device and the slope adjustment mechanism are mounted together on the frame (as shown in Figure 2-21).

Figure 2-20 Eccentric Linkage Headstock

1—Elbow Plate; 2—Eccentric Plate; 3—Elbow Plate Seat; 4—Adjusting Slider; 5—Handwheel; 6—Rocking Rod; 7—Spring

The bed surface is supported by four plate-type rocker arms, causing it to undulate in an arc shape during asymmetrical reciprocating motion, resulting in slight vibrations that help loosen mineral particles and facilitate longitudinal transport. The lateral slope of the bed surface is adjustable from 0° to 10°. The stroke is adjusted using a rotary handwheel. When adjusting the lateral slope and stroke, the axis of the bed surface tie rod remains unchanged, ensuring smooth operation. The bed surface is approximately a right-angled trapezoid, with a wooden base, a rubber sheet on top, and bed slats nailed on. Fiberglass bed surfaces are now partially used.

Figure 2-216-S Shaking table support device and slope adjustment mechanism

1—Handwheel; 2—Bevel gear; 3—Adjusting screw; 4—Adjusting seat plate; 5—Adjusting nut;

6—Saddle seat; 7—Shaking support mechanism; 8—Clamping channel steel; 9—Table surface tie rod

2.4.2.3 Spring-type Shaking Table

Its characteristic is the use of a pair of soft and hard springs with different rigidities as the headstock, and it was successfully developed by the Changsha Research Institute of Mining and Metallurgy in my country. It is mainly used for separating fine mud from ores such as tungsten, tin, and rare metal placer deposits. Its headstock structure is shown in Figure 2-22. It consists of a transmission device and a differential device.

Figure 2-22 Schematic diagram of spring-type rocker

1—Eccentric wheel; 2—Triangular belt; 3—Motor; 4—Rocker; 5—Handwheel;

6—Spring box; 7—Soft spring; 8—Soft spring cap; 9—Rubber hard spring;

10—Tie rod; 11—Seat surface; 12—Support and slope adjustment device

It consists of two parts. The transmission device includes components such as the eccentric wheel and rocker. The inertial force generated when the eccentric wheel rotates is transmitted to the differential device through the rocker, and then to the bed surface through the tie rod. The differential device consists of rubber hard springs, steel wire soft springs, a spring box, and a stroke adjustment handwheel. The differential characteristics of the bed surface movement are mainly determined by the difference in stiffness between the soft and hard springs, which can produce a large difference in positive and negative acceleration. The bed surface has triangular grooves along its longitudinal direction. The bed surface uses sliding supports, with four sliders at the four corners supported in four rectangular oil grooves. This support method allows the bed surface to make stable linear movements. The bed slope is adjusted using wedge blocks. When adjusting the slope, the tie rod axis changes, making it a variable-axis slope adjustment mechanism.

2.4.2.4 Suspended Multi-Layer Shaking Table

Its characteristic is that the headstock and multiple bed surfaces are all suspended, as shown in Figure 2-23. It is used for separating metal ore sands and fine mud, and can also be used for coal preparation. It is suitable for materials with relatively small changes in feed properties and for roughing operations. The headstock and multiple bed surfaces are suspended by steel wire ropes from prefabricated hooks on metal supports or buildings, eliminating the need for a heavy foundation and avoiding vibration impact on buildings. The inertial force of the headstock is transmitted to the shaking table frame through a ball-and-socket connector, linking the bed surfaces with the headstock. A self-locking worm gear slope adjustment device is installed on the steel frame, changing the slope of multiple bed surfaces together during adjustment. During operation, slurry and flushing water are fed into the feed troughs and water troughs of each bed surface, respectively. Because the bed surface has multiple overlapping layers, it can handle a large volume of food and saves floor space, but it is more complicated to monitor and adjust than a single-layer shaking table.

Figure 2-23 Schematic diagram of a suspended four-layer shaking table

1—Inertia headstock; 2—Headstock and frame connector; 3—Frame; 4—Table surface; 5—Ore receiving trough;

6—Slope adjustment device; 7—Ore and water feeding trough; 8—Suspension steel rope; 9—Frame

This type of shaking table uses a multi-eccentric inertia headstock, composed of two pairs of gears (as shown in Figure 2-24). An eccentric weight is mounted on the gear shaft, and the speed ratio of the large and small gears is 2. When the upper and lower gears rotate relative to each other, the vertical component of the eccentric weight always cancels each other out. When the eccentric weights on the large and small gear shafts are on the same side, the inertial centrifugal force in the horizontal direction reaches its maximum value. Conversely, the inertial centrifugal force in the horizontal direction reaches its minimum value. Therefore, a differential action is generated in the horizontal direction. The number of revolutions per minute of the large gear is the stroke of the table surface. The stroke of the table surface is adjusted by changing the weight of the eccentric weight. Both the E₁ and E₂ values ​​of the motion asymmetry criterion for the head of the bed are adjustable.

Figure 2-24 · Multi-eccentric inertia headstock

01, 0₂—rotation centers of the large and small gears; n₁, n₂—rotational speeds of the large and small gears;

r₁, r₂—distances between the center of gravity of the large and small gears and the rotation center; G₁, G₂—mass of the heavy object eccentrically mounted on the large and small gears

2.4.2.5 Suspended-Surface Shaking Table

Its characteristic is that multiple layers of bed surfaces are suspended, while the headstock is installed on a fixed ground foundation, forming a semi-suspended type. It was successfully developed by Yunnan Tin Company in my country. It adopts a cam lever headstock, with six bed surfaces suspended from the frame by steel wire ropes. It uses a drawer-type suspended bed frame, with each bed surface able to enter and exit like a drawer, making bed surface assembly and disassembly convenient and lightweight. The bed surface spacing is 170 mm, and the clear height between bed surfaces is 100 mm. Suitable for separating fine-grained metallic ores with a particle size of 0.074–0.019 mm. It features high space utilization and low power consumption.

2.4.3 Shaking Table Mineral Processing

The separation efficiency of a shaking table depends not only on its structural parameters but also, to a large extent, on its operating parameters. Reasonable process parameters should be formulated and adjusted based on the feed properties (particle size, density), operating location, and product quality requirements. The main process parameters affecting the separation efficiency of a shaking table are stroke, stroke frequency, bed slope, water addition, feed rate, and feed concentration.

2.4.3.1 Stroke and Stroke Frequency

The stroke and stroke frequency of a shaking table directly affect the speed and acceleration of the bed surface. Appropriate stroke and stroke frequency should loosen the bed and induce segregation, ensuring that heavy products are continuously discharged from the concentrate end at a sufficient speed.

The determination of stroke and stroke frequency mainly depends on the size of the feed particle size. Coarse-grained materials are prone to stratification and exhibit high longitudinal velocity. Therefore, for coarse-grained materials, fine separation operations, and heavy loads, a large stroke with a small number of strokes is recommended. For fine-grained materials, coarse separation operations, and lighter loads, a small stroke with a large number of strokes is recommended.

The processing capacity of a shaking table is related to the speed of the table surface. The speed of the table surface is inversely proportional to the product of the stroke and the number of strokes. Therefore, when adjusting the stroke and the number of strokes, a speed sufficient for the shaking table to handle its processing capacity should be maintained. The stroke and number of strokes for a shaking table are generally determined experimentally. Commonly used strokes and numbers of strokes are listed in Table 2-3.

Table 2-3 Range of Strokes and Frequency for Shaking Tables

2.4.3.2 Makeup Water and Bed Slope

Makeup water includes feed water and flushing water. The amount of makeup water should ensure that the water layer completely covers the bed, making the bed loose and allowing the coarse mineral particles with the lowest density on the top layer to be washed away by the water flow. However, the water flow velocity should be low to allow fine heavy mineral particles to settle on the bed surface, resulting in a wider fan-shaped distribution of materials on the bed surface and more accurate separation.

The transverse slope of the shaking table directly affects the amount of makeup water and the water flow velocity. The transverse slope of the bed surface should not be too large, mainly depending on the feed particle size. Generally, 3°~4° is used for coarse materials smaller than 2 mm, 2.5°~3.5° for medium-sized materials smaller than 0.5 mm, 2°~2.5° for fine materials smaller than 0.1 mm, and 1.5°~2° for slime smaller than 0.074 mm.

The longitudinal upward slope from the feed end to the concentrate end directly affects the concentrate quality. Generally, coarse-grained materials require 1°~2°, fine-grained materials around 1°, and slime 0.5°~1°.

The water replenishment rate for the shaking table depends on the particle size of the feed material and the operating location. Water consumption is relatively low in roughing of sands, generally 1~3 m³/ton; water consumption is higher in cleaning, generally 3~5 m³/ton; and water consumption in slime beneficiation is even higher, sometimes reaching 10~15 m³/ton.

2.4.3.3 Feed Rate and Concentration

The feed rate and concentration during shaking table operation should be stable; otherwise, it will affect the bed surface zoning and reduce separation efficiency. The feed concentration is generally 20%~30%. The finer the feed particle size, the lower the feed concentration. However, excessively low feed concentration will reduce the shaking table’s throughput.

The throughput of the shaking table is generally determined based on the actual production quota of similar beneficiation plants. Under normal conditions, the feed rate should not be too high. Increasing the feed rate will thicken the bed surface layer, which is not conducive to stratification, and heavy ore particles are easily lost in the light product, reducing the metal recovery rate.

The production quotas used in the design of the widely used 6-S type shaking table and Yunnan Tin type shaking table in China are listed in Table 2-4, and the comprehensive operating conditions are listed in Table 2-5.

Table 2-4 Production Quotas for Shaking Tables Used in Current Designs in my country

Table 2-5 Comprehensive Operating Conditions of Shaking Table