Wind power mineral processing

Air-Powered Mineral Separation

2.8.1 Principle of Air-Powered Mineral Separation

Air-powered mineral separation is a gravity separation method using air as the medium. During operation, the material is fed onto a fixed or movable porous surface of the mineral separation equipment, which is installed at an angle. An intermittent or continuous flow of rising air suspends and loosens the material, causing it to stratify according to density based on the difference in settling velocity, thus achieving mineral separation. Because the settling ratio of mineral particles in air is much smaller than that in water, the separation accuracy of air-powered mineral separation is low. Before feeding, the material must be screened or graded into narrow sizes, generally about twice the particle size. The moisture content of the feed material should be less than 4%–5%. Otherwise, the material will stick together, leading to a sharp decrease in separation efficiency and equipment processing capacity.

Air-powered mineral separation is mainly used in cold or arid regions for separating gold, rare metal, and asbestos mines.

Air-powered mineral separation equipment includes air jigs, air shaking tables, and air sluices.

2.8.2 Air-Powered Mineral Processing Equipment

2.8.2.1 Air-Powered Jig

The material is fed onto the porous screen surface of the jigging chamber. Air is intermittently blown in from under the screen to loosen the material and stratify it according to density. Then, it is separated along the material layer height to obtain heavy products, light products, and intermediate products. Figure 2-45 shows the structure of the coal preparation jig. The screen plate is divided into three sections along the longitudinal direction, which can obtain four products: ground stone, two types of middlings, and concentrate. The heavy products separated from each section are discharged through a fan-shaped discharge device, and the clean coal is transported away through a chute. The blasting airflow flows upward from the bottom air chamber through the double-layer screen plate. The double-layer screen plate can be staggered to adjust the air volume. Above the double-layer screen plate are upper and lower grid screens. Ceramic balls are placed in the small grids between the upper and lower grid screens to ensure that the air can be evenly distributed on the screen plate. The feed material is fed onto the upper grid screen. To ensure that the material is evenly distributed on the screen plate, a reciprocating screen plate is installed above the screen plate to limit the material surface. Air supplied by a blower is intermittently injected into the air chamber through a rotating intermittent air supply valve, creating an upward pulsating airflow. Under the action of this pulsating airflow and the reciprocating oscillation of the screen plate limiting the material surface, a loose and flowing bed is formed. Because the material has undergone narrow-level classification beforehand, a velocity difference exists between light and heavy minerals. More heavy minerals settle to the lower layer, where the particle density is higher. The gravity pressure difference then pushes some light minerals to the upper layer, thus essentially achieving stratification by density. The heavy minerals separated in each lower layer enter the discharge hopper at the end, while the light products flow forward for further selection. The final light products continue to move forward and are discharged through the outermost discharge chute. This method is used for separating coal with a particle size of 13–0.5 mm, and can also be used for separating smaller metal ores.

Figure 2-45 Baum-1 (ⅡOM-1) Type Pneumatic Jig

1—Air duct; 2—Inclined frame; 3—Heavy product discharge device; 4—Intermittent air supply valve;

5—Upper screen; 6—Lower screen; 7—Double-layer air inlet control screen plate; 8—Fan-shaped feeder;

9—Screen plate limiting the upper material surface; 10—Crank mechanism; 11—Light product feed trough;

12—Heavy product discharge trough; 13—Air chamber; 14—Exhaust duct

The structure of the wind-powered shaking table, as shown in Figure 2-46, mainly consists of a transmission mechanism, a bed surface, and a frame.

Figure 2-46 Bartley Shaking Table

1—Feed Funnel; 2—Longitudinal Inclination Adjuster; 3—Transverse Inclination Adjuster; 4—Bed Surface;

5—Blowering System; 6—Eccentric Drive System; 7, 8, 9—Discharge Tanks (Districts)

During operation, material is fed onto the porous bed surface via the feed funnel. The longitudinal slope, transverse slope, stroke, and stroke rate of the bed surface are all adjustable. Air is fed in from below the bed surface, forming intermittent or continuous pulsating airflow, suspending the solid bed layer and causing the pre-classified material to stratify according to density. Minerals with lower density are located in the upper layer and flow laterally under gravity, passing over the bed bars and concentrating for discharge in section 9. Mineral particles with higher density move longitudinally along the bed surface and are then discharged in section 8. Intermediate products are discharged in section 7.

The wind-powered shaking table can separate gold-bearing ores or other metallic ores with a particle size of 1–5 mm, and the upper limit for coal preparation particle size can reach 7 mm. It is highly adaptable to various ores and offers a wide range of equipment options. It has certain application value in arid, water-scarce, and frigid regions.

Pneumatic Sluice

Its structure is shown in Figure 2-47. The dry converging sluice is the simplest type of pneumatic sluice.

Its structure is similar to that of the wet converging sluice. It has a converging trough shape, and the bottom is made of porous material. Below the bottom is an air chamber; low-pressure air is introduced from one end of the trough and flows upward through the porous bottom. The material is fed from the top of the trough and forms a fluidized bed under the airflow, stratifying according to density as it moves along the trough surface. The lighter and heavier products are separated by a separator at the end.

Figure 2-47 Schematic diagram of a dry converging chute

1—Microporous trough surface; 2—Air chamber; 3—Chute; 4—Separator plate

Pneumatic sluices are used to separate ores such as tungsten, tin, and gold with particle sizes ranging from 3 to 0.074 mm, as well as coarser coal particles.

Pneumatic sluices have a simple structure, low manufacturing cost, and good separation effect. To save floor space, they can be configured in an inverted cone shape.