1The effect of washing and clay properties on the washing process
1 Washing effect
Most of the washing is used as a pretreatment before the sorting. When tin ore sand processing by the washing method of separating coarse particles contain waste rock ore, and then the resulting fine fraction desliming candidates, the amount of ore processing can be reduced. For hand-selection or photoelectric sorting operations, it is often necessary to wash the ore in advance for easy identification. Some ore-rich ore can avoid clogging crushers , screening machines and mining bins during operation to ensure smooth flow. Some ore's primary slime and nuggets are very different in terms of selectivity (such as floatability). Separation of mud and sand by washing methods can be carried out separately to obtain better sorting indicators. In this case, although washing is still an auxiliary operation, it has a significant impact on the entire production process.
For some of the manganese oxide ore talus the talus or residue, brown iron ore, bauxite ore, cement valuable minerals (clay) contained very little, as a final tailings discarded after washing, the resulting bulk The ore grade is high and can be used as a final product. The washing at this time makes it an independent sorting operation.
Some gum siliceous phosphate ore weathering hierarchical process flow proceeds to scrub desliming also possible to obtain the final product, often using kaolin desanding washing and grading operations to obtain the final product.
2 The effect of clay properties on the washing process
The nature of the cement (clay) in the ore has a major impact on the washability of the ore. The composition of the clay is a natural aeolian bauxite (Al203) silicate containing a mixture of mica , limonite, chlorite, quartz , calcite and hornblende, which has a fine particle size and is mainly composed of particles smaller than 2 μm. The moisture is firmly held in the middle of the fine particles. Thus clay is actually a two-phase system consisting of a solid phase and a liquid phase (water).
Whether the clay-containing ore is soaked by water is easily dispersed, which is related to the plasticity and expansion of the clay itself.
Plasticity is a property in which the clay is deformed under pressure within a certain water-containing range without being broken, and the pressure remains removed to maintain the original shape without flowing. The minimum water content in which clay remains plastic is called the lower plastic limit (or plastic limit). As the water content increases to a certain limit, the clay begins to have fluidity, and the water content at this time is called the plastic upper limit (or liquid limit).
The higher the plasticity index of clay, the more difficult it is to disperse in water, and the more difficult it is to wash.
The swelling property of clay refers to the property of increasing the volume of clay after it is wetted by water. The clay is fixed with a small amount of water before wetting, and the particles are under the action of the bonding force. After the water is in contact, the water molecules penetrate into the voids of the particles, and the bonding force is released and the volume is increased. The faster this process goes, the easier it is to break the ore.
The swelling of clay is related to its degree of compactness. The smaller the gap between the clay particles, the less likely the water will penetrate and the slower the expansion process progresses. At the same time, the expansion is also related to the wettability of the clay. The stronger the wettability of the solid particles, the easier the water molecules penetrate.
3 Ore washability
The washability of ore is related to clay plasticity, water content, swelling, permeability, and grain size composition of the ore. The smaller the plasticity of the clay, the stronger the expansion and permeability, the easier the ore is washed. The more the content of the bulk material in the ore, the greater the impact agitation in the washing, and the faster the process. Table 1 lists the classification of ore washability, which can be used for reference.
Table 1 Classification of ore washability 
Washing equipment
In the production, in addition to the fixed sieve, vibrating screen, roller screen and other screening machines, the addition of water spray pipe screening and washing in the same operation, also commonly used low-lying spiral classifier (spiral The washing machine, the cylinder washing sieve, the hydraulic washing sieve, the cylinder washing machine and the tank washing machine complete the washing operation.
l Screening machine type washing equipment
The fine particles adhering to the large ore can be washed away by means of tumbling on the sieve and hydraulically rinsing. The fixed sieve can be used to screen the ore before coarse crushing, the roller screen can be used to screen the ore before crushing, and the shaker can be used to screen the ore before or after crushing.
The sieving machine type washing equipment separates the coarse ore and the sieved mud sand product washed on the sieve. Generally, the sieved mud sand product needs to be further separated by the tank concentrator or the spiral classifier.
A hydraulic washing screen
Figure 2 shows the structure of the hydraulic washing screen. It consists of a high pressure water gun, a flat screen, an overflow screen, a diagonal screen and a bulk material screen. The flat screen and the inclined screen are about 3m wide, the flat screen length is 2~3m, the inclined screen length is 5~6m, the inclination angle is 20°~22°, and the large material screen tilt angle is 40°~45°. The overflow screen on both sides is perpendicular to the plane screen, and the screen strip is made of round steel of 25 ~ 30mm, and the spacing is generally 25 ~ 30mm.
Figure 2 Structure of hydraulic washing screen
1, 8 a transport trough; 2 a high pressure water gun; 3 a flat sieve; 4 an overflow sieve;
5 slant sieve, 6 large material sieve; 7 one sieve product discharge
The material is directly fed to the flat sieve by the transporting ditch. The fine particles with a smaller particle size than the meshing holes are then leaked through the mesh hole, while the coarse particles are deposited at the junction of the flat sieve and the oblique sieve. Under the high pressure water jet, the cement is cemented. The group was broken. The broken mud sand also leaks under the sieve, and along with the sieved sieved product, it is discharged along the transport chute 8 through the sieved product discharge port. The bulk material that has been rinsed is pushed onto the bulk material screen by the high pressure water column and then discharged.
The hydraulic washing sieve has the advantages of simple structure, large production capacity and easy operation. The disadvantage is that the water gun requires a higher water pressure, a higher power consumption, and a lower ability to break up fine agglomerates.
B vibrating washing screen
All kinds of vibrating washing screens for washing are formed by adding a high-pressure water washing device to the sizing machine (see Figure 3). Double-layer screens are often used for the treatment of ore before and after crushing or fine crushing.
The flushing water pressure is generally 0.2-0.3 MPa, and the water consumption per ton of ore is 1 to 2 m3. When the ore content of the ore is not large and the adhesion is not strong, the use of such equipment can meet the requirements of washing.
To uniformly spray the water flow along the width of the screen, a special shape spout as shown in Figures 5-9-4 can be used. The inclination angle between the center line of the nozzle and the surface of the material on the screen is generally l00°~110°, and the distance from the nozzle to the surface of the material is preferably 300mm.
Figure 3 Schematic diagram of the vibration washing sieve structure
The spout can be in the form of a swirler (water entering from the tangential direction) or a vortex bushing (water entering from the center). The vortex sleeve is conical and the inner wall is a spiral groove. The water creates a vortex after entering the spiral groove, creating a fairly uniform jet. The use of these two nozzles can improve the efficiency of washing while reducing water consumption.
C round washing sieve
When the ore needs to be subjected to a less severe scrub for disintegration, the cylindrical washing screen shown in Fig. 4 can be used. The sieving circle of this equipment is made of punched steel or woven mesh, or it can be made of steel rods. A high pressure flushing water pipe is arranged in the longitudinal direction of the cylinder. With the rotation of the cylinder screen, the ore blocks are turned over and collided with each other, and the ore is broken by hydraulic flushing. The flushing process is shown in Fig. 5. The washed mud is discharged through the sieve.
Figure 4 Structure of the circular washing sieve
1 one screen cylinder; 2 one roller; 3 one transmission device; 4 one main transmission wheel; 5 one clutch; 6 one transmission shaft; 7 one support wheel
Figure 5 High-pressure flushing water pipe in the circular washing sieve
In order to improve the washing effect, some cylinder washing screens are specially provided with a broken section without mesh holes at the ore end, and an obstacle plate, a chain, etc. are arranged inside to strengthen the broken effect.
The diameter of the cylinder of the cylinder washing sieve is 1. 0~3.0m, the length is 3. 0~ 7.5m, the rotation speed of the cylinder is 15-30r/min, and the production capacity is 30~400t/h.
2 with screen cylinder scrubber
The structure of the screened simple scrubber is shown in Figure 6, and is suitable for treating medium washable and difficult to wash ores with a particle size of up to 300 mm.
The screen cylinder scrubber is different from the round washer screen. It has a simple, non-porous, end cap with both feed and discharge ends, just like a ball mill . The inner wall of the cylinder body and the end cover are provided with manganese steel or rubber lining, and the lining plate has ribs to form a spiral line whose pitch gradually increases toward the discharge end, so that the material can be well broken and the material is discharged. End movement. Metal cylinder is by friction idler or rubber tires, gear or rotated.
Figure 6 Screened cylinder scrubber
1—Cylinder 2—ribbed liner 3—drive roller 4—cylinder screen 5—reducer 6—motor
The screen cylinder scrubber can be installed horizontally or tilted. In order to avoid the simplified axial movement during tilting installation, the cylinder can be supported by the thrust roller, and the installation angle is generally less than 6°. The diameter of the discharge opening is larger than the diameter of the feed opening, but the discharge opening has a certain (or adjustable) height of the annular cymbal to form a fixed material layer in the scrubber. Typically, the scrubber has a fill rate of up to 25%. The ore and water enter the cylinder at the same time from the feed port, and have a certain concentration (solid mass fraction of 40% ~ 50%), so that it has sufficient fluidity. 〜0.2MPa。 The water pressure is generally 0. 1 ~ 0.2MPa.
For ore that may experience significant wear and tear, the scrubber should use a lower number of revolutions (3o%-4o% critical speed). When dealing with difficult-to-wash high-plastic clay ore, high rotation speeds (70% to 80% critical speed) should be used. During the simplified rotation, the material forms a waterfall motion in the scrubber, causing the ore to fall off and generate strong friction, forcing the high plastic clay material to break. The bulk material washed by the high pressure water is discharged from the discharge port along with the slurry flow, and flows into the cantilever tapered cylindrical sieve installed on the scrubber to achieve sufficient separation of the mud sand and the bulk material.
3-tank washer
As shown in Fig. 7, the structure of the trough washer is similar to that of the spiral classifier. Two long shafts are arranged in an approximately semi-circular chute with discontinuous agitating blades.
The apex of the blade is a spiral, the diameter of the spiral is 800mm, and the pitch is 300mm. The two spirals rotate in opposite directions, and the upper blades are all rotated outward. The slurry is fed from the lower end of the tank, and the cement of the ore is cut, scrubbed, and washed by the high-pressure water fed from the upper end, and the clay and the ore block are released. The clay forming slurry is discharged from the lower overflow tank, and the coarse material is pushed by the blades and discharged from the discharge port at the upper end of the tank.
This kind of washing machine has strong cutting and scrubbing ability, and has strong ability to break up small mud. It is suitable for treating difficult-to-wash ore with medium ore size and more mud. It has high processing capacity and high washing efficiency; the disadvantage is that the size of the ore washed is limited, generally not more than 50mm, otherwise the spiral blade is easily broken or even broken.
The tank washing machine with the specification of 6660mm x 1500mm has a tank volume of 6m3. The treatment capacity of Yunnan Slope Sand and Tin Mine is 800~1100t/d, and the water consumption per ton of ore is 4~6m3.
Figure 7 Spiral classifier for sediment separation in washing operations
1—Clay overflow 2—Settling tank 3—feeding port 4—sanding sand
4 classifier type washing equipment
The low-end spiral classifier shown in Figure 8 can also be used as a washing equipment, but because it is not very weak, it is mainly used to treat the mud sand products discharged from other washing equipment, and further remove the muddy part. .
Figure 8 Silver spin classifier for washing sand and sand separation
1 a muddy overflow; 2 a settling tank; 3 a feed port; 4 a grit
3 washing process
There are basically two types of commonly used washing processes: one is the washing and separating process consisting of ordinary screening machines (grid sieve, vibrating screen, cylindrical sieve, etc.) and spiral classifier; the second is by special washing. The process of the device.
A washing process consisting of a common screening machine is usually combined with the crushing process of the crushing plant. The screening equipment in the crushing process is also a washing equipment, and no additional equipment is required. This process saves investment and is easy to operate. When the original screening equipment is not enough or suitable, a small amount of washing sieve and other equipment may be added. Such a process is suitable for treating ore with less ore in the ore, low plasticity index of the clay and little agglomeration.
For those ore with more clay, high plasticity and agglomerate, special washing equipment is needed, and it is necessary to carry out two or even three times of washing to separate the clay from the ore.
Under normal circumstances, after the washing process, there should be a slime concentration operation, mainly using sloping plate grading thickener, deep cone thickener, vertical sand silo and other equipment, and the overflow water from the concentration operation returns to the washing operation.
1 Washing process of Yunnan sand tin mine
Artificially deposited by the Huangmaoshan Concentrator of Yunxi Company (tailings selected in the early years) and naturally deposited sand-tin ore, the ore sent to the ore dressing contains 0.329% tin and 26.68% iron, at +50mm It basically contains no valence metal and can be discarded as waste rock. The -2mm grain size accounts for 88.42% of the original ore, and the -0.074mm grain size accounts for 59.96% of the original ore. Many of them belong to colloidal particles, and the bonding is strong. The coarse sand is bonded by them. Together, it is difficult to wash ore.
The Huangmaoshan Concentrator uses the washing process as shown in Figure 9. The ore is first washed by hydraulic washing sieve, the +50mm waste rock is separated and some mud is dispersed, and the -50mm grain ore is used for the second washing. The grit (+2mm) of the trough type washing machine is given a section of grinding machine. The overflow (-2mm) is used to classify and de-sludge the cyclone, and then send it to the sorting operation.
The yield of the grit is 14.86%, and the overflow yield is 85.4%. The content of a 0.074mm grain size in the grit is less than 4%; the content of the +2mm grain level in the overflow is only 0.23%. The washing efficiency reached 95.76%.
Figure 9 Washing process of Huangmaoshan Concentrator
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