Table 2 lists the static friction coefficient values ​​for several minerals.
The difference in the velocity of the turbulent flow in the turbulent flow is very inaccurate, so the coarse chute can only be used for rough selection, and the recovery rate is not high.
4. Separation of ore in a thin laminar flow film A slurry film with a weak turbulent flow, ranging in thickness from a few millimeters to a few ten millimeters. It is mostly used to treat fine-grained ores of less than 2 mm. The particles are distributed in multiple layers in the flow film. After the depletion of the particles, the bottom layer of the bottom layer is thickened, and the particles generally move along the layer, which may be referred to herein as a "rheological layer". The vortex above the rheological layer is rapidly formed and developed. Under the turbulent diffusion, the ore group is loosened and moves toward the discharge end. This layer is called the "suspension layer". The pulsation speed above the suspension layer is weakened, and only a small amount of fine particles are suspended, which is called a "surface layer" or a "dilution layer". The flow film structure is schematically depicted in Figure 12.
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The fine particles suspended in the dilution layer can no longer enter the bottom layer, so the pulsation speed of the layer determines the lower limit of the separation size, which is about 30-40 microns. The mineral particles entering the suspension layer continue to move up and down under the vortex disturbance, the heavy minerals are accommodated by the bottom rheological layer, and the remaining light minerals are suspended in the layer. As in the ascending water flow, the particles are distributed as "upper, lower, thicker, and thicker". The particles in the bottom rheological layer are in close contact and remain loose by shearing motion. The particles are transferred in different layers according to their own pressure, so this layer is the most effective static separation zone. Maintaining the layer with a certain thickness and shear rate is important for improving the recovery and grade of heavy minerals.
The heavy mineral layer in the weak turbulent flow film still moves along the groove, so continuous sorting can often be achieved. A sedimentary layer (such as in a centrifugal concentrator ) occurs only when the heavy mineral layer is subjected to excessive pressure, and a four-layer structure is formed.
The laminar slurry film has almost no turbulent diffusion, so it is suitable for processing fine fraction (-0.1 mm). The film is very thin, usually only 1~2 mm, and the flow layer of the centrifugal film is even less than 1 mm. However, it can still be divided into three layers, namely an upper dilution layer, an intermediate rheological layer and a bottom deposition layer. But the boundaries between the first two are very unclear. See Figure 13 of the laminar flow layer structure.
The following rheological layers function the same as in the weak turbulent flow described above. However, because of its low concentration, its most well-selected area is still close to the lower concentration zone, sometimes called the “transfer layerâ€. The underlying layer of the grading layer is the sedimentary layer. The fine particles and the groove surface tend to have a large cohesive force, so the sedimentary layer often does not flow, which causes the slurry film separation to be often intermittent.
Operating conditions of film casting: feeding volume, ore concentration, groove bottom inclination, groove surface vibration intensity or moving speed (such as belt chute), etc. are flow parameters through the flow film, including turbulence, slurry viscosity, speed Gradient, rheological layer thickness affects the selection index. Increasing the ore volume or decreasing the concentration will increase the turbulence of the slurry flow and increase the velocity gradient and reduce the thickness of the rheological layer. As a result, the concentrate grade will increase and the recovery rate will decrease. Conversely, reducing the ore volume or increasing the concentration will reduce the velocity gradient and pulsation velocity due to the decrease in flow rate and viscosity of the slurry, and thicken the rheological layer, resulting in an increase in recovery and concentrate. The grade is down. The vibration intensity and moving speed of the groove surface are also limited by these factors. The treatment of the fine-grained weak turbulent flow film itself has sufficient flow velocity, so that a considerable sorting result can be obtained on the fixed groove surface. For the slime chute, the natural flow velocity of the film is too low, the shear velocity gradient is insufficient, and the good sorting index is often not obtained. The mechanical method is used to force the bed surface to shear vibration, which has been proved to be improved. A good means of choosing the effect.
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