1. Dehydration operation overview
     The dewatering operation is a mechanical or heat drying method to separate the solid material from the liquid.
     Dehydration is the job of a beneficiation plant must assist job. This is mainly because:
     (1) The beneficiation product contains a large amount of water and is in a state of pulp. For example, the moisture in the concentrate obtained by the wet method is several times the weight of the solid, and the water content of the concentrate is one of the quality standards of the concentrate. The concentrate containing a large amount of water cannot be sent to the smelting plant for smelting.
     (2) In the beneficiation production, sometimes in order to improve the concentration of the ore in the lower section and improve the sorting effect, the intermediate product also needs dehydration, such as washing of cyanide pulp and dewatering of flotation mine.
     (3) In areas where water is scarce, the water in concentrates and tailings needs to be removed and purified and returned to the recycling plant for recycling.
     At present, the quality requirements for gold concentrates on production should be less than 14% by weight, and should be less than 8% for long distance transportation in winter.
     The dehydration methods commonly used in gold selection plants are concentration, filtration, drying, and the like.
     2. Concentrate
     The solid particles in the slurry settle to the bottom of the vessel under the action of gravity, and the clean water is squeezed upwards. The process of separating the thinner slurry into the clear liquid and the concentrated pulp is called concentration.
     Concentration is generally carried out in a continuous working concentrator. The concentrator consists of a circular tank (made of steel or concrete) and a rotating tweezers in the tank. The working principle of the concentrator (see Figure 1) is that the particles settle to the bottom of the pool by gravity in the pool. The rotating scorpion scrapes the concentrated solid particles to the sand discharge port, and the upper clarified liquid overflows from the overflow tank.
figure 1 
     The concentrator has two types: central transmission and peripheral transmission. The center of the central transmission concentrator has a vertical shaft, and the lower end of the shaft is fixed with a cross-shaped dice, as shown in Fig. 2. The peripheral drive concentrator has only one long arm with one end supported on the center post and the other end driven by the motor along the rail at the top of the concentrating tank wall, see Figure 3. [next]
figure 2
image 3 [next]
     The concentrator has a large area, and in order to save the floor space, the gold-making factory sometimes uses a multi-layer concentrator. The multi-layer concentrator is a plurality of concentrating machines stacked vertically, and a multi-layer shared a central shaft transmission truss, and FIG. 4 is a schematic diagram of the multi-layer concentrator.
Figure 4
The specifications of the concentrator are expressed in terms of the peripheral diameter (meter) of the pool.
     3. Filter
     Filtration is the process by which the slurry passes through a porous filter medium to separate the solid material from the liquid. The filter media is typically a filter cloth. The liquid passing through the filter cloth is called a filtrate, and the solid material trapped on the filter cloth is called a filter cake.
     In the gold selection plant, the filter used is a pressure filter (referred to as a filter press) and a vacuum filter:
     (1) Filter press: The water in the slurry is extruded by pressurization, and is dried due to the incompressibility of the solid particles. Commonly used filter presses are available in frame and box type, and are mostly used in cyanide plants.
     (2) Vacuum filter: There are intermittent and continuous types. Intermittent vacuum filters are simple to operate but have a large footprint and are rarely used in gold selection plants. Continuous vacuum filters are more commonly used in gold selection plants, especially those that use flotation and re-election methods. These filters are usually available in cylindrical, disc and horizontal types.
     The cylindrical vacuum filter is a horizontally mounted filter cylinder with the lower part immersed in the feed tank of the filter, see Figure 5. [next]
Figure 5
     4. Drying
     Drying is the process of removing moisture from a material by evaporation. The drying operation is the last process of dewatering the concentrate products of the gold selection plant, and is mostly carried out in a thermal rotary kiln.
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