During the precipitation process, the coarse particles (generally considered to be 0.5 to 0.07 mm) precipitate quickly, and the obtained precipitates have less water; while the ore particles smaller than 0.001 mm (10 μm) are small due to gravity. The surface tension and Brownian motion are balanced so that it can remain in equilibrium for a long time without sedimentation. In order to accelerate the sedimentation of these fine particles, it is necessary to polymerize the dispersed particles into a large aggregate, which is called agglomeration. There are mainly three types of compounds which can make agglomeration of fine material products.
(1) an inorganic electrolyte such as lime, alum, ferric sulfate, ferrous sulfate.
(2) Natural or synthetic high-molecular flocculants such as starch, polyacrylamide, and the like.
(3) The organic surface-active substances, such as collectors and the like.
In addition, the use of centrifugal dewatering equipment is an effective method for the dewatering of fine-grained materials, but its power consumption is large and the investment is high.
The agglomeration phenomenon accelerates the sedimentation due to the stability of the dispersion system formed by the destruction of the particles. The main reasons why fine particles are difficult to precipitate in the slurry are: 1 Because of the existence of the electric double layer, the ore particles have the same charge and mutually repel each other, so it is difficult to settle; 2 there is still a hydrated film on the surface of the hydrophilic ore particles. The hydration film exists because the surface of the ore particles adsorbs a layer of water molecules, or the outer layer ions of the electric double layer are tightly bound to the polar water molecules. In the former case, only the hydrated film is on the surface of the ore particles. One case is where both the hydrated film and the electrical layer are present.
For the surface of the hydrophobic ore particles, the surface of the ore particles can maintain the stability of dispersion due to the presence of the electric double layer. On the surface of the hydrophilic ore particles, since the hydrated film or the electric double layer exists at the same time, the stability of the dispersion of the ore particles can be maintained, and thus coagulation occurs. From the viewpoint of the surface electrical properties of the ore particles, it is necessary to remove the electric double layer and destroy the hydrated film.
The addition of the inorganic electrolyte is essentially to make the slurry and the ions causing the stability of the system (ie, the ions adsorbed by the surface of the ore particles), and the opposite ion concentration of the charge increases, thereby compressing the electric double layer or thinning the hydration film, so that more anti- The ions are adsorbed into the adsorption layer, causing the potential of the ore particles to drop to a minimum close to (but not equal to) zero. In this way, the ore particles collide with each other in the slurry to become a larger polymer under the action of van der Waals force. This is why the addition of inorganic electrolytes to the slurry can cause cohesion.
It should be noted that the condensation of the electrolyte is only one of the ions. The higher the valence of such ions, the stronger the agglomeration ability. Generally, the particles in the slurry are mostly negatively charged, so the agglomeration is mostly cations.
When using inorganic electrolytes, it should be noted that the dosage should be moderate, and it is necessary to have a certain concentration to achieve a significant agglomeration effect, and to avoid excessively causing the ore particles to have opposite electrical properties without agglomeration.
The reason why the natural or synthetic high-molecular flocculant is added to form the floc is mainly because the relative molecular mass of the compound is large, the molecule is very long, and a large number of polar groups are distributed throughout the molecule. (such as hydroxyl, carboxyl, amine, amide, etc.), such as electrolyte type, they can be electrostatically charged, such as nonionic, they can rely on hydrogen bonding or the like to join many fine ore particles to form a so-called floc, which The role is called "bridge" or "bridge". Therefore, the flocculation of natural or synthetic high-molecular flocculants is caused by bridging. The flocculation of polymer flocculants is caused by bridging. The coagulation effect of the polymer flocculant is extremely remarkable, but it is necessary to pay attention to the amount of control. When the amount is large, not only the flocculation effect but also the dispersion effect, the so-called "protection effect".
The flocculation of surface active substances (such as organic collectors) is due to the directional adsorption on the surface of the ore particles, the non-polar end of which faces the water, forming a non-wetting film, which is bonded when the ore particles are in contact with each other. body. This agglomeration is also commonly referred to as flocculation.
The difference between coagulation caused by electrolytes and flocculation caused by surfactants is shown in Figure 9-3.
The aggregate formed by agglomeration still retains the hydrated film, so the combination is weak and loose, and the flocculation is firmly combined, which is related to the flocculating agent, so the flocculating agent has a great relationship with the dehydration of the flotation product.
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