First, granulation process The method of granulation varies depending on the equipment used and the nature of the ore material. Regardless of the equipment, the basic process of granulation is the same. The process is as follows: the crushed ore, or the shale ore, the powder ore, etc. are uniformly mixed with the binder, and then water (or an aqueous solution containing the leaching agent) is added to the granulation equipment to make the water and the uniformly mixed material. After the agglomerates are aggregated, after the desired granules are obtained, they can be sprayed and leached by solidification and curing. The basic process is shown in the block diagram of Figure 1. Figure 1 Basic process of granulation Second, the main indicators of pellet quality The fine mud and mineral powder are agglomerated into a larger particle size agglomerate by adding some binder and water. This ore agglomerate is called agglomerate. The heap leaching pellets are different from the properties of the granulation process in the mineral processing , chemical, pharmaceutical, food and other industries. The main requirements for heap leaching pellets are: (1) The binder does not react chemically with the leaching agent, otherwise the pellet will be destroyed during the leaching process. (2) It has a certain mechanical strength and can withstand the pressure of the heap. The strength of the pellets is often expressed by the wet strength, and the wet strength of the pellets is required to be greater than 90%. (3) The pellet itself should be loose and porous to facilitate the diffusion of the leachate inside. (4) The particle size of the pellets is relatively uniform, the particle size should not be too wide, and the ratio of the maximum particle size to the minimum particle size should not exceed 3 to 4 times. (5) The moisture of the pellets should be able to meet the requirements of specific concrete materials. Third, the main factors affecting the quality of pellets (I) Moisture The amount of water added during the granulation process is related to the type and size of the specific ore. For example, the water content of the coarse quartz ore aggregate is 8% to 12%, the agglomerate water content of the flotation tailings is about 20%, and the agglomerate water content of the clay ore is up to 26%. However, for a particular specific material, there is an optimum (or optimal range) of moisture in the pellet. The optimum value of the moisture in the pellet is higher or lower, and the pellet strength is affected. as shown in picture 2. Figure 2 Effect of moisture on pellet strength It can be seen from Fig. 2 that the optimum water content of the agglomerates of the ore is 20%, and when the water content of the agglomerates is higher than 22% or lower than 18%, the wet strength of the agglomerates is significantly decreased. (B) the amount of binder added The amount of binder added depends on the type of binder and ore. Gold heap leaching multiple use Portland cement or lime, has both added simultaneously. Regardless of the binder (or mixed binder) used, the amount added should be determined in advance by testing. The amount is small, and the aggregation of the agglomerates is difficult. Even if the polymerization is carried out, the strength of the agglomerates is poor; after the amount is exceeded, the strength of the agglomerates is increased, but the cost is increased, and the porosity of the agglomerates is lowered. The best pH of the gold ore heap leaching solution is 9.4. It has been proved that once the pH of the leachate is higher than 12, the dissolution rate of gold decreases. Excessive addition of binder affects the pH of the leachate, which affects the leaching rate. The binder used in uranium ore granulation heap leaching is also cement and lime. (3) Curing and curing time This is also an important factor affecting the quality of pellets. The granulation mechanism believes that the ore powder and the ore powder, or the fine mud and the ore powder agglomerate into larger particle size agglomerates, which are initially aggregated by the action of water, and then rely on the "bridge effect" of the binder - mineral powder The effect of molecular cohesion between the binder and the binder is tightly coupled to each other in order to have a certain strength, otherwise the pellets are easily dispersed. "Bridge effect" takes a certain amount of time, and the length of this time is related to many factors such as ore, type of binder, amount of addition, and ambient temperature. The strength of the pellets can only be manifested after the "bridge effect" is completed. Practice has proved that when the newly formed pellets are put into the water, the pellets will immediately spread out, indicating that the pellets at this time are only gathered together under the action of moisture, and the "bridge" has not yet formed, so the strength is extremely poor. However, after the curing and curing period, the pile is piled up to a 3 m high heap, which is sprayed with the leaching solution until the unloading of the pile can be seen that most of the pellets are intact. Figure 3 is the relationship between curing curing time and permeation rate in a gold ore granulation heap leaching. Figure 3 Effect of curing curing time on permeability (d) The running time of the material in the granulation equipment here includes two time factors, one between the mineral powder, or between the mineral powder and the fine mud, or between the fine mud and the small ore in the binder and water. It takes a certain time to form the core of the pellet, which is necessary. The other is that after the formation of the core of the pellet, the pellet tends to become larger and larger with time. Practice has proved that the larger the particle size of the agglomerates, the worse the compressive strength. Therefore, the time of particle size increase should be controlled according to the needs of the process. (V) Operational factors The proportion of ore, binder and water in the pellets is determined experimentally; each pellet or most of the pellets formed during continuous production operations should meet this ratio requirement. For example, the amount of cement used in a mine granulation is 10kg/t ore, which means that 1% of cement is mixed per lkg or even 100g of ore in this ore; no part of the ore in this ore is allowed to be mixed with cement. The amount is much more than 1%, while the amount of cement mixed with some other ores is far less than 1%. This requires that the ingredients must be uniformly proportioned and uniformly mixed. 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