First, the characteristics of the sorting operation Different sorting methods can handle various types of ore, and the process flow is not the same, but there are many common features. For example, the processing of ore objects (except diamond ) is a coarse-grained nugget, and the picking process is relatively simple. There is no need for high-quality medium, fine crushing and grinding operations, and the total number of equipment is small. Disused is a block of waste rock that is easy to handle and use. The following describes the common features of the picking process, its preparation process, and the auxiliary process as follows:
(A) A step of preparing broken open stope underground or supplying a maximum particle size of the ore dressing plants, generally more than the upper limit of the particle size chosen. In order to prevent excessive ore from entering the sorting operation, it is necessary to crush the portion of the ore having a particle size larger than the upper limit of the sorting size. For the ore suitable for sorting the grain size, the larger the amount of the ore selected, the more waste rock can be sorted, and the more obvious the economic benefits. Therefore, it is necessary to carry out controlled crushing, that is, not only the ore which is suitable for the selected particle size should not enter the crushing, but also the finely divided material which cannot be selected in the crushed product should be reduced as much as possible, regardless of the crushing ratio. Since the purpose of the selection is mainly to discard the waste rock, as long as there is a block of waste rock to be sorted, and the useful mineral monomer is not required to be dissociated, the sorting operation is generally carried out after the coarse crushing, without the need for the second stage of crushing. The selection also has high requirements for the blasting and transportation operations of the mining process. When blasting, it is required to control the blasting parameters so that the ore size sent to the picking plant is moderate, and the number of oversized and oversized pieces that cannot be selected in the ore should be minimized. When the quality conditions of the mining site are basically the same, the grain size composition of the mined ore can be greatly changed, and the yield fluctuation range of the selected grain size (200~25 mm) can be as high as 10-20%. This shows that there is great potential to control the size of the nugget during the mining process. Reduce and improve the transportation of ore (such as electric rafts, slip mines, mine cars, dump trucks, mining bins, mining machines, etc.), and rationally select the discharge port of the crusher to reduce the fine-grained grade that cannot be selected. Material, which is good for picking.
B Screening In the general concentrating plant, in order not to increase the height of the plant, when the production capacity of the coarse and medium crusher is sufficient, no pre-screening is required, and the sorting plant requires pre-screening. The large ore sieved by the pre-screening enters the coarse crushing operation, and the coarsely crushed product and the undersize product are combined into a secondary sieve, and after the fine ore is sieved, an ore suitable for sorting is obtained. In order to improve the technical and economic indicators, these ores (such as 200 ~ 25 mm) generally need to be divided into several levels for sorting, so a third screening is required. In the third screening, the sieve ratio is generally taken from 1.3 to 3. The selection of the sieve ratio is related to the nature of the ore and the characteristics of the machine. The sieve ratio can take a large value for an easy-to-mine ore with a large difference in grade between the ore blocks or a picker with a weight measuring device. [next]
The upper limit of the particle size of the picking is generally not more than 200 mm. When the weight of the nugget exceeds 5 kg, it is inconvenient to select and mechanically select. The throughput of the picker is determined by the number of nuggets processed per second. When the particle size is small, the throughput of the sorter will drop significantly. In addition to diamond sorting small particle size limit to be 0.5 mm, the lower limit of the particle size chosen is generally not less than 10 mm. For ore with a particle size of 200~10 mm, it should be sieved into 4~6 grain sizes for separate treatment.
The screening efficiency of industrial sieving machines is about 85~90%. The screening efficiency of the screening machine is preferably greater than 95%. The screening efficiency is 90%, which means that 10% by weight of the undersize product is mixed in the coarse fraction, which is equivalent to about 25% of the number of nuggets, which will seriously reduce the throughput of the sorter. When the number of nuggets per second is constant, the weight of the nuggets is reduced and the amount of treatment is reduced.
C Washing For the hand-selection and photo-selection of picking according to the difference of the surface of the nugget, washing off the slime on the surface of the nugget can enlarge the color difference between the nuggets and facilitate the improvement of the picking index. When picking according to the natural radioactivity, conductivity and magnetic properties of the ore, the requirements for washing are not strict. However, in addition to the lack of water, it is advisable to set up washing operations. The washing operation can reduce the adhesion of the slime to the equipment, and can improve the sorting efficiency and reduce environmental pollution. When the fine mud grade is higher than the original mine, the washing operation is more necessary.
Washing is usually carried out by a cylinder washing machine or a washing screen. In the process, the ore washing is performed only after the screening operation, and only the ore entering the sorting operation is washed.
(II) Picking process The sorting method can be divided into three types: flow selection, selection and block selection. The advantage of using water flow selection and sorting is that the ore does not need strict screening, the process flow is simple, and the equipment handling capacity is large; the disadvantage is poor picking quality. In recent years, block picking has basically been adopted with the introduction of high-efficiency, high-processing block sorting equipment . Flow selection and selection have rarely been applied.
The purpose of the selection is mainly to remove the massive waste rock, save the transportation, crushing and the next processing of the waste rock, without requiring the selected ore to have a high grade and a large enrichment ratio. Therefore, picking is basically a job, and there is very little need for selection or sweeping.
Under the premise that the ore properties have been determined, the quality of the picking is mainly determined by the quality of the picking equipment. At present, the detection efficiency of various sorting machine detection systems is still large, and the efficiency of the sorting machine actuator is high, because the high-speed electromagnetic jet valve is put into use, the accuracy (purchase rate) of performing sorting is as high as 95. ~98%. The sorting efficiency of the tailings of the sorting unit has reached 70~95%.
Due to the improved quality of the sorting equipment, the number of mixed concentrate blocks in the mixed tailings and tailings products in the concentrate products has been greatly reduced. Under normal circumstances, one job can achieve the intended purpose, so the picking process is relatively simple. Figure 1 shows the principle of radioactive separation of uranium ore. [next]
(III) Auxiliary Process The grading operation and dewatering operation of the picking workshop are the auxiliary processes of the picking. [next]
The slime adhering to the ore block should be treated after washing down the washing operation. For medium-sized ore, the amount of slime in a washing water is about 2% of the original ore. During the washing process, some ore is produced by the friction between the ore and the washing machine. The maximum particle size is 10-20 mm. It needs to be separated from the slime water by a classifier and sent to the main building by a belt conveyor. In the case where the picking plant is far away from the selected mine, the coarse sand of the classifier can be combined with the sorted concentrate. The fine mud part needs to be dewatered by concentration, filtration, etc., and then transported to the concentrating plant as a filter cake.
Second, the application of picking
According to the difference in appearance and color of minerals, it is well known to select metal ore, non-metallic ore, building materials, etc. by hand selection method. This sorting method has been applied at home and abroad.
In recent years, the newly developed mechanical sorting method controlled by information processing machine (electronic computer) has not only been applied to the sorting of ores with different appearances and colors, but also for the sorting of ore and waste rock that are indistinguishable to the naked eye. Very good results have led to a great development in the selection process. Currently, new areas are constantly being developed.
The following is an application example of some sorting methods.
(I) Application of natural gamma radioactive sorting The use of natural gamma radioactivity of uranium ore for picking development was earlier. With the development of science and technology and the deepening of research and development, many countries have achieved good economic benefits. For example, a low-grade uranium mine in China is sorted by a domestic belt-type radioactive sorting machine, and 45.9% of the ore is selected, accounting for 19.6% of the ore. The concentrate is also well enriched. The results obtained are shown in Table 1.
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The radioactive sorting method can not only sort uranium ore, but also use uranium as a tracer element to enrich the metal with positive correlation with uranium when enriching uranium. In many mines in South Africa, the distribution of gold and uranium is positively correlated. In recent years, several gold uranium mines have installed radioactive sorting machines. The results of the selection of gold uranium ore by the M17 type radioactive sorting machine in the Walrivs plant in South Africa are listed in Table 2.
(B) Application of γ absorption low grade ore sorting Kryvyi Rih USSR (Криворог) iron ore, mined ore grade of less than industrial requirements. Iron concentrates with a grade of more than 50% were obtained by y absorption method, which met the requirements. The equipment used is a Минерал-50Т type sorting machine, the γ-ray source is 241 Am, and the indicators obtained by sorting are shown in Table 3. [next]
(III) Sorting by γ-scattering method In the Руhasalmi mine in Finland, several kinds of ores were sorted by Precon-type gamma scattering sorting machine. The obtained indicators are shown in Table 5 of Table 4. [next]
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