It can be concluded that if the gravel medium consumption is considered, when the other conditions are the same, the influence of the difference in grinding fineness on Q p /Q B is roughly as follows: In the formula, the γ -200 content is represented by a decimal. When the first stage is a two-stage grinding process with an open circuit (or a rod mill), m=2~3; when the first stage is a closed-stage two-stage grinding process, m=1. Airplane wings parts Dongguan Hongke Plastic Precision Mould Co.,Limited , https://www.hongkemold.com
With the application of grinding technology and ultra-fine pulverization technology and the development of grinding equipment , the type of structure of the grinding process has also changed greatly. Since the 1960s, the self-grinding process and the combined grinding process of conventional grinding and self-grinding have been widely used. Currently, mineral processing plants commonly used in grinding process can be divided into two types, namely conventional grinding process and autogenous grinding processes.
Second, the grinding process selection
(I) Influencing factors of grinding process selection The difference between rock ore and ore properties is related to its genesis, structure and structure. The igneous rocks and the crystallization of rocks or minerals of some metamorphic rocks are often directly related to each other without entraining other materials, so the nuggets are strong, hard and difficult to smash; the minerals and rock particles in the sedimentary rocks vary in shape and size. The two are glued together, and the particles often contain various cementing materials, such as siliceous lime or clay , self-tanning, etc., soft and brittle; the contact edges between the rock-forming mineral particles are smooth and flat, combined with slack or joint The developed ore is fragile and easy to grind. For example, strip-like coarse-grained ores are generally susceptible to dissociation. If the contact edges of the mineral are jagged or closely connected or interspersed with each other, or form a wrap structure, an opaque structure, a residual structure, a fine-grained structure, or a braided structure forming a concentric annular band, Solutions for grinding more difficult from fossil; bedding ore and its fractured without being affected comminution product size uniformity degree of dissociation; medium hard for coarse uniformly disseminated iron ore grinding process may be employed for some For multi-stage grinding process, it is suitable for difficult to grind ore with high hardness, fine mineral inlay size, unclear cleavage and strong toughness.
The degree of mud, the composition of the ore and the presence of beneficial or harmful elements in the ore also have a major impact on the choice of the grinding process. When the ore contains more mud or contains more soluble salts and affects the flotation process, it is necessary to set a pre-grading before the grinding operation to remove the slime. If the beneficial and harmful elements in the ore are combined together in the same state of the same type, the fineness of the grinding should be adequate, and further fine grinding has little effect on reducing the content of harmful elements in the concentrate.
The effect of ore properties on grinding is generally reflected by its grindability. Hard ore is generally difficult to break, but not necessarily difficult to grind, sometimes soft and brittle ore is often difficult to grind.
If the grinding fineness -200 mesh is required to account for 70-80%, or if it needs to be sorted after coarse grinding, a two-stage closed-circuit grinding process can be used; if the grinding fineness is -200 mesh, 80 to 85% is required. Above, a two-stage full closed-circuit grinding process can be used. If the ore is unevenly embedded in fine particles, and the final grinding product is required to have a very fine particle size and a high degree of dissociation is required, a multi-stage grinding process may be used. For example, when the concentrating plant produces iron concentrate for pelleting, Very fine grinding products are often required, and sometimes the concentrate needs to be reground to -325 and accounts for 85-90%. [next]
In order to achieve good technical and economic effects, large-scale concentrators can determine the best grinding process through comparison of multiple schemes. If necessary, two or more stages of grinding process may be adopted. Small ore concentrating plants sometimes deal with fine or coarsely unevenly embedded ore, sometimes from a economic point of view, often using a simple grinding process to simplify operations and management, thereby reducing capital investment and production costs.
For ore with useful minerals with uneven or fine grain inlays, large concentrators often use pre-selection, ie coarse-grain tailing before or after roughing operations, thus using a stage grinding process. For example the United States from Iraq in concentrator rod mill row of ore (4 ~ 0 mm) in addition to throwing magnetic separation tailings 47% of the amount of ore, ore dressing plant of Jinshan shop since the mill from 80 to 10 mm of row The tailings are removed from the mine by 5~6%. For iron ore with useful minerals in fine-grained inlay, in addition to pre-selection of coarse-grained waste rock, fine-screen re-grinding process can be used to properly coarsen the particle size of the grinding product in the front section. After regrind, the grade of the concentrate can be greatly improved, and the output of the mill can also be increased. China's Nanfen, Chengchao, Gongchangling and other iron ore dressing plants use this type of process, and have achieved significant economic benefits.
Grinding test data is an important basis for selecting the grinding process. There has been a clearer understanding of the structure and performance of conventional grinding processes and the type and role of media. However, there is no exact ready-made rule for the effect, production capacity, energy consumption and steel consumption of different ore grinding equipment with different grinding equipment, especially when self-grinding and flow are adopted, the ore must be The adaptation of the grinding, the greater the adaptability reference value of the self-grinding medium, the stronger the adaptability of the ore to self-grinding. If the value is less than 1, the ore is not suitable for self-grinding; if the work index ratio of the ore is too small, the medium is insufficient. On the basis of comprehensive comparison of various parameters measured in the laboratory, semi-industrial or industrial self-grinding tests are necessary to rationally select the self-grinding grinding process.
For the smooth construction of the concentrator, when selecting the grinding process, you should also understand the technical, economic and transportation geographical conditions, transportation conditions, sources and prices of grinding media, linings and electrical energy. In addition, the selection of the grinding process should take into account the convenient operation and management of the equipment, reliable operation, easy maintenance and inspection, and minimize the pollution of the environment caused by dust, noise and electromagnetic waves.
In short, there are many factors affecting the grinding process, and the relationship between them is more complicated. It is generally difficult to fully grasp through conventional research methods. At present, based on the semi-industrial or industrial tests conducted at the concentrator, the capital investment and production costs of each process are compared. Finally, the most suitable grinding process can be selected and the best expected results can be obtained. Due to the establishment of the mathematical model of the grinding process, the application and development of electronic computers, experience in this field is gradually accumulating at home and abroad.
The computerized program can be established based on the specifications of the grinding grades of various ores, as well as the technical parameters of the grinding process and the operation process. In the application, only the most basic grinding technical data of the ore (sometimes using batch grinding test data) can be sent into the computer, and the grinding process can be more accurately evaluated and selected through digital simulation. [next]
(2) Conventional grinding process Generally, the conventional process can be applied except for ore containing a lot of mud and high humidity. The self-grinding and semi-self-grinding processes have high power consumption and should be used with caution.
A section of open-circuit grinding process The upper limit of particle size and particle size distribution of open-circuit grinding process products are not strictly limited. Since the ore is only passed through the grinding machine once, the product has a coarser grain size. This type of process is commonly used in the single-stage rod grinding process or the first stage of the first section of the grinding process with a rod mill. The ore can be from 20 to 25 mm (soft ore up to 50 to 75 mm). Grind it to about 3 mm at a time. When processing tungsten, tin ore beneficiation intermediate product, can be ground to about 0.5 mm. Ball mills rarely use an open grinding process. The open road grinding process is simple, the production capacity is large, no grading and returning facilities are needed, the construction speed is fast, the production operation and maintenance are easy, and it is generally used for rough grinding. Especially when using a rod mill as the first stage of grinding, open grinding is more common.
B A closed-circuit grinding process When a grinding product is required to contain -200 mesh not more than 60-70%, a closed-circuit grinding process can be used.
When closed-circuit grinding, the grader return sand is mostly finer than the original ore. The sand returning is mixed with the ore newly fed into the mill, so that the average particle size of the ore in the grinding machine is reduced, the content of the ore near the grain size of the grinding product is increased, and the gap around the coarse ore is filled with fine sand. It is beneficial to form a favorable meshing between the crushing medium and the ore particles. Along the entire length of the grinding machine, the ratio of the size of the ball to the average diameter of the ore is relatively stable. The flow rate of the material in the grinding machine is relatively fast. Therefore, the productivity of the closed-circuit grinding machine is generally higher than that of the open grinding, and the product granularity is higher. Fine, uniform particle size, less pulverization. Closed-circuit grinding can also improve the selective grinding of heavy minerals.
The equipment configuration and operation management of the closed-circuit grinding process are complicated, but these shortcomings can be compensated for by the technical and economic benefits generated by the high efficiency and high output of the grinding machine. In short, closed-circuit grinding can control the particle size of the mill by changing the circulating load of the mill, and the production capacity can be improved, which brings a series of benefits that are beneficial to improve the beneficiation index.
The structure type and application examples of the closed-circuit grinding process.
C Two-stage grinding process The ore dressing practice shows that in each grinding section, the grinding ratio has a suitable value, and the grinding ratio of a conventional ball mill is generally about 80~100. It is uneconomical to have a large grinding ratio. The grinding efficiency is low, the energy consumption is high, and the product is easy to be crushed, which affects the sorting effect and economic benefits. Practice has shown that the more difficult to grind the ore, the less economically rational it is to use a grinding process. The two-stage grinding process overcomes the shortcomings of a grinding process. It can reasonably distribute the load according to the difference of the particle size of the materials in the grinding machine and the nature of the wear-resistant material, and it is easy to select the appropriate media size and ratio according to the different feeding materials and product granularity of the two-stage grinding machine. [next]
Generally, when the ore dressing plant requires more than 70% of the grinding products to contain -200 mesh or a large ore dressing plant to process hard and difficult to grind ore, and requires finer grain size of the grinding products, a two-stage grinding process can be used.
The rod mill-ball milling process is used more often in tungsten tin and other rare metal re-election plants or magnetic separation plants. In large iron ore, apatite ore and non-ferrous metals concentrator also employed. When the 20~30mm ore is ground to 3mm, it is simpler to configure than the conventional fine grinding process with closed-circuit fine crushing, low production cost, and can reduce the dust removal facilities in the crushing workshop. In the two-stage grinding process, if the first section uses a rod mill, the ore is ground from 20 mm to 3 to 1 mm, and its production capacity is larger than that of ball milling, and the grinding efficiency is also high. The rod mill product has a uniform particle size and is lightly pulverized. Therefore, rod grinding is a good means to provide suitable ore size for ball mills, jigs, and magnetic ore coarse pre-selection operations. The rod mill-ball milling process is more adaptable.
The measurement of foreign industrial production shows that the former has high grinding efficiency and large production capacity when the rod grinding-ball milling process and the ball milling-ball milling process are similar in processing and the grinding fineness is the same. The measurement results also show that the power consumption of the rod mill is only about 60% of that of the ball mill. Soviet Barr Hash (БаЛахащ) concentrator with Alma Lake (ÐрМаЛьІК) containing copper sulfide ore concentrator processing two ore hardness coefficient close (f = 12 ~ 16), the grinding fineness are -200 mesh 45% or so. The former uses a rod grinding-ball milling process, and the power consumption is 30% lower than the latter using a ball-ball milling circuit.
According to the experience of the former Soviet Union Krivorog mining area, in the first stage of grinding, the rod mill is used. The unit consumption of grinding medium is lower than that of the ball mill. It is generally 0.33~0.56kg/t ore.
D Multi-stage grinding process and stage grinding process When the ore is poorly grindable, and the grinding size is required to be extremely fine, or the concentrate is required to have a high grade and the ore is a fine-grained or unevenly embedded, Or when the old concentrator wants to increase the production capacity of the original grinding operation, it can use three or more stages of grinding process. For extremely easy muddy ore, in order to improve the grinding and beneficiation efficiency, prevent over-grinding, and recover the dissociated useful minerals as early as possible, stage grinding and stage selection process can be used. This utilizes selective grinding to maximize the recovery of useful minerals. Large-scale iron ore dressing plants that use a stage grinding process can choose to remove coarse-grain tailings or directly obtain coarse-grained final concentrates after a period of grinding, if the iron ore properties are suitable.
The advantages of the conventional grinding process are stable and reliable work, high operating rate, generally more than 90%, and some as high as 96~98%; the disadvantage is that the capital investment is high, when using small equipment, the amount is large, when dealing with clay or wet-bonded ore, The medium and fine crushing operations associated with it are prone to blockage. The conventional grinding process has lower energy consumption, higher operating rate and strong adaptability than the self-grinding process. In the conventional grinding system, the particle size segregation of the mill feed is small, because after multiple stages of crushing, storage and reclaiming, the ore has been mixed. When the self-grinding process is employed, it is common for the first stage mill to cause fluctuations in the mill capacity due to segregation of the feed size. [next]
(3) Self-grinding process A. General comparison between self-grinding process and conventional process According to domestic and international production practice experience, the advantages and disadvantages of self-grinding process compared with conventional grinding process can be summarized as follows:
(1) It saves medium and fine crushing operations, simplifies the process, and improves labor productivity.
(2) The self-grinding machine has a certain selective crushing effect, and the useful mineral may be dissociated according to the interface. It is reported that the self-grinding process products have a grade of 0.5 to 1.5% higher than the conventional grinding process.
(3) Not all ores are suitable for self-grinding operations. The ore that is most suitable for self-grinding must form a sufficient amount of medium during the self-grinding process. According to the experience of the former Soviet Union, it is most suitable for the use of wet self-grinding ore with a Platts hardness of 6-12. When the ore with high ore is treated, the washing operation can be eliminated, and the grinding process is greatly simplified. For example, the concentrators of the former Soviet Union, such as Yakutalmas (ЯкуТаЛМа3), Tasheyere (таÑеевÑкаg), and Lower Kuranach (Hиже-kуранахÑкаÑ), are treated with mud ore, and their power consumption and processing costs are lower than conventional. Grinding; these mud-bearing ore are difficult to process by conventional grinding process, while the self-grinding process is very high when the self-grinding process is used; the same is true of Dongshan Iron Mine in Maanshan and Tonglu Copper Mine in Daye.
(4) The output of the self-grinding mill varies greatly depending on the nature of the ore. According to statistics, the range of fluctuations in the output of the mill is ± (25 ~ 50)%, which is very unfavorable for the sorting operation, especially the flotation. In order to solve the impact of the fluctuation of ore properties on the output of the self-grinding mill, the former Soviet Union used a large mine stack in the mine to neutralize and mix the ore.
(5) The self-grinding operation rate is low, generally 78~88%, which is 6~10% lower than the conventional grinding process, which is mainly due to the short life of the self-grinding machine liner.
(6) The production cost of the self-grinding process has its advantages and disadvantages. The good side is that the steel ball is saved. The disadvantage is that the consumption of the lining and the power consumption are higher than the conventional grinding process. Usually, its power consumption is 10~35% higher than that of the conventional process, and it consumes 2~5 kWh per ton of ore.
(7) The material level of the self-grinding machine has a great influence on the output of the self-grinding machine. Therefore, the material level of the self-grinding machine should be strictly controlled during the production process so as not to cause large fluctuations. Automatic control is necessary to achieve this, which is more important for semi-self-grinding, because maintaining a suitable material level not only ensures high output from the mill, but also reduces the impact of the steel ball on the lining, thereby reducing the lining and The consumption of steel balls. [next]
(8) The Outokumpu block grinding-gravel grinding process has great advantages. The characteristic of this process is that the first section of the coarsely crushed product is sieved and divided into three products: +100 mm as a block grinding medium, -100+30 mm as a gravel grinding medium, and -30 mm into a block mill; The mill product is divided into three kinds of products after being sieved: -8 mm into the gravel mill, -30+8 mm is crushed by the cone crusher and returned to the block mill; -100+30 mm is used as the gravel grinding medium, and the excess is broken. After returning to the block mill. This kind of process can improve the output of the block mill by screening the hard-to-grind particles (-100+30 mm) before the block grinding; the change of the ore property is reflected in the cyclic load, and the cycle load can be adjusted by the cone crusher. The processing capacity of the whole system is stable; the size of the first-stage block mill is much smaller than that of the general self-grinding mill, and the aspect ratio is large, so the output can be improved.
In summary, it can be considered that in the selection of the grinding process, comprehensive consideration should be given to the factors such as the size of the deposit, the nature of the ore, the scale of the ore dressing and the regional conditions, and compare their capital investment and production costs, and finally decide which process to adopt. In general, the conventional process can be applied except for the ore containing more mud and humidity. Especially in the late 1970s, the ultra-fine crusher has gradually matured and been promoted and applied, which greatly reduced the production cost of the ball mill, and the self-grinding process There are many serious shortcomings, so in the past 10 years, domestic and foreign countries are not inclined to prefer the self-grinding process. However, the treatment of ore with high mud content has obvious advantages in self-grinding and semi-self-grinding.
B Comparison of economic indicators The economic and technical indicators of the self-grinding process and the conventional process are mainly compared from the aspects of infrastructure investment and production costs. Generally speaking, if the self-grinding process cancels the medium and fine crushing operation, the cost of buildings and structures is 30-40% lower than the conventional process, and the total infrastructure investment can be 15~25% less. If the conventional process of processing mud-containing ore needs to be increased, the washing is required. Mine operations (such as Dongshan Iron Mine, Huangmeishan Iron Mine), the self-grinding scheme is superior.
C Semi-self-grinding process compared with conventional grinding process According to the data report, the capital investment and production cost of the semi-self-grinding process are lower than the conventional process. Therefore, except for 60% of the concentrating plants put into operation in capitalist countries in the past 10-15 years Outside the process, the remaining 40% all use a semi-self-grinding process. According to the comparison data of the semi-autogenous grinding and the conventional grinding process based on the design and practice data of the concentrator of West Mill Kami, Lonex, Aylan, Afton, Pima, etc., it can be seen that the semi-self-grinding Process production costs are saved by 20~35%.
Production practices at the Sepulus and Pima copper ore dressing plants in the United States provide very useful experience for semi-self-grinding and conventional grinding processes. The normal process (crushing, rod grinding, ball milling) of the plant treats ore 30,000 tons per day, and the semi-self-grinding process treats the ore amount of 19,000 tons per day; the ore of the plant is divided into two parts after coarse crushing, and is sent to two processes for treatment, so its index Comparable. The semi-self-grinding of the plant is compared with the conventional process. The former's infrastructure investment is 20% lower, the production cost is 15-20% lower, the steel consumption is 14% lower, and the power consumption is 15% higher. The former is 16.47 kWh/ton, the latter is 14.26 kW • hour / ton. [next]
The Yugoslav Matampec Copper Ore Concentrator originally used a three-stage crushing, rod grinding, and ball milling process, and later expanded to use a semi-self-grinding and ball milling process. The latter process was carried out using a ф1.83 x 0.61 m semi-autogenous mill and a ф 0.915 x 0.915 m ball mill. The test results show that the specific power consumption of the two processes is related to the work index of the ore being grounded. The higher the work index of the ore, the greater the proportion of the power consumption of the semi-self-grinding process compared with the conventional process; although the lining of the semi-self-grinding process The board consumption is about 41% higher, but the total steel consumption is still about 42% lower. In addition, since the unit power consumption (kWh/hour/ton) is higher in the semi-self-grinding process, the steel consumption per unit of electricity consumption is / kW • hour) The semi-self-grinding process is about 13% lower than the conventional process.
The Liberia Bunge Concentrator originally used a wet self-grinding mill and a spiral concentrator to treat magnetite ore. Later, due to the finer size of the ore inlay, the processing capacity of the self-grinding mill was reduced by 10-15%. After the semi-self-grinding industrial test, a steel ball with a Rockwell hardness of 43 mm and a hardness of 43 to 60 was used, and the filling rate was 5%. The industrial results showed that the yield increased by 32.4% after the semi-self-grinding, and the power consumption decreased by 27.5%: However, due to the coarser grain size of the semi-self-grinding product, the concentrate grade decreased by 3.5%.
The semi-self-grinding process has a lower production cost per unit, mainly because of the addition of different proportions of steel balls to the mill, which increases the output. Whether a certain ore is suitable for semi-self-grinding, the economic benefits of the semi-self-grinding process and the appropriate ball addition should be determined by experiment. The output of the self-grinding mill increases with the increase of the ball addition, but the power consumption of the self-grinding machine also increases. The appropriate amount of ball added should be determined based on the optimum grinding efficiency e (ton/kWh). Generally, the ball filling rate Ñ„ B of a semi-self-grinding is 4 to 8%. However, according to recent experiments in the former Soviet Union, Ñ„ B can reach about 16%. A suitable media fill rate should be such that the grinding efficiency is highest or the specific power consumption (kWh/hr/ton) is the lowest under specified grinding conditions.
The size of the ball for semi-self-grinding is generally 100 to 140 mm. If the ball diameter is too small, the effect is not large, and the power consumption is increased. Increasing the ball diameter can improve the grinding efficiency, but the impact is harmful when the ball diameter is too large, and the consumption of the lining plate is intensified.
(4) Gravel grinding process The gravel grinding process mainly includes self-grinding and gravel grinding, ball milling and gravel grinding, and rod grinding and gravel grinding. The application of these processes depends primarily on the nature of the ore and the characteristics of the gravel milling process itself. The structure of the gravel mill itself is no different from that of the ball mill. The two can be used interchangeably. The output of the gravel mill is much lower than that of the ball mill, because when other conditions are the same, the mill output and grinding media [next] 
[next]
Product size, %-200 mesh Q p /Q B
55~60 0.31~0.43
84~94 0.82~0.96
96~97 ~0.94
That is to say, it is suitable to use gravel grinding when fine grinding. The dissociation properties of minerals in gravel milling are different. The dissociation of the monolithic monomers is better. The mineral particles have a more regular crystal lattice and less muddy, which is beneficial to the selection. This is mainly due to the fact that the coefficient of friction between the gravel and the ore particles is larger than that of the steel ball, so the ball mill can be considered to be ball milled in the fine grinding. In the general gravel grinding process, -80+30 mm gravel medium is added, and the consumption is 5-12% of the ore to be ground into the gravel mill. Therefore, considering this amount, the output of the gravel mill will be higher (see Figure 1). In addition, gravel grinding has the following advantages: (1) saving a large number of steel balls, especially in fine grinding, which is particularly suitable for avoiding iron materials and processes, such as uranium ore, cyanide-treated gold ore, which is chemically treated in the lower stage, and is easy to use. Smashed diamonds, etc.; (2) reduce noise; (3) reduce power consumption. However, gravel mill also has its defects, among which are: (1) the grinding concentration is low, generally 60~65%; (2) it must be ensured that the gravel grinding medium is added quantitatively and regularly to ensure the suitable gravel medium in the gravel mill. The filling rate must be automatically controlled for this purpose; (3) the preparation, storage, supply of gravel, the treatment of excess gravel, and the treatment of gravel fragments discharged from the gravel mill are more troublesome. Therefore, a special system must be designed. Make the process complicated. For example, the gravel grinding medium of the bar mill gravel mill or the ball mill plus gravel mill process is from the sieved part of the medium crushed product (about 20 mm of the sieve hole), and the lower part of the sieve is finely crushed; the excess medium is also processed into finely divided . If the grind grinding process for the rod mill (the early process of the Fenghuangshan copper mine in China and the Etpic concentrator from the Swedish company Polidon) is broken, the open circuit is used; for the ball mill and the gravel grinding process, the closed circuit is used. Production practice shows that the rod grinding and gravel grinding process is less adaptable and therefore rarely promoted.
For the self-grinding and gravel grinding process, the gravel medium is prepared by two methods: (1) all supplied by self-grinding (Spikedon York Concentrator, Etitake Concentrator, Sweden); (2) The mill supply is supplied with a portion of the medium crush and there is a gravel storage bin to adjust for changes in the demand of the gravel mill. The disadvantage of the former solution is that the supply of gravel cannot be adapted when the ore property changes, but the process is simple and the output of the self-grinding machine can be improved; the advantage of the latter solution is that the grinding medium can be provided with sufficient grinding medium as needed, and can be improved. The disadvantage of self-grinding machine production is the complexity of the process.
The bottom line is whether the cost of steel balls and electricity saved after gravel grinding can compensate for the increased capital investment and production costs. In general, if the grinding fineness -200 mesh is required to account for more than 80%, or the iron process can be considered to use the grinding process including gravel grinding, otherwise it is not suitable because the semi-self is adopted in general. The grinding scheme is superior to the method of discharging gravel from the mill (including the ABC process). [next]
Sweden's Bolden has provided very useful experience in the comparison of conventional processes, self-grinding and gravel grinding processes. The Attic concentrator handles low-grade chalcopyrite-pyrite ore, medium hardness, and the upper limit of the size of the sulfide mineral inlay is 0.1-0.5 mm, and the granule crystal size is 0.5-2.0 mm. In the early stage, the rod mill-gravel grinding process was adopted, and the rod mill discharge was directly fed into the gravel mill. The gravel mill discharges the grade into the spiral classifier. The return sand (containing gravel) is returned to the rod mill, and the overflow is fed into the hydrocyclone; the cyclone overflow is sent to the flotation, and the grit is returned to the gravel mill. The production practice shows that the gravel mill discharges into the spiral classifier to remove the gravel to avoid the plugging of the cyclone grit, and can keep the gravel mill from being affected by the critical hard-wearing particles, so the production is very stable. The plant was later expanded to use a self-grinding-gravel grinding process. The investment cost of the latter process was 18% lower than the previous process: due to the finer grain size of the grinding-grinding process, the copper concentrate grade and recovery rate were both Higher, but the energy efficiency of the grinding is lower than that of the rod mill-gravel grinding process.
In recent years, the Outokumpu block grinding and gravel grinding process adopted in Northern Europe has achieved good results.
Third, the grinding process calculation
The purpose of the grinding process calculation is to determine the weight Q (ton/hour) and the yield γ (%) of each product in the process, which are used as the basis for selecting and calculating the grinding and grading equipment , and for preparing the beneficiation process. Provide basic information on various technical data or a correct evaluation of the production status of the concentrator. According to the principle of balance of feed and discharge weight in each operation in the grinding process, various calculations of the grinding process can be carried out. Usually, the number of materials in a certain size range required for each product of the operation is used as the calculation object. This particular range of granularity is called the calculation level, and the material contains the number of calculation levels to represent the fineness of the material. Generally, -0.074 mm is used as the calculation level. In the case of rough grinding or very fine grinding, -0.15 and 0.040 mm can be used as the calculation level, respectively.
The appropriate fineness of the ore dressing product is determined by the beneficiation test. In the case that the ore composition is single and the ore properties are relatively clear, it can also be determined by referring to the production experience of the same ore concentrator.
(1) Raw materials used in the calculation of the grinding process A Production capacity of the grinding workshop Q (ton/hour)
The grinding workshop for processing the ore mine has the same production capacity as the concentrating plant, that is, the dry ore volume processed by the concentrator in the whole year divided by the number of hours of operation of the mill. If there is a washing or pre-selection tailing operation before grinding, the abandoned tailings or fine mud should be deducted, and the grinding machine production capacity should be calculated; the grinding machine set between the beneficiation processes has a production capacity equal to The amount of thousands of ore that actually enters the grinding operation per hour in the process. [next]
B. Granularity distribution of feeds and products Since the selection and calculation of mills is usually based on a new specific grade of pellets, there should be data on mill feedstock and product particle size distribution. In general, there is a relationship between a fine fraction of grinding ore and products (including graded overflow and returning sand) and the nominal size of the product (calculated according to the 95% sieve size).
Sand content relationship -0.074 overflow level and product particle size classifier return density is 2.7 to 3.0 g in terms of hard ore / cm 3. For dense ore (such as dense sulphide ore), the content of -0.074 mm in the return sand will increase by 1.5 to 2.0 times. For pre-grading or overflow control grading, if the content of -0.074 in the grader is more than 30~40%, the content of -0.074 mm in the returning sand should be the upper limit of the value in the table. When grading with a hydrocyclone, the relationship between the maximum particle size of the overflow and the content of -0.074 mm in the overflow can be found in the monograph on the hydrocyclone.
C Closed-circuit grinding appropriate cyclic load c value The appropriate cyclic load is determined by industrial tests, or the actual production data or statistics of similar concentrators are used. A suitable cyclic load allows for maximum grinding benefits with minimal grinding costs. Due to the limited ability of the ore to transport ore during operation, the selected cyclic load must ensure that the total amount of ore (including new ore and return sand) per unit volume of the mill is not greater than that of the mill. The actual passing capacity (ton / m 3 • hour), otherwise it will cause the mill to work abnormally. The passing capacity of the mill is related to the mill specifications, type and operating conditions; for example, when the ф2.7×3.6 m lattice ball mill processes Nanfen iron ore, its passing capacity is 16-18 tons/ m3 • hour.
In addition, the appropriate ball-to-batch ratio should be maintained in the mill. Generally, the grinding ratio is better when the ball-to-batch ratio is between 0.6 and 1.2. [next]
Based on the above reasons, in the closed-circuit grinding, especially the ball mill should have a suitable returning sand ratio, and the grinding machine has the highest processing capacity in the range of the returning sand ratio.
D m value and K value calculation In the two-stage grinding, the easy-grinding part of the ore will be first ground in the first section of the grinding machine; the harder part will enter the second stage of the grinding machine. Therefore, the unit production capacity of the second-stage grinding machine is usually lower than that of the first-stage grinding machine; the volume of the second-stage grinding machine is also larger than that of the first-stage grinding machine, especially the first stage is open-circuit grinding or rod This is especially true when grinding. The ratio of the ratio of the volume of the second section of the mill to the volume of the first section of the mill during the two-stage grinding is:
The ratio of the unit volume production capacity of the second section of the mill to the unit volume production capacity of the first section of the mill according to the newly calculated calculation level is:
(II) Calculation of grinding process The basic principle of grinding process calculation is material balance. The calculation of a grinding process is simple.
In fact, the new ore that participates in the calculation of the production capacity of the grinding machine can only be returned to the sand after the Q4 has been pre-classified. To this end, the second stage of the grinding operation of the two-stage full closed-circuit grinding process is developed into the form of Figure 2. In the figure, Q ′ 8 is the new ore supply to the second section of the grinding machine. However, Q ′ 8 is only a considerable amount of material, and its weight cannot be directly measured. It can only be calculated by sampling with other products and indirectly by theoretical formula. This algorithm was first proposed by the former Soviet Union Zazov, and the Soviet Union and China's mineral processing design department have been using this algorithm. The calculation method of Q ′ 8 in the expanded form of Figure 2 is as follows: [next]
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Type, application and calculation of grinding process (1)
First, the type and application of grinding process