Grinding equipment, is the key equipment of beneficiation plant, mill investment and operating costs miner section, the ratio of share of the entire concentrator are great, and the grinding fineness can meet the requirements for the design of processing plant can Achieving design metrics is also decisive, and the ore grindability is an extremely important raw data in the design of the concentrator. However, in practice, we can often see that the productivity of the mill calculated according to the laboratory grindability test results often does not match the actual, which means that the existing laboratory grindability measurement method is imperfect and needs Research improvements in practice.
There are many methods for determining the grindability that have been proposed, and the differences mainly represent the following two aspects:
First, the measurable metrics are different
There are many ways to express the ore grindability, but in general they can be classified into two categories.
The first type is the grindability of the production capacity per unit volume mill, which generally refers to the output per unit time, but also refers to the output per revolution of the grinding machine; and the production quantity refers to the specified feed and product. The amount of ore processed under the particle size refers to the amount of new-200 mesh product, while the other refers to the new production surface-ton (ie, the total surface area of ​​the newborn = specific surface area × tonnage).
The second category measures the grindability of the unit's electricity consumption, that is, the electricity consumption per ton of ore (kilowatt hours/ton) at the specified feed and product size, or the consumption of fresh materials per ton-200 mesh. Electricity consumption (kWh/ton - 200 mesh), or power consumption per kiloton of ore per 1000 cm 2 / cm 3 surface area (kWh / ton -10002 cm / cm 3).
Whether using the first or second type of representation method, it can be divided into absolute method and relative method. The former measures the grindability by the measured absolute value of the unit volume production capacity or unit power consumption, and thus It is called absolute grindability; the latter is the ratio of the unit volume production capacity or unit power consumption of the sample to be tested to the standard sample, and is also called relative wear. Since the grinding conditions of the laboratory grinder and the industrial grinder are far apart, the absolute value is difficult to directly quote, so the relative grindability is currently measured.
Second, different grinding test methods
According to the different grinding test methods, it can be divided into two types: open-circuit grinding method and closed-circuit grinding method.
(1) Unit volume production capacity method
1. Open road grinding method
Take a sample of -3 (2) + 0.15 mm ore (500 or 1000 grams per serving), and grind at different times in a fixed grinding condition, and then use each part of the grinding product separately. Screen (or only use a 200-mesh standard sieve) to screen and plot the grinding time versus the cumulative yield of each sieve (or sieve) in the product to find the desired specimen to be ground. The grinding time T required for fineness (in terms of -200 mesh content or 90% less than a specified particle size).
The unit volume production capacity of the grinding machine, that is, the absolute grindability, shall be calculated according to the amount of ore:
(1)
Where q- is the capacity per unit volume calculated according to the amount of ore given at the specified ore and product size, kg/L;
P-sample original weight, kg;
V-test grinding machine volume, liter;
T-grind to the time required to specify the fineness.
According to the new-200 mesh product, it should be:
(2)
In the formula q-200- according to the amount of new-200 mesh product volume production capacity, kg / liter · hour;
Γ-200-newborn-200 mesh content, %.
When measuring the relative grindability, a standard ore is used as a control. If under the same conditions, the time required to grind the standard ore to a fineness is To, and the absolute grindability is qo or qo-200.
(3)
Since the P, V, and γ-200 are the same when grinding the ore and the standard ore, the calculated relative grindability formula is calculated whether the production capacity is calculated according to the ore or new-200 mesh product.
(4)
Thus, the task of the test is only to find To and T.
Newborn-200 mesh content method
This is the most commonly used method. As shown in Figure 1, if curves 1 and 2 represent the standard ore and the ore to be tested at different times, the grinding product is sieved with a 200 mesh standard sieve. The required content of -200 mesh is x. A horizontal line from x on the ordinate intersects with curves 1 and 2, respectively, and the abscissa of the two intersections is the desired To and T.
Figure 1 Relative grindability measurement curve
90% less than the specified particle size method
Some units in China have also adopted a method of measuring the fineness of grinding by 90% less than a specified particle size when measuring the grindability.
Figure 2 Screening curve of grinding products at different times
(For some reason, the chart is unclear, you can call for free if you need it)
Fig. 2a and Fig. 2b show the results of sieve screening of a certain ore and the ore to be determined at different times. The size of the sieve mesh is 0.3, 0.15, 0.10, 0.074 mm.
As can be seen from the graph, the time required to grind the two ores to 90% less than 0.3, 0.15, 0.10, 0.074 mm (in the figure, 10% greater than each of the particle sizes) is shown in Table 1.
Table 1 Open road grinding to 90% less than the following time required for the following particle size
Mineral sample | Particle size (mm) | |||
0.30 | 0.15 | 0.10 | 0.074 | |
Standard ore Ore to be tested | 4.1 11.3 | 8.5 24.5 | 13.4 31.0 | 20.6 33.0 |
According to formula 1, the unit volume production capacity calculated by the ore amount under different grinding fineness is calculated, that is, the absolute grindability is as shown in Table 2.
Table 2 Capacity per unit volume under different grinding fineness kg/L···
Mineral sample | Particle size (mm) | |||
0.30 | 0.15 | 0.10 | 0.074 | |
Standard ore Ore to be tested | 1.90 0.69 | 0.92 0.32 | 0.58 0.25 | 0.38 0.24 |
Calculated according to formula 3, the relative grinding of the ore to be tested is shown in Table 3.
Table 3 Relative grindability of ore to be tested under different grinding fineness K
Particle size (mm) | 0.30 | 0.15 | 0.10 | 0.074 |
Relatively grindable (K) | 0.36 | 0.35 | 0.41 | 0.63 |
It can be seen from the above that the ore to be tested is much harder to grind than the standard ore, but as the grinding size is reduced, the difference in the grindability is also reduced.
2, closed-circuit grinding assay
After a certain amount of ore of about -3 mm is screened out of the qualified product of the specified particle size, grinding is performed at different times. Closed 10 times at each time. That is, each time the grinding product is screened out after passing the qualified product of the specified particle size, it is returned to the grinding machine for re-grinding, and at the same time, the original part of the qualified product is screened to make up the sieved part, so that the total amount of ore in the grinding machine remains unchanged. As the number of closed circuits increases, the amount of qualified products in the product will gradually increase, but the increase will gradually decrease. After about 10 closed circuits, the process can be basically stable. The cycle load and the wearability index were then calculated using the last two test data.
The cyclic load c can be calculated as follows:
(5)
The average yield of qualified products in the γ-last two grinding products.
The unit volume production capacity of the mill is calculated by the following formula:
(6)
The average yield of qualified products in the γ-last two grinding products.
The relative wearability K is calculated as follows:
(7)
Where q and qo - the absolute grindability of the ore to be tested and the standard ore, ie the capacity per unit volume, kg / liter · hour;
γ and vo - the yield of qualified products in the last two grinding products when the ore and standard ore are closed for grinding at the same grinding time (and thus T = To).
Different grinding time, the amount of sand return will be different, according to the production practice data, select the qualified sand return amount, and then determine the grinding time according to the required amount of sand return, and calculate the grindable time under the grinding time degree.
(2) Unit power consumption method
The unit power consumption method can also be called the unit power method. For example, if the unit power consumption is defined by the power consumption of a ton of raw ore at a specified feed and product size, the unit is kilowatt-hour/ton, but it can be rewritten as kilowatts/hour. The latter definition is It is the power required to grind one ton of ore per hour. The total power of the desired mill can then be calculated based on the throughput of the designed grinding phase. The same is true when calculating the unit power consumption by the amount of new-200 mesh product or surface area.
The grinding test operation is similar to the unit volume production method, but the torque of the mill used can be accurately measured and recorded so that the net power consumption of the grinding can be accurately calculated (total consumption - power consumption at no load) Quantity) or net power.
The calculation of the grindability is based on the third law of breaking, and the equation used is:
(8)
In the formula, W-measured unit power consumption, kilowatt hours / ton, that is, unit power, kilowatts / ton / hour;
Ω-work index, that is, absolute wearability, the unit is the same as W;
P-product particle size, micron;
F-feeding particle size, micron.
Relative griffability refers to the ratio of standard ore to the ore work index to be measured:
(9)
In the formula, W-measured unit power consumption, kilowatt hours / ton, that is, unit power, kilowatts / ton / hour;
Ω-work index, that is, absolute wearability, the unit is the same as W;
P-product particle size, micron;
F-feeding particle size, micron;
Where the "o" refers to the standard ore, the one without the standard refers to the ore to be tested.
If the grinding machine used in the test cannot measure the net power, the ore to be tested and the standard ore can be ground at the same time, and it is assumed that as long as the grinding conditions are the same and the ore size is similar, the electricity consumption is the same when the grinding time is the same. Also equal, thus Wo=W in Equation 9, at which point the relative grindability can be calculated directly from the sieved data (P and F).
Precautions for the measurement of the wearability:
1. Since the relative grindability is measured at present, the standard ore used for comparison must be stable and reliable. Ores of mines with stable ore properties, normal operation, stable and reliable production data, and similar ore properties should be selected as standard ore samples. Professional test research units should also regularly stock a sufficient amount of the same standard ore sample, and do not change it from time to time.
2. Since the relative grindability value is related to the grinding fineness, the selected grinding fineness must be determined according to the design requirements. If the grinding fineness is not finalized during the beneficiation test, the grindability must be calculated separately for several possible particle sizes, and the original curve must be attached directly to the designer. If the production is to adopt a two-stage grinding or stage grinding process in the future, the grinding degree should also be determined in stages during the ore dressing test.
3. Whether it is dry or wet grinding, it should be consistent with industrial production. When using the closed-circuit grinding method, the magnitude of the amount of sand return is consistent with the actual production.
4. The laboratory grindability measurement results cannot be used as raw data for the design of the self-grinding mill .
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