Overview
High-grade iron ore in India's secondary iron deposits. However, where there is the need to remove silica and alumina. Most beneficiation plant using multi-stage hydrocyclone to obtain fine iron ore (-100μm). During the hydrocyclone classification process, a large amount of fine fraction containing clay minerals enters the coarse-grained product with the feed water, thereby reducing the concentrate iron grade. Btadley reported different ways to reduce the amount of water entering the underflow of the hydrocyclone. One of these is to throttle the discharge of the underflow to control the amount of water entering the underflow. Such systems are prone to severe wear and require more maintenance. Another approach is to improve sorting efficiency through multi-stage grading. The multi-stage grading system uses multiple hydrocyclones in series to classify, that is, the underflow of one cyclone sequentially enters the next cyclone. This configuration results in a significant reduction in the fines content entering the coarse product. Rao reports that the Rakha copper concentrator in India uses a two-stage cyclone system for grading. According to this report, the tandem grading system improves the overall grading effect, but this configuration requires an increase in the pumping and pumping system and an increase in maintenance effort. Moreover, this two-stage grading process is susceptible to fluctuations in plant operations.
A third method to improve the classification effect is to inject pressurized water into the cyclone through the end of the coarse product discharge. The pressurized water injection technology was first used in the demineralization of mining products. Kelsall et al. proved that the method has better classification accuracy when used in a 75 mm diameter cyclone. They proved that in normal operation, 48% of the ~10μm fines in the ore were fed into the underflow, and only 11.5% to 10μm of fine particles entered the underflow when using the water injection cyclone. Water injection cyclones are used in the paper industry to increase the recovery of fibers in the overflow. Firth et al. used a water injection cyclone to classify fine coal . Patil et al. reported that the Krebs type water injection cyclone with a diameter of 100 mm has some advantages over the conventional hydrocyclone for the treatment of silica sand. Honaker et al. reported the importance of using a water jet cyclone to classify fine coal. Recently, a water injection cyclone has been used to recover fine particulate matter in the cyclone overflow product. A patented water injection cyclone, commonly referred to as "Cyclowash", is already commercially available.
This study uses this technology to produce iron concentrates with more than 66% iron concentrate, while reducing the iron concentrate silica and alumina content.
A water injection cyclone (Fig. 1, a) can be considered as a common hydrocyclone with a water injection system installed above the grit nozzle. This system therefore has all the features of a conventional hydrocyclone, for example, having a main cylinder connected to an inverted cone, a tangential feed opening in the upper part of the cylinder, and a cylinder protruding outside the cylinder. A vortex overflow tube is located in the center of the vortex shaft and extends to the lower portion of the feed port. The water injection device is linked in the lower part of the common cyclone vertebral body. The water injection device (Fig. 1, b) consists of an outer cylinder and an inner cylinder. There are many tangential water inlet holes on the inner cylinder periphery, and the distance between the inlet holes is equal. The outer cylinder is connected to the reservoir by a pipe. Fresh water is injected into the device at a certain pressure from a tangential line in the inner cylindrical wall. Between the main cyclone and the water injection system is a truncated cone that limits the pressure of the underflow slurry at the water injection hole to prevent the slurry from entering the fresh water jacket through the water injection hole.
The feed slurry is fed into the water injection cyclone through the feed port. The main grading process takes place in the main part of the cyclone. The fine fraction enters the vertical flow around the cyclone shaft and then enters the vortex overflow tube. The coarse fraction enters the underflow slurry after reaching the cyclone wall. The coarse-grained underflow passes through the truncated cone and enters the water injection device. The injected water passes transversely through the underflow slurry, during which the feed water entering the underflow is replaced by injected water, thereby causing the entrained fines to enter the overflow.
Figure 1 Water injection cyclone (a) and water injection device (b)
First, the test
(1) Sample collection and feeding characteristics
Iron ore slurry is collected from a concentrator in India. These samples represent the overflow product of the jaw classifier. These products are enriched in a concentrator by a hydrocyclone in series. These slurries were filtered and then dried at 100 °C. Dry solids (approximately 400 kg) were mixed and 10 kg of each ore sample was prepared using standard sampling techniques. Chemical analysis showed that these dry ore samples contained 63.5% Fe, 2.5% Al 2 O 3 and 3.5% SiO 2 . These samples were then subjected to particle size analysis and chemical analysis to understand the distribution of Fe, Al 2 O 3 and SiO 2 . Figure 2 shows the results of chemical analysis of each particle size. As can be seen from Figure 2, the particle size composition of the feedstock is 75% to 45 μm, 50% to 25 μm. The iron content decreases as the particle size decreases. However, the content of iron in the -25 μm fraction fell sharply to 58.53%, indicating that alumina and silica were enriched in this fraction.
Figure 2 Feeding grade and iron content
â–³-yield; â—-iron grade
(2) Test equipment and test process
Figure 3 is a schematic view of the test apparatus. The test unit consisted of a 200L feed cylinder and a 100L water injection tank, both mounted on a fixed platform. The bottom of the feed cylinder is connected to a centrifugal pump driven by a three-phase 5.5 kW motor. The pump outlet is connected by a pipe to a 100 mm diameter water injection cyclone feed port that is vertically mounted above the slurry drum. The swirl pressure drop was measured by a diaphragm gauge. The pressure drop in the water injection cyclone is kept constant by adjusting the flow rate of the bypass pipe through the control valve.
The dimensions of the vortex overflow tube, truncated cone and grit nozzle are matched to the experimentally designed water injection cyclone. The weighed solids and water were mixed in the feed tank for 10-15 minutes and the solids concentration of the feed slurry was 25%. Fresh water was first injected into the water injection device according to the test design. Thereafter, the feed slurry is fed into the cyclone by opening the control valve, and the return valve is controlled to maintain the feed pressure at 70 kPa. In the steady state (up to 15s), the overflow and the underflow are separately sampled. The samples were filtered, dried and weighed and analyzed for iron, alumina and silica content. By weight distribution, and metal content, the metal balance, and calculating the recovery of alumina and silica removal of iron concentrate.
Figure 3 water injection cyclone test device diagram
(3) Experimental design
In this test, an orthogonal test method was used, which contained 16 tests (2 4 : 2 level, 4 factors), including the water injection flow rate, the truncated cone diameter, the diameter of the grit nozzle and the diameter of the overflow pipe. The level of the factors is shown in Table 1. The diameter of the truncated cone, the diameter of the overflow pipe, the diameter of the grit nozzle, and the flow rate of water injection are represented by A, B, C, and D, respectively. The lower and upper limits studied are as follows:
Table 1 Factors and levels in the test
factor | name | unit | Actual low value | Actual high value | Low level | High level |
A | Truncated cone diameter (TCD) | Mm | 19.05 | 25.40 | -1 | +1 |
B | Overflow tube diameter (VFD) | Mm | 25.40 | 31.75 | -1 | +1 |
C | Sanding nozzle diameter (SPD) | Mm | 22.23 | 26.97 | -1 | +1 |
D | Water injection flow rate (IWR) | L/min | 1500 | 3000 | -1 | +1 |
2 overflow pipe diameter: 25.4 and 31.75 mm;
3 diameter of the sinking nozzle: 22.23 and 26.9 7 mm;
4 water injection flow rate: 1500 and 3000 L/min
In the statistical analysis, the low level is represented by -1 code and the high level is represented by 1 code.
Second, the results and discussion
Table 2 shows the iron grade and recovery of iron concentrate obtained under different test conditions, and the removal rates of alumina and silica. It can be seen from Table 2 that under different operating conditions, the iron concentrate (cyclone underflow product) has an iron grade of 65.2% to 67.9%, an alumina content of 0.31% to 1.33%, and a silica content of 1.39%. ~ 2.40%. The tailings (cyclone overflow product) has an iron content of 40.9% to 45.6%, an alumina content of 8.25% to 13.15%, and a silica content of 10.0% to 13.1%. The recovery of iron was 86.6% to 92.3%. The removal rate of alumina was 54.0% to 89.0%, and the removal rate of silica was 39.6% to 65.0%.
Table 2 Test conditions and test results
test Numbering | Test conditions | ||||
TCD | VFD | SOD | IWR | ||
1 | 25.40 | 31.75 | 26.97 | 1500 | |
2 | 25.40 | 31.75 | 26.97 | 3000 | |
3 | 25.40 | 31.75 | 22.23 | 1500 | |
4 | 25.40 | 31.75 | 22.23 | 3000 | |
5 | 25.40 | 25.40 | 22.23 | 1500 | |
6 | 25.40 | 25.40 | 22.23 | 3000 | |
7 | 25.40 | 25.40 | 26.97 | 1500 | |
8 | 25.40 | 25.40 | 26.97 | 3000 | |
9 | 19.05 | 25.40 | 26.97 | 1500 | |
10 | 19.05 | 25.40 | 26.97 | 3000 | |
11 | 19.05 | 25.40 | 22.23 | 1500 | |
12 | 19.05 | 25.40 | 22.23 | 3000 | |
13 | 19.05 | 31.75 | 22.23 | 1500 | |
14 | 19.05 | 31.75 | 22.23 | 3000 | |
15 | 19.05 | 31.75 | 26.97 | 1500 | |
16 | 19.05 | 31.75 | 26.97 | 3000 | |
test results (%) | |||||||||||
iron | Alumina | Silica | Fe recovery rate | Al goes Removal rate | Si removal rate | UFsol | |||||
RIW% | OF | UF | OF | UF | OF | UF | |||||
1 | 37.2 | 43.1 | 65.8 | 12.0 | 0.69 | 11.0 | 2.0 | 90.7 | 73.2 | 46.8 | 15.3 |
2 | 64.9 | 44.7 | 66.6 | 11.8 | 0.63 | 11.4 | 1.9 | 90.4 | 73.9 | 47.1 | 13.2 |
3 | 56.7 | 44.7 | 66.5 | 12.8 | 0.35 | 10.9 | 1.6 | 89.8 | 86.2 | 54.2 | 25.8 |
4 | 96.7 | 45.6 | 67.6 | 11.0 | 0.33 | 10.6 | 1.5 | 86.6 | 88.5 | 61.5 | 15.2 |
5 | 42.78 | 40.9 | 65.5 | 11.4 | 1.13 | 11.9 | 1.8 | 90.7 | 62.5 | 52.1 | 13.7 |
6 | 69.1 | 44.7 | 65.8 | 10.6 | 1.03 | 12.5 | 1.8 | 86.9 | 69.4 | 60.6 | 8.2 |
7 | 37.6 | 43.3 | 65.2 | 13.0 | 1.33 | 13.1 | 2.4 | 92.6 | 54.0 | 39.6 | 15.9 |
8 | 51.7 | 41.3 | 65.3 | 13.0 | 1.31 | 13.0 | 2.0 | 92.3 | 54.8 | 44.0 | 10.4 |
9 | 44.0 | 45.6 | 66.0 | 10.3 | 1.20 | 11.6 | 1.9 | 91.2 | 54.7 | 45.7 | 25.2 |
10 | 82.4 | 41.8 | 66.8 | 10.4 | 1.13 | 12.0 | 1.9 | 88.0 | 66.2 | 57.3 | 9.9 |
11 | 50.9 | 42.2 | 66.3 | 10.5 | 0.87 | 12.5 | 1.8 | 87.5 | 71.9 | 64.7 | 15.9 |
12 | 71.0 | 43.8 | 66.9 | 10.6 | 0.99 | 12.5 | 1.7 | 89.8 | 64.9 | 56.7 | 9.8 |
13 | 58.1 | 44.1 | 66.8 | 12.3 | 0.33 | 13.0 | 1.5 | 878.0 | 89.0 | 65.0 | 21.1 |
14 | 84.4 | 45.6 | 67.9 | 11.2 | 0.46 | 11.0 | 1.5 | 88.8 | 81.9 | 57.9 | 20.4 |
15 | 52.0 | 44.3 | 66.7 | 10.9 | 0.63 | 11.8 | 1.9 | 89.0 | 76.2 | 53.6 | 19.3 |
16 | 47.0 | 43.5 | 66.9 | 13.2 | 0.61 | 11.7 | 1.7 | 88.0 | 83.2 | 59.6 | 8.8 |
UF-water injection cyclone underflow (iron concentrate)
Rec-recovery rate
Rej-removal rate
UF sol - percentage of solid mass in the underflow
R IW - water injection ratio (injected water flow to underflow water flow ratio)
The test results also show that there is an interaction between the variables. In order to understand the effects of exchange effects between individual variables, the results of the test were statistically analyzed using the commercial Design Expert software. The effects of different variables on iron grade, recovery, alumina and silica removal rates are shown in Table 2.
The general formula used to evaluate individual and interaction effects is:
Yi = α0 + α1A + α2 B + α3C + α4 D + α5 AB + α6AC + α7 AD + α8 BC + α9 BD + α10 CD + α11 ABC + α12 ABD + α13 ACD + α14 BCD + α15 ABCD (1)
Where: Yi-response (i represents iron grade, iron recovery, alumina removal and silica removal); α0 - intercept; α1 ... α15 - model parameters; A, B, C and D- treck diameter, The value of the vortex overflow tube diameter, the diameter of the grit nozzle, and the amount of water injected.
The code values ​​of A, B, C and D can be calculated by the following formula
A=(A R -A a )/(A a -A l ) (2)
B=(B R -B a )/(B a -B l ) (3)
C=(C R -C a )/(C a -C l ) (4)
D=(D R -D a )/(D a -D l ) (5)
Where: A R - the desired level of the diameter of the truncated cone; A a - the average of the high and low levels of the truncated cone diameter; the low level of the A l - truncated cone diameter. B R , B a and B l ; C R , C a and C R ; D a and D l have similar meanings.
Although all the parameters in the model are mentioned for the sake of model integrity, in order to explain the physical mechanism, only the effects of the univariate and bivariate that have a large influence are discussed below.
(1) Effect of variables on water injection ratio (R IW )
In the reinjection cyclone, the main grading takes place in the main cyclone and the secondary grading takes place in the water injection system. In the water injection system, the newly injected water replaces the water in the underflow slurry. In this process, the injected water enters the overflow and the underflow, respectively, and the ratio of the water entering the overflow to the underflow depends on the diameter of the sinking nozzle. The diameter of the truncated cone, the diameter of the overflow tube and the flow rate of the water injection. Accurate quantification of water injection separation is difficult. Therefore, it is a good alternative to use the ratio of water injection flow to underflow water flow to describe the mechanism of classification. Therefore, in this study, the effect of each variable on this ratio (represented by R IW ) is analyzed and then used to describe its effect on other sorting indicators. The R IW values ​​obtained under different test conditions are shown in Table 2.
The water injection ratio varied between 37.2% and 96.7% under different test conditions. The model formula for the water injection ratio is:
R IW =59.2-2.07A+2.97B-7.05C+11.75D+3.83AB-2.19AC+1.78AD-4.80BC+0.65BD-2.36CD+1.20ABC+4.03ABD-0.72ACD-3.09BCD+3.11ABCD (6)
It can be seen from the model constant that the increase in the diameter of the truncated cone and the diameter of the grit nozzle reduces the R IW value. When these variables are operated at a higher level, the water from the feed and the injected water are largely in the underflow, so this value is reduced. The constants before the overflow tube and the water injection flow variable are positive, indicating that as these variables increase, the R IW value increases.
The cross-cone diameter and the diameter of the grit nozzle (AC), the diameter of the overflow pipe and the diameter of the grit nozzle (BC), and the interaction between the diameter of the grit nozzle and the water injection flow (CD) indicate that all interactions with the diameter of the grit nozzle are negative effects. . The exchange effect associated with the truncated cone, for example, the cross-sectional cone diameter and the overflow tube diameter (AB) and the cross-sectional cone diameter and the water injection flow (AD) interaction are positive effects. The interaction between the diameter of the truncated cone and the diameter of the grit chamber should be a negative effect, which indicates that the diameter of the grit chamber has a major influence.
The effects of the variables on the R IW values ​​are used to demonstrate the effect of the variables on concentrate iron grade, recovery, silica and alumina removal rates.
(2) Influence of variables on concentrate iron grade
The iron concentrate grade model formula is as follows. The actual values ​​agree well with the model predictions, with R 2 of 0.98 and a standard deviation of 0.23.
Fe gr =66.3-0.246A+0.509B-0.203C+0.174D+0.160AB-0.189AC-0.159BC+0.188BD-0.189CD+0.217ACD-0.132ABCD (7)
It can be seen from the above formula that in the influence of independent variables, the diameter of the overflow pipe has the greatest influence on the iron grade, followed by the diameter of the truncated cone, the diameter of the grit nozzle and the flow rate of water injection. The overflow tube diameter and the water injection flow are positive effects, which indicates that the iron concentrate grade increases with these variables. The diameter of the truncated cone and the diameter of the sand spout are negative effects, indicating that as these variables increase, the grade of concentrate iron decreases.
Similar to the effect of the water injection ratio, the interactions associated with the diameter of the grit nozzle (AC, BC, and CD) are negative effects, suggesting that while increasing these variables, the iron concentrate grade is reduced. The reduction in iron grade can be explained by the following mechanism:
1. The increase of AC indicates that the size of the truncated cone and the grit nozzle becomes larger, which will shorten the residence time of the feedstock in the main cyclone and the water injection system. In the water injection system, the injected water cleans the underflow slurry;
2. For CD, since the diameter of the grit nozzle and the water injection flow increase simultaneously, most of the injected water enters the underflow, improving the cleaning of the underflow;
3. The effect of the overflow pipe is a positive effect. At the same time, increasing the diameter of the overflow pipe and the grit nozzle (BC) will have a negative effect, which indicates that the influence of the diameter of the grit nozzle is dominant.
The above mechanism can be demonstrated by the decrease in R IW value by an increase in the discharge of the slurry stream through the underflow.
The effect of the combination of the frustum diameter and the diameter of the overflow pipe (AB) is a positive effect, which indicates that as the variable increases, the concentrate iron grade increases. This may be due to the increased diameter of the overflow pipe to increase the amount of clay carried by the overflow. Moreover, when the truncated cone opening is widened, the fine-grained clay can be effectively washed into the overflow due to the increase of the vertical upward flow of the injected water (as can be seen from the positive value of R IW ).
(III) Effect of variables on recovery rate of concentrate iron
The refined iron recovery rate model is as follows. The measured values ​​agree well with the model predictions, with R 2 of 0.99 and a standard deviation of 0.33.
Fe rec =89.3+0.804A-0.405B+1.095C-0.336D-0.246ACB-0.519AC-0.498AD-0.367BC+1.064ACD+0.271BCD-0.351ABCD (8)
It can be seen from equation (8) that among all the independent variables, the diameter of the grit nozzle has the greatest influence on the iron concentrate recovery rate, followed by the truncated cone diameter, the overflow pipe diameter and the water injection flow rate. The increase in the diameter of the truncated cone and the grit chamber increases the iron recovery of the iron concentrate. The effect of the overflow pipe and the water injection flow is a negative effect, which indicates that the iron concentrate recovery rate decreases as the overflow pipe diameter and the water injection flow rate increase.
Interactions between variables The results of the study indicate that the effects of the combination of the diameter of the truncated cone and the diameter of the grit chamber (AB, AC, AD, and BC) are significant. The effect of all these combinations is a negative effect, indicating that increasing the level of these combinations reduces the iron recovery of iron concentrate. An increase in the diameter of the truncated cone or the diameter of the grit chamber indicates that the pores that discharge solids to the underflow are larger, thereby increasing the recovery of concentrate iron.
(4) Effect of variables on the removal rate of alumina and silica
The alumina and silica present in the fine iron ore are derived from clay minerals. In addition, silica is also derived from quartz . Microscopic observation showed that the clay in the feed had a particle size of less than 5 μm and 90% of the silica had a particle size of less than 10 μm. The model formula for alumina and silica removal rates is shown below.
Al rej =71.9-1.59A+9.61B-4.88C+0.95D-1.46AC+0.40AD+1.54CD-2.52ACD (9)
Si rej =54.2-3.41A+1.57B-4.93C+1.44D-1.43AC+1.12AD-1.00BC+1.35CD-2.74ACD (10)
The measured values ​​of the alumina removal rate agree well with the model predictions, with R 2 of 0.99 and a standard deviation of 1.7. Similarly, the measured values ​​of silica removal were in good agreement with the model predictions, with R 2 of 0.98 and a standard deviation of 1.5.
From equation (9), in all independent variables, the diameter of the overflow pipe has the greatest influence on the removal rate of alumina, followed by the diameter of the grit nozzle, the diameter of the truncated cone and the flow rate of water injection. The diameter of the grit nozzle has the greatest influence on the removal rate of silica (formula (10)), followed by the diameter of the truncated cone, the diameter of the overflow pipe and the flow rate of water injection. The overflow tube diameter and water injection flow have a positive effect on the removal rate of alumina and silica, indicating that increasing the overflow tube diameter and water injection flow rate can increase the removal rate of alumina and silica. The diameter of the truncated cone and the grit nozzle produces a negative effect, which indicates that increasing the diameter of the truncated cone and the diameter of the grit nozzle reduces the removal rate of alumina and silica.
The effect of exchanges between variables shows that AC effects are negative effects and AD and CD effects are positive effects. The increase in the diameter of the truncated cone and the sinking nozzle leads to an increase in the entrained clay and other silica-containing minerals in the concentrate due to the increased flow rate of the downward slurry, thus reducing the removal rate of alumina and silica. .
The results of AD interaction studies show that increasing the variables at the same time increases the removal rate of alumina and silica. Simultaneously increasing the diameter of the truncated cone and the flow rate of the water injection will increase the rising flow rate of the injected water, which can be seen by the positive value of R IW (formula (6)) in the model. The vertical upflow in the injection system is capable of flushing clay and fine-grained quartz mineral into the overflow, thus increasing the removal rate of silica and alumina.
Simultaneously increasing the diameter of the grit nozzle and the water injection flow rate (CD) increase the removal rate of alumina and silica.
(5) The variable should be the first to the underflow solid content
The model formula for the solids content in the underflow is as follows:
UF sol =66.3-0.794A+1.870B-0.763C-3.512D+0.789AB-0.261AC+0.560AD-2.478BC+0.538BD-0.641CD+1.717ACD+0.560ABCD (11)
In the independent variables, the water injection flow has the greatest influence on the solids content of the underflow, followed by the diameter of the vortex overflow pipe, the diameter of the truncated cone and the diameter of the grit nozzle. The overflow pipe effect is a positive effect, which indicates that as the water injection flow rate increases, the underflow solid content increases. The diameter of the truncated cone and the grit nozzle reduces the solids content in the underflow.
At the same time increasing the combination of the diameter of the grit nozzle (such as AC, BC and CD) will reduce the solids content in the underflow. The increase in the AC combination indicates that the values ​​of the diameter of the truncated cone and the grit are larger, which facilitates the entry of the dilute slurry into the water injection system and also allows more of the injected water to enter the underflow product. The truncated cone opening is further increased, and the effect of the combination of the diameter of the truncated cone and the diameter of the overflow tube (AB) and the diameter of the truncated cone and the diameter of the truncated cone and the diameter of the overflow tube (AD) is Positive effect.
Third, the conclusion
(1) The material containing 63.0% Fe, 2.5% alumina and 3.5% silica is classified by a water injection cyclone to obtain iron with a Fe grade greater than 66.0% and containing 1.5% alumina and 2.0% silica. Concentrate.
(2) With a water injection cyclone with an overflow pipe diameter of 31.75 mm and a grit nozzle diameter of 22.23 mm, the iron concentrate recovery rate of the iron concentrate can be greater than 85%, alumina and two under the premise of maintaining the above-mentioned concentrate iron grade. The removal rates of silicon oxide are higher than 80% and 50%, respectively.
(3) The statistical analysis of the influence of variables shows that increasing the diameter of the overflow pipe and the water injection flow, as well as reducing the diameter of the truncated cone and the diameter of the grit nozzle can increase the iron grade of the concentrate and increase the removal rate of alumina and silica.
(d) When the diameter of the truncated cone is small, the water injection flow required to obtain the required iron grade is low.
(5) An underflow product (concentrate) with a high solid content can be obtained with a small grit nozzle diameter, a wide overflow pipe diameter, and a low water injection flow rate.
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