Y. H . Tang, Y. B. Zhu, J. Q. He
Guangdong Key Laboratory of Mineral Resource Development and Comprehensive Utilization,
Guangzhou Research Institute of Nonferrous Metals, Guangzhou, China
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Abubaker F. Spat
Department of Mining Engineering, AL-Fateh University, Libya Tarabulus Tripoli
ABSTRACT
For its surface features, micro-sized hematite is usually difficult to recover by magnetic separation; especially, the existing high gradient magnetic separator in industry can not utilize collecting matrix with thin silky rods for its property of being easily blocked; the lower size limit for recovery of micro-sized weak magnetic minerals is about 0.019mm, some even is 0.037mm. This paper introduces the application of the combined new technique of water-air joint discharging of concentrate and collecting matrix with different diameter silky rods in the field of recovery of micro-sized hematite by high gradient magnetic separator. The commercial test result for recovery of a certain hematite with size about —0.037mm shows that the recovery can be promoted by 16.8 1% with basically same concentrate grade.
Keywords: Micro-size fraction; Magnetic separation of hematite; Collecting matrix; Water-air joint discharging of ore
FOREWORD
In recent years, China has made amazing achievements in the separation of refractory micro-sized hematite; the technique of high intensity magnetic separation (HIMS for short) and reverse-floatation by anion collector has greatly promoted the quality of iron concentrate, meanwhile, the recovery is also ensured. Even so, more than 60% of metals lost in tailings are of particle size of —0.019mm; likewise, particles of —0.037mm also lost a lot. This phenomenon exists in the hematite ore dressing plants owned by several large sized national iron and steel companies, such as Meishan Iron Mine of Baoshan Iron and Steel Corp., ore dressing plant of Hainan Iron and Steel Company, ore dressing plant of Jiuquan Iron and Steel Corp. (Tang, 2005), Kunming Shangchang ore dressing plant and East Anshan ore dressing plant of Anshan
Iron and Steel Company, etc.. The reason for the difficulty in recovery of micro-sized hematite is the high production cost of direct floatation technology and the lower size limit for HIMS-flotation technology. The lower size limit of flotation recovery is 0.010mm; if crude ore is processed by floatation without pre-concentration, it will cause large consumption of flotation reagents, high production cost and indistinctive economic benefits; if HIMS is added ahead of floatation, it not only can enrich the feed ore for floatation, but also has the effects of de-sliming, hence decreasing the total production cost. Nevertheless, up to now, the lower size limit for recovery of weak magnetic minerals by HIMS is usually 0.019mm both at home and abroad.
The theoretic lower size limit of recovery by HIMS is related to the kinds of collecting matrix adopted and the size of silky rods (Changren Wang, 1985). The thinner the rod size, the smaller the lower size limit of recovery; while, if a fine collecting matrix is used, it is difficult to discharge concentrate (magnetic products), and the magnetic materials are easy to be accumulated in collecting matrix, causing decrease in separation effects of equipment.
In allusion to the above problems, this paper uses combined new technique of water and air joint ore-discharging and collecting matrix with different diameter silky rods in high intensity magnetic separator to recover micro-sized hematite.
WATER-AIR JOINT CONCENTRATE
DISCHARGING TECHNIQUE
The existing high intensity magnetic separators solely use water flushing to discharge the concentrate; as the collecting matrix is composed of several layers of tight rods and nets, therefore, large sum of water should be used in flushing to enhance the discharging effects. Still, there are parts of magnetic materials attached on collecting matrix and can not be flushed out clearly. This part of concentrate which is not flushed out will cover the effective surface of collecting matrix, if a great deal of flushing water is used to discharge the concentrate, the pulp will become very dilute, causing waste of water resources and difficulties in next stage of operation as well as possible necessary thickening operation when its density can not meet the requirements. When large-sized equipment utilizes fine collecting matrix to recover micro-sized weak magnetic materials, this kind of problem will become extremely obvious; the more the layers of collecting matrix used in large-sized equipment, the bigger their thickness; in this case, in order to ensure the efficiency for concentrate flushing, the quantity of water should be increased, and the rotation speed of separation ring should be decreased, which means the corresponding decrease in the throughput of equipment.
Be dead against the above technical issues, a structure of concentrate discharging unit combined by water and wind flushing effectively is adopted with its wind speed (about 3300m3/h) being dozens times of water speed (about 100m3/h) (Tang et al., 2007), this type of flux of mixed water-air greatly increases the flushing speed (see Fig. 1), and largely promotes the flushing rate of magnetic materials.
Fig. 1 Comparative chart for discharging ways based on different techniques
Test is made for discharging ways based on different technologies; test results are shown in Table 1.
It is shown from the test results of unit matrix in Table 1 that the adoption of new technique can promote separation index: concentrate weight brought out with each unit matrix is increased about 155g ( increase of 65g before discharging, decrease of 90g after discharging), totally increased by 28.97%; the recovery is also advanced by 28.97% with similar quality of concentrate; the density of concentrate is increased by about 7.30% because of water-saving, which is 2.6 times of previous density; the reason for the increase in concentrate density mainly lies in that the concentrate can be clearly flushed out with much less water; by simplifying operation or easing thickening operation, the concentrate density is increased from originally 4.49% to 11.79%; its pulp volume is decreased by many times; such kind of pulp can be sent directly to next operation without thickening, even if it is required to be condensed further, the amount of pulp entering into operation is decreased a lot.
Table 1 Comparative test results for different discharging ways 1)
COMBINED TECHNIQUE FOR COLLECTING MATRIX WITH DIFFERENT DIAMETER RODS
The collecting matrix used on all high intensity magnetic separators adopts multilayer, relatively compact rods and nets with same specification or plates with opposite teeth. In practical production, the upper limit and lower limit of particle size as well as magnetic property of target minerals among materials processed by high intensity magnetic separators are very wide and uneven. As the magnetic force on a particle placed in magnetic field is proportional to its weight, susceptibility, strength of background magnetic field and magnetic field gradient, therefore, those particles with larger diameters, their weight and susceptibility are also larger; likewise, those particles with smaller diameters, their weight and susceptibility are also smaller. If the magnetic matrix with same specification is adopted, the magnetic force on a particle of target mineral with larger diameter will be quite large, and the magnetic force on a particle of target mineral with small diameter will be quite small. When the strength of background magnetic field is increased to intensify the recovery of particles of target minerals with small diameters, the magnetic force on the particles of target minerals with larger diameter will be very large, and it is easy to form magnetic jams; when the strength of background magnetic field is decreased, the magnetic force on the particles of target minerals with small diameter is too weak for particles to be recovered effectively, which means the applicability of equipment is poor.
In order to solve the above-mentioned problems, following technical program is applied: the distribution of collecting matrix is formed by coarse, medium and thin different silky rods along with the flowing direction of pulp. This distribution may effectively separate out particle group with different diameters and different magnetic properties by high intensity magnetic separator, hence making the efficiency of wet separation for fine, micro-sized weak magnetic minerals by high intensity magnetic separator to be promoted greatly.
COMMERCIAL APPLICATION
Separation principle
When above-mentioned new technique is used to high intensity magnetic separator (Yuhe Tang, et al., 2002), its working principle is as follows:
The pulp is sent evenly into separation space through feed tank (see Fig. 2),because of the action of magnetic force, the mineral particles are attached on the surface of collecting matrix arranged from thick ones to thin ones according to the magnetic property of particles(from strong to weak) and along the direction from top
to bottom. The tailings pulse mechanism is adjusted to ensure the pulse frequency and peak value to be relatively small, in this case, the driving force of fluid produced is small, the magnetic force on extremely weak magnetic and non-magnetic particles is extremely small, the driving force of fluid on the particles is greater than the magnetic force, the particles can not be attached by collecting matrix and will enter into tailings’ tank through matrix’s interspaces; the rest particle group absorbed on the surface of collecting matrix will turn with separation rings, the middling pulse mechanism is adjusted to ensure the pulse frequency and peak value to be increased, hence the driving force of fluid produced will be increased, the magnetic force on the relatively weak magnetic particles and locked particles is smaller than the driving force of fluid, the particles will drop from the surface of collecting matrix and will enter into middling tank through matrix’s inter- spaces; as the magnetic force on the attached relatively strong magnetic particle group is greater than the driving force of fluid, particles will be firmly absorbed on the surface of collecting matrix and will continue to rotate with separation rings, and gradually leave the magnetic field entering into discharging area of magnetic products; as the magnetic field in this area is quite week, the magnetic materials flushed out from the surface of collecting matrix by water and air will enter into concentrate tank, becoming magnetic product, hence the effective separation of the particle group with different magnetic properties is realized.
Fig. 2 Sketch map of high intensity magnetic separator. 1 -magnetic winding; 2- collecting matrix; 3-separation rings; 4-speed-down machine; 5-gears; 6-feed tank; 7-middling pulse mechanism; 8-middling tank; 9-tailing pulse mechanism; 10-tailing tank; 11-concentrate tank; 12-upper magnetic pole; 13-lower magnetic pole; 1 4-supporting frame
Property of separated materials (a kind of hematite)
The size characteristics of separated materials (a kind of hematite) is shown in Table 2.
Table 2 Size characteristics of separated materials (a kind of hematite)
COMPARATIVE TEST RESULTS
The comparative test results between high intensity magnetic separators with or without new technique are shown in Table 3.
Table 3 Comparative test results (%)
Table 3 indicates that with same conditions of feed, the adoption of new technique can advance the yield rate of concentrates by 12.85%, with recovery increased by 16.81%.
CONCLUSIONS
From theoretic analysis, the adoption of fine collecting matrix is an effective way to promote the recovery of micro-sized hematite beneficiation.
The unit test shows that as compared with normal technique, the adoption of water and air flushing technique can increase the flushing rate from 67.29% to 85.83%(18.54% increase), and upgrade the concentrate density from 4.49% to 1 1.79%(7.30% increase).
The comparative results of commercial application indicate that by adoption of the high intensity magnetic separator which utilizes new technique of water-air mixed flushing and collecting matrix combined with coarse, middle and fine different diameter silky rods, the yield of concentrate is increased by 12.85% with recovery increased by 16.8 1%.
REFERENCES
Tang X L, 2005.Research for optimization of technological flow-sheet of HIMS in the Mill of Jiuquan Iron and Steel Company Metallic Mine, (1): 34-38.
Tang Y H, He and Zhao M, et al., 2007.A Kind of High Gradient Magnetic Separator (Patent Application Number: 200610132432.3), Public #: CN1994578A, date of being published 11th July 2007.
Tang Y H, Xiang F Z, He J Q, et al., 2002.A Double Frequency and Vertical Ring Pulse High Gradient Magnetic Separator (Patent Number: ZL 02 1 14994.1), Application date of patent: 22nd March, 2002.
Wang C G, 1985.Magnetic and Electrical Beneficiation. Beijing: Metallurgy Industry Publishing Company.
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