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Minerals Engineering 71 (2015) 2126

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Minerals Engineering

journal homepage: www.elsevier .com/locate /mineng

Development of a high gradient permanent magnetic separator (HGPMS)

http://dx.doi.org/10.1016/j.mineng.2014.10.0090892-6875/ 2014 Elsevier Ltd. All rights reserved.

Corresponding author.E-mail address: [email protected] (S. Zeng).

Shanglin Zeng a,, Weilong Zeng a, Liuyi Ren b, Dengqi An a, Huiyue Li aa Changsha Research Institute of Mining and Metallurgy, 966 Lushan South Road Changsha, Hunan 410012, Chinab College of Resources and Environment Engineering, Wuhan University of Technology, Wuhan 430070, China

a r t i c l e i n f o

Article history:Received 18 June 2014Accepted 14 October 2014Available online 27 November 2014

Keywords:High gradient permanent magneticseparatorSeparating cylinderIlmenite

a b s t r a c t

An innovative high gradient permanent magnetic separator (referred here as ZCLA HGPMS) was devel-oped for recovering weakly magnetic minerals. Effect of key operating variables on the separation perfor-mance of a full-scale ZCLA HGPMS for recovering ilmenite from Pan Steels Midi Concentration Plant wasinvestigated. Results indicated that the rotation speed and slope of the separating cylinder played a majorrole in enhancing the concentrate grade and titanium recovery. A titanium recovery of 80.8% with a con-centrate grade of 19.6% was obtained by ZCLA-U500 400 HGPMS at 7.0 t/h feed volume. While theZCLA-U950 1800 HGPMS recovered of 77.5% at a concentrate grade of 19.5% at 30 t/h feed volume.These results outperformed the vertical ring high gradient magnetic separator installed in the plantdue to achieving higher separation efficiency through containing and no separation matrix that can clogwhile utilizing less energy all reason why the ZCLA HGPMS was developed.

2014 Elsevier Ltd. All rights reserved.

1. Introduction

Magnetic separation techniques are the simplest method toseparate magnetic from nonmagnetic materials. They have a vari-ety of applications in different industries such as: mineral benefi-ciation, food, textiles, plastic and ceramic processing industries(Veranda et al., 2013). The first attempt to apply permanent mag-nets to the dressing of magnetite ores was back in the 17th centurywith fuller a patenting the separation of iron ore using a magnet in1792 (Derkach and Datsuk, 1947).

Since the early 1990s, the development of rare earth permanentmagnet materials has greatly rekindled the research and develop-ment of magnetic separation technology and equipment using per-manent magnets. High gradient magnetic separation (uses anapplied electric field to generate magnetism) as an effectivemethod for recovering fine weakly magnetic particles separationhas undergone dramatic developments, and has also achievedextensive application during this time (Svoboda and Jujita, 1987).However, conventional electromagnetic high gradient magneticseparators greatest challenges to overcome when applied to treatmetallic minerals such as hematite are the after matrix cloggingand high energy consumption (Zeng and Zeng, 2009). This is whythe ZCLA HGPMS was developed to solve these issues of highenergy consumption by utilizing the magnetic force generatedfrom permanent magnets and possessing no matrix that could clog.

2. Experimental

2.1. ZCLA HGPMS and its principle

The ZCLA HGPMS consists of permanent magnet, separating cyl-inder, support platform and drive (Fig. 1). As shown in Fig. 2, themagnetic system is the core of the ZCLA HGPMS. It uses high per-formance rare-earth permanent magnet materials to generate therequired magnetism for the separation based on the properties ofmagnet and the characteristics of particle size being beneficiated.The magnetic system is fixed outside the separating cylinder: Thepoles face is concave, producing a concave magnetic field. Betweenthe two main poles and auxiliary poles, extrusion magnetic polesare formed, enhancing the magnetic field intensity of magneticpole surfaces which we call the magnetic system. Separating cylin-der adopts the permeability stainless steel materials. The magne-tism permeates through the stainless steel separating cylinderwhile the permanent magnetic medium is installed inside the cyl-inder, which improves the recovery rate of magnetic materials.

By adopting the earth permanent magnetic materials to makingspecial combination, the magnetic system of ZCLA HGPMS formedan introverted type of magnetic circuit structure. Compared withthe open counterpart, its magnetic pole face reserved for concavearc, and the distribution of magnetic field is similar to a semiclosed magnetic system, which increases the depth and intensityof magnetic field (Fig. 3). The surface magnetic field of magneticseparation drum reaches 0.9 T.

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Fig. 2. Separation principle of ZCLA HGPMS: 1 = magnetic drum, 11 = iron yoke, 12 = separating cylinder, 13 = the main magnetic system, 14 = deputy magneticsystem, 4 = concentrate trough, 10 = feed device.

Fig. 3. Magnetic field intensity with the same magnetic materials and differentmagnetic field magnet structure.

22 S. Zeng et al. / Minerals Engineering 71 (2015) 2126

When the separator is in operation, feed materials are intro-duced into the separating cylinder from the feed trough. A non-homogeneous magnetic field is produced in the separating cylinderby the fixed magnetic system. Magnetic minerals are attractedclose to the cylinder by the magnetic force, and are transportedto the top of the separating cylinder as it rotates, and dischargedwith the assistance of flushing water to concentrate trough. Thenon-magnetic minerals pass through the cylinder and dischargesout the non-magnetic discard launder.

The main parameters of the separator are listed in Table 1.

2.2. Property of ore samples

The ilmenite concentrate from the vanadic titanomagnetite oreof Panzhihua in Sichuan province, China, is the primary source fortitanium dioxide in China. It accounts for more than 90% of the tita-nium resource in China and over 35% globally (Wu et al., 2011), andregarded as a strategically important titanium reserve. This tita-nium ore has a relatively high Fe and TiO2 grade. A complicatedflowsheet combining gravity, magnetic separation, flotation andleaching processes are be used to extract the TiO2 and Fe valuesfrom the ore (Belardi et al., 1998; Li et al. 2006, Li and Yang2011). From November 7 to December 26, 2011, on-site tests usingthe ZCLA-U500 400 HGPMS were carried out in Pan Steels MidiConcentration Plant.

The feed assay is shown in Table 2 with the mineralogical com-position presented in Table 3. The target mineral, TiO2 is containedin ilmenite, titanomagnetite and silicates and has a feed concentra-tion of 9.11%. The main gangue mineral in the ore is silica (SiO2)with a content of 34.43%.

2.3. Test conditions

The optimum process parameters for the ZCLA-U500 400HGPMS were investigated though changing the rotating speed ofcylinder, slope of cylinder, feed rate, and tailings rinse water test.With the optimal parameters used for the production run. Due tothe limitation of plant operating conditions, the feed concentrationwas kept at 25% solids due to limitation of the plant operating sys-tem. During the test, a sample was taken every hour while four

Fig. 1. The chart of ZCLA HGPMS: 1 = magnetic drum, 2 = concentrate water pipe, 3 = bull gear, 4 = concentrate trough, 5 = concentrate discard launder, 6 = tailings waterpipe, 7 = tails or non-magnetic discard launder, 8 = tilt platform, 9 = rotary bearing bracket, 10 = feeding trough, 11 = magnetic cylinder brackets, 12 = feed tube mountingbracket, 13 = inlet box installation, 14 = magnetic medium of spacing.

Table 1Parameters of ZCLA HGPMS.

Parameters ZCLA-U500 400 ZCLA-U950 1800

Cylinder diameter (mm) 540 950Magnetic field intensity (T) 0.90 0.90Power (kw/h) 1.5 7.5Feed size (mm) 05 05Feed solid density (%) 1050 1050Slurry throughput (m3/h) 1530 80150Ore throughput (t/h) 510 5080Mass of machine (t) 3 8Dimension of

machine(L W H) (mm)1800 1500 1700 4000 2200 2200

Table 2Chemical composition of material.

Compound TFe TiO2 V2O5 SiO2 Al2O3 CaO MgO MnO

Content% 14.39 9.11 0.072 34.43 12.08 9.65 8.43 0.22

Table 3Phase analysis of titanium of material.

Mineral Ilmenite Titanomagnetite Silicate Total

Content of TiO2 (%) 7.63 0.42 1.06 9.11Distribution of TiO2 (%) 83.75 4.61 11.64 100.00

Fig. 4. Effect of rotation speed of cylinder on performance: (1) feed concentra-tion = 25.00%, (2) magnetic medium of spacing = 3 mm, (3) treatment capac-ity = 6.25 t/h, (4) slope of cylinder = 10, (5) closed tailings rinse water.

Fig. 5. Effect of slope of cylinder on performance: (1) feed concentration = 25.00%,(2) magnetic medium of spacing = 3 mm, (3) treatment capacity = 6.25 t/h, (4)rotation speed of cylinder = 15 r/min, (5) closed tailings rinse water.

S. Zeng et al. / Minerals Engineering 71 (2015) 2126 23

samples were taken for the analytical sample. The results of thesefour analytical samples were averaged to given that result for agiven parameter.

2.4. Evaluation method

The concentrate grade, titanium recovery and separation effi-ciency were used for evaluating the separation performance. Tita-nium recovery and Separation efficiency were calculated as.

e ba hab h 1

E e 1 abM bbbM a

2

where a is the feed grade, is the concentrate grade, e is the titaniumrecovery of concentrate, bM is the maximum titanium grade ofilmenite mineral (50% TiO2), E is the separation efficiency.

3. Results and discussion

3.1. Effect of rotation speed of cylinder

The effect of rotation speed of cylinder in the separating zone ofthe ZCLA-U500 400 HGPMS was first studied, with the separatorat a feed solid content of 25%, treatment capacity of 6.25 t/h, andmagnetic medium of 3 mm spacing, respectively. As shown inFig. 4, the rotation speed has a very significant effect on the tita-nium recovery of concentrate product and separation efficiency.Both recovery and separation efficiency increased with increasingrotation speed. A maximum recovery and separation efficiencygained at the rotation speed of 17 r/min. Further increasing therotation speed resulted in reduced recovery and separation effi-ciency. On the other hand, the concentrate grade was found virtuallyindependent of the rotation speed of the cylinder. The rotation speedof cylinder determines the retention time of the ores in the separat-ing cylinder, thus posing a significant impact on the separation

performance of the separator. As can be seen from Fig. 4, a rotationspeed of 15 r/min was suitable for the tested minerals. A too slowrotation speed of cylinder, nevertheless, would inevitably decreasethe solids throughput of the separator.

3.2. Effect of slope of cylinder

The separation results of the ZCLA-U500 400 HGPMS appliedto the material as a function of the slope of the cylinder is shown inFig. 5. It can be seen that slope of the cylinder was an important

24 S. Zeng et al. / Minerals Engineering 71 (2015) 2126

variable in determining the titanium recovery and the separationefficiency of magnetic product. The recovery started to decreasewhen the slope of the cylinder was higher than 12. Based on theresults in Fig. 5, the optimal slope of the cylinder was set at 12for all proceeding tests.

Adjusting the slope of the cylinder would cause a change in flowvelocity of the slurry. The greater the slope of the cylinder, the fas-ter the slurry flow velocity in the cylinder. As shown in Fig. 5, theilmenite recovery decreased as the slope of the cylinder increased.This decrease in the recovery was due to the fact the flow velocityof the slurry in the cylinder is too fast to recover the ultrafine orpartially liberated ilmenite minerals so were washed out whenthey are subjected to stronger hydrodynamic forces against rela-tively weaker magic capturing forces. At a cylinder slope of 12, aconcentrate grade of 17.02% and a titanium recovery of 86.02%were obtained for the Panzhihua ilmenite.

Fig. 6. Effect of treatment capacity on performance: (1) feed concentra-tion = 25.00%, (2) magnetic medium of spacing = 3 mm, (3) slope cylinder = 12,(4) rotation speed of cylinder = 15 r/min, (5) closed tailings rinse water.

3.3. Effect of feed rate

As shown in Fig. 6, the titanium recovery decreased as the feedrate increased. At a slow feed rate, the ZCLA HGPMS could capturealmost all magnetic mineral particles, resulting in a high recovery.As the feed rate increased more mineral particles get into the sep-arating cylinder for a given time. As the feed rate increased therewas more magnetic particles to recover and due to the units fixedmagnetic intensity only the first layer of the magnetic mineralscould be captured as concentrate product. Along with hydrody-namic and mechanical forces the recovery and separation effi-ciency reduced with increasing feed rate. Surprisingly that theconcentrate grade did not change with additional increase in feedrate. Based on the results in Fig. 6, it is apparent that a feed rate of7.0 t/h was ideal to be used in subsequent tests, using the ZCLA-U500 400 HGPMS separators.

Fig. 7. Flow sheet of the commercial comparison tests of Slon-2000/1500 withZCLA-U950 1800.

3.4. Effect of tailings rinse water

In ZCLA HGPMS separators tailings rinse water was installed toimprove the quality of magnetic products by losing the magneticmedia matrix and by washing away non-magnetic solids trappedin the captured magnetic particles. Therefore, adding tailings rinsewater can generally give higher concentrate grades. There was noflow meter installed in ZCLA-U500 400 HGPMS, we could onlycompare the results with (or opened)/without (or closed) tailingsrinse water. According to the separating results in Table 4,whenfeed concentration (25%), magnetic medium of spacing (3 mm),

Table 4Comparison tests with/without tailings rinse water.

Tailings rinse water TiO2 Grade (%)

Feed Concentrate Tailings

Closed 10.52 17.02 3.14Opened 10.51 20.15 3.72

Operating conditions: (1) feed concentration = 25.00%, (2) magnetic medium of spacitreatment capacity = 7.0 t/h.

Table 5Performance of ZCLA-U500 400 HGPMS under optimum conditions (including operation

Separator TiO2 grade (%)Freed Concentrate Tailings

ZCLA-U500 400 HGPMS 10.81 19.56 3.8

Operating conditions: (1) feed concentration = 25.00%, (2) magnetic medium of spacitreatment capacity = 7.0 t/h, (6) opened tailings rinse water.

slope of cylinder (12) and rotation speed of cylinder (15 r/min.)were kept optimum adding tailing rinse water by turning on tail-ings rinse tater increased concentrate grade (from 17.02% to20.15%), but decreased recovery (from 86.02% to 79.23%). However,the overall separation efficiency still increased (from 41.61% to

Weight (%) Titanium recovery (%) Separation efficiency (%)

53.17 86.02 41.6141.33 79.23 47.99

ng = 3 mm, (3) slope cylinder = 12, (4) rotation speed of cylinder = 15 r/min, (5)

data without using the HGPMS).

Weight (%) Titanium recovery (%) Separation efficiency (%)

44.48 80.48 45.93

ng = 3 mm, (3) slope cylinder = 12, (4) rotation speed of cylinder = 15 r/min, (5)

Fig. 8. ZCLA-U950 1800 HGPMS in Pan Steels Midi Concentration Plant.

Table 6Performance comparison of ZCLA HGPMS and SLon HGMS under optimum conditions.

Separator Process TiO2 Grade (%) Weight (%) Titanium recovery (%) Separation efficiency (%)

Feed Concentrate Tailings

ZCLA HGPMS 10.60 19.52 4.12 42.09 77.49 44.93

Slon HGMS Roughing 10.77 16.83 3.80 53.49 83.59 38.36Concentration 16.83 20.16 6.20 76.15 91.21 22.71

Total 10.77 20.16 4.32 40.73 76.24 45.26

Slon-2000/1500 HGMS operating conditions: magnetic induction = 1.0 T, pulsating stroke = 12 mm, pulsating frequency = 300 min1, feed throughput = 30 t/h, feed solidsdensity = 25%.ZCLA-U950 1800 HGPMS operating conditions: magnetic induction = 0.9 T, slope cylinder = 12, rotation speed of cylinder = 15 r/min, tailings rinse water, feed through-put = 30 t/h, feed solids density = 25%.

S. Zeng et al. / Minerals Engineering 71 (2015) 2126 25

47.99%). Therefore, the intensity of tailings rinse water has to becontrolled to ensure the removal of non-magnetic particles withminimal effect on the magnetic solids.

3.5. Comparison of separation performance

Table 5 shows the results of ZCLA-U500 400 HGPMS for thatwas operated continuously for 30 days in Pan Steels Midi Concen-tration Plant with under optimal operating conditions. The resultsshowed the ZCLA-U500 400 HGPMS achieved excellent results,with 80.48% recovery at a concentrate grade of 19.56% TiO2.

Due to the excellent performance of the ZCLA-U500 400HGPMS, in 20102011, a ZCLA-U950 1800 HGPMS was installedin magnetic separation process of Pan Steels Midi ConcentrationPlant. The results were compared with those of the vertical ringhigh gradient magnetic separator (Slon-2000 HGMS and SLon-1500 HGMS). (as shown in Figs. 7 and 8). The optimum separationresults are illustrated in Table 6. It is clear that similar or evenslightly better separation performance could be obtained by asingle stage separation using the ZCLA-U950 400 HGPMS, as

compared with the two-stage separation using the SLon-2000/1500 HGMS. The test results demonstrated that the ZCLA HGPMSis effective in processing Panzhihua ilmenite ores.

4. Conclusions

The ZCLA HGPMS method, which combines a magnetic systemformed outside the separating cylinder with the ore slurry feedinginto the separating cylinder, presents an innovative HGMStechnology.

The rotation speed and slope of separating cylinder are operat-ing controlling variables that affect the concentrate grade and tita-nium recovery. For Panzhihua ilmenite ores, there was an optimumof rotation speed and slope of separating cylinder in which themaximum separation efficiency was achieved.

The ZCLA HGMPS is a new generation of continuous HGMS witha higher beneficiation ratio, without matrix clogging. The equip-ment is suitable for processing ilmenite, hematite, limonite andother weakly magnetic minerals.

26 S. Zeng et al. / Minerals Engineering 71 (2015) 2126

Acknowledgements

The authors gratefully acknowledge Changsha Research Insti-tute of Mining and Metallurgy for financial assistance.

References

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Li, C., Liang, B., Guo, L.H., Wu, Z.B., 2006. Effect of mechanical activation on thedissolution of Panzhihua ilmenite. Miner. Eng. 19 (14), 14301438.

Svoboda, Jujita, 1987. Magnetic Methods for the Treatment of Minerals.Developments in Mineral Processing.

Veranda, S., Samik, N., Sunil, K.T., 2013. Particle flow modeling of dry induced rollmagnetic separator. Powder Technol. 244, 8592.

Wu, F.X., Li, X.H., Wang, Z.X., Wu, L., Guo, H.J., Xiong, X.H., Zhang, X.P., Wang, X.J.,2011. Hydrogen peroxide leaching of hydrolyzed titania residue prepared frommechanically activated Panzhihua ilmenite leached by hydrochloric acid. Int. J.Miner. Process. 98 (12), 106112.

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Development of a high gradient permanent magnetic separator (HGPMS)1 Introduction2 Experimental2.1 ZCLA HGPMS and its principle2.2 Property of ore samples2.3 Test conditions2.4 Evaluation method

3 Results and discussion3.1 Effect of rotation speed of cylinder3.2 Effect of slope of cylinder3.3 Effect of feed rate3.4 Effect of tailings rinse water3.5 Comparison of separation performance

4 ConclusionsAcknowledgementsReferences