Challenges in Processing of Iron Ores of India. B. Das & B.K. Mishra CSIR-IMMT, Bhubaneswar

Transcription

1 Challenges in Processing of Iron Ores of India B. Das & B.K. Mishra CSIR-IMMT, Bhubaneswar 1

2 Overview Indian iron ore scenario Low grade/difficult to treat ore Process synthesis/optimization Alternate methods Pelletization Future directions Conclusions 2

3 Iron Ore Scenario Past Present Future Selective mining Scrubbing and classification Sintering Gravity and magnetic separation Sintering & Pelletization Roasting followed by beneficiation Flotation & Pelletization Iron ore production (million tons) FY10 FY11 FY12 FY13 FY14 FY15 * Odisha Karnataka Goa Chhatishgarh Jharkhand Others Total Policy issues: Mining lease Environment Sustainability There are technical issues: Low grade ore utilization Waste treatment Use of secondary resources 3

4 Types of Iron Ore BHJ Hematite Iron ore BHQ Limonite Goethite Hard Ore banded type Flaky/Friable ore Lateritic ore Goethitic ore Black goethite Limonitic ore Secondary sources 4

5 Problems in Low Grade Iron Ore Processing Intimate association of goethite, clay, and hematite -Liberation is a problem Higher amount of ochreous goethite, which contain more alumina compared to massive vitreous goethite Colloform-banded goethite has higher phosphorus contents (P 2 O 5 : %) 5

6 Problems in Low Grade Iron Ore Processing (contd.) Constituents Wt.% Fe(T) 57.5 Fe 2 O Al 2 O SiO LOI

7 Beneficiation of Hematite Sample, Locations Weight, % Fe, % Al 2 O 3, % SiO 2, % Al 2 O 3 /SiO 2 Barbil >1 Concentrate Rejects Barjamada <1 Concentrate Rejects Hospet <1 Concentrate Rejects Barbil <1 Concentrate Rejects

8 Flotation Response of Hematite Hematite Ore: Si:Al>1 Si:Al<1 % Recovery % Fe 54% Fe Preprocessing of ore affect flotation response Quartz containing ores are more suitable for flotation compared to their high alumina counter parts Crystalinity plays a role Reagent Concn., g/t Sample with 42% Fe contains more of quartz with some blue dust Sample with 54% Fe contains Al bearing kaolinite clays 8

9 BHQ ore: Easy to float BHQ is easy to float Anionic & cationic collectors work well Works well in cell (lab and large scale) Hematite Liberation % Liberated BHQ Particle size, µm 9

10 BHQ vs. BHJ Ore: Anionic Flotation Behavior wt.% weight, % Fe, % wt.% weight, % Fe, % ph ph 10

11 Jasper/Quartz derived from the respective ore Dissolution study Silica derived from Top: BHJ Bottom: BHQ Clearly jasper is contaminated with iron which decreases the flotation response Silica in BHQ has no trace of Fe 11

12 BHJ Ore Coarse and fine quartz grains and fine intergrowth of quartz with hematite Disseminated minute hematite grains are within jasper 12

13 Difficult to treat ores Reagent Products Weight, % Fe, % Anionic Cationic Float Non-float Float Non-float Ore Characteristics Goethitic ore Some amount of limonite is present Small amount of hematite present within goethite Collector selection is critical to float such type of ores 13

14 Difficult to treat ores (contd.) Hematite-ring structures Liberation is a problem 14

15 Process Synthesis & Plant Optimization 15

16 Mineral Liberation 16

17 Mineral Liberation 17

18 Mineral Liberation 18

19 Image Processing 19

20 Volumetric Grade 20

21 Modelling & Simulation Plant Scale Testing Site-Specific Identifies Upgrade Options Explicitly Defines Reliability Process Modeling Range of Options with Varying Sophistication Requires Differing Degrees of Knowledge Millsoft Modsim Data Interpretation 21

22 Process Modeling and Simulation Approach Mill Type: AG ( m) Mill Speed: 12.7 rpm Lifter : B H θ // Lifter type: Hi-Lo; 40 rows Power draw (kw): 3779 No. Impacts > 10J : 1577 No. Impacts > 5 J : 4926 Comments: 22

23 Ball mill Final Product Cyclone Bank Jig Reject ( Non-magnetic) Magnetic separator Spiral cluster Ball mill Thickener Process Synthesis 23

24 Ball Mill: DEM Simulation m dv dt = f c + f d + fb + mg B.K. Mishra, International Journal of Mineral Processing, 71(1-4), 73-93,

25 Jigging Fluidization liquid ma y + m ( a y a ) = F + mg F f d b A.K. Mukherjee, B.K. Mishra, International Journal of Mineral Processing, 81(3), ,

26 Spiral Concentrators Volume of fluid (VoF) model Momentum balance equation Mass balance equation Tracking of particles Secondary flow along the radial direction of the spiral is responsible for separation of heavier particles from lighter particles of same size and larger particle from smaller particles of same density. a b c d e a b c d e B.K. Mishra, Alok Tripathy, International Journal of Mineral Processing, 94(3-4), , Swati Mohanty and B.K. Mishra, CFD Simulation of Liquid Flow on a Spiral Concentrator. Paper presented in IMPC-2012, New Delhi

27 Wet High Intensity Separator Experimental set-up Contour of the square of the strength of the magnetic field, A 2 m _2 Concentration on an iso-surface at z = 0.1 m. S. Mohanty, B. Das and B. K. Mishra, A Preliminary Investigation into Magnetic Separation Process Using CFD, Minerals Engineering, 24, ,

28 Fluidized bed find wide application in industries because of better fluid solid contact. Suitable for feed with wide size distribution and exothermic reaction Velocity of gas decreases with increasing cross sectional area Larger particles at the bottom are lifted by the fluid at a higher velocity Lighter particles at the top are prevented from getting entrained Fluidized bed Applied Mathematical Modelling 35 (2011)

29 Alternate Techniques Reduction roasting followed by magnetic separation Microwave-assisted heating and reduction Colloidal magnetic carrier technology Liberation Shock-plasma treatment HPGR Ultrasonic Use of sea water 29

30 Reduction Roasting Some low grade ores are not amenable to conventional treatment e.g. goethitic, limonitic, and banded ores Reduction roasting allows phase transformation which favors separation 45% Fe Exp. No. Reduction time Reductant conc. Temp Fe Grade Reco. hr % 0 C % %

31 Hematite Ore (52% Fe) 31

32 Microwave Heating Microwave: non-contact heating; rapid & material selective heating; heating starts from interior of the material body Treatment of ores with complex mineralogy to enhance the liberation Microwave assisted grinding Carbothermal reduction of oxide ores Roasting & Leaching Grade, % % C Feed grade: 48% Fe Grade Recovery Time, min Recovery, % % Reduction W Time (s) 873 K 973 K 1073 K 573 K 673 K 773 K 750 W 32

33 Magnetic Carrier Technology Hematite Separation can be achieved at a lower Magnetic field strength. Grade, % Grade-Slime with OCM Recovery-Slime with OCM Magnetic Intensity, kg 33 Recovery, %

34 High Voltage Pulse Assisted Breakage Comminution assisted by highvoltage pulses Selective fragmentation at grain boundaries and better liberation Generates a coarser product (less fines) Enhanced liberation at coarser sizes PSD curves of the products comminuted mechanically and electrically for copper sulphide-gold ore particles in a mono feed size of mm. Equipment used: SelFrag Wang et al., Miner. Eng.,

35 High Pressure Grinding Rolls HPGRs were first applied in More than 10 HPGRs operate in pellet plants in Sweden, Brazil, India and Russia. Configurations for comminution circuits that utilize HPGR technology Replacing crushing and pre-grinding stages (Los Coloradosplant, CMH, Chile, Empire iron ore, US) Replacing AG/SAG grinding SNIM, Zouerate iron ore, Mauretania Regrinding stage for surface generation for pelletizing(kudremukh) Phosphate ore, (RSMML, Udaipur) Retro-fit to an existing plant 35

36 HPGR test for lead zinc ore Triple pass HPGR product FEED HPGR products exhibits higher Zn & Pb recoveries as compared to conventional grinding by ball mill. 36

37 Sea Water in Mineral Processing The use of inorganic electrolytes in flotation, is known as Salt Flotation It is not widely developed because of their corrosive properties but today shortages of fresh water has forced several mills to conduct flotation in sea water Sea water is a frother since inorganic salts are known to raise the surface tension of water Elements Concentration (mg/l) Sea water Fresh water *ph Na Mg P K Ca Cr 0 0 Mn Fe Co Ni Cu Zn Cd Pb Cl

38 Use of Sea Water Sea water Structure breaker Structure former Usage Graphite beneficiation Settling of iron ore slurry red mud Gravity separation using spirals Viscosity, Pascel-sec Fe, rec.% normal water sea water ph 38

39 Pelletization Existing: 54 Mt To be installed: 73 Mt 39

40 Pelletisation Process Raw material preparation Green pellet formation Induration Drying Preheating Firing Cooling High LOI High Blaine Water Spray Iron Ore Feed Pellets Water Zone Scraper Ore Feed Zone Feed movement on the disc 40

41 Low Grade Indian Iron Ore Fragile nature Liberation size < 200 micron High Blaine No. Goethite Kaolinite High LOI Flotation as a part of beneficiation process Hydrophobic nature of iron ore concentrate 41

42 Pelletisation Kinetics Effect of LOI B. K. Mishra, C. Thornton, and Dhaksha Bhimji Computer simulation of particle agglomeration using the discrete element method, Minerals Engineering, Vol. 15, No.1-2, pp ,

43 Relationship between compression strength and firing temperature 43

44 Kiln Design Green pellets (10 18 mm) Downdraft Oil firing Oil firing Rotary Kiln Rotary cooler Preheating zone Induration zone Cooling zone Hardened pellets Stack 44

45 Future Direction: Need to develop a compressive utilization plan for Indian iron ore < 50% Fe 50-55% Fe 56-60% Fe 45

46 Conclusions Low grade ore processing has been a challenge particularly with respect to presence of goethite, clay, LOI, and intermixing of phases Care should be taken from accurate process synthesis and optimization Alternate techniques must be pursued to achieve suitable concentrate Agglomeration of concentrates must be carried by considering the nature of the ore Finally, a comprehensive method for optimal utilization of difficult-to-treat mineral resources must be determined 46

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