Pelletisation of ferromanganese ore with particle sizes less than 4mm – an introduction

1. Pelletisation of ferromanganese ore with particle sizes less than 4mm – an introduction TC Kruger and JD Steenkamp

2. Introduction • Ferromanganese is produced in a SAF • SAF requires a permeable burden • Pellets are preferred • higher porosity, uniform size and uniform shape • Up to 30 per cent of ore produced is smaller than 3mm (fines) • Large fines dumps are common both at mines and at smelter plants • One process to utilise fines is pelletisation

3. This paper gives an overview of: • the factors relevant to pelletisation in general • the pelletisation of manganese ore fines specifically • reports on initial pelletisation test work conducted on -4mm manganese ore fines

4. Principles • Wetting and nucleation • a binder liquid is added to the feed • individual wet particles ‘stick together’ to form nuclei

5. Principles • Consolidation and growth • nuclei are joined by more fines through collision and further ‘sticking together’ to form a micro pellet • two micro pellets - surrounded by liquid films - are brought into contact with each other • A seed pellet is formed that capture dry and wet particles until the desired pellet size is obtained • Pellet porosity decreases due to the continual impact

6. Principles • Breakage and attrition • Breakage occurs when: • Equilibrium size is reached, and • Binding force can no longer maintain the load. • The surface of the pellet is smoothened by attrition of the sharp edges

7. Pellet growth • Growth pellets is controlled by two properties: • plasticity of the green pellet and • the viscosity of the superficial water layer • Plasticity is controlled by moisture content • The minimum plasticity defines the minimum moisture content required • The minimum moisture content value is material specific

8. Pellet growth • Binder liquid is ‘squeezed’ to the pellet surface • The viscosity of the binder liquid influences the rate • The viscosity has to be low enough for colliding pellets to combine within the time available during collision (uncontrolled growth if too low) • Viscosity of binder liquid is influenced by: • Binder dosage; • Temperature; • Material properties of the binder • Process parameters

9. Processes • Pressure • Briquetting, compaction, tableting • Tumbling • Drum, disc, cone and pin agglomerator • Extrusion • Screw and gear pelletiser as well as pellet mills • Thermal • Sintering, prilling, pastillating and flaking processes

10. Binders • Binders accomplish two important functions in pelletisation, namely: • Makes the moist ore plastic; and • During drying and sintering, the binder holds the particles in the pellets together

11. Binders • Types of binders • Bentonite (0.25 to 2.5 per cent by mass) • Cement (5 per cent by mass) • Lime (5 per cent by mass) • Cane molasses (3 per cent by mass) • Calcium chloride • Silicate or fluorosilicate of sodium

12. Characterisation • Pellet size distribution • Pellet shape • Pellet hardness • Pellet solubility in a liquid i.e. slag • Pellet dispersability in a liquid i.e. slag • Binder addition requirements • Pellet impact strength • Pellet abrasion strength • Pellet attrition index • Pellet compression strength • Pellet reducibility • Pellet porosity

13. Impact strength (drop strength) • Represents its ability to survive multiple drops in material handling systems • Is determined by repeatedly dropping a pellet onto an iron surface from a fixed height until the pellet fractures or chips • Is quantified as the number of drops that a pellet survived before fracture. • A typical value for green pellets is between 5 and 20 drops

14. Compression strength (crushing strength) • The compression strength of a pellet represents its ability to resist compressive forces without breaking • Is determined by placing pellets between two steel plates and evenly applying a measured pressure until the pellet fractures • The compression strength is expressed as the applied pressure in Newton or kilogram per pellet • A typical value for green pellets is between 0.5 and 5 kg per pellet

15. Equipment • Disc pelletiser • Drum pelletiser • Extruder • Pin agglomerator • Briquette making machines • Sintering machines • High-intensity mixers

16. Case studies • Mexico • Purpose of Study • Material Pelletised • Particle Sizes • Equipment / Process • Binder and quantity • Moisture and quantity • Curing / Drying • Firing • Testing • Drop Tests • Cold crushing strength • Tumble index

17. Case studies • Brazil (INCOMI) • Purpose of Study • Material Pelletised • Particle Sizes • Equipment / Process • Binder and quantity • Moisture and quantity • Curing / Drying • Firing • Testing • Drop Tests • Cold crushing strength • Tumble index

18. Case studies • Brazil (University of Sao Paulo) • Purpose of Study • Material Pelletised • Particle Sizes • Equipment / Process • Binder and quantity • Moisture and quantity • Curing / Drying • Firing • Testing • Drop Tests • Cold crushing strength • Tumble index

19. Case studies • India (Visvesvaraya regional college of Engineering) • Purpose of Study • Material Pelletised • Particle Sizes • Equipment / Process • Binder and quantity • Moisture and quantity • Curing / Drying • Firing • Testing • Drop Tests • Cold crushing strength • Tumble index

20. Case studies - comments

21. Trials • Aim • To produce pellets from South African manganese ore fines with sufficient strength to be used in major processing units i.e. in sintering and SAF operations

22. Experimental design • porosity was used as design control variable • literature was used as reference for aim porosity • less than 30 per cent • controlling pellet porosity by controlling the content of very fine material in the mix resulted in high strength pellets • bentonite as a binder • pellets characterised by measuring their compression strength (aim of 5 kg per pellet)and impact strength (a minimum of 5 drops for a green pellet and 20 drops for a dried pellet)

23. Samples • Sample 1 consisted of material smaller than 4mm which represented fines screened from ore at the mines prior to transportation and at smelter plants prior to processing. • Sample 2 consisted of material smaller than 1400 microns; and • Sample 3 consisted of material smaller than 250 microns

24. Porosity • Bulk porosity of the ore was measured using the method of volume displacement

25. Binder Where: • b = bentonite in grams • P = aim porosity in ml • SVb = Swelling Volume of bentonite = 22-26 (ml/2g)23 • m = mass of material to be pelletised in grams • Calculated bentonite content of each pelletising mix was thus calculated as: • Sample 1 – 0.53 mass per cent; • Sample 2 – 0.57 mass per cent; and • Sample 3 – 0.55 mass per cent.

26. Pelletising • 5 kilogram sample of each size fraction • Measured bentonite • Placed in the Eirich RV02 high intensity mixer and mixed for 60 seconds • 1.2m diameter Radicon disc pelletiser • Angle of 35°and a rotation speed of 75 rpm • Pellet diameter was controlled between 10 and 12.5mm

27. Testing • Compression strength: • 30 balls of each sample • Instron Technologies crushing strength machine, model 1011 • Impact strength: • 30 balls of each sample • Drop height of 450mm

28. Compression strength

29. Impact strength

30. Conclusion • Larger particles can be pelletised • Characteristics improved with increase in top size • Results show that pellets produced may have adequate strength for sintering processes • Further work is required to produce pellets suitable for SAF operations

31. Recommendations • Increasing the size range of particles • Increasing the -250 micron material content of pellets in increments; • Expanding the range of binders; • Increasing the range of the quantity of binder added; • Using a single, experienced operator to produce all pellets in the test program; • Characterising pellets by microscopic analyses; • Studying the effect of bulk porosity of pellets on the strength of pellets

32. Acknowledgements • Mr. L Lourens, Manager, Technology and IP, Exxaro Resources, Alloystream • Mr. A Dippenaar; Kumba Iron Ore, R&D Raw Material Technology • Dr. A-M Bonthuys, Independent Contractor (Editor, Translator, Proof reader, Writer) • Mr B Allison, contractor, Exxaro Resources, Alloystream

33. Questions