Pelletisation of ferromanganese ore with particle sizes less than 4mm

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

• TC Kruger and JD Steenkamp

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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

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• 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

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Principles

• Wetting and nucleation
• a binder liquid is added to the feed
• individual wet particles stick together to form
  nuclei

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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

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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

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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

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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

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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

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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

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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

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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

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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

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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

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Equipment

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

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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

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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

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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

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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

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Case studies - comments
Mexico2 Brazil (INCOMI)3 Brazil (University of Sao Paulo)4 India (Visvesvaraya regional college of Engineering)5
Comments Wider size distribution of feed materials yields higher pellet strength. This was achieved by mixing the ore with off gas dust in a ratio of 21. The first commercial plant in the world to successfully produce pellets from manganese ores. Bentonite increased the drop test values (to 30) and the dry compression values by 100. Notes were made of the effect of particle sizes on the results obtained In general, the smaller particles performed better than the larger particles Larger particles required more water for pelletising and Larger particles are more suitable to bentonite but have on average lower strengths. Increasing the bentonite content improved pellet properties (commercial limit 1.5 mass per cent). Slip of material indicated the optimum moisture content. Pellets opening due to centrifugal forces indicated insufficient moisture content. Particle size distribution was the dominating factor for good strength. Large contact surfaces (small particle sizes) and capillary forces were required for high wet and dry strength and required less moisture resulting in green pellets with lower porosity and moisture content produced in shorter time intervals.
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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

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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)

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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

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Porosity

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

Manganese Sample Porosity
Sample 1 (4mm) Sample 2 (1.4mm) Sample 3 (250 µm) 32.2 33.3 30.6
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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.

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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 35and a rotation speed of 75 rpm
• Pellet diameter was controlled between 10 and
  12.5mm

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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

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Compression strength
Sample Average Min Max Std Dev
Sample 1 5.7 3.7 8.3 1.3
Sample 2 4.4 1.8 6.9 1.4
Sample 3 1.5 0.4 2.2 0.8
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Impact strength
Sample Average Min Max Std Dev
Sample 1 6.1 3 12 2.9
Sample 2 8.4 2 17 5.2
Sample 3 1.5 1 2 0.5
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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

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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

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Acknowledgements

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

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Questions