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

Pelletisation of Pelletisation of ferromanganese ore with ferromanganese ore with particle sizes less than particle sizes less than 4mm – an introduction4mm – an introduction

TC Kruger and JD SteenkampTC Kruger and JD Steenkamp

IntroductionIntroduction

Ferromanganese is produced in a SAFFerromanganese is produced in a SAF SAF requires a permeable burden SAF requires a permeable burden Pellets are preferred Pellets are preferred

higher porosity, uniform size and uniform shapehigher porosity, uniform size and uniform shape Up to 30 per cent of ore produced is smaller Up to 30 per cent of ore produced is smaller

than 3mm (fines)than 3mm (fines) Large fines dumps are common both at mines Large fines dumps are common both at mines

and at smelter plants and at smelter plants One process to utilise fines is pelletisationOne process to utilise fines is pelletisation

This paper gives an overview of:This paper gives an overview of: the factors relevant to pelletisation in general the factors relevant to pelletisation in general

the pelletisation of manganese ore fines specificallythe pelletisation of manganese ore fines specifically

reports on initial pelletisation test work conducted on reports on initial pelletisation test work conducted on -4mm manganese ore fines-4mm manganese ore fines

PrinciplesPrinciples

Wetting and nucleation Wetting and nucleation

a binder liquid is added to the feeda binder liquid is added to the feed individual wet particles ‘stick together’ to individual wet particles ‘stick together’ to

form nucleiform nuclei

PrinciplesPrinciples

Consolidation and growthConsolidation and growth

nuclei are joined by more fines through collision and nuclei are joined by more fines through collision and further ‘sticking together’ to form a micro pelletfurther ‘sticking together’ to form a micro pellet

two micro pellets - surrounded by liquid films - are two micro pellets - surrounded by liquid films - are brought into contact with each otherbrought into contact with each other

A seed pellet is formed that capture dry and wet A seed pellet is formed that capture dry and wet particles until the desired pellet size is obtainedparticles until the desired pellet size is obtained

Pellet porosity decreases due to the continual Pellet porosity decreases due to the continual impactimpact

PrinciplesPrinciples

Breakage and attritionBreakage and attrition

Breakage occurs when:Breakage occurs when: Equilibrium size is reached, and Equilibrium size is reached, and Binding force can no longer maintain the load. Binding force can no longer maintain the load.

The surface of the pellet is smoothened by The surface of the pellet is smoothened by attrition of the sharp edgesattrition of the sharp edges

Pellet growthPellet growth

Growth pellets is controlled by two properties: Growth pellets is controlled by two properties: plasticity of the green pellet and plasticity of the green pellet and the viscosity of the superficial water layer the viscosity of the superficial water layer

Plasticity is controlled by moisture contentPlasticity is controlled by moisture content The minimum plasticity defines the minimum The minimum plasticity defines the minimum

moisture content requiredmoisture content required The minimum moisture content value is The minimum moisture content value is

material specificmaterial specific

Pellet growthPellet growth

Binder liquid is ‘squeezed’ to the pellet surfaceBinder liquid is ‘squeezed’ to the pellet surface The viscosity of the binder liquid influences the The viscosity of the binder liquid influences the

rate rate The viscosity has to be low enough for colliding The viscosity has to be low enough for colliding

pellets to combine within the time available pellets to combine within the time available during collision (uncontrolled growth if too low)during collision (uncontrolled growth if too low)

Viscosity of binder liquid is influenced by: Viscosity of binder liquid is influenced by: Binder dosage; Binder dosage; Temperature; Temperature; Material properties of the binder Material properties of the binder Process parameters Process parameters

ProcessesProcesses

PressurePressure Briquetting, compaction, tabletingBriquetting, compaction, tableting

TumblingTumbling Drum, disc, cone and pin agglomeratorDrum, disc, cone and pin agglomerator

ExtrusionExtrusion Screw and gear pelletiser as well as pellet millsScrew and gear pelletiser as well as pellet mills

ThermalThermal Sintering, prilling, pastillating and flaking processesSintering, prilling, pastillating and flaking processes

BindersBinders

Binders accomplish two important Binders accomplish two important functions in pelletisation, namely:functions in pelletisation, namely: Makes the moist ore plastic; andMakes the moist ore plastic; and During drying and sintering, the binder holds During drying and sintering, the binder holds

the particles in the pellets togetherthe particles in the pellets together

BindersBinders

Types of bindersTypes of binders Bentonite (0.25 to 2.5 per cent by mass)Bentonite (0.25 to 2.5 per cent by mass) Cement (5 per cent by mass)Cement (5 per cent by mass) Lime (5 per cent by mass)Lime (5 per cent by mass) Cane molasses (3 per cent by mass)Cane molasses (3 per cent by mass) Calcium chlorideCalcium chloride Silicate or fluorosilicate of sodiumSilicate or fluorosilicate of sodium

CharacterisationCharacterisation

Pellet size distributionPellet size distribution Pellet shapePellet shape Pellet hardnessPellet hardness Pellet solubility in a liquid i.e. slagPellet solubility in a liquid i.e. slag Pellet dispersability in a liquid i.e. slagPellet dispersability in a liquid i.e. slag Binder addition requirementsBinder addition requirements Pellet impact strengthPellet impact strength Pellet abrasion strengthPellet abrasion strength Pellet attrition indexPellet attrition index Pellet compression strengthPellet compression strength Pellet reducibility Pellet reducibility Pellet porosityPellet porosity

Impact strength (drop strength)Impact strength (drop strength)

Represents its ability to survive multiple drops Represents its ability to survive multiple drops in material handling systems in material handling systems

Is determined by repeatedly dropping a pellet Is determined by repeatedly dropping a pellet onto an iron surface from a fixed height until onto an iron surface from a fixed height until the pellet fractures or chipsthe pellet fractures or chips

Is quantified as the number of drops that a Is quantified as the number of drops that a pellet survived before fracture. pellet survived before fracture.

A typical value for green pellets is between 5 A typical value for green pellets is between 5 and 20 dropsand 20 drops

Compression strength (crushing Compression strength (crushing strength)strength)

The compression strength of a pellet The compression strength of a pellet represents its ability to resist compressive represents its ability to resist compressive forces without breakingforces without breaking

Is determined by placing pellets between two Is determined by placing pellets between two steel plates and evenly applying a measured steel plates and evenly applying a measured pressure until the pellet fractures pressure until the pellet fractures

The compression strength is expressed as the The compression strength is expressed as the applied pressure in Newton or kilogram per applied pressure in Newton or kilogram per pelletpellet

A typical value for green pellets is between 0.5 A typical value for green pellets is between 0.5 and 5 kg per pelletand 5 kg per pellet

EquipmentEquipment

Disc pelletiserDisc pelletiser Drum pelletiserDrum pelletiser ExtruderExtruder Pin agglomeratorPin agglomerator Briquette making machinesBriquette making machines Sintering machinesSintering machines High-intensity mixersHigh-intensity mixers

Case studiesCase studies

MexicoMexico Purpose of StudyPurpose of Study Material PelletisedMaterial Pelletised Particle SizesParticle Sizes Equipment / ProcessEquipment / Process Binder and quantityBinder and quantity Moisture and quantityMoisture and quantity Curing / DryingCuring / Drying FiringFiring TestingTesting Drop TestsDrop Tests Cold crushing strengthCold crushing strength Tumble indexTumble index

Case studiesCase studies

Brazil (INCOMI)Brazil (INCOMI) Purpose of StudyPurpose of Study Material PelletisedMaterial Pelletised Particle SizesParticle Sizes Equipment / ProcessEquipment / Process Binder and quantityBinder and quantity Moisture and quantityMoisture and quantity Curing / DryingCuring / Drying FiringFiring TestingTesting Drop TestsDrop Tests Cold crushing strengthCold crushing strength Tumble indexTumble index

Case studiesCase studies

Brazil (University of Sao Paulo)Brazil (University of Sao Paulo) Purpose of StudyPurpose of Study Material PelletisedMaterial Pelletised Particle SizesParticle Sizes Equipment / ProcessEquipment / Process Binder and quantityBinder and quantity Moisture and quantityMoisture and quantity Curing / DryingCuring / Drying FiringFiring TestingTesting Drop TestsDrop Tests Cold crushing strengthCold crushing strength Tumble indexTumble index

Case studiesCase studies

India (Visvesvaraya regional college of Engineering)India (Visvesvaraya regional college of Engineering) Purpose of StudyPurpose of Study Material PelletisedMaterial Pelletised Particle SizesParticle Sizes Equipment / ProcessEquipment / Process Binder and quantityBinder and quantity Moisture and quantityMoisture and quantity Curing / DryingCuring / Drying FiringFiring TestingTesting Drop TestsDrop Tests Cold crushing strengthCold crushing strength Tumble indexTumble index

Case studies - commentsCase 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 2:1.

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.

TrialsTrials

AimAim To produce pellets from South African To produce pellets from South African

manganese ore fines with sufficient manganese ore fines with sufficient strength to be used in major processing strength to be used in major processing units i.e. in sintering and SAF units i.e. in sintering and SAF operationsoperations

Experimental designExperimental design

porosity was used as design control variableporosity was used as design control variable literature was used as reference for aim porosityliterature was used as reference for aim porosity

less than 30 per centless than 30 per cent controlling pellet porosity by controlling the content of controlling pellet porosity by controlling the content of

very fine material in the mix resulted in high strength very fine material in the mix resulted in high strength pelletspellets

bentonite as a binderbentonite as a binder pellets characterised by measuring their compression pellets characterised by measuring their compression

strength (aim of 5 kg per pellet)strength (aim of 5 kg per pellet) and impact strength (a and impact strength (a minimum of 5 drops for a green pellet and 20 drops for minimum of 5 drops for a green pellet and 20 drops for a dried pellet)a dried pellet)

SamplesSamples

Sample 1 consisted of material smaller than Sample 1 consisted of material smaller than 4mm which represented fines screened from 4mm which represented fines screened from ore at the mines prior to transportation and at ore at the mines prior to transportation and at smelter plants prior to processing. smelter plants prior to processing.

Sample 2 consisted of material smaller than Sample 2 consisted of material smaller than 1400 microns; and 1400 microns; and

Sample 3 consisted of material smaller than Sample 3 consisted of material smaller than 250 microns250 microns

PorosityPorosity

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

Manganese SampleManganese Sample % Porosity% Porosity

Sample 1 (–4mm)Sample 1 (–4mm)

Sample 2 (–1.4mm)Sample 2 (–1.4mm)

Sample 3 (–250 µm)Sample 3 (–250 µm)

32.2%32.2%

33.3%33.3%

30.6%30.6%

BinderBinder

Where:Where: bb == bentonite in gramsbentonite in grams P P == aim porosity in mlaim porosity in ml SVSVbb == Swelling Volume of bentonite = 22-26 (ml/2g)23Swelling Volume of bentonite = 22-26 (ml/2g)23 mm = = mass of material to be pelletised in gramsmass of material to be pelletised in grams

Calculated bentonite content of each pelletising mix was thus calculated as:Calculated bentonite content of each pelletising mix was thus calculated as: Sample 1 – 0.53 mass per cent;Sample 1 – 0.53 mass per cent; Sample 2 – 0.57 mass per cent; andSample 2 – 0.57 mass per cent; and Sample 3 – 0.55 mass per cent.Sample 3 – 0.55 mass per cent.

PelletisingPelletising

5 kilogram sample of each size fraction5 kilogram sample of each size fraction Measured bentoniteMeasured bentonite Placed in the Eirich RV02 high intensity mixer Placed in the Eirich RV02 high intensity mixer

and mixed for 60 secondsand mixed for 60 seconds 1.2m diameter Radicon disc pelletiser1.2m diameter Radicon disc pelletiser Angle of 35°and a rotation speed of 75 rpm Angle of 35°and a rotation speed of 75 rpm Pellet diameter was controlled between 10 and Pellet diameter was controlled between 10 and

12.5mm12.5mm

TestingTesting

Compression strength:Compression strength: 30 balls of each sample30 balls of each sample Instron Technologies crushing strength Instron Technologies crushing strength

machine, model 1011 machine, model 1011

Impact strength:Impact strength: 30 balls of each sample30 balls of each sample Drop height of 450mmDrop height of 450mm

Compression strengthCompression strength

SampleSample AverageAverage MinMin MaxMax Std DevStd Dev

Sample 1Sample 1 5.75.7 3.73.7 8.38.3 1.31.3

Sample 2Sample 2 4.44.4 1.81.8 6.96.9 1.41.4

Sample 3Sample 3 1.51.5 0.40.4 2.22.2 0.80.8

Impact strengthImpact strength

SampleSample AverageAverage MinMin MaxMax Std DevStd Dev

Sample 1Sample 1 6.16.1 33 1212 2.92.9

Sample 2Sample 2 8.48.4 22 1717 5.25.2

Sample 3Sample 3 1.51.5 11 22 0.50.5

ConclusionConclusion

Larger particles can be pelletisedLarger particles can be pelletised Characteristics improved with increase in Characteristics improved with increase in

top sizetop size Results show that pellets produced may Results show that pellets produced may

have adequate strength for sintering have adequate strength for sintering processesprocesses

Further work is required to produce Further work is required to produce pellets suitable for SAF operations pellets suitable for SAF operations

RecommendationsRecommendations

Increasing the size range of particlesIncreasing the size range of particles Increasing the -250 micron material content of pellets Increasing the -250 micron material content of pellets

in increments;in increments; Expanding the range of binders; Expanding the range of binders; Increasing the range of the quantity of binder added;Increasing the range of the quantity of binder added; Using a single, experienced operator to produce all Using a single, experienced operator to produce all

pellets in the test program; pellets in the test program; Characterising pellets by microscopic analyses; Characterising pellets by microscopic analyses; Studying the effect of bulk porosity of pellets on the Studying the effect of bulk porosity of pellets on the

strength of pelletsstrength of pellets

AcknowledgementsAcknowledgements

Mr. L Lourens, Manager, Technology and IP, Mr. L Lourens, Manager, Technology and IP, Exxaro Resources, AlloystreamExxaro Resources, Alloystream

Mr. A Dippenaar; Kumba Iron Ore, R&D Raw Mr. A Dippenaar; Kumba Iron Ore, R&D Raw Material TechnologyMaterial Technology

Dr. A-M Bonthuys, Independent Contractor Dr. A-M Bonthuys, Independent Contractor (Editor, Translator, Proof reader, Writer)(Editor, Translator, Proof reader, Writer)

Mr B Allison, contractor, Exxaro Resources, Mr B Allison, contractor, Exxaro Resources, AlloystreamAlloystream

QuestionsQuestions