METS Processing Engineer covers several reasons why high pressure grinding rolls (HPGR) are used such as cost and micro-cracking, which is a technique used on various iron ores including hematite and magnetite operations both in Australia and around the world

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Insights Session
HPGR in the Iron Ore Industry
Presented by Karri Dorrington,
Process Engineer

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Outline
• What is HPGR?
• Benefits of HPGRs
• Iron ore types around the globe
• HPGR use in the iron ore industry
• HPGR in iron ore plant design
• Testwork

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What is HPGR
• High Pressure Grinding Rolls (HPGR)
• Similar to the typical fixed roll crusher
• Force applied to push one roll towards the fixed roll
and raise pressure between the rolls
• Force on the material mainly compressive
• Introduces micro cracking – favourable for further comminution
• Higher reduction ratios than fixed rolls
Source: Mine Engineer Website (2012)

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HPGR
• Reduced power consumption hard ores – 10 to 15%
• Requires secondary crushed feed
• Reduced BWI
• Replaces SAG mill-smaller ball mill
• CAPEX similar
• 10% moisture in feed
Source: Technomine Website (2012)

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HPGR
Source: Weir Minerals Website (2012)
Source: World of Mining Professionals Website (2012)

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HPGR vs Cone Crusher
• HPGR and Cone Crusher Product

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Benefits to Magnetic Separation
0
10
20
30
40
50
60
70
80
Wt.FeSiO2Al2O3MgO
MagneticRecoverey,%
HPGR Coarse Cob
Cone Coarse Cob
0
10
20
30
40
50
60
70
80
90
100
Wt.FeSiO2Al2O3MgO
Assay,%
HPGR Coarse Cob
Cone Coarse Cob

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HPGR vs Cone Crusher
• More even size distribution
• Finer size distribution
• Lower magnetic recovery of gangue minerals such as MgO, Al2O3 and
SiO2
• Lower mass recovery
• Typically a higher iron grade (and other metallics)

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Iron Ore Types Around the World
Brazil:
Itabirite, Hematite
Australia:
Hematite, Magnetite
South Africa:
Hematite, Magnetite
China:
LG Hematite
East Africa:
Itabirite, Hematite India:
LG Itabirite
Canada:
Hematite, Magnetite
USA:
Hematite, Magnetite
Russia:
Hematite

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HPGR in Iron Ore Processing
• Applied to iron ore industry mainly for regrinding of pellet feed to
improve properties in the pelletising process
• Over time has been applied to other iron ore processes to improve
concentrates
• Australia
− Magnetite (Karara)
− Vanadiferous, Titaniferous Magnetite (Future: Mount Peake)
• South Africa
− Hematite (Khumani)
• Brazil
− Itabirite (Samarco)

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Karara Project
• JV project
• Long life magnetite concentrate operation (30+ years)
• Low-grade magnetite to produce a high-grade premium concentrate
• Have issues getting the power efficiency to the SAGs and therefore
optimum operating
• 2011 installation of HPGR
• Installed downstream of the secondary crusher
• HPGR significantly lifted feed rates

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Karara Project

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Karara Project

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Mount Peake Project – FS Underway
• Polymetallic ore body
• Two stage HPGR installed after the secondary crusher
• Lower operating cost
• Efficient in producing the required feed size (two stages required)
• Micro-cracking
• Reduced mass recovery on coarse cobbing
• Changes to the process – HPGR still beneficial

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Mount Peake Project (Scoping Study)

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Khumani Mine
• High grade hematite deposit in South Africa
• Formally BKM Project (Bruce, King and Mokaning)
• 10 Mt export quality iron ore per annum increasing to 16 Mt
• Civil construction began in 2006
• December 2007 first delivery to Bruce primary crusher
• Late 2007 construction of jigs and HPGR
• HPGR utilised to reduce middlings particle size

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Khumani Mine

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Khumani Mine
• Single HPGR located after Jigging of the Lump
• Size reduction from -32.0 +6.0 mm to -6.0 mm
• More efficient than cone crusher
Source: International Mining (2008)

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Samarco Project
• JV between BHP Billiton and Vale
• Low grade itabiritic ore
• Ore Reserve = 451 Mt (wet) as of 2008
• Conveyor belts transport the ore to the beneficiation plant, whilst a
396 km slurry pipeline transports the pellet feed to the pellet plant on
the coast
• HPGR prior to grinding, de-sliming and flotation

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Samarco Project

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Samarco Project

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Samarco Project

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HPGR Plant Design
• Normally HPGR is located after the primary/secondary crushing
• Can replace tertiary crushing with SAG mill, where a ball mill is still
required
• Can replace secondary/tertiary/quaternary crushing
• Not suitable for all ore types
− High fines/clays lead to impaired comminution
− High ore competency and abrasiveness will lead to increased wear rates
− High moisture (>10%) will cause washout of the autogenous layer

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HPGR vs. SAG Mill Design
1. Original circuit design SAG/AG mills
and ball mills (Huckleberry SABC
circuit), however very energy
intensive and also energy inefficient
accounting for ~80% of the overall
process plant energy (depending on
the overall process)
2. Changes to design lead to HPGR
and ball mill circuits, thus lowering
the energy consumption costs
slightly
3. Further examination, HPGR and
stirred mills circuits demonstrated it
is technically feasible and showed
promising benefits over traditional
options
1
2
3
Source: E&MJ News (2013)

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Why Choose HPGR? What are the
Drivers?
• Benefits to downstream processing – magnetic separation, flotation,
leaching
• Better energy efficiency – lowering costs
• Replacement of equipment to increase grinding efficiency
• Willing to investigate with testwork to see if ore is amenable

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Testwork
• Prior to selection of HPGR testwork is required
• Testwork involves:
− Pressure tests
− Roll speed tests
− Roll gap tests
• Testwork reveals if the ore is amenable to HPGR
• HPGR settings influence throughput, product size distribution and
micro-cracking

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References
• Karara Mining Ltd (2013) Energy Efficiency Opportunities KML Expansion Project
• TNG Limited (2012) Executive Summary Mount Peake Project Pre-Feasibility Study
• Moore, P (2011) Samarco – An Iron Ore Pioneer, International Mining, Dec 2011
• Burchardt, E (2013) HPGRs in Hard Rock Mining, Mining Magazine
• Wang, C., Nadolski, S., Mejia, O., Drozdiak, J., Klein, B (2013) Energy and Cost Comparisons of HPGR-Based
Circuits, E&MJ News
• Morley, C (2010) HPGR-FAQ, Journal of the Southern African Institute of Mining and Metallurgy

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