Iron Ore Final Grinding by HPGR and Air ClassificationAusIMM Iron Ore Conference 2015Prepared by F.P. van der Meer, E. Lessing, R. StoccoPresented by Evert Lessing

Outline

• Why should we go dry?• Experience from the Cement Industry• HPGR application in Minerals• Air Classification• Dry Magnetic Separation• Application in Iron Ore

Why should we go dry?

The number of projects dealing with, or considering, dry processing increases due to factors such as• Low water availability in arid locations, such as the high Andes or Sahara desert• Dry downstream processing or beneficiation with high fines requirement• Mining in Australia – 2% of nations total water usage (CRC ore 2013)

Dry processing can provide an alternative to cope with• Low water availability, high supply cost, desalination requirements, drinking water

preservation• High effort and cost in fine wet product screening, sedimentation, and filtration• Difficulties from high water content in HPGR recycle where wet screening is applied

Experience from the Cement Industry

• In cement plants processing limestone, blast furnace slag, or clinker, dry processing with HPGR and air classification is a well established industry standard

• Feed sizes of up to 80mm, and products down to 80% < 25µm (Blaine specific surface up to about 5,000cm²/g)

HPGR with Static and Dynamic air classifiers used in Cement

Experience from the Cement Industry (Cont)

ENERGY CONSUMPTION 16kWh/t feed

ENERGY CONSUMPTION 10kWh/t feed

ENERGY REDUCTION

35 %for a 125µm Product

Comparison: Dry HPGR-Ball Mill vs. HPGR-Air Classifier energy for cement finish grinding system

HPGR application in Minerals

Capacity & size increases to cater for minerals market• Machines that can handle 4,000tonne/hr• Roll diameter of 3.0m • Roll width of 3m • Swing frame with easy roll removal and

transport carriage• Studded tyres achieving up to 16,000hr life

Well established in Diamond, Iron ore and Hard Rock mining

• Roll 2.2m Ø x 2.0m wide• Roll weight 75,000kgs

HPGR application in Minerals (cont)

• HPGR established as energy efficient alternative operating in a tertiary crush/ SAG mill duty

• Compared to SABC circuit• 15 – 20% Reduction in direct energy• 23 – 25% Reduction in comminution costs

• Not utilising the full potential due to requirement for effective classification

• Restricting product size that can be produced

Conventional SAG Circuit (SABC)

SavingsDirect energy: 15% – 20% Cost: 23 – 25%

Conventional HPGR Circuit

HPGR application in Minerals (cont)

• Move HPGR to more grinding than tertiary crushing application

• More efficient grinding than Ball Mill• Utilising more of the capability of the

HPGR to deliver finer product size• Compared to conventional HPGR circuit

• 15 – 20% Reduction in direct energy• 23 – 25% Reduction in comminution costs

Dry HPGR Circuit

SavingsDirect energy: 15% – 20%Cost: 23 – 25%

SavingsDirect energy: 30% – 40%Cost: 40 – 50%

Conventional SAG Circuit (SABC)

Conventional HPGR Circuit

Air Classification

Plant Components• Static cross-flow separator

• classification cut sizes 80-1,500µm

• Dynamic cage wheel separator • classification cut sizes 25-150µm

• Drop-box type scavenger separator • for cleaning coarse particles from static

classifier

• Air cyclones • for fines recovery and gas stream cleaning

Operating principle of static (cross-flow) air separator

• Feed cascades over the louvers• Flakes are deagglomerated• Cross-flow air sweeps-out fines• Coarse discharges at bottom• Fines leave top with air flow

Operating principle of dynamic (cage wheel) air separator

• Feed enters by gravity or in airstream from static classifier

• Coarsest particle rejected by impact on vanes

• Cross-flow air sweeps-out fines

• Coarse discharges at bottom

• Fines leave top with air flow

Dry grinding plant arrangement

• HPGR fresh feed is sent to the static classifier

• Fines are pneumatically transported to the dynamic classifier

• Fines product gets removed by the dynamic classifier

• Fines oversize from dynamic classifier reports back to HPGR

• Static classifier oversize is conveyed by bucket elevator to feed into HPGR

• HPGR discharge product is sent to static classifier

HPGR with Static and Dynamic classifier used in Cement

Magnetic separators

Iron Ore beneficiation – Wet or Dry process?

• Wet drum separators can handle particles from 25µ up to 1mm, while Dry drum separators can handle particles from 100µ up to 30mm

• Dry separators are therefore used to reject barren waste (Cobbing) and for the production of a concentrate and a pre-concentrate for Wet Plant feed in arid regions

Material size No. of Poles Drum speed (m/s)

25 x 6 11 1.5 - 2.56 x 1 22 2.5 - 4.0

1 x 0.1 39 3.5 - 5.0D50 ≤ 150µ 42 4.0 - 7.0

Feed

Magnetic Drum

MagneticsNon-Magnetics

Application in Iron Ore

• HPGR discharge product is sent to static classifier• Fines are treated in a dynamic classifier and recovered• Coarse material is recycled over LIMS magnetic separator back to HPGR

Example Magnetite Iron Ore grinding

Fines Product 80% < 45µmFeed 100% < 40mm

Example Magnetite Iron Ore grinding with HPGR, Air Classification and LIMS

Example Magnetite Iron Ore grinding with HPGR, Air Classification and LIMS

Circulating load reduced by 35%

15% LIMS rejection

Mass Rates without LIMSMass relative to Plant feed Mass relative to HPGR Feed

Fresh Feed 60 mm 100 16HPGR Feed (circulating load) 611 100

Coarse + 5 mm 132 22Middlings - 5 mm +150 µm 378 62

Fines - 150 µm 100 16Magnetics - 5 mm +150 µm 378 62

Non Mags Reject - 5 mm +150 µm 0 0

Mass Rates with LIMSMass relative to Plant feed Mass relative to HPGR Feed

Fresh Feed 60 mm 100 25HPGR Feed (circulating load) 394 100

Coarse + 5 mm 85 22Middlings - 5 mm +150 µm 244 62

Fines - 150 µm 65 16Magnetics - 5 mm +150 µm 209 53

Non Mags Reject - 5 mm +150 µm 35 9

Example Magnetite Iron Ore grinding with HPGR, Air Classification and LIMS

Upgraded from 27% to 40%

15% LIMS rejectionMass Rates with LIMS

Mass relative to Plant feed Mass relative to HPGR FeedFresh Feed 60 mm 100 25

HPGR Feed (circulating load) 394 100Coarse + 5 mm 85 22

Middlings - 5 mm +150 µm 244 62Fines - 150 µm 65 16

Magnetics - 5 mm +150 µm 209 53Non Mags Reject - 5 mm +150 µm 35 9

Iron BalanceFe Assay, % *) Fe Distribution, % *)

Fresh Feed 60 mm 27 100HPGR Feed (circulating load) 32 473

Coarse + 5 mm 30 95Middlings - 5 mm +150 µm 31 283

Fines - 150 µm 40 96Magnetics - 5 mm +150 µm 36 278

Non Mags Reject - 5 mm +150 µm 3 4*) Satmagan Magnetite Basis

Summary of considerations

• Dry processing with HPGR and air classification is expected to become more prominent in the near future, due to water availability issues in arid areas and downstream dry processing options

• Dry processing involves well established industry standard technology, with processes and equipment readily available based on cement operations

• Significant energy and overall comminution cost savings are possible by exploiting the advantage of the HPGR for final grinding

• Dry processing provides a technically feasible technology that can be applied in fields of minerals processing, generating beneficiation feeds at P80 sizes down from 1, 500µm to 25µm

• Application of low intensity magnetic separation in magnetite grinding does reduce the circulating load and thus the basic equipment size

• Low intensity magnetic separation in magnetite grinding can significantly increase the fine ground pre-concentrate grade at a minimal value loss

Thank you for your attention