Transcript Lonmin and UG2 Ore

LONMIN AND UG2
Presentation to the MMMA President’s Technical Seminar
JJ Steyn
20 May 2011
PRESENTATION CONTENT
•
Background
•
UG2 Challenges
•
Processing of UG2
•
Types of UG2
•
Lonmin Results on UG2
•
Conclusions
BACKGROUND
•
Lonmin’s typical production profile:
Merensky Ore
UG2 Ore
Lonmin Production (%)
20
80
PGM Grade (g/t)
3.50
5.00
Cr2O3 Grade (%)
1
25
Cu/Ni Grade (%)
0.25
0.1
SG
3.1
3.8
BACKGROUND
•
Advantages of UG2 vs. Merensky
• More PGM’s per ton (head grade)
• More tons per meter advanced (SG)
•
Disadvantages of UG2 ore vs. Merensky
• UG2 reef deeper than Merensky
• Less Cu/Ni per ton
• More Cr2O3 per ton
UG2 CHALLENGES
•
Smelter Constraints:
• Total Cr2O3 in concentrate < 2.2%
• Total Cu/Ni in concentrate > 3.8%
•
UG2 Mineralogy – PGM’s associated with:
• Base metal sulphides (±30m BMS grains)
• Locked in siliceous minerals (±5m PGM grains)
• On gangue and BMS grain boundaries
•
Classification:
• Density difference between chromite and silica host
• Reverse classification
UG2 ORE PROCESSING
•
Material report to flotation conc. via two mechanisms
• True flotation (dependant on particle surface properties)
• Entrainment (dependent on particle size and density)
True Flotation:
PGM
BMS
Floatable gangue
Entrainment:
Chromite
Non-floatable siliceous gangue
THE UG2 DILEMMA…
•
Needs fine grinding to liberate PGM’s
• 5m PGM’s are locked in gangue
•
Chromite entrains at fine grinds
•
Fine particles don’t float well
• Reduced chance of particle-bubble collision
• Reduced chance of particle-bubble attachment
• Increased chance of particle detachment
• Gangue surface coatings more detrimental for fines
•
The result – complicated circuits and innovative
designs
ACHIEVING A FINE GRIND
•
Installed Power
• Merensky Plant - ± 14 kWh/ton
• Karee B & K4 - ± 28 kWh/ton
•
Dedicated coarse and fine mills
•
Cleaner circuit milling
MINIMISE CHROMITE ENTRAINMENT
•
Don’t over-grind chromite!
•
Two-stage flotation - float as coarse as possible in
primary rougher
•
Reverse classification in hydrocyclone
• Cyclone classifies on mass
• Chromite is a lot denser than siliceous minerals
• Results in fine chromite in cyclone underflow
• Results in coarse siliceous minerals in cyclone overflow
•
Solution – mills in open circuit
UG2 MILLING CIRCUITS
Flotation
Flotation
Prim Tails
Flotation
Flotation
ROM
Prim Tails
Primary Mill
Secondary Mill
FINES FLOTATION
•
Increase particle-bubble collisions
• Frother – finer bubbles
• High energy cells – finer bubbles
•
Increase chance of particle-bubble attachment
• High energy cells – particle momentum
•
Decrease chance of particle detachment
• Shallow froths
•
Clean surfaces
• Dispersant
•
Separate cleaning circuits for fast and slow floating material
•
MINTEK PROCESS
MINTEK PROCESS – CLEANING CIRCUIT
•
First recover fast floating particles – High Grade
•
Then focus on slow floating particles – Low Grade
•
High depressant dosages
•
High frother dosage
•
Shallow levels
•
These conditions also favour water recovery
•
Thus higher entrainment and chrome recoveries
•
Running on the edge!
EPC FLOW SHEET
Primary Mill
Primary Roughers
To Secondary Mill
Secondary Mill
Secondary Roughers
Final Tails
Primary Cleaners (3 Stage)
ISA Mill
To Secondary
Cleaners
Final Tails
DIFFERENCE TYPES OF LONMIN UG2
•
Western UG2 (Karee, Western Platinum)
•
Eastern UG2 (Eastern Platinum)
•
Split Reef (WPL)
•
IRUP (WPL)
•
Mechanised Ore (mostly EPL)
BASIC MINERALOGY OF LONMIN UG2
WPL
EPL
Split
IRUP
Mech
BMS
34
7
23
16
10
BMS-Gan
36
19
40
27
22
Lock-Gan
19
63
26
46
58
PGM Sul
9
4
7
3
3
Lock-Cr
2
7
4
8
7
100
100
100
100
100
3
4
3
24
5
Met
PERFORMANCE OF LONMIN UG2
WPL
EPL
Split
IRUP
Mech
Head Grade (g/t)
5.2
4.8
3.8
4.5
4.5
Mass Pull (%)
1.0
0.8
1.2
1.2
1.1
Recovery (%)
90
86
86
83
80
Conc Grade (g/t)
470
520
270
310
330
Cleaner Tails (g/t)
2.2
1.8
2.2
3.5
3.5
CONCLUSIONS
•
UG2 needs fine grind for valuable recovery
• Lots of power
• Two stage milling
•
Cr2O3 is recovered at fine grinds
• Open circuit milling
•
Fines recovery
• Mintek process