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transcript
Challenges for future mineral processing
Energy, Water and Masses
Hermann Wotruba, Henning Knapp
Unit of Mineral Processing, RWTH Aachen University
Outline
Introduction
Energy consumption
Water consumption
Mass movement
• Processing of very fine (<20 µm) and ultra fine (<5 µm) particles
Conclusion
December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France
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Introduction
Quality of mineral resources (in terms of grade, depth/accessibility
and complexity) is degrading ,
More material has to be extracted and processed to produce the
same amount of product
Per unit of product this results in
– more energy consumption
– more water consumption
– more mass movement and increased amount of tailings
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System limits
The allocated energy and water consumption per unit of product depends on the system limits:
The whole process chain has to be considered
Mineral Processing is only one part of the process chain
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Mineral Processing
Transport Mineral Processing
Mining Transport Mineral Processing Mining Transport Mineral Processing Tailings deposition
Exploration Mining Transport Mineral Processing Tailings deposition Consumables Exploration Mining Transport Mineral Processing Tailings deposition Consumables Water management
Exploration Mining Transport Mineral Processing Tailings deposition Consumables Water management Smelting/Refining etc.
Energy
Global energy consumption has risen and will be rising
Most of our energy is produced from fossil fuels (CO2)
Mining, Mineral processing and metallurgical processing consume a considerable amount of energy
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Oil
Coal
Gas
Biomass Nuclear
Other renewables
0
2 000
4 000
6 000
8 000
10 000
12 000
14 000
16 000
18 000
1970 1980 1990 2000 2010 2020 2030
Mto
e
Source: Energy consumption
prognosis (IEA modelling
2006)
Average energy consumption by stage of production (Ore open pit) [KWh/1000t]
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400 500 700 600
3500
5600
300 450 800
2800
9950
350 150
10450
1300
12000
9500 1800
1500 1500
27600
800
38850
Drilli
ng
Bla
sting
Exc
avation
Handlin
g
Tra
nsport
Tota
l w
aste
rock r
em
oval
Drilli
ng
Bla
sting
Exc
avation
Tra
nsport
Tota
l ore
exc
avation
Dew
ate
ring
Min
e s
upport
Tota
l m
inin
g
Cru
shin
g
Grindin
g
Oth
er
pro
cessin
g
Taili
ngs
Pro
cess w
ate
r
Oth
er
pla
nt
Tota
l m
ill /
concentr
ato
r opera
tio
ns
G &
A
Tota
l opera
tio
ns
KW
h/1
000t
Source: Benchmarking the Energy Consumption of Canadian Open Pit Mines, CIPEC, Canada, 2005, modified
Strategies to reduce energy consumption
Incremental improvements
– Improve unit processes (usually: “bigger is better”)
– Improve process control, online analysis and automation
– Reduce overgrinding
– Optimize mine-to-plant integration (e.g. intensified blasting as first crushing
step)
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Strategies to reduce energy consumption
Step-change improvements
– Waste reduction by
• Selective mining
• Waste removal after primary crushing (e.g. by sensor-based sorting, gravity concentration)
– Improved comminution technology
• HPGR
• Vertical roller mill
• New fine grinding mills (Isa-mill, tower mill)
• Alternative fine grinding processes (e.g. shockwaves etc.)
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Strategies to reduce energy consumption
Step-change improvements
– Coarse particle recovery
• Coarse flash flotation
• Step-wise milling and concentration
– Near-to-face processing
• Near-to-face pre-concentration
– Underground pre-concentration
• Satellite pre-concentration with central processing plant
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Water
Global water consumption is increasing
Main increase is expected in
– Africa (+44 %)
– Asia (+43 %)
– South America (+38 %)
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2000: 3900 km³ 2025: 5100 km³ (+31%)
(Data: Shiklomanov, I. A. und Rodda, J. C. (2003): World Water Resources at the Beginning of
the 21st Century)
Water in mineral processing
Washing and scrubbing
Medium for grinding and separation
– Wet screening
– Wet ball mill
– Wet gravity concentration
– Wet magnetic separation
– Flotation
– Leaching
Medium for transport (slurry)
Dust precipitation
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Impacts of mineral processing on water
Chemical impacts
– Acidity/alkalinity
– Heavy metals (arsenic, mercury, etc.)
– Reagents (acids, cyanides, organics)
– Radioactivity
– Oxygen content
Physical impacts
– Turbidity/siltation
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Typical environmental impacts of mining on water resources
Demand for local water sources
– River water
– Lake water
– Ground water
– Captured rain water
– Sea water
Discharge of contaminants into ground water
Depression of ground water table
Erosion of unprotected surfaces – increased sediment load in streams
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Water cleaning generates costs
Sedimentation
Filtration
Neutralization
Cyanide oxidation/destruction
Heavy metal precipitation
Storage and pumping
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Strategies to reduce water consumption
Online analysis, automation and process control
Dry processing
– Dry gravity separation
• Dry jigging
• Dry fluidized bed separation
• Dry shaking table
– Dry magnetic separation
– Electrostatic separation
– Sensor-based sorting
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Sensor-based
sorting Screen
Mill
Primary
crusher
Secondary
crusher
Product Waste
ROM
Flotation
Coarse waste to:
• Dump
• (underground) backfill
• Market (as construction
material) Fine
Quantity and quality of process water
About 3-4 parts of water per part of solids
Quality of process water depends on processing method (flotation and leaching have a high impact)
Processes without the use of reagents are preferable
– Wet gravity concentration
– Wet magnetic separation
If possible, non-toxic and degradable reagents should be used
Long term behavior of many process chemicals are not fully understood (e.g. flocculants)
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Masses
Mining and mineral processing requires movement of large quantities of masses
Ratio between ore and waste depends on the mining method
– Underground 1:1 or better
– Surface from 1:1 to 1:10
Percentage of usable material in ROM depends on mineral and deposit
– Close to 100 % for coal
– Less than 1 ppm for gold in open pit
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Masses
Non usable material from mineral extraction:
– Overburden and waste rock
– Mineral processing tailings
Mass movement for copper, iron and gold (without overburden/waste)
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Commodity World Production 2007
Mio. t
World Production 2011
Mio. t
Increase 2007-2011
%
Mass ore 2011
Mio. t
Copper (metal) 15.5 16.1 4 1610 (at 1% Cu)
Gold (metal) 0.00235 0.00266 13 887 (at 3g/t Au)
Iron 1070 1390 20 2940
Source: USGS
Quality of masses
Not only quantity but also quality of masses influences the environmental impact
– Particle size (coarse waste vs. flotation tailings)
– Physical and chemical activation (leaching, bacterial activity…)
– Acid generation potential
– Heavy metal potential
– Mechanical stability
The quality of masses is influenced by their nature and by the process
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Strategies to reduce mass movement
Similar to water and energy reduction
– Selective mining
– Transition from open pit to underground
– Waste removal prior to milling and concentration
– Coarse particle concentration
– Near-to-face processing
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Processing of very fine and ultra fine particles
Due to increasingly complex mineralogy, processing of very fine (<20 µm) and ultra fine particles (<5 µm) becomes more and more important (Source: R. Sivamohan, 1989)
Necessary liberation requires fine grinding and separation at small particle sizes
Technologies allowing a reliable separation at <20 µm have to be developed/improved
– Ultra fine flotation
– Ultra fine gravity separation
– Ultra fine magnetic separation
– Selective flocculation
– Carrier flotation
– New dry ultra fine particle separation (electrostatic, etc.)
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Relation of energy, water and masses in mineral processing
Energy consumption, water consumption and mass movement are related
Any measure to reduce mass movement reduces
– Energy consumption
– Water consumption
– Environmental impacts
– Costs
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Mass movement
Environmental impact
Water consumption
Energy consumption
Summary & Conclusion I
Energy is the major cost factor for mineral processing
– High energy prices lead to high commodity prices
High commodity prices are affordable for developed countries but are harmful for poor countries
– Increasing imparity between rich and poor countries
Social acceptance (“social license”) of mineral processing strongly depends on environmental impacts (water, energy…)
Mineral extraction, mineral processing and mineral refinement (smelting, etc.) have to be considered as one process chain
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Summary & Conclusion III
Processing of fine particles (<20 µm) will become increasingly important
Reduction of moved and treated masses reduces energy and water consumption
Some low-grade deposits cannot be exploited with todays technologies
Increased water and energy efficiency can turn reserves into resources
European equipment manufacturing companies are world leader in mayor fields
– Energy efficient fine and ultra fine grinding
– Sensor-based sorting
– Dry separation processes
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