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 (

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

December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

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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

December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

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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 Demand and strategies to reduce energy

consumption

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]

December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

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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 Demand and strategies to reduce water

consumption

Water

Global water consumption is increasing

Main increase is expected in

Africa (+44 %)

Asia (+43 %)

South America (+38 %)

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2000: 3900 km 2025: 5100 km (+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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Mass movement Strategies to reduce mass movement

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