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  • 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

    Henning Knapp 3

  • 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

    Henning Knapp 4

    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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 6

    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

    Henning Knapp 7

    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)

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 8

  • 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.)

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 9

  • 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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 10

  • 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 %)

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 12

    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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 13

  • 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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 14

  • 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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 15

  • Water cleaning generates costs

    Sedimentation

    Filtration

    Neutralization

    Cyanide oxidation/destruction

    Heavy metal precipitation

    Storage and pumping

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 16

  • 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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 17

    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)

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 18

  • 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

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 20

  • Masses

    Non usable material from mineral extraction:

    Overburden and waste rock

    Mineral processing tailings

    Mass movement for copper, iron and gold (without overburden/waste)

    December 17, 2014 PROMETIA Scientific Seminar, Marcoule, France

    Henning Knapp 21

    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