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Kullan talteenotto malmeista – uutta ja ikivanhaa Jaakko Leppinen
Rikastustekniikan seminaari, Oulu 23-24.8.2016
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World gold production in 2012
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Europe
Finland 10,800
Sweden 6,000
Spain 3,600
Serbia 0,900
Greece 0,800
Romania 0,600
Poland 0,500
Slovakia 0,300
Denmark 0,100
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Gold production routes
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Hydrometallurgical processing of gold
ores and concentrates is currently
dominated by cyanide leaching and
around 60% of all gold is produced
using cyanide.
Hydro
metallurgy Smelting
Artisanal mining
Amalgamization
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Artisanal gold mining
• 10 to 15 million artisanal miners
producing around 380-450 tonnes
Au/a in more than 70 countries
• About 100 million people – workers
and their families - depend on
artisanal mining compared to about
7 million people worldwide in
industrial mining
• These gold mining operations are
particularly dangerous, as they
often use the mercury
amalgamation process to extract
gold from ores.
• •
•Rikastustekniikan seminaari 2016 •4
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Gold production in the past
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Gold washing Wash table Manual grinding
Smelting
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Gold production today
•6 •Rikastustekniikan seminaari 2016
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Developments in gold ore processing
• Gold collected from stream beds (8000 BC)
• Washing of alluvial gold (before 3500 BC)
• Mining of gold (3500 BC)
• Smelting (3000 BC)
• Cupellation to separate other metals from gold-silver alloys (2000 BC)
• Parting to separate silver from gold (600 BC)
• Amalgamization (100 BC)
• Leaching with aqua regia (700 AC)
• Leaching with chloride (1850 AC)
• Cyanidation (1890)
• Flotation process 1905
• Refractory ore treatment with pressure oxidation (1985)
• Refractory ore treatment with bio-oxidation (1986)
• Use of alternative lixiviants for gold leaching (2000-)
• Sensor based ore sorting for gold ores (2000-)
•Rikastustekniikan seminaari 2016 •7
High-temperature techniques Gravity separation techniques
Amalgamization
Leaching
Sensor based
ore sorting
Cyanidation
Hydrometallurgical
treatment of refractory ores
Flotation
Alternative
gold lixiviants
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Mineralogical considerations for gold ore types
•Rikastustekniikan seminaari 2016
LIBERATED GOLD
COMPOSITE GRAIN
LOCKED PARTICLEIN SILICATE
LOCKED PARTICLEIN SULFIDE
INVISIBLE GOLD IN SULFIDE
FINE INCLUSIONS IN SULFIDE
FREE-MILLING GOLD ORE REFRACTORY GOLD ORE
Leaching?
Flotation?
Fine grinding?
Gravity separation?
Leaching?
Flotation?
Fine grinding?
Gravity separation?
Decompostion of gold bearing minerals?
•8
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Process options for gold processing
•Rikastustekniikan seminaari 2016
•9
Flotation
Gold concentrate to
smelter or leaching
Crushing Grinding
Crushing Grinding
Agitated Cyanide
Leaching Flotation Pre-oxidation Gold
Crushing Grinding
Flotation
Gold
Agitated Cyanide
Leaching
Free
Milling Au
Ore
Refractory
Au Ore
Gravity
concentrate
Heap Leaching
Gold
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Mineral Processing Plant
Crushing Grinding Flotation
Ta
il
in
g
Concentrate
Sorting
ORE
Thickening
Filtration
Concentrate
Tailing
Classification
Paste
thickening
Thickening Filtration
•Rikastustekniikan seminaari 2016
Gravity separation
Gravity concentrate
•10
CRUSHING
GRINDING
FLOTATION
THICKENING
FILTRATION
TAILINGS
TREATMENT
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Mineral Processing Plant
Crushing Grinding Flotation
Ta
il
in
g
Concentrate
Sorting
ORE
Thickening
Filtration
Concentrate
Tailing
Classification
Paste
thickening
Thickening Filtration
•Rikastustekniikan seminaari 2016
Gravity separation
Gravity concentrate
•11
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Size range applicability of gravity separation equipment
•Rikastustekniikan seminaari 2016 •12
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Shaking table
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Main Applications of Flotation in Gold Processing
•Rikastustekniikan seminaari 2016
1. Flotation of free gold and gold-bearing sulfide minerals to produce a gold-
rich concentrate. The concentrate can be treated by:
o Cyanidation
o Regrinding and cyanidation
o Intensive cyanidation,
o Oxidative pretreatment and cyanidation
o Direct smelting
2. Flotation of carbonaceous material, carbonates, or other material that
would otherwise interfere with processing
•14
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Cyanidation process for gold
•Rikastustekniikan seminaari 2016 •15
Crushing
Grinding
Cyanide leaching
Gold ore
Comminution
Leaching
Recovery
Sorption in activated
carbon
Elution from
activated carbon
Electrowinning
Smelting
Gold
Zinc cementation
Merrill-Crowe
S
L
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Carbon-in-pulp (CIP) process
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ELUTION
REGENERATION
TAILING
ACTIVATED CARBON
ORE FROM
GRINDING
LOADED CARBON
BARREN CARBON
ELECTROWINNING
CYANIDE LEACHING CARBON ADSOPTION
slurry
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Cyanidation process routes for gold
•Rikastustekniikan seminaari 2016 •17
Crushing
Grinding
Cyanide leaching
Zinc cementation
(Merrill-Crowe)
Carbon in Pulp
CIP
Carbon in Leach
CIL Carbon in Column
CIC
Solid-liquid separation
Gold ore
Gold is
precipitated from
cyanide solution
using zinc powder
Gold adsorbed on
activated carbon
from cyanide
solution (CIC)
Gold adsorbed on
activated carbon
from cyanide
solution with
solids. Adsorption
take place in a
separate stage
(CIP)
Gold adsorbed on
activated carbon in
slurry cyanide
solution with
solids. Adsoprtion
takes place
simultaneously
with leaching (CIL)
Comminution
Leaching
Recovery
Heap leaching
Heap leaching
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Cyanidation process for gold
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Cyanide leaching
Gold ore
Sorption in activated
carbon
Elution from
activated carbon
Electrowinning
Smelting
Gold
Carbon
Refining
Tailings
1-10 g/t
Solution 1-5 mg/l
5-10 kg/t
100-1000
mg/l
70-80%
99.99%
0.1-1 g/t
Au in ore
Au in solution
Au in carbon Dore bars
Gold bullion
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Cyanidation process
Some milestones:
1867 First patent on cyanide leaching
1889 First cyanidation plant : Crown Mine in New Zealand
1890 First cyanidation plant in South Africa: Robinson Deep
1891 First cyanidation plant in USA: Mercur, Utah
1894 Johnson patents charcoal adsorption from cyanide solutions
1904 Merrill introduces zinc dust for gold precipitation
1906 Crowe applies vacuum deareation to zinc precipitation
1949 First CIP plant at San Andreas in Honduras
1951 CIP process patented by McQuiston and Chapman
1952 USBM develops carbon elution process (Zadra)
1970 First cyanide heap leach operation in Carlin, Nevada
1973 AARL elution process
1985 First pressure oxidation plant at Homestake McLaughlin (USA)
1986 Start-up of cencentrate biological oxidation plant in Fairview,
South Africa
•Rikastustekniikan seminaari 2016 •19
First commecial scale plant
Zinc cementation for gold
recovery from solution
Carbon in pulp CIP
New elution methods from
activated carbon
Heap leaching of gold
Pre-treatment methods
for refractory gold
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Treatment of gold concentrates in copper smelters
•Rikastustekniikan seminaari 2016 •20
Electro
refining Copper
cathodes
Anode
slime
Anode
slime
treatment
Gold
Palladium
Platinum
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Treatment of gold concentrates in copper smelters
•Rikastustekniikan seminaari 2016 •21
Electro
refining Copper
cathodes
Anode
slime
Anode
slime
treatment
Gold
Palladium
Platinum
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•Rikastustekniikan seminaari 2016 •22
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Hand sorting in 1556
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Sorting of vein-type gold ore
•Rikastustekniikan seminaari 2016
Laser image Sorting image Photo
•24
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Preconcentration of material – Sensor Based Ore sorting
•Rikastustekniikan seminaari 2016
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• Feeding of unsorted material
• NIR sensor
• Color sensor
• Separation chamber
•1
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• Suitable particle size 10-250 mm
• Depending on ore characteristics
10 to 70 % of material can be
rejected
• Capacities capable of meeting the
needs of many concentrators (upto
500 tph per unit)
• Today - mature technology
• Good understanding of mineralogy
and ore geology is required
• The most common sensors:
optical and X-ray transmission
(XRT) ..\..\..\TOMRA\CommodasUltrasort_QUARZITE.mov
•25
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•Rikastustekniikan seminaari 2016 •26
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Refractory gold ore
•Rikastustekniikan seminaari 2016
INVISIBLE GOLD IN SULFIDE
FINE INCLUSIONS IN SULFIDE
•27
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•Rikastustekniikan seminaari 2016 •28
CONCENTRATION
FINE GRINDING PRESSURE
OXIDATION BIO OXIDATION ROASTING
CHEMICAL
OXIDATION
CYANIDATION
GOLD ORE
GOLD
Process options for refractory gold ores
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Occurence of gold in recractory ores, examples
•Rikastustekniikan seminaari 2016 •29
Ccp Sp Gn Bou Apy Py Total
% % % % % % %
Conc A 0.17 < 0.1 < 0.1 0.02 9.05 65.28 74.53
Conc B 2.47 1.58 0.54 0.31 15.60 63.48 83.98
Ccp = chalcopyrite (CuFeS2)
Sp = sphalerite (ZnS)
Gn = galena (PbS)
Bou = bournonite (PbCuSbS3)
Apy = arsenopyrite (FeAsS)
Py = pyrite (FeS2)
Mineral composition in concentrates
Distribution of gold between minerals
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Chemical reactions in pressure oxidation
Autoclave
2FeS2 + O2 + 2H2O 2FeSO4 + 2H2SO4
4FeSO4 + O2 + 2H2SO4 Fe2(SO4)3 + 2H2O
2FeAsS + 7O2 + 2H2O + H2SO4 2H3AsO4 + Fe2(SO4)3
4CuFeS2 + 17O2 + 2H2SO4 4CuSO4 + Fe2(SO4)3 + 2H2O
•Rikastustekniikan seminaari 2016 •30
Decomposition of sulfide
minerals through
oxidation
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Five-compartment autoclave
•Rikastustekniikan seminaari 2016 •32
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Alternative lixiviants for gold
Thiosulfate
Barrick Gold introduced thiosulfate leaching circuit that achieved commercial production in Q3
2015 and is expected to complete its ramp up by Q3 2016. Barrick Gold’s Goldstrike mine will be
the largest scale use of the alternative lixiviant the world has ever seen.
Thiourea
Has been used to treat antimony –rich concentrate in Australia. No large scale operations so far.
Thiocyanate
Acidic thiocyanate has been investigated by Newmont Gold
Chloride
Outotec is developing it own non-cyanide technology basing on chloride leaching and solvent
extraction. No full-scale operations so far.
•Rikastustekniikan seminaari 2016 •34
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Barrick Gold Goldstrike operation with thiosulfate leaching
•Rikastustekniikan seminaari 2016 •35
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General diagram for Outotec chloride leaching process
Leaching S/L
S/L
S/L
S/L
S/L
Au extraction
Ag extraction
Au stripping
Ag stripping
Ag cementation
Au reducing
Effluent treatment
Effluent treatment
Evaporation
Cu-Zn precipitate
Solution bleed
Cu-powder
Au -product
Ag -product
Steam
Hydroxide precipitate
Au -concentrate
Oxygen Reductant
Leach residue
•36 •Rikastustekniikan seminaari 2016
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Conclusions
• History of gold processing is long, extending back thousands of years
• Minerals processing, hydrometallurgical and pyrometallurgical
techniques are commonly used for gold recovery
• Hydrometallurgical methods play the predominant role in gold
processing
• Currently main new developments are ore sorting and alternative
lixiviants for cyanide
• In addition to conventional mineral processing engineering students
should acquire basic knowledge of gold hydrometallurgy
•Rikastustekniikan seminaari 2016 •37