Outotec and Sustainability

Kullan talteenotto malmeista – uutta ja ikivanhaa Jaakko Leppinen Rikastustekniikan seminaari, Oulu 23-24.8.2016 World gold production in 2012

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

Hydrometallurgical processing of gold ores and concentrates is currently dominated by cyanide leaching and around 60% of all gold is produced Artisanal mining using cyanide. Amalgamization

Hydro

metallurgy Smelting

• 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.

Gold washing Wash table Manual grinding

Smelting

Gold production today

• Gold collected from stream beds (8000 BC)

Gravity separation techniques • Washing of alluvial gold (before 3500 BC) • Mining of gold (3500 BC)

• Smelting (3000 BC) High-temperature techniques • Cupellation to separate other metals from gold-silver alloys (2000 BC) • Parting to separate silver from gold (600 BC) Amalgamization • Amalgamization (100 BC)

• Leaching with aqua regia (700 AC) Leaching

• Leaching with chloride (1850 AC) Cyanidation • Cyanidation (1890)

• Flotation process 1905 Flotation

• Refractory ore treatment with pressure oxidation (1985) Hydrometallurgical • Refractory ore treatment with bio-oxidation (1986) treatment of refractory ores

• Use of alternative lixiviants for gold leaching (2000-) Alternative gold lixiviants • Sensor based ore sorting for gold ores (2000-) Sensor based ore sorting

FREE-MILLING GOLD ORE REFRACTORY GOLD ORE

LOCKED PARTICLE IN SILICATE

LIBERATED GOLD

INVISIBLE GOLD IN SULFIDE COMPOSITE GRAIN FINE INCLUSIONS IN SULFIDE LOCKED PARTICLE IN SULFIDE

Leaching? Leaching? Flotation? Flotation? Fine grinding? Fine grinding? Gravity separation? Gravity separation? Decompostion of gold bearing minerals?

Heap Leaching Gold

Flotation Agitated Cyanide Crushing Grinding Leaching Gold Free Milling Au Gravity Ore concentrate

Crushing Grinding Flotation Gold concentrate to smelter or leaching

Refractory Agitated Cyanide

Crushing Grinding Flotation Pre -oxidation Leaching Gold

Au Ore

Gravity concentrate

Gravity separation CRUSHING TAILINGS TREATMENT

ORE Paste T

thickening a Classification

GRINDING i

THICKENING l Crushing Grinding Flotation Thickening Filtration

FILTRATION i n

Concentrate FLOTATION

Sorting Tailing Thickening

Filtration

Concentrate

Gravity concentrate

Gravity separation

ORE Paste T

thickening a

Classification i

Crushing Grinding Flotation Thickening Filtration l

i n

Concentrate

Sorting Tailing Thickening

Filtration

Concentrate

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

Gold ore

Crushing Comminution Grinding Leaching Cyanide leaching S L

Sorption in activated carbon Zinc cementation Merrill-Crowe Recovery Elution from activated carbon

Electrowinning

Smelting

Gold

ORE FROM GRINDING CYANIDE LEACHING CARBON ADSOPTION

slurry

ACTIVATED CARBON

LOADED CARBON

ELECTROWINNING ELUTION TAILING

REGENERATION BARREN CARBON

Gold ore

Crushing Comminution Heap leaching Grinding

Leaching Cyanide leaching

Heap leaching Solid-liquid separation

Zinc cementation Carbon in Column Carbon in Pulp Carbon in Leach Recovery (Merrill-Crowe) CIC CIP CIL Gold is Gold adsorbed on Gold adsorbed on Gold adsorbed on precipitated from activated carbon activated carbon activated carbon in cyanide solution from cyanide from cyanide slurry cyanide using zinc powder solution (CIC) solution with solution with solids. Adsorption solids. Adsoprtion take place in a takes place separate stage simultaneously (CIP) with leaching (CIL)

Gold ore 1-10 g/t

Tailings 0.1-1 g/t Cyanide leaching Solution 1-5 mg/l

Sorption in activated carbon Carbon 5-10 kg/t Elution from activated carbon

100-1000 Au in ore mg/l Electrowinning Au in solution

Dore bars Smelting 70-80% Au in carbon

Some milestones: 1867 First patent on cyanide leaching

1889 First cyanidation plant : Crown Mine in New Zealand First commecial scale plant 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 Zinc cementation for gold 1904 Merrill introduces zinc dust for gold precipitation recovery from solution 1906 Crowe applies vacuum deareation to zinc precipitation Carbon in pulp CIP 1949 First CIP plant at San Andreas in Honduras 1951 CIP process patented by McQuiston and Chapman New elution methods from 1952 USBM develops carbon elution process (Zadra) activated carbon 1970 First cyanide heap leach operation in Carlin, Nevada

Heap leaching of gold

1973 AARL elution process 1985 First pressure oxidation plant at Homestake McLaughlin (USA) Pre-treatment methods

1986 Start-up of cencentrate biological oxidation plant in Fairview, for refractory gold South Africa

Electro Copper refining cathodes

Anode slime

Anode Gold slime Palladium treatment Platinum

Electro Copper refining cathodes

Anode slime

Anode Gold slime Palladium treatment Platinum

Laser image Sorting image Photo

• Suitable particle size 10-250 mm •1 • Depending on ore characteristics •2 10 to 70 % of material can be rejected

• Capacities capable of meeting the •3 needs of many concentrators (upto 500 tph per unit) • Today - mature technology

• Good understanding of mineralogy •4 and ore geology is required •1 • Feeding of unsorted material • The most common sensors: •2 • NIR sensor

optical and X-ray transmission •3 • Color sensor (XRT) •4 ..\..\..\TOMRA\CommodasUltrasort_QUARZITE.mov • Separation chamber

INVISIBLE GOLD IN SULFIDE FINE INCLUSIONS IN SULFIDE

GOLD ORE

CONCENTRATION

PRESSURE CHEMICAL FINE GRINDING BIO OXIDATION ROASTING OXIDATION OXIDATION

CYANIDATION

GOLD

Mineral composition in concentrates 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) Distribution of gold between minerals Apy = arsenopyrite (FeAsS)

Py = pyrite (FeS2)

Autoclave

2FeS2 + O2 + 2H2O 2FeSO4 + 2H2SO4 Decomposition of sulfide minerals through 4FeSO4 + O2 + 2H2SO4 Fe2(SO4)3 + 2H2O oxidation

2FeAsS + 7O2 + 2H2O + H2SO4 2H3AsO4 + Fe2(SO4)3

4CuFeS2 + 17O2 + 2H2SO4 4CuSO4 + Fe2(SO4)3 + 2H2O

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.

Oxygen Reductant

Au - concentrate Leaching S/L Au Au Au extraction stripping reducing

Leach residue Ag S/L Au -product extraction

Effluent Ag Effluent treatment stripping treatment

Ag Cu-powder Evaporation S/L S/L Hydroxide cementation precipitate

Steam Cu-Zn S/L Solution precipitate bleed

Ag -product

• 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