Cu, Ni & Co Extraction

Extraction of Base Metals (Copper, Nickel and Cobalt) S. K. Sahu Metal Extraction & Forming Division National Metallurgical Laboratory, Jamshedpur

Introduc Copper – the most extensively tion next only to steel & aluminium

32%

35%

3% 8%

used metal

10%

7% 5%

Electrical (35%)

Telecommunications (5%)

Power Transmission (7%)

Automobile industry (10%)

Building construction (8%)

Railway equipment (3%)

Miscellaneous (32%) Copper Consumption

Its chemical, physical & aesthetic properties make it suitable for wide range of domestic, industrial & technological applications Global demand for Cu – 18 million tons (Primary production - 88% & secondary production - 12%) Cu demand is growing by an avg. of 4% per year

Indian demand for Cu – 4.5 lakh tons i.e. ~ 3% of world copper market Birla Copper, Sterlite Copper & Hindustan Copper Ltd. – three major Cu producers in India Indian production of refined copper : 6.5 lakh tons India is emerging as a net exporter of refined copper Over 90% of concentrate requirement is imported

9%

20%

Nick el

10%

6%

7% 8%

65%

Cob alt 22%

9% 11%

22% 11%

Stainless steel (65%)

Batteries (22%)

Other steel and non-ferrous alloys & suoper alloys (20%)

Catalys ts (11%)

Hardmetals (11%)

Electroplating (9%)

Pigments (9%) magnets (7%)

Tyre adhesives/driers (8%) others (10%)

Coins & nickel chemicals (6%)

Nickel Consum ption

Nickel is the most volatile owing to its strong demand and tight supply Global demand for nickel – 1.3 million tons & consumption rate increasing @ 3% a year About 65% Ni is used in manufacture of stainless steel Due to lack of Ni reserves nickel market in India is import dependent India imports ~30,000 tons of nickel

Superalloys (22%)

Coba lt C on su m p tion

Cobalt is least abundant element compared to Cu & Ni In terms of application, Co regarded as a specialty metal

is

Global demand for Co – 60,000 tons It lacks any primary cobalt resources India consumes ~ 700 tons Co for application in the metallurgical & chemical sector

World Copper Usage, 1900-2006 Thousand metric tonnes Source: ICSG

Copper Ore Grades mined in USA Year

Ore Grade (Mean Cu %)

1932

1.80

1939

1.23

1949

0.90

1960

0.73

1970

0.61

2000

0.48

Demand for refined copper increasing by an average of 4% per year Due to continuous mining and processing, mineral grades of promary resources are declining However, newer & energy efficient processes are being developed to recover metal from low grade ores & secondaries to meet the requirement of the society

Extraction of Copper Copper exists in nature mostly in the form of copper sulfide Oxides or oxidised ores are found only in limited quantities Some common minerals of copper are: Chalcopyrite (CuFeS2); Covelite (CuS); Chalcocite (Cu2S), Cuprite (Cu2O); etc. Chalcopyrite is most abundant copper bearing mineral (70% of world Cu reserves) Sulfide ore containing 0.5-2.0% Cu is considered satisfactory for Cu extraction by pyrometallurgy From poor grade ores, Cu extracted by hydrometallurgical processes

Conventional Process for extraction of Copper from sulfide concentrate Possible to roast sulfide ore of copper to oxide & then reduce it by carbon in the blast furnace Concentrate also contains iron sulfide which form iron oxide Cu2S does not oxidise until FeS is fully oxidised yielding Fe2O3 Fe2O3 is difficult to remove by slagging

Therefore, blast furnace smelting is not used for copper extraction Cu extracted by matte smelting process without using any reductant

Ore (1-2% Cu) Grinding Flotation Concentrate (15-35% Cu)

Conventional route

Newer routes

Hearth/fluid bed roasting Discard slag (0.3-0.8% Cu)

Drying

Reverberatory/ele ctric furnace smelting

Flash smelting

Matte

Matte (35-60% Cu) Converting

Slag

Converting

Blister copper (98.5% Cu) Anode slime for recovery Refining of precious metals Cathode copper (99.99% Cu)

Continuous smelting Slag for cleaning & discard

Bleed electrolyte

Roast ing

Iron sulfide is partly converted to FeO for subsequent removal by slagging

2CuFeS2 (s) + O 2 (g) → Cu 2S(s) + 2FeS(s) + SO 2 (g) FeS + 3 2 O 2 (g) → FeO(s) + SO 2 (g)

Smel tin g

FeO removed by slagging with silica (SiO2) at 1200-1300 OC in reverberatory furnace Cu2S melt collected as matte

Converti ng

FeS(l) + 3 2 O 2 (g) → FeO(l) + SO 2 (g)

Cu 2 S(l) + 3 2 O 2 → Cu 2 O(l) + SO 2 (g)

ΔH01200 = -5.1 x 105 kJ/kg mol ΔG01200 = -2.3 x 105

Cu 2 S(l) + 2Cu 2 O(l) → 6Cu(l) + SO 2 (g) ΔG01200 = -0.5 x 105 Cu 2S(l) + O 2 (g) → 2Cu(l) + SO 2 (g)

ΔG01200 = -0.2 x 105 ΔH01200 = -2.2 x 105 kJ/kg mol

FeO separated as slag No external heat supply required – the reactions are exothermic No reducing agent required for removal of oxygen from the oxide

Flash smelting Conventional smelting operation is a melting

Concentrate

process rather than oxidation process Its offgas – dilute in SO2 & difficult to remove Energy intensive process because heat not generated during smelting

Flux

Drying

Air/O2

Flash smelting Matte Converting Blister copper Refining

Controlled oxidation of Fe & S – offgas strong enough in SO2 for efficient recovery as H2SO4 Evolution of large amount of heat – making the process autogenous and energy efficient

Copper cathode

Slag for cleaning & discard

Outokumpu process

Dry particulate feed and pre heated oxygen enriched air blown through the concentrate burners down into the furnace Produce matte containing 45-65% Cu under autogenous condition depending on the quantity of fuel used & degree of oxygen enrichment employed A closed process – captures upto 99% sulfur rich gases to produce H2SO4

INCO process Uses commercial oxygen (95-98% O2), rather than oxygen enriched air Oxygen blast & prticulate feed blown horizontally into the furnace No external fuel is used – all of the energy comes from oxidation of Fe & S The matte produced contains 45% Cu Slag contains 05-06% Cu – discarded Offgas containing 70-80% SO2 captured to produce H2SO4

Continuous smelting Copper concentrate Continuous smelting

Blister copper

Refining Copper cathode

Slag for cleaning & discard

Combines smelting & converting in a single furnace

WORCRA process Combines smelting, converting & slag cleaning operations in separate but interconnected zones Directly produces metal, rather than matte from a concentrate

Concentrate

In the converting zone, countermovement of slag & matte takes place, that leads to effective removal of impurities from the matte Conserves energy by utilizing heat evolved during smelting and converting in the reactor itself

Oil or coal

SiO2 Flux

Acid plant

Gas cleaner Heat exchanger Air

WORCRA Furnace

The Cu content of the slag is very low & can be discarded Blowers

Copper

Slag

Mitsubishi  Smelting furnace, slag cleaning furnace process & converting furnace - connected in cascade fashion

 Concentrate & oxygen enriched air enter S-furnace through lances to produce matte and low Cu slag  In the C-furnace matte gets oxidised to blister copper

Main features All of the furnaces are stationary, driving mechanisms viz. furnace tilting, tuyere punching, hood driving etc. are not required Molten products are transferred from one furnace to the next furnace under gravity Molten products overflow continuously through the outlet hole of the furnace eliminating need for tapping and slag skimmig operations

IsaSmelt/Ausmelt process A high intensity smelting process producing matte from Cuconcentrate & secondary materials Uses an extremely efficient top-submerged lance & a simple stationary refractory-lined furnace Air, oxygen & fuel are fed through the lance into the molten bath, creating a high turbulant environment that promotes rapid reaction of raw materials Depending upon the grade of raw materials, matte containing upto 75% Cu can be produced

Advantages Low capital cost due to simple furnace construction & peripheral system arrangements Flexibility to use various fuel types (coal, oil, gas) Ability to produce high grade product from low grade materials Small furnace foot-print

Energy The table compares the energy requirements for seven smelter types, consumptio including the energy equivalents of the materials consumed by each process. n

Energy requirements vary for the different pyrometallurgical processes. Flash furnaces make the most efficient use of the thermal energy released during the oxidation of sulfides; they generate sufficient heat to provide a large proportion of the thermal energy for heating and melting the furnace charge. Electric furnaces use electrical energy efficiently because of the low heat loss through the effluent gas, they make limited use of the heat produced during oxidation of the sulfide minerals, and their energy costs are high because of the high price of electricity.

Hydrometallurgical extraction of Cu Environmental aspects

Hydrometallurgical extraction of Cu

Exploitation of complex & low grade ores Small isolated deposits Simplified flow-chart Leach-SX-EW Process Ore or mine waste

Leaching

Solid waste Acid make up

Cu loaded organic Cu loaded leach liquor

Extraction

Stripped organic

Stripping

Aq. solution of Cu

Spent electrolyte

EW

Cu cathode

Chalcopyrite is a very stable mineral, therefore it very hard to leach Cu from chalcopyrite concentrate However, under oxidising condition Cu can be leached from chalcopyrite concentrate

Ferric chloride CuFeS + 4FeCl → CuCl + 5FeCl + 2S leaching 2

3

2

2

CuFeS2 + 3CuCl2 → 4CuCl + FeCl2 + 2S

Electrolysi s Half Cu is deposited cathodically Cu+ + e → Cuo

at cathode

Rest half Cu is oxidised to Cu2+ at anode Cu+ - e → Cu2+

at anode

Produces elemental sulfur as a by-product – eliminates setting up of sulfuric acid plant

Pressure sulfuric acid Sulfide concentrates can be leached in leaching the acidic system under oxygen pressure

Sulphide concentrate Pressure Acid Leach

CuFeS2 + 2H2SO4 → CuSO4 + FeSO4 + 2S + 2H2O Iron ppt FeSO4 +1/2H2SO4 + 1/4O2 →1/2Fe2(SO4)3 + 1/2H2O

Solution purification Leach liquor

LIX 84

1/2Fe2(SO4)3 + 3H2O → Fe(OH)3 + 3H2SO4

Cu Extraction CYANEX 272

Cu Stripping Co Extraction Cu Solution Co Solution CuSO4/Cu

CoSO4/Co

Ni Solution NiSO4/Ni

Extraction of nickel & cobalt The principal ore of nickel is pentlandite [(NiFe)9S8] Cobalt does not have any primary ore Cobalt is extracted as a by-product of Cu, Ni, Zn or precious metals

Process flow sheet for Ore extraction of nickel (1.3% Cu, 1.2% Ni)

Tailings (0.1% Cu, 0.2% Ni)

Grinding Flotation

Roasting Reverberatory furnace smelting

Bulk Cu-Ni Concentrate (6% Ni, 7% Cu) Cu concentrate (30% Cu, 1% Ni)

Copper cliff mill Ni concentrate (10% Ni, 2% Cu)

Flux

Pyrrhotite concentrate (0.9% Ni)

Matte (20% Ni, 7% Cu) Slag Converting

Slag discard

Matte (50% Ni, 25% Cu, 20% S)

1

1 Cu concentrate (70 % Cu, 5% Ni)

Slow cooling Grinding Magnetic separation Flotation Low Cu (0.8%) Nickel sulfide

Fluid bed roasting

Metallics to precious metals recovery (64% Ni, 16% Cu, 10% S) High Cu (3-4%) Nickel sulfide

Fluid bed roasting

Nickel oxide (low copper)

Nickel oxide (high copper)

Reduction Reduction Metallic nickel (95% Ni)

Reduction smelting

Carbonylation Nickel pellets (99.95%)

Nickel powder (99.93%)

Electrolysis Electronickel (99.93%)

Extraction of nickel & cobalt from lateritic ore Laterites are weathered, metal rich rocks (oxides) either in the form of limonite or serpentine Limonites are mainly iron oxide containing Ni & Co & minor amount of magnesium silicate Serpentine comprise nickel ferrous hydrated magnesium silicate From such lateritic ores Ni & Co are extracted either by highpressure acid leaching or by ammonia leaching (Caron process) Serpentines are not treated by high pressure acid leaching because high magnesium content results in excessive acid consumption

SERPENTINE

LIMONITE

H2SO4

CO

Pressure acid leaching

Reduction

CO2

NH3+(NH4)2CO3

Filtration

Residue to waste

Cooling Air Leaching

Neutralisation NH4HS Filtration

Filtration

Precipitation

Precipitation

Filtration

Filtration

Residue to waste & NH3 recovery

H2S

Acid to waste

CoS + NiS

Acid to waste

CoS + NiS

Process for recovery of Ni & Co from scrap H2SO4

India does not have any primary resource for Ni & Co Indian refiners depend on imported feed materials Type of materials imported to India for recovery of Co & Ni are sludges, scrap, metallic grinding dust, slags, etc.

Process for recovery of Ni & Co from sludge

Process for recovery of Ni & Co from slag