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Autoclave Technology -Applications for Sulphide
Concentrates and Laterite Ores
CICITEM Annual Meeting, Antofagasta, Chile,
28th and 29th July 2010
Arthur Barnes
Introduction to Xstrata and Xstrata Process Support
3
Xstrata Process Support
Falconbridge, Sudbury, Ontario, Canada
4
Xstrata Process Support
History
Originally Falconbridge Technology Centre:• Initial research centre in Thornhill, Ontario.
• New centre opened in Sept. 1997, in memory of Frank Pickard (President & CEO of Falconbridge 1991 to 1996 who was a constantchampion of technological advancements with strategic vision.
• Built for a cost of $18m, following in-depth strategic planning.
• Incorporated Noranda Technology Centre in 2005 when Falconbridge
and Noranda merged.
• Acquired by Xstrata in 2007
• Now a fully independent consultancy and test centre, available to external clients as well as Xstrata
• ~55 employees, 4 divisions
5
Background to Xstrata Plc.
Xstrata Plc is a major global diversified mining group.
Headquartered in Zug, Switzerland, Xstrata maintains a position in
the following major international commodity markets:
• copper, coal, ferrochrome, nickel, and zinc,
• recycling facilities,
• additional exposures to gold, lead, silver vanadium and
Platinum group metals
• suite of global technologies (Xstrata Technology).
The Group's operations and projects span 18 countries:
Argentina, Australia, Brazil, Canada, Chile, Colombia, Dominican
Republic, Germany, Jamaica, New Caledonia, Norway, Papua New
Guinea, Peru, South Africa, Spain, Tanzania, the USA and the UK.
Xstrata employs 43,000 people (including contractors).
6
Process Control - Identify and deliver robust process control technology and engineering solutions.
Process Mineralogy - Design, implement and optimize mineral processing flow sheets by matching the flow sheet to the mineralogy.
Extractive Metallurgy – Provide high-end extractive metallurgy services. Flow sheet/project development using modeling, laboratory tests and piloting.
Materials Technology - Improve the reliability of critical equipment through appropriate implementation of well proven materials engineering practices at essential stages of design, procurement and operation.
XPS Specialist Services
Applications of Pressure leaching to sulphides and oxides
Contents
8
Contents
1 Introduction- Pressure Leaching
2 Overview- Sulphide & Laterite ore Leach Chemistry
3 Overview- Pressure Leach Reactors
4 Sulphide and Laterite Installations
5 Operational Challenges- Case Studies
6 Materials of Construction
7 Appendix: Design Principles (Not presented in this lecture)
Pressure Leaching
Some Basic Principles -
10
Introduction
• Leaching is a natural process of mineralogical alteration
(weathering) involving water. Most natural leaching involves
oxidation.
• The rate at which oxidation occurs can be increased by the
presence of reagents. e.g. acid; by increasing temperature
and by increasing concentrations of reagents, and by the
presence of solvents. The Arrhenius equation is a useful
guide:
k= A e –Q/RT where: k= rate;A= rate constant
R= gas constant; Q= Activation energy
11
Introduction- continuedThe use of Pressure
• Increasing temperature alone leads to issues relating to boiling of reagents and volatility of solvents. The use of pressure permits increased concentrations and temperatures, allowing leaching of otherwise very unreactive minerals.
• Improved kinetics allow more compact reactors
• The operating conditions impose more demands on the equipment.
12
The “Autoclave”
. •Strong walls- pressure vessel
•Maximum pressure controlled (or else dangerous!)
•Batch and continuous reactors need a pressure transition concept for loading and discharging
•Operating temperature above normal boiling point of water
13
Continuous Autoclave Components
Impeller
Compartment Wall
(Air, Oxygen, Acid)
Compartment
Drive
14
Typical Sulphide continuous pressure leach arrangement “Pox”
15
Copper- Total Pressure oxidation
16
Pressure Leach Applications-Some Examples
• Sherrit ammoniacal nickel sulphide concentrate leach
• Xstrata Nikkelverk matte chloride leach
• Laterite leaching (Moa bay, Goro, Murrin Murrin)
• Sherrit Sulphuric acid matte leach (RSA base metal ops)
• Norilsk pyrrhotite leach
• Refractory gold full pressure oxidation
• Kidd Zinc pressure leach
• Chambishi Metals cobalt matte-alloy leach
• Outotec DON process
17
Typical Chemistry (Simplified)
Sulphide leaching: (Pressure oxidation)
Reaction sequences depend on pH and pO2
MS+ H2O+O2= MO + S0 + H+
S0 + O2= SO32-
SO32- + H2O= H2SO4
SO32- + MO= MSO4
“Water + Oxygen + sulphide= soluble metal + acid”
Laterite Leaching (Pressure acid leach)
2(Ni,Fe)OOH + H+ = Ni2+ + Fe2O3 +2H2O
via: 2NiO + 4H + = 2Ni2+ + 2H2O and
2FeOOH= Fe2O3 +H2O
(Note Ni in ore is not = Fe in ore)
“Ore + acid = soluble metal + residue + water”
18
Poirbaix Diagram (Eh-pH)
14121086420
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
S - H2O - System at 25.00 C
C:\HSC4\S25HiOx.iep pH
Eh (Volts)
S
H2S(a)HS(-a)
HSO4(-a)SO4(-2a)
S2O8(-2a)Sulphur-water system
Increasingoxidation
IncreasingAcid
1914121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
+00
+00
+00+00
-03
-03-03
-06
-06-06
+00
+00
-03
-03
-03-06
-06
-06+00
+00
-03
-03
-06
-06
-03
-03
-06
-06
Zn - H2O - System at 25.00 C
pH
Eh (Volts)
Zn
ZnOZn(+2a)
ZnO2(-2a)
Pourbaix Diagram Zn-waterEffect of Zn concentration
Increasingdilution
20
Differences between Sulphide Leaching and Laterite Leaching
SULPHIDES
• Minerals need oxidation, i.e. oxygen-slurry mixing. Oxygen transfer controls kinetics.
• Control of sulphur and passivation can be key at lower temperatures
• 110-170oC vessels –design lead lined steel vessels with acid resistant brick
•Temperature Control (exothermic)
•Diluted feed required
LATERITES
•Species already oxidised,
•Fe precipitation and Mg content in feed control sizing and economics
•>240oC vessels -design method commonly Ti cladding (no bricks)
•First order reaction kinetics r=k[H+]
•Temperature Control (endothermic)
Examples of Pressure leach operations
22
Vale Nickel Sulphide Pressure leachVoisey’s Bay)
23
Typical Matte Leach circuit
Case Study 1
Chalcopyrite leaching
25
The Problem Of Chalcopyrite
• Chalcopyrite is the one of the most difficult sulfide minerals to leach.
• There are two INTERFACE problems in treatment of chalcopyrite
• Passive films of copper polysulfide form with mild leaching in sulfate
• Liquid sulfur occludes unleached chalcopyrite preventing complete extraction
• Passive films can be prevented by ultra fine grinding (5-15 um)
• How to solve the problem of liquid sulfur occlusion? Surfactants!
• Pressure leaching deals with both problems
26
Chalcopyrite leach chemistry
Compare the simple leach chemistry:
MS+ H2O+O2= MO + S0 + H+
S0 + O2= SO32-
SO32- + H2O= H2SO4
SO32- + MO= MSO4
For chalcopyrite: The overall reaction
2CuFeS2 + 17/2O2 + H2O= 2CuSO4 + Fe2O3 + 2H2SO4
does not go to completion because the intermediate
S0 reaction results in an inert boundary layer
= “passivation”.
27
Sulphur oxidation in acid medium
28
Sulphide leaching challenges
Elemental sulphur melts in hot water
Above 160oC it becomes very viscous
29
To be successful in leaching chalcopyrite at T < 119oCrequires avoidance of passivation of chalcopyrite by copper polysulfide
To be successful in leaching of chalcopyrite at 150o C in presence of elemental sulfur requires process conditions that prevent liquid sulfur occlusion of un-reacted sulfides and avoidance of passivation due to presence of copper polysulfide layer.
To be successful in leaching chalcopyrite at T > 200o C, requires managing the excess acid produced in the copper autoclave process.
Rules for Chalcopyrite Leaching in Sulfate Systems
30
Sulphate Process Options For Chalcopyrite Leaching Typical Parameters
PROCESS TEMP PRESSURE P80 Special S Yield
(˚C) (ATM) (μm) (%)
ACTIVOX 110 12 7 70
ALBION 85 1 7 50
ANGLO-UBC 150 12 7 SURFACTANTS 70
BIOLEACH 45 1 7 MESOPHILES 0
BIOCOP 85 1 37 THERMOPHILES 0
CESL 150 12 37 12 g/L Cl 90
DYNATEC 150 12 37 COAL + RECYCLE 60
GALVANOX 85 1 37 VARIOUS 95
MT GORDON 90 8 100 CHALCOCITE
PLATSOL 225 30 15 10 g/L NaCl 0
SEPON-ATM 85 1 100 CHALCOCITE
SEPON-AC 225 30 100 PYRITE 0
TOTAL POX 225 30 40 0
Case Study 2
Laterite High Pressure Acid Leach
32
Laterite Ore Body -Description
SiO2
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Ni
MgO40 %MgO,% Fe,% SiO
1 2 3
Co x10
GEOCHEMISTRY
20
GRENAILLE
0FERRICRETE
RED LIMONITE
YELLOW LIMONITE
EARTHY SAPROLITE
ROCKY SAPROLITE
FRESH PERIDOTITE
TRANSITIOALLIMONITE
ASBOLANE
40 – 45m
Fe
%Ni, %Co x10
SiO2
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Ni
MgO40 %MgO,% Fe,% SiO
1 2 3
Co x10
GEOCHEMISTRY
20
GRENAILLE
0FERRICRETE
RED LIMONITE
YELLOW LIMONITE
EARTHY SAPROLITE
ROCKY SAPROLITE
FRESH PERIDOTITE
TRANSITIOALLIMONITE
ASBOLANE
40 – 45m
Fe
%Ni, %Co x10
TypicalHydroprocessing
TypicalPyroprocessing
33
HPAL for laterites
34
Xstrata Nickel – Strategic Options
Laterite Smelting
Pressure Acid Leaching
Improved Caron Process
Saprolite Ore Calcine FerronickelCalcinationReduction
SmeltingRefining
Limonite Ore Mixed Sulphide Mixed Oxide to FNALeachingPrecipitation
Roasting
Limonite Ore Calcine Mixed Oxide to FNACalcinationReduction
LeachingPrecipitation
35
Nickel Eh-pH chart
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Ni - S - H2O - System at 25.00 C
C:\HSC4\NiS25.iep pH
Eh (Volts)
Ni3S4
Ni
NiSNi3S2
Ni3S2
NiONi(+2a)
36
SIX COMPARTMENT AUTOCLAVE
MIXEDSULPHIDES
TO REFINERY
HEATING TOWERS
TRIMHEATER
PARTIALNEUTRALIZATION
HEATER H2S PRECIPITATION THICKENER
FILTERPRESS
TAILINGS DAM
HP STEAM
HEAT RECOVERY
ACIDSULPHURICACID
PLANT
7 CCD'S
To TailingsDISPOSAL
WASHSOLUTION FILTRATE TO EFFLUENT
TREATMENT
BARREN SOLN TOCCD
SO2/LIMESTONE/ LIME
PREGNANTSOLUTION
SCREENS
WATERWATER
O/S TOBALL MILL
L-ORE
REPULP DRUM
PARTIALNEUTRALIZATION
LIMESTONE
HYDROGEN SULPHIDE
Mn FixationRoaster
Pressure Acid Leach (Generic)(Ivory Coast & Koniambo)
37
Pilot Autoclave
Materials Selection Issues
Corrosion of Components
39
Considerations for Material Selection
Specific process conditions:
T,P, pO2 pH, [Cl-], [S] etc.
Gangue minerals
Secondary elements
Precipitates
Site conditions ( Arid/ Humid/ Arctic/ Tropical)
Implication: every orebody is unique, every reactor must be designed for the specific ore and reagents available
Extended Piloting testwork and equipment evaluation is essential!
40
Piloting testwork–Pressure Acid LeachCanada: ~$3.5 million, 1 year duration
96 L effective volume, 6 compartment
Ti-2 autoclave with Ti-7 inlay (Parr heads)
41
Piloting –CCD CircuitCanada: $0.5m ½ year
6 stage CCD circuit (Ti-2) with external dilution wells (floc)
42
New Materials - HPAL
• Isolation Valves (material selection)
� VPS TiO2 no bond coat (corrosion, porosity, adhesion & wear)
� Life increased from 7 hours to 3 months!
� The limiting factor became coating delamination
− Delamination at edges (predominant mode in VPS TiO2)
− Corrosion of substrate (high porosity in coatings)
Cawse – Discharge Ball (10” Ti Gr 7 Cr2O3 Coated)
Xstrata – Discharge Ball (½” Ti Gr 7 TiO2 Coated)
43
Thank you