1. SAL OR DESAL
SEAWATER SUPPLY OPTIONS
FOR THE MINING INDUSTRY
Raymond Philippe, Richard Dixon and
Silvana Dal Pozzo
Hatch Ingenieros y Consultores Ltda, Chile
2. Decision Seawater
Saline - desalinated
• Is not (should not be):
– CAPEX Saline = CAPEX desalinated – CAPEX desal plant +
corrosion compensation
– Trade-off based on SWOT analysis (qualitative)
• Depending on the mining project, water supply may
represent up to 10-30% of CAPEX of the overall project
• Requieres engineering to get to a project feasibility estimate
3. Contents
• Experience use of seawater in mining
• Identification of differences salt vs.
desalinated seawater
– Chemical aspects
– Conveyance
– Aspects on the use of seawater in mining
processes
• Conclusions
4. Characteristics
Chilean Mining Project
• Norte Chile (desert), water scarcity
• High volumes (500 -10000 m3/h)
• Project altitude (1500 – 4500 masl)
• Distance to ocean (80-200 km)
• Copper mining (Copper/moli, copper/gold)
• Copper flotation
– Greenfield
– Technology conversion from oxides to sulphides processing
6. Experience seawater usage
• Salt water (seawater/ saline well water)
• Michilla, Chile
• Las Luces, Chile
• Mantos de la Luna, Chile
• BHP Nickel, Australia
• Texada Mines, Canada
• Batu Hijau, Indonesia
• Esperanza, Chile (under construction)
8. Batu Hijau (Indonesia) Texada (Canada)
All existing direct salt seawater usage is in mining projects at short
distance and relatively low altitudes compared to the majority of the
actual mining projects in Chile
• Simple and economical conveyance systems
• Water conveyance costs do not require process optimization
(recirculation, thickened tailings)
11. Salt vs desalinated seawater
Possible impact differences in:
• Seawater intake (outfall)
• Pretreatment
• Desalination plant
• Conveyance system
• Mineral Processing
• Environment
• Financing
12. Salt vs desalinated seawater
Seawater intake and outfall
• Intake volume capacity
• Outfall from desalination plant
• Permitting/Studies
• Coastal space availability and concessions
13. Salt vs desalinated seawater
Desalination plant
• CAPEX
– Mayor capital investment
– For saline water: eventual requirement of smaller
desal plant at minesite
• Operation costs
– Desalination well understood, global experience
– Specialized personnel, due to distance, difficult to
integrate with minesite
14. Salt vs desalinated seawater
Pretreatment
– Desalination process requires pretreatment
– But salt water conveyance also requires pretreatment
– Chemicals handling/storage
– On site personnel
– Effluent and solids generation
– Organic matter
• Removal instead of destruction
• Red Tide events
16. Conveyance -Genijev criterium
Pipe internal roughness as a function of time and fluid
εt = ε0 + a t Genijev Roughness
9
– Salt water <a> = 0.51 8
– Desalinated water <a> = 0.025 7
6
Roughness (mm)
5 Desalinated
4 Saline
3
2
1
0
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Year
Generally used Formula of Colebrook-White does
not consider time or fluid dependency of pipe roughness
17. Salt vs desalinated seawater
Conveyance
Should consider and compensate for
• Project life time
• Required availability of water supply system
• Difference in minimum pipe thickness requirements
• Difference in pressure drop between desalinated and
salt water L ρ
– Piping design (include time dependency) ΔP = λ v2
– Number and position of pumping stations D 2
** Avoid risk of underestimating pump capacities for salt water
18. Salt vs desalinated seawater
Environment
• Environmental
– Desalination plant outfall
– Contamination
– Leakages
– Tailings pond infiltration
– Emergency systems (containment ponds)
• Community issues
– Desal plant location + size
– Desalination plant outfall
19. Salt vs desalinated seawater
Corrosion handling
Materials selection (base case: carbon steel)
• Desalination plant
• Conveyance system
• Concentrator
OPEX
• Antiscalant/Anticorrosion reagents
• Spare parts (2% CAPEX/yr)
20. Salt vs desalinated seawater
Copper Mineral Processing
Consideration: Most processes were developed based on industrial
experience with “good” water quality, not salt water
• Sulphide processing (flotation), differences in
– Tailings (conventional and thickened)
– Molibdenum recovery
– Concentrate quality
– Carbonate/Gypsum scaling
– Corrosion
• Leaching
– Oxides
– Sulphides (bioleaching)
21. Salt water
Tailings management
• There is global industrial experience in conventional
tailings deposits using salt water, however, there is none
using thickened tailings
• Thickened tailings with salt water behavior
– Sedimentation velocity
• Difference specific gravity
• Capillary forces
– Transport
• Viscosity differences?
• Salt precipitation (scaling)
22. Salt water
Molibdenum recovery
• Poor recovery of molibdenum in selective
flotation step
– Requires good quality water
• Requires small desalination plant to wash rougher
concentrate (CAPEX/OPEX)
• Additional installations
– Washing ] (2-3 steps)
– Thickening ]
– Eventually Filtering
• Salt water requires higher dosification of reagents
– Costs
– Corrosion/scaling risk
23. Salt water
used as Process Water
• High concentrations of Cl y SO4
• Salt water recirculation costs (OPEX)
• Higher reagents consumption
• Build-up of salts in process water
– Evaporation losses
– Desalination at site: reject to process water
• Molibdenum
• Potable water
• Concentrate humidity
• Result: Process water may have even higher scaling and
corrosion potential than fresh salt seawater
24. Salt water
Reagents and consumables
• Extra process modifications required
– pH control
– Flotation reagents efficiency
– Pyrite depression
– Organic reagent degradation due to chloride contact
• Flocculants
• Flotation reagents
• Evaluate anticcorrosives (phosphates) interference in
flotation processes
• Higher steel consumption in ball mills
25. Salt vs desalinated seawater
Electrical energy requirements
• Seawater desalination
– Reverse Osmosis (Chile) 4-5 kWh/m3
• Conveyance
– Pipeline length
– Project altitude
– Pumping stations
In general (new projects Chile):
Energy consumption for conveyance >>> desalination
26. Salt vs desalinated seawater
Financing
Desalination plant financing
• EPC as package within EPCM contract
• BOO/BOT,…
• US$/m3
Advantages
• Take investment off of balance sheet
• Lower OPEX?
Disadvantages
• Control
• Supply assurance
27. Execution Program
Mining projects
• Conceptual Engineering
– Definition water requirements
– Trade-off salt vs desalinated water
• (Pre)feasibility studies
• EIA
• Basic Engineering (acquisition major equipment)
• Detailed Engineering and Construction
28. Execution program
Seawater supply system
Indicative timing
• Preliminary Engineering 3-6 months
• Base line studies 6-12 months
• EIA/Permits/Rights of way 6-18 months
• Acquisitions and delivery 10-14 months
• Construction 6-12 months
• Mining vs water supply project:
– Velocity/timing differences
– Pressure on water project
– Influence sal/desal definition
29. Analysis
salt vs desalinated water
• CAPEX (water supply + mine)
• OPEX (water supply + mine)
• Costs/Penalties/Opportunities (water supply + mine)
• Risks (water supply + mine)
• Environment and Community aspects
• Minelife
Based on cuantitative analysis and differences, mining
company can base it’s decision
30. Conclusions
Salt vs desalinated seawater
• Economic evaluation for both cases should consider not
only differences in water supply systems but also
associated costs to the overall mining project.
• Industry experience: In general not all relevant aspects
for the alternatives evaluation are being considered
• Both alternatives should be developed to at least
prefeasibility level (quantified) before decision is taken
– Impact on CAPEX
– Compatibilize execution programs