School of Process, Environmental and Materials Engineering FACULTY OF ENGINEERING Potokwe Tholego Ramakoba Aubrey Ranna W. Katlego Othusitse Nhlanhla Seporo Stephen Shomana Thapelo M3-Production of copper concentrate and 99.99% copper cathode from low-grade copper ore in Frank, Northern Chile Our mineral potential turns your world 4 th May 2012
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School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING
Potokwe Tholego
Ramakoba Aubrey
Ranna W. Katlego
Othusitse Nhlanhla
Seporo Stephen
Shomana Thapelo
M3-Production of copper concentrate and 99.99% copper cathode from low-grade copper ore in Frank,
Secondary Cone Crusher:• Open circuit, size 3050 mm • c.s.s ≈ 25 mm
Cone size = Head Diameter, c.s.s. = closed side setting
Fine Ore Storage Bin
A 2000 t bin, mass flow system with a belt feeder
Lining: Bisalloy 360 Domite Ni Hard
Dimensions: Hopper angle, 20o; Height, 18.3
m; Opening diameter, 0.34 m; Shell diameter, 6.1 m
Grinding and classification
Ball Mill
Ball sizes, 14.96 cm Spout feeder preferred since its
suitable for hydroclone classifier Over-flow discharge mechanism will be
used 2 ball mills to operate:
Shell diameter, 4.45 m Inside diameter, 4.39 m Rubber lining, 0.18 thick with
waves Length 5.71 m 40 % by volume charge
Hydrocyclone
Due to inconsistent design data, a close example was used to estimate the shell diameter, Dc
The closest reference is the Africa u-ground concentrator with a product size of 100 µm.
The plant has 8 hydrocyclones with 0.25 m diameter, this is the size and the number of cyclones used in the project.
School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING
Froth Flotation
Aubrey Ramakoba
PROSS Flotation Flow sheet
CONDITIONING
Supplied by Denver Mineral Engineers Inc
• Xanthates• lime
Reagents
• 200 t/hr solids
• 600t t/hr water
Feed
8m
FLOTATION EQUIPMENT
MECHANICAL CELL
Drive mechanism
impeller
Cylindrical tank
PNEUMATIC MACHINE
FLOTATION CELLS
MECHANICAL MACHINESBetter suited for early stages
• Impellers makes it easy to float the valuable from the gangue
• Suitable where fines/slimes are present
PNEUMATIC MACHINESBest for cleaning stage;
• high recoveries and optimized grade
• One stage cleaning
• Cheap
• Easy to use
ROUGHER/ SCAVENGER CELLS
Distinctive features of Denver mechanical cell;
•Aeration can be easily controlled- supercharging can be employed for sluggish pulps
•No short circuiting
•No pumps needed to move pulp from one cell to another but uses gravity
•Selective flotation can be achieved as a result of the combination of machine features
ROUGHER/ SCAVENGER CELLS
Compared to the Denver cell;
• The Wemco cells lacks positive pull from the other cells to the impeller without a special pumping system.
• Pumps are needed to move the pulp from one cell to the other in the cells
CLEANER 2 EQUIPMENT
The main advantages of Metso columns are;
•Maximum particle-bubble contacts
•Effective reagent activation from the mechanical operation of the pump
•Wash water
•Increased carrying capacity
•Low operating cost
SUMMARY
Stage Equipment Supplier Size
Conditioning Conditioning tank Denver Minerals Engineers
22 m3
Roughers / Scavengers
Denver cells Denver Minerals Engineers
2.8- 36.1 m3
Cleaner 1 Denver cells Denver Minerals Engineers
2.8- 36.1 m3
Cleaner 2 Metso flotation column
Maelggwyn Mineral Services Limited
2.5 – 80 m3
School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING
Agitation Leaching
Wathuto Katlego Ranna
AGITATION LEACHING
WHAT IS IT?
Agitation leaching is a process where the ore is slurried with the extraction fluid for a period of time.
When equilibrium between the metal on the mineral surface and the metal contained by the solution is approached, the solubilisation of the metal in the solids is slowed, and the extraction is considered to be complete.
Comparison with other methods
•Agitation leaching provides a means for high recovery in short residence time.
•It is meant for ore that has high metal content
WHY AGITATION LEACHING
PROCESS DESIGN
Why Agitation•Needed to bring the lixiviant and ore into contact to recover the pregnant liquor.
•To maintain physical and chemical uniformity
•Finely ground ore solids are kept in suspension by use of agitators.
•Axial- flow impeller will be used, this design is said to be both energy efficient and mechanically sound for all agitation application.
•A more consistent mixture can be achieved by use of axial flow impellors
PROCESS DESIGN
Tank Sizing And Configuration•Leach tanks will be arranged such that the leach slurry flows by gravity from one tank to the next.
•Helps save on power that could be used to pump the slurry
•The operation is such that one tank is always free for maintenance and overflow emergencies
•Agitation tanks, agitator shafts and impellers will be constructed using mild steel as it is suitable for acidic conditions.
1/12 of the tank diameter
Case studies- A summary
The larger the surface area of exposed mineral, the higher the recovery
The following conclusions can be drawn from analysis of these case studies;
•Stirring speed and particle size are two of the most important factors in copper dissolution.
• Solubility of copper increases with decreasing particle size, and increasing stirring speed.
More important factors listed include reaction
temperature,
residence time and
a low solid-liquid ratio
KINETICS AND ADDITIVES
Sulphuric acid of pH 2
CuCO3Cu(OH)2 + 2H2SO4 2CuSO4 + 3H2O + CO2
Additive: Chloride
Chloride is an ideal surfactant for leaching: • It provides an ideal environment for the dissolution of
malachite.
• Enhances leaching as it facilitates electron transfer.
Oxide leaching is diffusion controlled
GANGUE AND ACID CONSUMPTION
Silicate gangue minerals are often present in oxide porphyry copper ores
-high chemical stability- Moderate strong extractant- work well in solutions with
High crud generation
PROCESS CHEMICAL SELECTION
Diluents
Reduce the viscosity of extractants
Shellsol 2046 (selected)
Low viscosity
Contains low aromatics
Has flash point
diluents
Shellsol 2325
-flash point 89ºC
-19% v/v aromatics
-viscosity 2.2
Shellsol 2046- 17% aromatics- Flash point 78ºC- viscosity 2.0
Orform
Flash point 77ºC
23% aromatics
PROCESS FLOW DIAGRAM
Merits
-Low capital cost
-Flexible operation
-High extraction efficiency
-Low solvent consumption
Circuit configuration
2E X 1S2E X 1EP X 2S
2E X 2S2E X 1EP X 2S
EQUIPMENT DESIGN AND SELECTION
Mixer settler designs
Four units designs: krebs, outokumpu vf, reverse flow and conventional mixer settler.Mixer
2 cylindrical mixing tanks per stage
Residence time : 3 minutes.
Tank volume = (solution flow rate x residence time)/effective volume
Tank volume: 6.62m3
Diameter=: 2.63m
EQUIPMENT DESIGN AND SELECTION
Curved bladed impeller
Fitted in the first mixer. Installed to generate the liquid liquid dispersion and to achieve the required head flow rate of the solution.
Advantages: low power consumption, low organic and air entrainment and high hydraulic efficiencies (35-45%).
A6000 HYDROFOIL IMPELLER
maintain the initial liquid-liquid dispersion generated by the curved bladed pumper.
Advantage: enhance high copper transfer at low power consumption.
Bladed cross section thickness and optimum twist and chamber has made it a better selection over other impellers.
EQUIPMENT DESIGN AND SELECTION
SETTLERS
Characteristics:
0.5m aqueous phase, 0.3 m organic layer, 1 m deep settler, residence time 5 minutes, settling area 3m3/hr m2.
Rectangular in shape.
Picket fences and chevrons for smooth flow.
Settling area =
Length=18m
Width 2.70
EQUIPMENT DESIGN AND SELECTION
Conventional Mixer settler
Meet the requirements of copper solvent extraction plant
Low power consumption and low organic air entrainments
Process optimisation and control are simple
Easy crud removal
SUMMARY
The whole plant will be 93% efficient
Electrolyte concentrated from 9.76g/l to 45g/l
LIX 84-I selected as the extractant
Conventional mixer-settler
School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING
Copper Electrowinning
Nhlanhla Othusitse
Electrowinning of aqueous electrolyte solution to produce 99.99% copper cathodes
What is electrowinning?
Solution discovery technique in which a metal is separated from solution by causing it
to deposit at the cathode when current is passed through the solution
Principle
H2OH+ + OH- 2H++ 2e-
E0=-1.23V
Cu2+(aq) + 2e- Cu(s)
E0=0.34V
Nernst Equation:It states that the standard electrode potential is the potential difference between energy states of products and reactants
Overall reaction
H2O+Cu2+ + SO2- 0.5O2 + Cu+2H++ SO2- Eo= -0.89V
PRROSS Copper EW
Electrowinningtankhouse
Electrode handling and cathode
stripping
Advanced electrolyte: 45g/L Cu & 170g/L H2SO4
1275m3/h
Spent electrolyte: 40g/L Cu & 190g/L H2SO4
510m3/h
765m3/h
456t of 99.99% harvested every 4days
Bleed electrolyte: 45g/L Cu & 170g/L H2SO4
Active storage tank 2900m3
Process conditions
Conditions
Acid mist management
balls and beads
mist suppression
foams
Good tank house
ventilation
Additives
Cobalt
Guar gum
balls and beads
Guar gum
Materials of construction
Equipment Chosen Other
Cell Polymer concrete lead, FRP and PP, HDPE plastics
Cathode 316L Stainless steel Copper starter sheet
Anode Pb-Sn-Ca Pb-Sb
Stripping Xstrata Robotic CSM ISA 2000 CSM, ISA Flexor stripper and roller stripper
Busbar Triangular Double contact
And ‘dogbone’ contact
Production
Number of cathodes
4250
Plating thickness, m
0.006
Mass of copper, kg/ cathode
107.28
Mass of copper harvested in 4 days, kg
455940
≈456t Cu
Plating rate, kg/h 1.12
The sizing of the EW plant by Farady’s law
Mass balance production known, so working out no. of cell = 4250
PRROSS EW tankhouse specifications
Production (tonnes. y-1) 39 900
Electrowinning cells
Length X width X depth (inside dimension of cell) m
5.5×1.1×1.2
Total number of cells 85
Anodes/cathodes per cell 51/50
Anode
material 98.5%Pb-1%Sn-0.5%Ca
Length X width X thickness /m
0.9 X 0.9 X 0.006
Cathodes
type ISA 316L Stainless Steel
Length X width X thickness /m
1 X 1 X 0.003
Electrolyte composition
Electrolyte feed
Cu/g.l-1 45
H2SO4/g.l-1 170
Spent electrolyte
Cu/g.l-1 40
H2SO4/g.l-1 190
Cell conditions
Cathode current efficiency/ %
90
Energy consumption/ kWh.kg-1Cu
1.87
Tankhouse representation
School of Process, Environmentaland Materials EngineeringFACULTY OF ENGINEERING
Tailings Management Facility
Stephen Seporo
LOCATION AND SITE CHARACTERISATION
Location: North Chile (Atacama desert)
Climate: Desert (precipitation less then 1mm per year).
Topography: Flat ground and sandy soils.
Hydrology: Very few surface and underground water resources
Geological hazards: High chances of earthquakes
INTRODUCTION TO TAILINGS STORAGE
TAILINGS STORAGE METHODS
SLURRY IMPOUNDMENT
-50% to 60% water
-Pumping possible
-Requires containment dam
PASTE
-35% to 40% water
-Pumping possible
-Do not segregate
DRY STACKING
-20% water
-Can not be pumped
-Dense and stable
WHY DRY STACKING…?
•Nature of the process
•Reduced water consumption
•Stable landform, reduced risk of impoundment failure
•Progressive rehabilitation of landform is possible
•Smaller footprint
THICKENING AND FILTRATION
Column thickener• 42.8 m diameter• Made of concrete
Horizontal belt filter• Filter leaf test for sizing
• Counter current washing
STACK DESIGN CONCEPT
•Transport and placement done using a conveyor and a radial stacker.
•Truncated square pyramid shape.
•Slope ratio 3H:1V and maximum height of 100m
•33 million tonnes of tailings produced over 20 years.
•Total footprint of 4800 hectares.
FOUNDATIONAND STABILITY
GEO-SYNTHETIC DRAIN: Allows seepage to drain from the stack
GEOSYNTHETIC CLAY LINER: Stops seepage from perforating into the ground
DRAINAGE BLANKET: Control subsurface water
REHABILITATION AND CLOSURE
Re-vegetation: Initial revegetation would involve seeding grass to help with stabilization and seeding of other native vegetation would follow thereafter.
Cover material: Required to resist runoff erosion, prevent dusting and create an appropriate growth media.