MINE 292
Introduction to Mineral Processing
Lecture 21
John A Meech
Hydrometallurgical Processing
1. Comminution (Grinding)
2. Leaching Metal (Quantity - %Recovery)
3. Removal of Metal from Pulp
a. Solid/Liquid Separation
- CCD thickeners
- Staged-washing filtration
b. Adsorption (Carbon-in-Pulp and/or Resin-in-Pulp)
- granular carbon or coarse resin beads
Hydrometallurgical Processing
4. Purification (Quality - g/L and removing other ions)
- Clarification and Deaeration (vacuum)
- Precipitation
(Gold: Zn or Al dust)
(Copper: H2S or scrap Fe or lime)
(Uranium: yellow cake)
(Zinc: lime)
- Solvent Extraction (adsorption into organic liquid)
- Ion Exchange (resin elution columns)
- Elution (contact carbon or resin with an electrolyte)
Hydrometallurgical Processing
5. Electrowinning or Precipitation followed by Smelting
Hydrometallurgical Processing
Hydrometallurgical Processing
Hydrometallurgical Processing
Feed Grade
%Recovery during Grinding
%Recovery during Leaching
%Recovery during CCD
%Recovery Total
Underflow Densities
Leach Density
Classifier O/F Density
Pregnant Solution Flowrate
Barren Bleed Flowrate
Gold in Barren Solution
= 5 g Au/t Ore
= 60% >>> solids content = 2.00 g/t
= 35% >>> solids content = 0.25 g/t
= 0%
= 95%
= 50%solids
= 40% solids
= 40%solids
= 300%
= 25%
= 0.05 g/t
Calculate the gold content of the Pregnant Solution and the U/F
water from each thickener. What is the actual mill recovery? What
difference would occur if fresh solution was added to Thickener E
rather than Thickener B?
Metal Recovery by Dissolution
• Primary extraction from ores
• Used with ores that can't be treated physically
• Secondary extraction from concentrates
• Used with ores that can be beneficiated to a
low-grade level
Metal Recovery by Dissolution
• Applied to
– Copper (both acid and alkali)
CuO + H2SO4 → CuSO4 + H2O
Cu+2 + 4NH4OH → Cu(NH3)4+2 + 4H2O
– Zinc (acid)
ZnO + H2SO4 → ZnSO4 + H2O
– Nickel (acid and alkali) – Nickel Laterite Ores
NiO + H2SO4 → NiSO4 + H2O
NiO + 6NH4OH → Ni(NH3)62+ + H2O
Ammonia Leaching of Malachite
NH4Cl → NH4+ + Cl–
NH4+ + H2O → H3O+ + NH3
CuCO3·Cu(OH)2 + 2H3O+ → Cu2+ + CO2 + 3H2O + Cu(OH)2
Cu(OH)2 + 2H3O+ → Cu2+ + 2H2O
Overall Leaching Reaction
CuCO3·Cu(OH)2 + 4 NH4Cl → 2Cu2+ + 4Cl– + CO2 +3H2O +4NH3 (5)
Formation of complex amine ions
Cu2+ + 2NH3 → Cu(NH3)22+
Cu(NH3)22+ + 2NH3 → Cu(NH3)42+
Zinc Roasting/Leaching/Electowinning
Nickel Lateritic Ores
acid heap leaching method similar to copper
H2SO4 much higher than for copper (1,000 kg/t)
patented by BHP Billiton
being commercialized by
– Cerro Matoso S.A. in Columbia
– Vale in Brazil
– European Nickel Plc in Turkey, Balkans, Philippines
Metal Recovery by Dissolution
• Applied to
– Aluminum (alkali)
Al2O3 + 3H2O + 2NaOH → 2NaAl(OH)4
– Gold and Silver (cyanidation / alkali)
– Uranium (acid and alkali)
Alumina Leaching
Aluminum Smelting
• Fused Salt Electrolysis – Hall-Herault Process
Aluminum Smelting
• Fused Salt Electrolysis – Hall-Herault Process
Uranium Acid Leaching
• Oxidize tetravalent uranium ion (U4+) to hexavalent uranyl ion (UO22+) using MnO2 or NaClO4
• About 5 kg/t of MnO2 or 1.5 kg/t of NaClO4
• UO22+ reacts with H2SO4 to form a uranyl sulfate
complex anion, [UO2(SO4)3]4-.
Leaching Processes
Tank Leaching (Agitation)
Vat Leaching
Pressure Leaching (high temperature/pressure)
Biological Leaching (Bacteria)
Heap Leaching
In-situ Leaching (solution mining)
• Lixiviant is a liquid medium used to selectively
extract a desired metal from a bulk material. It must
achieve rapid and complete leaching.
• The metal is recovered from the pregnant (or
loaded) solution after leaching. The lixiviant in a
solution may be acidic or basic in nature.
- H2SO4
- HCl
- NH4Cl or NH4CO3
- HNO3
Tank versus Vat Leaching
• Tank leaching is differentiated from vat leaching
as follows:
Tank Leaching
– Fine grind (almost full liberation)
– Pulp flows from one tank to the next
Vat Leaching
– Coarse material placed in a stationary vessel
– No agitation except for fluid movement
Tank versus Vat Leaching
• Tanks are generally equipped with
– agitators,
– baffles,
– gas nozzles,
• Pachuca tanks do not use agitators
• Tank equipment maintains solids in suspension
and speeds-up leaching
• Tank leaching continuous / Vat leaching batch
Tank versus Vat Leaching
• Some novel vat leach processes are semicontinuous with the lixiviant being pumped
through beds of solids in different stages
• Retention (or residence) time for vat leaching
is much longer than tank leaching to achieve
the same recovery level
Important Efficiency Factors
Retention time
= total volume of tanks / slurry volumetric flow
- normally measured in hours
- gold: 24 to 72 hours
- copper: 12 to 36 hours
- sequence of tanks called a leach "train"
- mineralization & feed grade changes may need
higher retention times
Important Efficiency Factors
Particle Size
- material ground to size to expose desired mineral
to the leaching agent (“liberation”),
tank leach >>> size must be suspendable by an agitation
vat leach >>> size must be most economically viable
- high recovery achieved as liberation increases or
kinetics faster is balanced against increased cost of
processing the material.
Pulp density - percent solids determines retention time
- determines settling rate and viscosity
Important Efficiency Factors
Pulp density
- percent solids determines retention time
- determines settling rate and viscosity
- viscosity controls gas mass transfer and leaching rate
Important Efficiency Factors
Numbers of tanks
- Tank leach circuits typically designed with 4 tanks
Dissolved gases
- Gas is injected below the agitator or into the vat
bottom to achieve the desired dissolved gas levels
- Typically, oxygen or air, or, in some base metal plants,
SO2 is used.
Important Efficiency Factors
- Adding/maintaining appropriate lixiviant level is critical
- Insufficient reagents reduces metal recovery
- Excess reagents increases operating costs and may lead
to lower recovery due to dissolution of other metals
- recycling spent (barren) solution reduces need for
fresh reagents, but deleterious compounds may
build-up leading to reduced kinetics
Pressure Leaching
Sulfide Leaching more complex than Oxide Leaching
Refractory nature of sulfide ores
Presence of competing metal reactions
Pressurized vessels (autoclaves) are used
For example, metallurgical recovery of zinc:
2ZnS + O2 + 2H2SO4 → 2ZnSO4 + 2H2O + 2S
• Reaction proceeds at temperatures above B.P. of water
(100 °C)
• This creates water vapor under pressure inside the vessel.
• Oxygen is injected under pressure
• Total pressure in the autoclave over 0.6 MPa.
Sulfide Heap Leaching
• Ni recovery much more complex than Cu
• Requires stages to remove Fe and Mg
• Process produces residue and precipitates from
recovery plant (iron oxides/Mg-Ca sulfates)
• Final product – Ni(OH)2 precipitates (NHP) or
mixed metal hydroxide precipitates (MHP) that
are smelted conventionally
• Thiobacillus ferrooxidans used to control ratio of ferric
to ferrous ions in solution (Tf acts as a catalyst)
4Fe2+(aq) + O2(g) + 4H3O+ → 4Fe3+(aq) + 4H2O
• Ferric sulfate used to leach sulfide copper ores
• Basic process is acceleration of ARD
• Typical plant leach times for refractory gold ore is
about 24 hours
Bio-Leaching at Snow Lake, Manitoba
• BacTech to use bio-leaching to deal with As and
recover gold from an arsenic-bearing waste dump
• Two products
– Chemically-stable ferric arsenate precipitate
– Gold-rich Residue Concentrate
110 tpd of concentrate for 10 years
Annual production = 10,400 oz plus some Ag
CAPEX = $21,400,000OPEX = $973/oz
Gold Recovery after toll-smelting = 88.6%
SX - Solvent Extraction
• Pregnant (or loaded) leach solution is emulsified
with a stripped organic liquid and then separated
• Metal is exchanged from pregnant solution to
• Resulting streams are loaded organic and
raffinate (spent solution)
• Loaded organic is emulsified with a spent
electrolyte and then separated
• Metal is exchanged from the organic to the
• Resulting streams are stripped organic and rich
Solvent Extraction Mixer/Settler
Reason for 4 Stages of SX
Solvent Extraction and Heap Leaching
Ion Exchange Resins
• AMn = synthetic ion-exchange resin
(class A - 0.6–1.6 mm)
• Phenyl tri-methyl ammonium functional groups
• Macro-porous void structure
• Similar to strong base anion exchange resins
Zeolite MPF (GB)
Amberlite IRA (USA)
Levatite MP-500 (FRG)
Deion PA (JPN)
Resin-In-Pulp Pachuca Tank
Resin-In-Pulp Pachuca Tanks
Resin-In-Pulp Pachuca Tanks
Kinetics of RIP for Uranium
Effect of pH on RIP for Uranium
RIP Recovery in each stage
In-situ Leaching
• In 2011, 45% of world uranium production was by ISL
• Over 80% of uranium mining in the US and Kazakhstan
• In US, ISL is seen to be most cost effective and
environmentally acceptable method of mining
• Some ISLs add H2O2 as oxidant with H2SO4 as lixiviant
• US ISL mines use an alkali leach due to presence of
significant quantities of gypsum and limestone
• Even a few percent of carbonate minerals means that
alkali leach must be used although recovery does suffer
In-situ Leaching
Average grades of sandstone-hosted deposits
range between 0.05% to 0.40% U3O8.
In-situ Leaching
In-situ Leaching
In-situ Leaching
• Acid consumption varies depending on operating philosophy
and geological conditions
• In Australia, it is only a fraction of that used in Kazakhstan
• In Kazakh , about 40 kg acid per kg U (ranging from 20-80)
• Beverley mine in Australia in 2007 was 7.7 kg/kg U.
• Power consumption is about 19 kWh/kg U (16 kWh/kg U3O8)
in Australia and around 33 kWh/kg U in Kazakhstan
In-situ Leaching – well patterns
EMF Chart

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