### Lecture 21

```Hydrometallurgy
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
(CIP/RIP or CIL/RIL)
- 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
Classifier
Hydrometallurgical Processing
%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
Metal Recovery by Dissolution
• Applied to
– Copper (both acid and alkali)
CuO + H2SO4 → CuSO4 + H2O
CuO + 2NH4OH + (NH4)2CO3 → Cu(NH3)4 CO3 + 3H2O
– Zinc (acid)
ZnO + H2SO4 → ZnSO4 + H2O
– Nickel (acid and alkali) – Nickel Laterite Ores
NiO + H2SO4 → NiSO4 + H2O
NiO + 4NH4OH + (NH4)2CO3 → Ni(NH3)6CO3 + 5H2O
Copper Leaching by Ammonium Carbonate
azurite
malachite
pseudomalachite
tenorite
chrysocolla
cuprite
=
=
=
=
=
=
Cu3(OH)2(CO3)2
Cu2(OH)2CO3
Cu5(PO4)2(OH)4
CuO
CuSiO3.2H2O
Cu2O
63.5x3+17x2+60x2
63.5x2+17x2+60
63.5x5+17x4+95x2
63.5+16
63.5+16x3+28+2x18
63.5x2+16
=
=
=
=
=
=
55.3%Cu
57.5%Cu
55.2%Cu
79.9%Cu
36.2%Cu
88.8%Cu
Cu3(OH)2(CO3)2 +
5NH4OH
+
(NH4)2CO3 = 3Cu(NH3)4CO3 + 12H2O
Cu2(OH)2CO3
+
6NH4OH
+
(NH4)2CO3 = 2Cu(NH3)4CO3 +
8H2O
CuO
+
2NH4OH
+
(NH4)2CO3 =
Cu(NH3)4CO3 +
3H2O
Cu2O
+
4NH4OH
+ 2(NH4)2CO3 =
Cu(NH3)4CO3 +
5H2O
xCu5(PO4)2(OH)4 + yNH4OH + z(NH4)2CO3 = aCu(NH3)4CO3 + bH3PO4 + cH2O
Ammonia Leaching of Malachite
NH4Cl → NH4+ + Cl–
(1)
NH4+ + H2O → H3O+ + NH3
(2)
CuCO3·Cu(OH)2 + 2H3O+ → Cu2+ + CO2 + 3H2O + Cu(OH)2
Cu(OH)2 + 2H3O+ → Cu2+ + 2H2O
(3)
(4)
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+
(6)
(7)
Zinc Roasting/Leaching/Electrowinning
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-.
Yellowcake
•
•
•
•
•
uranyl hydroxide
uranyl sulfate
sodium para-uranate
uranyl peroxide
various uranium oxides
yellowcake typically contains 70% to 90% triuranium
octoxide (U3O8) and other oxides
• uranium dioxide (UO2) and
• uranium trioxide (UO3)
Leaching Processes
•
•
•
•
•
•
Tank Leaching (Agitation)
Vat Leaching
Pressure Leaching (high temperature/pressure)
Biological Leaching (Bacteria)
Heap Leaching
In-situ Leaching (solution mining)
Lixiviants
• 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
- NH4OH
- HCl
- NH4Cl or NH4CO3
- HNO3
- NaOH/KOH
- HCN >> NaCN/KCN
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
grinding & processing the material.
Pulp density - percent solids determines retention time
- determines settling rate and viscosity
- viscosity controls gas mass transfer and leaching rate
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
Reagents
- Adding/maintaining appropriate lixiviant level is critical
- Insufficient reagent reduces metal recovery
- Excess reagent increases operating costs and may lead
to lower recovery due to dissolution of other metals
- recycling spent (barren) solution reduces need for
fresh reagent, but deleterious compounds may
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
Bio-Leaching
• 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
Bio-Leaching
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
organic
• 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
electrolyte
• Resulting streams are stripped organic and rich
electrolyte
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
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 used 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
www.world-nuclear.org/info/Nuclear-Fuel-Cycle/Mining-ofUranium/In-Situ-Leach-Mining-of-Uranium/#.UUihT1fQhLo
In-situ Leaching – well patterns
EMF Chart
```