1. MINE 292 Introduction to Mineral Processing Lecture 21 John A Meech
Hydrometallurgy
MINE 292
Introduction to Mineral Processing
Lecture 21
John A Meech

2. Hydrometallurgical Processing
Comminution (Grinding)
Leaching Metal (Quantity - %Recovery)
Removal of Metal from Pulp
a. Solid/Liquid Separation
- CCD thickeners
- Staged-washing filtration
b. Adsorption (Carbon-in-Pulp and/or Resin-in-Pulp)
(CIP/RIP or CIL/RIL)
- granular carbon or coarse resin beads

3. 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)

4. Hydrometallurgical Processing
5. Electrowinning or Precipitation followed by Smelting

5. Hydrometallurgical Processing

6. Hydrometallurgical Processing
Classifier

7. Hydrometallurgical Processing
Feed Grade = 5 g Au/t Ore
%Recovery during Grinding = 60% >>> solids content = 2.00 g/t
%Recovery during Leaching = 35% >>> solids content = 0.25 g/t
%Recovery during CCD = 0%
%Recovery Total = 95%
Underflow Densities = 50%solids
Leach Density = 40% solids
Classifier O/F Density = 40%solids
Pregnant Solution Flowrate = 300%
Barren Bleed Flowrate = 25%
Gold in Barren Solution = 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?

8. 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

9. Metal Recovery by Dissolution
Applied to
Copper (both acid and alkali)
CuO + H2SO4 → CuSO4 + H2O
Cu NH4OH → Cu(NH3) H2O
Zinc (acid)
ZnO + H2SO4 → ZnSO4 + H2O
Nickel (acid and alkali) – Nickel Laterite Ores
NiO + H2SO4 → NiSO4 + H2O
NiO + 6NH4OH → Ni(NH3)62+ + H2O

10. Ammonia Leaching of Malachite
NH4Cl → NH Cl– (1)
NH H2O → H3O NH3 (2)
CuCO3·Cu(OH)2 + 2H3O+ → Cu2+ + CO H2O + Cu(OH)2 (3)
Cu(OH) H3O+ → Cu H2O (4)
Overall Leaching Reaction
CuCO3·Cu(OH) NH4Cl → 2Cu Cl– + CO2 +3H2O +4NH3 (5)
Formation of complex amine ions
Cu NH3 → Cu(NH3) (6)
Cu(NH3) NH3 → Cu(NH3)42+ (7)

11. Zinc Roasting/Leaching/Electowinning

12. 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

13. Metal Recovery by Dissolution
Applied to
Aluminum (alkali)
Al2O3 + 3H2O + 2NaOH → 2NaAl(OH)4
Gold and Silver (cyanidation / alkali)
Uranium (acid and alkali)

14. Alumina Leaching

15. Aluminum Smelting
Fused Salt Electrolysis – Hall-Herault Process

16. Aluminum Smelting
Fused Salt Electrolysis – Hall-Herault Process

17. Uranium Acid Leaching
Oxidize tetravalent uranium ion (U4+) to hexa-valent 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-.

18. Leaching Processes Tank Leaching (Agitation) Vat Leaching
Pressure Leaching (high temperature/pressure)
Biological Leaching (Bacteria)
Heap Leaching
In-situ Leaching (solution mining)

19. 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.
- H2SO NH4OH
- HCl NH4Cl or NH4CO3
- HNO NaOH/KOH
- HCN >> NaCN/KCN

20. 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

21. 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

22. Tank versus Vat Leaching
Some novel vat leach processes are semi-continuous 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

23. 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

24. 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
- viscosity controls gas mass transfer and leaching rate

25. Important Efficiency Factors
Pulp density
- percent solids determines retention time
- determines settling rate and viscosity
- viscosity controls gas mass transfer and leaching rate

26. 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.

27. Important Efficiency Factors
Reagents
- 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

28. 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.

29. 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

30. 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 about 24 hours

31. Bio-Leaching

32. 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 = $21,400,000 OPEX = $973/oz
Gold Recovery after toll-smelting = 88.6%

33. 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

34. Solvent Extraction Mixer/Settler

35. Reason for 4 Stages of SX

36. Solvent Extraction and Heap Leaching

37. 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)

38. Resin-In-Pulp Pachuca Tank

39. Resin-In-Pulp Pachuca Tanks

40. Resin-In-Pulp Pachuca Tanks

41. Kinetics of RIP for Uranium

42. Effect of pH on RIP for Uranium

43. RIP Recovery in each stage

44. 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

45. In-situ Leaching
Average grades of sandstone-hosted deposits range between 0.05% to 0.40% U3O8.

46. In-situ Leaching

47. In-situ Leaching

48. 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

49. In-situ Leaching – well patterns

50. EMF Chart