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8/13/2019 Introduction to Hydrometallurgy_UI_Lecture Slides
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Department of Metallurgical & Minerals Engineering
Introduction to Hydrometallurgy
Introduction to Extractive Metallurgy
Don C. Ibana, PhD
Head of Department & Assoc Professor of Hydrometallurgy
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Department of Metallurgical & Minerals Engineering
Processing Steps in HydrometallurgyOre
Pre-treatment
Leaching
Solid/Liquid Separation
Leach Regeneration/Reagent Recovery
Solution Purification/
Concentration
Metal/ProductRecovery
Residue TreatmentTailings Disposal
Impurities
Additives forPurification1
2
3
4
RecycleLiquor
MakeupReagent
PLS
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Pre-treatment Processes
1. Roasting of auriferous pyrite (600 oC)
porous and insoluble Fe2O3
2. Segregation roasting (600 oC)
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Pre-treatment Processes
3. Reductive roasting of ilmenite (900 oC)
4. Pug-roasting (100-200 oC)
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Leaching1. Water solvation
–
dissolution of naturally solublesalts in water
2. Acid attack – use of acid to form a soluble salt
of the metal oxide
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Leaching3. Alkali attack
–
dissolution with a base (alkali)
4. Complexation – formation of a complex ion
(often involves redox reactions)
Examples:
, , , ,
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LeachingRedox reactions in leaching processes
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Leaching
• Reduction of oxygen
Industrially important cathodic reactions (reduction)
O2 + 4H+ + 4e- 2H2O 1.23 V (6a)
O2 + 2H2O + 4e- 4OH- 0.40 V (6b)
Fe3+ is a weaker oxidant than O2 but concentration can be increased!
• Reduction of ferric ion
Fe3 + e- Fe2+ 0.77 V (7)
lno RT E E Q
nF -
Redox reactions in leaching processes
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Complete Leaching Processes1. Leaching of gold (redox-complexation)
O2(g) + 2H2O(l) + 4e- 4OH-(aq)
Au(s) Au+
(aq) + e-
Au+(aq) + 2CN-(aq) Au(CN)2-
4Au + 4CN- + O2 + 2H2O 4Au(CN)4
- + 4OH -
4NaCN(s) 4Na+(aq) + 4CN
-(aq)
H2O(aq) + CN-(aq) HCN(g) + OH
-
CaO(s) + H2O(l) Ca2+
(aq) + 2OH-(aq)
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2. Leaching of uranium
3. Leaching of nickel laterite (Caron Process)
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4. Leaching of chalcopyrite
5. Leaching of zinc sulfide – 200 oC in H2SO4 with air
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6. Leaching of nickel sulfide (Sheritt Gordon Process) – 105 oC
in NH3
with air (8 atm)
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Stability constants and Leaching Selectivity
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Morestabilityconstants
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Leaching Techniques1. In-situ – ore shattered by explosive, leach
solution is percolated, pregnant liquor stream
(PLS) collected through network of sumps and
pumped to the surface for purification, e.g. Cu &
U (~50% dissolution)
2. Dump/heap leaching – fractured rock (0.1 – 1 m) is
removed from the mine, heap is built on plastic lining,PLS collected through network of sumps and pumped to
purifying plant, e.g. Cu & U (~60% dissolution).
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4. Solution Purification Concentration4.1 Impurity removal
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Solution Purification Concentration cont...Reduction potentials - (useful in reagent selection)
Au3+ + 3e- Au0 1.41 V
Cu2+ + 2e- Cu0 0.34 V
Ni2+ + 2e- Ni0 -0.24 V
Cd2+ + 2e- Cd0 -0.40 V
Fe2+ + 2e- Fe0 -0.44 V
Zn2+ + 2e- Zn0 -0.76 V
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Solution Purification Concentration cont...
Hydroxide Precipitation
Cr 3+(aq) + 3OH- Cr(OH)3(s)
Fe3+(aq) + 3OH- Fe(OH)3(s)
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Solubility Product Constants – Guide on Selective Precipitation
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Solubility Product Constants (Hydroxides)
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Solubility Product Constants (Sulfides)
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Use of solubility product constants (K sp)
• A good guide on determining the solubility of an ionic solid in
water.
33 OHFe -+sp
K
Example
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Sample calculat ion
f
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Solution Purification Concentration cont...4.2 Concentration
–
selective extraction of the valuablemetal ions from the pregnant liquor stream (PLS) into
another medium for further processing.
4.2.1 Ion-exchange (IX)
Solid
(resin)
solution Solid
(resin)
solution
immobile mobile immobile mobile
D f M ll i l & Mi l E i i
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IX Technology
manhole
water inlet
brine distributor
ion-exchange material
graded gravel underbed
treated water outlet
collecting system
brine inlet
D t t f M t ll i l & Mi l E i i
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Step 3 - Stripping
Step 1 - Extraction
Barrenelectrolyte
Recoveredextractant
Loadedextractant
Electrolyte
MRn + nH+ nRH + Mn+
Extractant Loaded
Extractant
PLS Raffinate
Mn+ + nRH MRn + nH+
Step 2 - Scrubbing
4.2.2 Solvent Extraction (SX) – selective transfer of valuable
from the PLS to an immiscible organic phase using an
extractant.
D t t f M t ll i l & Mi l E i i
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Types of Extractants
Type Functional Group Application
ChelatingR - C - C - R (oximes)
HON OH
Cu, Ni
AcidicRCOOH (carboxylic), (R)2POOH (phosphinic),R2PSSH (dithiophosphinic),
Cu, Co, Ni, Zn
Basic 1o, 2o amines U, Th, rare earths
3o, 4o amines U, Mo,
Solvating Phosphoric ester (RO)3P=O (TBP) U, Zr/Hf,
Phosphine sulphide (R3P=S) Ag/Cu, Pt/Pd
Phosphine oxide (R3P=O), (TOPO) U
Ketones Au, Hf/Zr
Ethers Au
D t t f M t ll i l & Mi l E i i
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Some Extraction Reactions
R
OH N OH
+ Cu2+
R
O N OH
Cu
R
ON
+ 2H+
HO
2• Chelation
• Ion exchange P
O
OH(C8H17)
(C8H17)
+ M2+ P
O
(C8H17)
(C8H17)
O + 2H+
2
M2
Depa tment of Metall gical & Mine als Enginee ing
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• SX Technology (Mixer-Settler)
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• SX Technology (Pulse column)
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5.0 Metal/Product Recovery5.1 Cementation
Further purified by electrorefining or pyrometallurgy.
5.2 Gaseous reduction
Sherritt Gordon Process – 200 oC, elevated H2 pressure
Department of Metallurgical & Minerals Engineering
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5.0 Metal/Product Recovery5.3 Electrowinning
Reduction of the metal ion, e.g. Cu2+, Ni2+, Zn2+, Co2+
Most expensive but highest purity
5.4 Hydrolysis/Precipitation
Cooling (160 to 100 oC) with seeding of the digestion liquor in the BayerProcess
Department of Metallurgical & Minerals Engineering
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5.0 Metal/Product Recovery5.4 Hydrolysis/Precipitation
• Blowing steam into the sulfate solution increases K of the reaction &
acidity favouring hydrolysis
• Blowing steam into the NH/NH4+ solution of Ni2+ in Caron Process
leads to recovery of Ni(OH)2 and NH3.
Department of Metallurgical & Minerals Engineering
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6.0 Electrowinning Electrorefining Electrowinning is recovery of metal from solution;
electrorefining is refining of impure metal.
• Competing cathodic reactions are
• Main cathodic reaction is reduction of metal
(s)(g)(aq)n MnM + -+ e
(aq)
2
(aq)
3
FeeFe
+-+
+
(s)2(g)(aq) Hn2H + -+ e
(l)2(aq)(aq)2 OH2e4H4O ++ -+
i(l)(aq)
ni MneM +
-+
Department of Metallurgical & Minerals Engineering
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Electrowinning Electrorefining cont...
• Competing anodic reactions
• Main anodic reactions
(g)n(aq)(s) nMM -+
+ e
-++
+ eFeFe (aq)3
(aq)2
-+
+ enMM (aq)n
(s)i
Electrorefining
-+
++ eH O 44O2H (aq))g(2(l)2 Electrowinning
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Electrowinning Electrorefining cont...•
In acidic electrowinning, anode is usually lead alloy withsmall amount of antimony and silver. A protective PbO
forms and O2 evolution occurs on oxide layer
• In basic electrowinning (gold), anode is stainless steel.
• Cathodes are either starter sheets of the metal to be
reduced or stainless steel (permanent).
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Periodic Table
Department of Metallurgical & Minerals Engineering
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THE END
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