Introduction to Hydrometallurgy_UI_Lecture Slides

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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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.



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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



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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



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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



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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.



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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 +

-+



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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



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Introduction to Hydrometallurgy_UI_Lecture Slides