5. Leaching Processes

7/23/2019 5. Leaching Processes

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HydrometallurgyHydrometallurgy

55 Leaching ProcessesLeaching Processes

Fathi HabashiFathi Habashi

Department of Mining, Metallurgical, and Materials EngineeringDepartment of Mining, Metallurgical, and Materials Engineering

Laval University, QuebecLaval University, Quebec City,,CanadaCity,,Canada

[email protected]@arul.ulaval.ca

Leaching Processes


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Leaching of MetalsLeaching of Metals

Gold & SilverGold & Silver

CYANIDATION 1CYANIDATION 1

The dissolution of gold and silver inThe dissolution of gold and silver in

cyanide solutions was one of the puzzlescyanide solutions was one of the puzzles

that faced metallurgists for many years forthat faced metallurgists for many years for

two reasons:two reasons:

Gold, the most noble metal that dissolved onlyGold, the most noble metal that dissolved only

in aquain aqua regiaregia, dissolved readily in a very dilute, dissolved readily in a very dilute

solution of sodium cyanide.solution of sodium cyanide.

Although gold did not tarnish in air, air wasAlthough gold did not tarnish in air, air was

essential for its dissolution.essential for its dissolution.


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CyanidationCyanidation 11

Cyanide is derived from GreekCyanide is derived from Greek

meaning blue, because hydrocyanic acidmeaning blue, because hydrocyanic acid

(blue acid) was derived for the first time(blue acid) was derived for the first time

from Prussian blue pigment when heatedfrom Prussian blue pigment when heated

withwith sulfuricsulfuric acid.acid.


NaCN concentration

Rate(mgsqin1h

r1)

3.5

0

Gold3.0

2.5

2.0

1.5

1.0

0.5

0

Silver

0.1 0.2 0.3 0.4 0.5%


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According to thisAccording to this stoichiometrystoichiometry, 1 gram mole of oxygen, 1 gram mole of oxygenand 4 gram moles ofand 4 gram moles of NaCNNaCN should be present inshould be present insolution. At room temperature and at atmosphericsolution. At room temperature and at atmosphericpressure, 8.2 mg Opressure, 8.2 mg O22 are dissolved in 1are dissolved in 1 literliterof water. Thisof water. Thiscorresponds to 0.27 x 10corresponds to 0.27 x 1033 mol/L. Accordingly, goldmol/L. Accordingly, golddissolution should occur at a concentration ofdissolution should occur at a concentration of NaCNNaCNequal to 4equal to 4 0.27 x 100.27 x 1033 49 = 0.05 g/L or 0.005%. Thus49 = 0.05 g/L or 0.005%. Thusa very dilute sodium cyanide solution would be enougha very dilute sodium cyanide solution would be enoughfor dissolving gold.for dissolving gold.

The fact that oxygen was necessary for dissolution wasThe fact that oxygen was necessary for dissolution was

not readily recognized because as seen from the abovenot readily recognized because as seen from the abovecalculations, oxygen in solution as a result of aircalculations, oxygen in solution as a result of airsolubility is enough to bring about the reaction.solubility is enough to bring about the reaction.

Cyanidation 6


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NaCN concentration

Rate(mgcmi

n2

hr

1)

30

0

20

0

7.48 ATM

0.02 0.04 0.06

10

3.40 ATM


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]}O[4+]CN[{

]O[]CN[A2=Rate

2O2

-CN-

2-

O2CN-

DD

DD


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Cyanidation 8

pH

Concentration,%

100

CN

80

60

40

20

00 2 4 6 8 10 12 14

HCN

It is essential that the cyanide solution be kept alkaline during leaching

to prevent the formation of HCN

Cyanidation 9

It is essential that the cyanide solution be

kept alkaline during leaching to prevent

the formation of HCN which is extremely

poisonous gas.

Hydrogen cyanide may form as a result of

absorption of atmospheric CO2:

CO2 + H2O H2CO3H2CO3 + CN

HCN + HCO3


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Cyanidation 10

[KOH]

Rateofdissolution

gmolcm2sec1

25 103

Gold

20

15

10

5

0103 102 101 1.0

Silver

g mol/L

Cyanidation 11

Rate(mgcm

2hr1)

10

Gold

3

2

1

11 12 13 14

Ca(OH)2

NaOH

Silver

Ca(OH)2

KOH

20

10.8

10

011.8 12.8

R

ate(mgcm

2hr1)

pHpH


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Cyanidation 12

Weightofgolddissolved/unittime

0

150

20 40 60 80 100

140

130

120

110

100

90

Temperature, C

Cyanidation 13Leaching

agent

Leaching

Filtration

Ore

RecoveryBleed

ResidueRecycle

Metal


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Recovery of CyanideRecovery of Cyanide

Acidification and recovery of HCN

When SO2 is bubbled in bleed solutions, HCN

is formed: It can be collected and absorbed in a

solution of NaOH to form NaCN for recycle:

CN+ H+ HCN

Recovery of HCN


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Destruction of Cyanide

While the cyanide ion is highly poisonous, its

oxidation product, the cyanate ion, is not.

Chlorine is usually used as oxidizing agent for

this purpose:

CyanidationCyanidationRecent AdvancesRecent Advances

Heap leaching

Treatment of refractory ores

Cyanidation under pressure


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Refractory Gold Ores 1Refractory Gold Ores 1

Gold locked up in pyrite or arsenopyrite

crystals, unresponsive to cyanidation

Roasting followed by leaching

Hydrometallurgical approach

Bacterial leaching

Aqueous oxidation in autoclaves


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Refractory Gold Ores 3Refractory Gold Ores 3BarrickBarrick Gold, Elko, NevadaGold, Elko, Nevada

Refining of GoldRefining of Gold

HydrometallurgyHydrometallurgy

PyrometallurgyPyrometallurgy

ElectrometallurgyElectrometallurgy


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RefiningRefining

Separation of gold from silver and otherSeparation of gold from silver and otherimpurities (Cu, Pt metals, etc.) is usually carriedimpurities (Cu, Pt metals, etc.) is usually carriedout by electrolysis or by chlorination. However,out by electrolysis or by chlorination. However,on a small scale, e.g., in mints, refining is doneon a small scale, e.g., in mints, refining is doneby selective leaching.by selective leaching.

The method used depends on the gold contentThe method used depends on the gold contentas well as on the type of impurities present.as well as on the type of impurities present.While silver is soluble in both nitric and sulfuricWhile silver is soluble in both nitric and sulfuricacids, and gold is insoluble, yet these acidsacids, and gold is insoluble, yet these acids

cannot be used to dissolve silver away from ancannot be used to dissolve silver away from analloy containing more than 25alloy containing more than 25

% Au.% Au.

For highFor high--gold alloysgold alloys

AquaAqua regiaregia is therefore used. In such alloys, gold isis therefore used. In such alloys, gold isleached, while silver forms an insoluble residue.leached, while silver forms an insoluble residue.

Gold is soluble in aquaGold is soluble in aqua regiaregia, but a gold, but a goldsilversilveralloy containing more than 8alloy containing more than 8% Ag cannot be% Ag cannot beattacked due to the formation of an insoluble layerattacked due to the formation of an insoluble layerofof AgClAgCl..

Therefore, the aquaTherefore, the aqua regiaregia leaching process is usedleaching process is used

only for refining highonly for refining high--grade bullions, where thegrade bullions, where thesilver does not amount to more than 8silver does not amount to more than 8 %, or to%, or tocases where the bullion contains enough copper tocases where the bullion contains enough copper toopen it up to attack in spite of the silver present.open it up to attack in spite of the silver present.


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Alloy

composition [%]

Attack by

Ag AuHNO

3or

H2SO

4

1Aquaregia

2

Remarks

Low-goldbullion

10075

025

Bullion treated byHNO

3or H

2SO

4.

70502510

30507590

Bullion must be alloyedwith Ag beforetreatment with HNO

3

or H2SO

4.

High-gold

bullion

8

0

92

100

Bullion treated by aqua

regia.1Ag is soluble but Au is insoluble.2Au is soluble but Ag is insoluble due to the formation of AgCl.

In both cases, the bullion is first meltedIn both cases, the bullion is first melted

and poured in water to obtain granulesand poured in water to obtain granules

suitable for leaching.suitable for leaching.


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Platinum Metals 1Platinum Metals 1

Native platinum ores

Gold ores: Platinum metals enriched in the anodicslimes

Copper and nickel sulfide ores: Platinummetals concentrated in the following fractions:

In the magnetic fraction separated from the

sulfide matte

In anodic slimes of copper or nickelelectrolytic refining


Aqua regia, also known as royal wateror eau rgalebecause it can solubilize gold the most noble metal

A mixture of one part concentrated nitric acid andthree parts concentrated hydrochloric acid

The dissolving action is due to the formation ofchlorine and nitrosyl chloride:

2Cl Cl2 + 2e

4H+ + NO3+ 2eNO+ + 2H2OOverall reaction:HNO3 + 3HCl Cl2 + NOCl + 2H2O


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Platinum Metals

Leaching

Filtration

Au precipitation

Filtration

(NH) [PtCl ]precipitation

4 2 6

Filtration

Cementation

Calcination

Leaching

Leaching

Cementation

Precipitation Calcination

Formation of[Pd(NH) ]Cl3 4 2

Precipitation of[Pd(NH) ]Cl

3 2 2

Filtration

To waste

Aquaregia

FeSO

solution4

NHCl4

NH OH4

HCl

Zn

Residue Ru, Rh, Ir and Os concentrate

Residue Gold sand (washing, melting, anode

casting and electrolysis)

NHCl4

CrudePt sponge

Aqua regia

PurePt sponge

Residue

HCl Fe

Pdconcentrate

Recovered tracesof Pt and Pdfrom solution

Platinummetals

concentrate


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Copper, Nickel, and CobaltCopper, Nickel, and Cobalt

Selective dissolution from low-grade ores byaqueous ammonia in presence of air (oroxygen) to form the ammine complexes[M(NH3)n]

2+

Ammonium hydroxide is selected inpreference to H2SO4, which is less expensivefor two reasons:Presence of excessive acid-consuming gangue such as limestone

or dolomite in the orePresence of an iron oxide matrix which partially dissolves in acidand makes the separation of the metal values difficult

Ammonia LeachingAmmonia LeachingThe dissociation of ammonium hydroxide is small:

NH3 + H2ONH4+ + OH

NH3 can be considered as the active complexing agent.

Oxidation: M M2+ + 2e

Complex formation: M2+ + nNH3 [M(NH3)n]2+

Overall reaction:

M + nNH3 +1/2O2 + H2O [M(NH3)n]

2+ + 2OH


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Recovery from Leach Solution 1Recovery from Leach Solution 1

Solution is boiled to distill off excessammonia and to decompose the amminecomplex to precipitate a hydroxide or abasic carbonate:

[M(NH3)n]2+ + 2OH M(OH)2 + nNH3

2[M(NH3)n]2+ + 2OH + CO3

2

M(OH)2MCO3 + 2nNH3

Recovery from Leach Solution 2Recovery from Leach Solution 2

The precipitate is filtered, washed, andcalcined to yield a high-grade oxidecontaining 7578% metal

The gases evolved are absorbed in waterand recycled.

Ammonia retained in the gangue residue isrecovered by steam stripping

Instead of calcination, the precipitated basic

carbonate is sometimes dissolved inammonium sulfate solution and the puremetal is precipitated by hydrogen underpressure


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Nickel & Cobalt 1Nickel & Cobalt 1

Laterite nickel ores at Nicaro in Cuba, at

Marinduque in the Philippines, and at Greenvale

in Australia containing much acid-soluble

gangue are first reduced then leached with

ammonia.

Manganese nodules found on ocean floor

containing about 1% Cu and 1% Ni. It was

suggested to recover copper and nickel from this

source by reducing the nodules then leachingselectively by ammonia.

Nickel & Cobalt 2Nickel & Cobalt 2

Oxidation of iron sulfides followed by

selective reduction. For example, at the

International Nickel Company in Sudbury,

pyrrhotite concentrate


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SUMMARY

Leaching of Oxides,Leaching of Oxides,

Hydroxides,Hydroxides,

and Complex Oxidesand Complex Oxides


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OXIDES & HYDROXIDES

Bauxite

Laterites

Copper, manganese, and uranium ores. A

minor amount of zinc occurs as oxide,

carbonate, and basic carbonate

A great part of zinc sulfide is first oxidized to

oxide which is then treated by wet methods.

Bauxite 1


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Bauxite 2

Bauxite 3

Aluminum minerals in bauxite are soluble indilute H2SO4 but this process is not used onlarge scale for the following reasons:

Iron minerals and to some extent titanium minerals are also soluble; thiswill lead to an excessive reagent consumption and solution purificationproblem later.

Al(OH)3 precipitated from acid solutions is gelatinous and difficult tofilter and wash.

Acid leaching is used only on a small scale to

produce aluminum sulfate needed for watertreatment.


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Karl Josef Bayer (1847-1904)

Leaching of Bauxite


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Bayer ProcessBayer Process

BAUXITE

Sand

Grushing

Washing

Drying

Grinding

Leaching

Water

Settling

Dilution

Seed

Thickener

Filtration

Precipitation

Filtration

Evaporation

Centrifuge

make-up

NaOH

NaOH

Recycle

Red mud

Red mud

Solid impurities

Washing CalcinationPure

Al2O3

Processing of Bauxite


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Aluminate Solution

COPPER MINERALS


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Processing of Copper OresProcessing of Copper Ores

H2SO4

Leaching

Filtration

RecoveryBleed

Copper

Flotation

solution

Smelting

Copper oresSO2

Copper

Oxides

Sulfides

Residue

Copper Oxide Ores

Acid LeachingAcid Leaching

Filtration

Electrowinning

Electrolyticcopper

Leaching

Copper ores

H2SO4

Residue

Sulfideconcentrate

Cementation

Cementcopper

Flotation

Solution


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Processing of Copper Oxide OresProcessing of Copper Oxide Ores

Flotation

Cement copper

Leaching

Oxidized ores

H2SO4

Gangue

Solutionto

waste

Sponge Fe

Filtration Filtration

Solutionto

wasteand sulfideconcentrate

Precipitation

Float

A

Flotation

Leaching

Oxidized ores

Gangue

Filtration Filtration

Sulfideconcentrate

Precipitation

Sink

H2SO4

H2S

Float

B

ChalcopyriteChalcopyriteCrushing

and grinding

Bulk

flotation

Steaming

Selective

flotation

Chalcopyrite

concentrate

MoS2

Leaching Roasting Dust

collector

SO2

Chalcopyrite ore

Cu2+ MoO3 Re2O7

Tailings


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Copper- Cobalt Ores

Processing of CuProcessing of Cu--Co oresCo oresH2SO4

Leaching

Gangue

Copper-cobalt ore

Copper

Filtration

Electrowinning

Cobaltrecovery

Cobalt


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Acid Leaching of

Copper Oxide Ores

Ammonia Leaching of Copper OxideAmmonia Leaching of Copper Oxide

OresOres

Filtration

Leaching

Ore2CuCO3 Cu(OH)2

Distillation

Calcination

Absorption

Recycle

Water

Residue

Basic

NH4OH + (NH4)2CO3

carbonate

NH3

CO2

CuO


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Laterites 1

Manganese Ores


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Processing of Manganese OresProcessing of Manganese OresManganese oxide

ore

Reduction

LeachingLeaching

Filtration

H2SO3MnO

Fe2+ or C

H2SO4H2SO4

Filtration

Leaching

Filtration

MnSO4

Gangue Gangue Gangue

MnSO4 MnSO4

Manganese Nodules


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Uranium Ores

Uranium OresUranium OresCarbonate LeachingCarbonate Leaching

Filtration

Leaching

Calcination

Precipitation

Filtration

Uranium ore

Gangue

O2

NaOH

Na2CO3+

NaHCO3

Na2U2O7


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Zinc Oxide

Leaching ofLeaching of ZnOZnO

Filtration

Leaching

Zinc oxide calcine

H2SO4

Reduction

(rotary kiln)

Fuming

Purification

Electrolysis

Pure zinc

Lead

Slag

Dilute Recycle ZnO fumes

Residue

Reduction

(blast furnace)


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Leaching ofLeaching of ZnOZnOThe problem of ferritesThe problem of ferrites

Filtration

Leaching

Zinc oxide calcine

Dilute H2SO4recycle

Purification

Electrolysis

Pure zinc

ResidueLeaching 95 C

Filtration

Iron

precipitation

Filtration

Concentrated

H2SO4

Gangue

Iron - containing residue

Zinc Oxide LeachingDisposal of Residue


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Complex Oxides

MINERALS


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Pyrometallurgical method. Partial reduction withanthracite in an electric furnace to get cast iron anda slag rich in titanium. Titanium slag in mainly ironmagnesium titanate, (Fe,Mg)Ti4O10, and a smallamount of silicates

Hydrometallurgical method. Leaching of iron oxideand obtaining a residue rich in titanium (9095%TiO2) known as synthetic rutile.

The slag and synthetic rutile can then be processedto TiO2 pigment or titanium metal.

Leaching ofLeaching of IlmeniteIlmenite

Baking

Ilmenite

Residue

Conc.H2SO4

Leaching

Filtration

Crystallization

Centrifuge

Hydrolysis

Filtration

Drying

Calcination

H2O

H2O

Dilute

H2SO4

Seed

TiO2

FeSO4 4H2O

FeTiO3 + 4H+

Fe2+ + TiO2+ + 2H2O


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Titanium Raw Materials

SyntheticSynthetic RutileRutile

Ilmenite

Synthetic

Digestion

Filtration

Fe2O3

HCl

Oxyhydrolysis

rutile

FeTiO3 + 2H+

TiO2(impure) + Fe2+ + H2O


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Synthetic Rutile PlantWestern Australia

Oxyhydrolysis of FeCl2

2FeCl2 + 2H2O + O2

Fe2O3 + 4HCl


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Processing ofProcessing of

Titanium SlagTitanium Slag

Baking

slag

Residue

Conc.H2SO4

Leaching

Filtration

Hydrolysis

Filtration

Drying

Calcination

H2O

H2O

Dilute

H2SO4

Seed

TiO2

Titanium

Chromite 1

Chromite is usually reduced in electric

furnace to make ferrochromium

For the production of high-purity chromium,

chromite is dissolved in acid then the

aqueous solution of pure chromium alum is

electrolyzed.


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Chromite 2

FeCr2O4 + 8H+

Fe2+ + 2Cr3+ + 4H2O

Chromite 3


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Niobium & Tantalum 1

Niobium & Tantalum 2 Columbite, tantalite, and pyrochlore are mainly used

to prepare ferroniobium and ferrotantalum by

pyrometallurgical methods

To prepare metallic niobium and tantalum a pure

oxide is usually prepared first by treating the

concentrates by hydrometallurgical methods

Tin slags, especially those from Malaysia and

Thailand, were at one time an important source ofniobium, tantalum, as well as tungsten.


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Niobium & Tantalum 3

Wolframite and Scheelite 1


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Acid digestion

Sulfuric should not be used


Alkaline Digestion


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Leaching of Sulfides


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Sulfides

Disulfides, S2

2

PYRITE, FeS2


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Sulfide-Disulfide

COVELLITE, CuS

Arsenopyrite

FeAsS contains the diarsenide ion

As22


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Thermal Properties

FeS2 FeS + S

FeAsS

FeS + As

CuI4Cu2II(S2)2S2 3Cu

I2S + 3S

Aqueous Behaviour

FeS2(s) Fe2+

(aq) + S22

(aq)

Cu4ICu2

II(S2)2S2(s)

4Cu+(aq) + 2Cu2+

(aq) + 2S22

(aq) + 2S2

(aq)

2FeAsS(s) 2Fe2+(aq)

+ As2

2

(aq)+ S

2

2

(aq)


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Autooxidation of Disulfide Ion

S22 2S + 2e

S22+ 2e 2S2

Overall reaction:

S22 S + S2

Behaviour similar to peroxide ion

O22 O2 + 2e

O22+ 2e 2O2

Overall reaction:

2O22

O2 + 2O2

2H2O2 O2 + 2H2O

PotentialPotential pH DiagrampH Diagram

E(Volts)

0.8

3

pH

0.4

0

0.4

0.8

1.27 111

Oxidizing

HSO4

Elemental sulfur

SO42

H2S

S2Acid BasicR

educing HS


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Apparent Anomalous

Behaviour

Cu2S

Ni3S2

Aqueous oxidation of Cu2S

Aqueous oxidation takes place in two steps

Cu2S + 2H+ + 1/2O2 CuS + Cu

2+ + H2O

CuS + 2H+ + 1/2O2 Cu2+ + S + H2O

This sulfide behaves as if it were solid

solution of a metal and a sulfide

Cu2S behaves like Cu + CuSCu + 2H+ + 1/2O2 Cu

2+ + H2O

CuS + 2H+ + 1/2O2 Cu2+ + S + H2O


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Aqueous oxidation ofNi3

S2

Ni3S2 + 2H+ + 1/2O2 2NiS + Ni

2+ + H2ONiS + 2H+ + 1/2O2 Ni

2+ + S + H2O

Ni3S2behaves like Ni + 2NiS

Ni+ 2H+ + 1/2O2 Ni2+ + H2O

NiS + 2H+ + 1/2O2 Ni2+ + S + H2O

Heating of Elemental Sulfur

Heated

Cooled


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Viscosity of ElementalViscosity of Elemental SulfurSulfur

Viscosity,poise

Temperature, C

120

103

160 200 240 280 320

102

10


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Oxidation products of sulfides in

neutral or alkaline medium


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Aqueous Oxidation of Sulfides

Franz von Soxhlet (1848-1926)


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Industrial Applications 1

Falconbridge ProcessTreatment of a mixture of Cu2S Ni3S2 obtained by smelting a copper

nickel sulfide concentrate

Ni3S2 + 6HCl 3NiCl2 + 2H2S + H2

Insoluble Cu2S is separated by filtration for copper recovery


Equity Silver Process

Copper concentrate is leached for 16 hours at

110C to solubilize arsenic and antimony

sulfides

As2S3 + 3S2 2AsS3

3

Sb2

S3

+ 3S2 2SbS3

3

After filtration, the copper concentrate is

shipped to smelters


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Dissolution of nickel, cobalt, and copper

sulfides

MS + 2O2(aq) MSO4

Industrial Applications 4 Aqueous Oxidation of PbS-ZnS Concentrates


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Aqueous oxidation of molybdenum sulfide in

water

Hydrolysis accompanies oxidation and as a result

molybdic acid is formed as a white precipitate: MoS2Mo

4+ + 2S2

Mo4+ + 3H2O +1/2O2 H2MoO4 + 4H

+

S2+ 2O2 SO42


Aqueous oxidation of molybdenum sulfide in

alkaline medium MoS2Mo

4+ + 2S2

Mo4+ + 6OH- + 1/2O2 MoO42- + 3H2O

S2+ 2O2 SO42

Overall reaction

MoS2 + 6OH

+9

/2O2 MoO42

+ 2SO42

+ 3H2O


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Sherritt-Gordon Process (now Dynatec):

Treating concentrates of copper, nickel, and

cobalt by ammonia to form soluble ammine

complexes

MS + nNH3 + 2O2 [M(NH3)n]2+ + SO4

2

SherrittSherritt--Gordon ProcessGordon Process

Leaching

80 C. 700kPa

H2S

Concentrate

Air

Filtration

Ni-Co-Cu sulfide

NH3

Residue: gangue

Fe (OH) 3, PbSO4,

precious metals

Boiling

Filtration CuS

Precipitation of

traces of Cu 2+

Filtration

Oxidation

Filtration

CuS, NiS, CoS

recycle to leachingcircuit

Fe(OH)3

Air

Purified ammoniacal ammonium

sulfate solution containing

45g/L Ni and 1g/L Co


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Industrial Applications 8Industrial Applications 8

Aqueous oxidation ofAqueous oxidation of Zinc sulfide

ZnS + 2H+ + 1/2O2 Zn2+ + S + H2O

Aqueous Oxidation ofAqueous Oxidation of ZnSZnS 11

concentrate

Leaching

Sulfide

Make upH2SO4

O2

Filtration

Purification

Electrolysis

Gangue, S, PbSO 4FeOOH

Spent

electrolyte

Metal


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Aqueous Oxidation of ZnS 2

Aqueous Oxidation of Pyrrhotite 1

In absencec of acid:

FeS + 2O2(aq) FeSO4(aq)

In presence of acid:

2FeS + 3/2O2(aq) Fe2O3 + 2S


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Aqueous Oxidation ofAqueous Oxidation of PyrrhotitePyrrhotite 22

Fe2+

Concentration

Time

Fe2+

Time

H+

Concentration

Ferric Ion in Leaching 1

Filtration

Leaching

FeCl3 CuFeS2

Cementation

S recovery

Filtration

Crystallization

Oxidation

Cyanidation

Cu

Fe

Fire refining

Cl2

S0

Au, Agrecovery

Copper

FeCl 4HO2 2

Gangue andpyrite


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Ferric Ion in Leaching 2PbS concentrate

Leaching

Fused saltelectrolysis

Lead

Chlorine

Lead chloride

FeCl + NaCl3

FeCl + NaCl

solution2

Hot filtration

Crystallization

Centrifuge

S + gangue0

Oxidation

Aqueous Oxidation of Pyrite 1Aqueous Oxidation of Pyrite 1

0

2

3

4

5

1 2 3

pH

[SO

2]/[Fe

2+]

4

1


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Aqueous Oxidation of Pyrite 2

FeS2 + 2H+ + 1/2O2 Fe

2+ + H2O + 2S

FeS2 + H2O +7/2O2 Fe

2+ + 2H+ + 2SO42

Molar ratio [SO42]/[Fe2+] varies from 0 to 2

Mechanism

FeS2(s) Fe2+

(aq) + S22

(aq)

Disulfide ion undergoes autooxidation

S2

2 S + S2

Overall reaction depends on leaching conditions


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5. Leaching Processes

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Transcript of 5. Leaching Processes