B01 Fleming

8/8/2019 B01 Fleming

1/31

THE FERRIC ION -GODS GIFT TOHYDROMETALLURGISTS

TO KEEP EM HUMBLE

By Chris Fleming

SGS Lakefield Research Ltd.


2/31

TOPICS

The first SEx war

Theres nothing basic about basic ironsulphate


3/31

THE FIRST SEx WAR

History

Great interest in solvent extraction in the 1960s, initially

for uranium and then for copper.

Low grade oxide copper ores were being processed in the

USA and Chile by acidic heap leaching (small scale).

Copper sulphate in solution was recovered by cementation

onto scrap iron, and then smelted and refined.

Most leach liquors contained ferric ions, which reacted

with the scrap iron wastefully, and the process was:(i) Expensive

(ii) Yielded an impure copper product


4/31

THE FIRST SEx WAR

History

Early economic projections predicted the cost of SEx/EWwould be half the cost of cementation/smelting/refining.

The perfect reagent had to be able to extract copper (II)

from weak acid leach solution (pH 1-2), be strippable instrong acid (50 -100g/L H2SO4) to be compatible with EW,and be very selective for copper particularly versus theferric ion.

Copper SEx reagent development was spearheaded bytwo US companies, General Mills, who produced the LIX

reagents, and Ashland Chemical, who produced Kelex100.


5/31

H

O

RN

HYDROXYQUINOLINE

KELEX

C = N

R

HO

LIX

HYDROXYOXIME

OH

COPPER SEx REAGENTS


6/31

THE FIRST SEx WAR

History

The first copper SEx plant was built at the Blue BirdMine in Arizona in 1968 (6000 tpa Cu), soonfollowed by a much bigger plant at Nchanga minein Zambia (65,000 tpa Cu).

More plants followed, and 3% of world copperproduction was via SEx/EW by 1975. By 2007, thishad grown to 22% of annual Cu production, (3.5Mtons of cathode copper). This was being producedin 70 SEx/EW plants in 16 countries (60% in Chile).

But who was making the SEx reagents and whowas winning the reagent war?


7/31

Copper extraction with LIX and KELEXreagents as a function of pH

-10

10

30

50

70

90

0 1 2 3 4 5 6

pH

Copper

Extraction

(%)

LIX 63 4.8

LIX 64 3.3

LIX 64N 2.9

LIX 70 2.6

KELEX 100 1.8

0

Initial Rate of Copper Extraction (g/L/min)

KELEX 100 0.98

LIX 64N 0.11


8/31

KINETIC AND STABILITY CONSTANTSFOR THE REACTION OF Cu(II) AND Fe(III)

WITH HYDROXYQUINOLINES

Initial Rate ofExtraction with Kelex

100 (g/L/min)

III

Metal

Cu( )Fe( II)

0.980.067

Stability with8 HydroxyQuinoline

Log 2 = 23.0Log 3 = 36.9


9/31

RATES OF EXTRACTION OF Cu(II) ANDFe(III) BY KELEX 100

0

25

50

75

100

0 50 100 150 200

Stirring time, min

Extraction with

10% KELEX 100

(%)

Cu

2+

from pH 1 solutionCu

2+from pH 2 solution

0

25

50

75

100

0 50 100 150 200

Stirring time, min

Extraction with

10% KELEX 100

(%)

Cu

2+

from pH 1 solutionCu

2+from pH 2 solution

Fe3+

from pH 1 solution

Fe3+

from pH 2 solution


10/31

61575910005552508020

49483940604038200100

CuCuCu432 h24 h1 hmol %mol %

Metal Extracted (%)Salicyl-aldoxime

LIX65N

RATES OF EXTRACTION OF Cu(II) ANDFe(III) BY LIX65N AND ITS PRECUSOR,

SALICYLALDOXIME

Fe21

21

Fe21

22

Fe21

0.30.1


11/31

THE MORAL OF THE STORY

If you want to win a SEx war, it is

better to be slow and selectivethan to be fast and flirtatious.


12/31

THERES NOTHING BASIC ABOUT

BASIC IRON SULPHATE


13/31

BACKGROUND

Basic iron sulphate (BFS) is a solid compound that isformed under certain conditions during the oxidation ofpyrite or other iron sulphide minerals with oxygen at hightemperatures in an autoclave.

Iron sulphide minerals are oxidized in an autoclave toproduce ferric sulphate and sulphuric acid in solution. Theferric sulphate then hydrolyzes slowly, precipitating backout of solution as hematite and/or BFS.


14/31

OXIDATION

2FeS2 + 702 + 2H2O 2FeSO4 + 2H2SO4

4FeSO4 + 2H2SO4 + O2

2Fe2(SO4)3 + 2H2O

Overall:

4FeS2 + 1502 + 2H2O 2Fe2 (SO4)3 + 2H2SO4


15/31

HYDROLYSIS

Ferric sulphate hydrolyzes to hematite at higher temperaturesand lower acidity

Fe2(SO4)3 + 3H2O Fe2O3 + 3H2SO4

and it hydrolyzes to BFS at lower temperatures and higheracidity

Fe2(SO4)3 + 2H2O 2Fe(OH)SO4 + H2SO4


16/31

OXIDATION AND HYDROLYSIS

Overall reaction for the oxidation of pyrite to ferricsulphate followed by hydrolysis to hematite

4FeS2 + 15O2 + 8H2O 2Fe2O3 + 8H2SO4

Overall reaction for the oxidation of pyrite to ferricsulphate followed by hydrolysis to BFS

4FeS2 + 15O2 + 6H2O 4Fe(OH)SO4 + 4H2SO4


17/31

Stability domains of compounds of the ferric ion inwater as a function of temperature and pH

20

60

100

140

180

220

260

0 2 4 6 8 10 12

pH

Temp

(C)

Fe3+

Fe (OH)3

Goethite

FeO.OH

Hematite

Fe2O3

Basic Iron Sulphate

Fe(OH)SO4


18/31

WHY IS BFS BAD NEWS IN ACYANIDATION CIRCUIT?

BFS is not basic, it is actually acidic..and it must be

neutralized before cyanidation

The rate of release of acid by BFS is extremely slow inweakly acidic solution (pH 7 Fe(OH)3 + CaSO4

pH3.5

very slowFe(OH)SO4 + CaCO3 + H2O Fe(OH)3 + CaSO4 + CO2


19/31


20/31

WHY IS BASIC IRON SULPHATE BADNEWS IN CYANIDATION CIRCUITS

For health and safety reasons related to HCN formation,the BSF must be fully neutralized prior to cyanidation.This will take 12-24 hours and add significantly to plantcapital cost.

As a result, most of the sulphate generated in theautoclave has to be neutralized with hydrated lime, ratherthan limestone. Lime can be at least 10 times the price oflimestone.

If not dealt with appropriately, the increased capex and

opex associated with BFS formation could eliminate POXfrom consideration for many refractory gold projects


21/31

WHAT IS THE BEST SOLUTION?

THE HOT CURE PROCESS


22/31

The basis of the hot cure process is the fact that thehydrolysis reaction that produces BFS in the autoclave isreversible at lower temperatures:

BFS Formation

BFS Decomposition


Fe2(SO4)3 + 2H2O Fe(OH)SO4 + H2SO4T>150C

Fe(OH)SO4 + H2SO4 Fe2(SO4)3 + 2H2O

90-140C

fastRT

very slow


23/31

2Fe(OH)SO4 + H2SO4 Fe2(SO4)3 + 2H2O


20

60

100

140

180

220

260

0 2 4 6 8 10 12

pH

Temp

(C)

Fe3+

Fe (OH)3

Goethite

FeO.OH

Hematite

Fe2O3

BFS


24/31


Once the basic iron sulphate has decomposed to ferric

sulphate, it can be separated from the solids by CCD orfiltration, and neutralized with limestone

Fe2(SO4)3 + 3CaCO3 + 3H2O 2Fe(OH)3 + 3CaSO4 +3CO2


25/31

NEUTRALIZATION OF THE ACIDAND SULPHATE WITH LIMESTONE

(1) Fe2(SO4)3 + 3CaCO3 +H2O 2FeO.OH + 3CaSO4 + 3CO2

(2) Fe2(SO4)3 + 3CaCO3 +3H2O 2Fe(OH)3 + 3CaSO4 + 3CO2

20

60

100

140

180

220

260

0 2 4 6 8 10 12 14

pH

Temp

(C)

Fe3+

Hematite

Fe2O3

BFS

Goethite

FeO.OH

Fe(OH)3

(1)

(2)


26/31

A REFRACTORY GOLD POX FLOWSHEETINCORPORATING HOT CURING

Oxygen

Concentrate

Pressure

Oxidation

Hot Cure

Solid/LiquidSeparation

SolidLiquid

Solid/Liquid

Separation

Neutralisation

Solid

CaSO4Fe(OH)3

Cyanide

Leach

Gold

Recovery

Cyanide

DestructionTailings

Steam90 100 C4 to 12 hours

CO2

NaCN

Ca(OH)2

Liquid

Base MetalRecovery ?

CaCO3


27/31

QUIMSACOCHA PROJECT, ECUADOR(IAMGOLD CORPORATION)

Fe (mass/mass) = 18.1%

SO4 (mass/mass) = 32.0%Fe/SO4 = 0.57

0

10

20

30

40

-3 0 3 6Time at 90C (hr)

Fe

SO4

ACD

Conc. InAutoclaveDischarge

Solids(%)


28/31

QUIMSACOCHA PROJECT

0

10

20

30

40

50

60

70

-3 0 3 6

Time (hr)

Autoclave

Discharge Solution(g/L)

Fe

H2SO4

ACD


29/31

QUIMSACOCHA PROJECT

Concentrate head grade: 24 g/t Au, 104 g/t Ag

PRODUCT RECOVERY ALKALI CONSUMED APPROX. COST

Au % Ag % CaCO3 kg/t Ca(OH)2 kg/t $/tAutoclaveDischarge

99.6 94.8 370 260 43

Hot CureDischarge

99.4 91.9 704 15 9


30/31


31/31

Documents

B01 Fleming