ZINC STRIPPING FROM STEELWORK DUST

Kamil Wichterle, Jan Cieslar, Jana Wichterlová VSB-Technical University of Ostrava,

70833 Ostrava Poruba, Czech Republic kamil.wichterle@vsb.cz

What is the steelwork dust ?

World steel production

Oxygen steelmakingBOF (basic oxygen furnace)

Electric steelmakingEAF (electric arc furnace)

O2

CaO

Direct reduction

Sponge ironFe, (Si,P,S,…)

Iron ore

Blast furnace

Pig ironFe, C, (Si,P,S,…)

Dust30 mil. t /y

2-5 mil. t Zn /y

Steelmaking slag

Steel1 400 mil. t /year

40%

Scrap

Fe0,5%Zn, 0,03%Pb,

60%

Statistics for USA and Canada (year 2000) for EAF mostly (50%): Fe 15-30% Zn 12-25% Pb 1-2% Cd 0,02-0,05%

Dust composition depends mostly on the quality of scrap

In particular our samples from the tandem furnaces Arcelor Mittal contained

Fe about 50% Zn 8-16% Pb 1% Cd 0,02%

Percentage of iron is higher and percentage of the heavy metals is lower in the dust from BOF process (as the heavy metals are absent in the entering pig iron)

1 tonne PRICE

NaOH $ 400 CaO $ 25ZnFe2O4 $ -20

Dust as a basic neutralizing agent

Steelmaking dust processingPyrometalurgy:

Reduction roasting at 1000-2000°C

Distillation of Zn (boiling point 907°C) and its condensation in oxidizing environment in form of ZnO

Hydrometalurgy:

Total dissolution (both Fe and Zn oxides) in conc. H2SO4 or HCl

Hydrolysis at increasing pH in large volume of water leads to iron precipitation = haematite, goethite, or jarosite

Filtration

Chlorine metalurgy:

Reaction of Cl2 or HCl with the dust –chlorides formation

The iron chlorides decompose at higher temperature to oxides and HCl

ZnCl2 (boiling point 756°C) is volatile and it condenses as a water-soluble salt

problems:

problems:

problems:

Experimental studiesof the reactions of HCl with

metallurgy dust VŠB -Technical University of Ostrava

Faculty of Metallurgy and Material EngineeringDepartment of Chemistry

Jan CieslarŠárka LangováJuraj LeškoDalibor MatýsekRadim ŠkutaJana WichterlováKamil Wichterle

The dust in Arcelor Mittal Steel plant is separated by textile filtres and collected as a water suspension

– after a sedimenttion in Dorr thickenners the mud is dumped in deposits

Arcelor Mittal Steel – Tandem Furnaces

Distribution of particle size for the TP dust sample

The dust in Arcelor Mittal Steel plant is collected by textile filtres and transferred to water suspension

– after a sedimenttion in Dorr thickenners the mud is dumped in deposits

Mineralogy of the sample TP

 %

w/w% Zn

distribution Zn %

Hematit 3,2    

Magnetit 35,6    

Wuestit 3,2    

Franklinit 36,6 9,9 69,0

Grafit 4,4    

Zinkit 5,6 4,5 31,0

amorphous 11,4    

Laboratory equipment

Oven

Condenser

Inlet HCl

Quartztube

2 HCl(g) + 1/3 Fe2O3(s) = 2/3 FeCl3(s,l,g) + H2O(g) (1)2 HCl(g) + 1/4 Fe3O4(s) = 1/4 FeCl2(s,l,g) + 1/2 FeCl3(s,l,g) + H2O(g) (2)2 HCl(g) + FeO (s) = FeCl2(s,l,g) + H2O(g) (3)2 HCl(g) + ZnO (s) = ZnCl2(s,l,g) + H2O(g) (4)2 HCl(g) + 1/4 ZnFe2O4(s) = 1/4 ZnCl2(s,l,g) + 1/2 FeCl3(s,l,g) + H2O(g) (5)2 HCl(g) + ZnFe2O4(s) = ZnCl2(s,l,g) + Fe2O3(s) + H2O(g) (6)FeCl2(s,l,g) + ZnFe2O4(s) = ZnCl2(s,l,g) + Fe2O3(s) + FeO (s) (7)2/3 FeCl3(s,l,g) + ZnFe2O4(s) = ZnCl2(s,l,g) + 4/3 Fe2O3(s) (8)

EQUILIBRIUM DATA

-80

-40

0

40

80

200 400 600 800 1000

Temperature, °C

Gib

bs

ener

gy,

kJ/

mo

l

Eq.(1) Eq.(2) Eq.(3)Eq.(4) Eq.(5) Eq.(6)Eq.(7) Eq.(8)

Evidently, iron chlorides are unstable at temperatures higher than 300°C.

Zinc chloride is generally chemically stable up to 700°C

However, ZnCl2 at higher temperatures leaves the reaction space as a vapor (its boiling point is 756°C) which affects the equilibrium

Therefore, higher temperatures

are suitable to separate ZnCl2 vapors from the solid residuum of iron oxides

Zn, Fe, and HCl conversions as functions of temperature for the TP dust sample (45 minutes reaction)

0

10

20

30

40

50

60

70

80

90

100 200 300 400 500 600 700 800 900

T [°C]

X [

%]

X(Zn)

X(Fe)

X(HCl)

X(Zn)+X(Fe)

0,0

20,0

40,0

60,0

80,0

100,0

0 10 20 30 40 50

t [min]

X [

%]

X(Zn)

X(Fe)

X(HCl)

Zn, Fe, and HCl conversions as functions of reaction time for the TP dust sample (temperature 900°C)

World steel production

Oxygen steelmakingBOF (basic oxygen furnace)

Electric steelmakingEAF (electric arc furnace)

O2

CaO

Direct reduction

Sponge ironFe, (Si,P,S,…)

Iron ore

Blast furnace

Pig ironFe, C, (Si,P,S,…)

Dust30 mil. t /y

2-5 mil. t Zn /y

Steelmaking slag

Steel1 400 mil. t /year

40%

Scrap

Fe0,5%Zn, 0,03%Pb,

60%

World zinc production

2009 8 millions tonnes Zn

China (continental) 2.9

Peru 1.4

Australia 1.3

United States 0.7

Canada 0.7

Zinc lossed in steelmaking dust:

3 millions tonnes of Zn !!!!!!1 tonne of Zn = $ 1500 - $ 2500 (2009-2010)

Efficient way of zinc recycling is worth to be studied

Thank you for the attention