1. 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

2. What is the steelwork dust ?

3. World steel production Oxygen steelmaking BOF (basic oxygen furnace) Electric steelmaking EAF (electric arc furnace) O2O2 CaO Direct reduction Sponge iron Fe, (Si,P,S,…) Iron ore Blast furnace Pig iron Fe, C, (Si,P,S,…) Dust 30 mil. t /y 2-5 mil. t Zn /y Steelmaking slag Steel 1 400 mil. t /year 40% Scrap Fe 0,5%Zn, 0,03%Pb, 60%

4. Statistics for USA and Canada (year 2000) for EAF mostly (50%): Fe15-30% 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% Pb1% Cd0,02% 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)

5. 1 tonnePRICE NaOH$ 400 CaO$ 25 ZnFe 2 O 4 $ -20 Dust as a basic neutralizing agent

6. Steelmaking dust processing Pyrometalurgy: 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. H 2 SO 4 or HCl Hydrolysis at increasing pH in large volume of water leads to iron precipitation = haematite, goethite, or jarosite Filtration Chlorine metalurgy: Reaction of Cl 2 or HCl with the dust –chlorides formation The iron chlorides decompose at higher temperature to oxides and HCl ZnCl 2 (boiling point 756°C) is volatile and it condenses as a water- soluble salt problems:

7. Experimental studies of the reactions of HCl with metallurgy dust VŠB -Technical University of Ostrava Faculty of Metallurgy and Material Engineering Department of Chemistry Jan Cieslar Šárka Langová Juraj Leško Dalibor Matýsek Radim Škuta Jana Wichterlová Kamil Wichterle

8. 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

9. 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

10. Mineralogy of the sample TP % w/w % Zn distribution Zn % Hematit3,2 Magnetit35,6 Wuestit3,2 Franklinit36,69,969,0 Grafit4,4 Zinkit5,64,531,0 amorphous11,4

11. Laboratory equipment Oven Condenser Inlet HCl Quartz tube

12. 2 HCl(g) + 1/3 Fe 2 O 3 (s) = 2/3 FeCl 3 (s,l,g) + H 2 O(g)(1) 2 HCl(g) + 1/4 Fe 3 O 4 (s) = 1/4 FeCl 2 (s,l,g) + 1/2 FeCl 3 (s,l,g) + H 2 O(g)(2) 2 HCl(g) + FeO (s) = FeCl 2 (s,l,g) + H 2 O(g)(3) 2 HCl(g) + ZnO (s) = ZnCl 2 (s,l,g) + H 2 O(g)(4) 2 HCl(g) + 1/4 ZnFe 2 O 4 (s) = 1/4 ZnCl 2 (s,l,g) + 1/2 FeCl 3 (s,l,g) + H 2 O(g)(5) 2 HCl(g) + ZnFe 2 O4(s) = ZnCl 2 (s,l,g) + Fe 2 O 3 (s) + H 2 O(g)(6) FeCl 2 (s,l,g) + ZnFe 2 O 4 (s) = ZnCl 2 (s,l,g) + Fe 2 O 3 (s) + FeO (s)(7) 2/3 FeCl 3 (s,l,g) + ZnFe 2 O 4 (s) = ZnCl 2 (s,l,g) + 4/3 Fe 2 O 3 (s) (8) EQUILIBRIUM DATA

13. Evidently, iron chlorides are unstable at temperatures higher than 300°C. Zinc chloride is generally chemically stable up to 700°C However, ZnCl 2 at higher temperatures leaves the reaction space as a vapor (its boiling point is 756°C) which affects the equilibrium

14. Therefore, higher temperatures are suitable to separate ZnCl 2 vapors from the solid residuum of iron oxides

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

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

17. World steel production Oxygen steelmaking BOF (basic oxygen furnace) Electric steelmaking EAF (electric arc furnace) O2O2 CaO Direct reduction Sponge iron Fe, (Si,P,S,…) Iron ore Blast furnace Pig iron Fe, C, (Si,P,S,…) Dust 30 mil. t /y 2-5 mil. t Zn /y Steelmaking slag Steel 1 400 mil. t /year 40% Scrap Fe 0,5%Zn, 0,03%Pb, 60%

18. 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)

19. Efficient way of zinc recycling is worth to be studied

20. Thank you for the attention