Treatment of lead and zinc slags in hollow electrode DC-EAF

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1 Treatment of lead and zinc slags in hollow electrode DC-EAF E. Hecker, B. Friedrich, J. Böhlke IME Process Metallurgy and Metal Aachen University, Germany Prof. Dr.-Ing. Bernd Friedrich

2 Motivation for Starting position Pb/Zn-production lead/zinc oxidic slags dumping building material production EAF treatment - Pb/Zn-loss - Pb/Zn-loss - dumping costs - environmental risk - environmental risk- slag: ltd. use - slag: no use - lower Pb/Zn-loss - minimisation of environmental risk - slag: mineral material as raw material

3 Basic idea for this project liability for dumping Status Expected Situation quo after situation slag by treatment stricter legislation handling effort environmental risk operating costs Zn-loss Pb-loss Aim: Minimisation of the area between the directives

Comparison of treatment processes and EAF process Slag

05 % Pb Advantages high Zn yield easy handling process

production of metallic lead and zinc impossible clinker

(ISA/Ausmelt) final slag: < 1.0 % Zn < 0.

process control low carbon consumption Fe can be hold in

4 Comparison of treatment processes and EAF process Slag fuming EAF final slag: % Zn % Pb Advantages high Zn yield easy handling process Disadvantages high offgas volume high carbon consumption production of metallic lead and zinc impossible clinker process necessary (due to re-oxidation) lance consumption (ISA/Ausmelt) final slag: < 1.0 % Zn < 0.1 % Pb Advantages flexible design/application simple process control low carbon consumption Fe can be hold in liq. phase Zn product as ZnO or Zn Pb product as PbO or Pb liq Disadvantages lower turbulent conditions high energy costs

5 Zinc and lead concentrations in industrial slags - Imperial Smelting Furnace - Lead Shaft Furnace - QSL Reactor - VARTA Shaft Furnace - KIVCET - ISAsmelt/Ausmelt Zn (wt.-%) Pb (wt.-%) Our project partners: MHD Sudamin GmbH Berzelius Stolberg GmbH VARTA GmbH

6 Slag compositions investigated by EAF process analysis of QSL-slag (wt.-%) SiO 2 26 Al 2 O CaO 10 MgO 1.3 Pb 7.1 PbO 1.2 FeO 23 ZnO 14 ZnS 0.3 Fe 0 Fe 2 O 3 14 analysis of IS-slag (wt.-%) CaO 16 Al 2 O SiO 2 22 PbO 1.2 MgO 4.4 Fe 0.5 Pb 0 ZnO 7,9 FeO 29 ZnS 7.3 Fe 2 O 3 3.7

7 Thermochemical modelling of Zn-reduction in slags (1) RTln(p O 2 ) (kj/mol) Process requirement: - avoidance of Fe-reduction to pig iron calculation considering activities of the IS-slag, neglecting interactions (e.g. between FeO/ZnO) temperature ( C)

8 Thermochemical modelling of Zn-reduction in slags (2) RTln(p O 2 ) (kj/mol) calculation considering activities of the IS-slag and interactions (e.g. between FeO/ZnO) temperature ( C)

9 Kinetics model of coke/slag interaction gaseous reduction route intermediate slag phase reduction route CO, CO 2, Zn g Zn g bulk gas coke particle slag Fe ZnO CO CO CO 2 Fe FeO CO 2 ZnO FeO

10 concentration in offgas (wt.-%) Thermochemical modelling of Zn-reduction in slags (3) 10 8 IS-slag; beginning of reduction; inertgas atmosphere; 2.5 % C in charge Zn 6 CO 4 2 Pb CO 2 ZnS temperature ( C)

11 Pilot EAF at IME Technical data Max. current: 5.3 ka Max. voltage: 110 V Shell diameter: 980 mm Shell height: 1250 mm Electrode diameter: 150 mm Electrode hole diameter: 65 mm Hollow electrode charging system Water cooled current supply Graphite electrode Offgas system Tap holes Water cooled Cu-anode Ladle

12 Test run patameters Test run parameters Slag charge: 250 kg Coke charge: 7.0 kg Temperature: C Av. current: 2.8 ka Av. voltage: 65 V Processing time:140 min

13 Pilot EAF at IME

14 Pilot EAF at IME Temperature meassurement

15 Zn, Pb (wt.-%) Test run results in pilot scale QSL-slag IS-slag test run time t total (min)

16 IS-slag composition after treatment analysis of IS-slag before treatment (wt.-%) CaO 16 Al 2 O SiO 2 22 PbO 1.2 MgO 4.4 Fe 0.5 ZnO 7.9 FeO 29 ZnS 7.3 Fe 2 O analysis of IS-slag after treatment (wt.-%) CaO 20 Al 2 O 3 10 PbO 0.09 MgO 5.5 SiO 2 27 ZnO 1.2 ZnS 0 FeO 31 Fe 2.8 Fe 2 O 3 3.7

17 General assessments and conclusions DC electric arc furnace with hollow electrode technique: - Realises high temperatures necessary for Zn-reduction - No solid iron phase during treatment - Low offgas volume - Allows addition of reasonable carbon fines - Well-adjustable proportioning of coke possible - Avoidance of injection gas - Kinetics sufficient for treatment in t < 120 min Products: - Improvement of usage for the final slag - Final slags keeping expected limits for heavy metals - High grade flue dust ( (PbO; ZnO) ~ 100 %) - Zink metal winning possible (investigated by MINTEK) - Crude lead recovery - Silver recovery (in crude lead)

18 Thank you for your attention Project supported by BMBF (Federal Ministry of Education and Research)

19 Slag composition of Pb-Zn-slags Technical requirements: SiO 2 - low melting temperature (~ 1,000 1,200 C) - low viscosity (control of FeO-content) - minimisation of total slag output QSL-Slag IS-Slag CaO FeO

4th Slag Valorisation Symposium, April Conditioning of Lead and Zinc Slags in Pilot Scale SAF for further Utilization

4th Slag Valorisation Symposium, 15-17 April 2015 Conditioning of Lead and Zinc Slags in Pilot Scale SAF for further Utilization Frank Kaußen, Jörn Böhlke, Christoph Kemper, Bernd Friedrich IME Process