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

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4th Slag Valorisation Symposium, 15-17 April 2015 Conditioning of Lead and Zinc Slags in Pilot Scale SAF for further Utilization Frank Kaußen,

1 4th Slag Valorisation Symposium, 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 Metallurgy and Metal, RWTH Aachen University Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich

2 Motivation Slags of lead smelters contain up to 10 wt.-% Pb and up to 15 wt.-% Zn Entrapment of Pb and Zn in slags is inevitable due to: metallurgy (kinetics and thermochemistry) process technology profitability of production Possible Consequences of Pb and Zn in slags: excess of legislative limit values loss of Pb and Zn environmental risk only limited applications available landfill may become necessary treatment process for the slags is recommended

Slag Treatment Process Requirements: Expected benefits: recovery of Zn and Pb by reduction and vaporisation (Zn, Pb) or settling (Pb) process integrated in-line treatment of liquid slag increase of

3 Slag Treatment Process Requirements: Expected benefits: recovery of Zn and Pb by reduction and vaporisation (Zn, Pb) or settling (Pb) process integrated in-line treatment of liquid slag increase of yield and profit decreased amount of slag improved slag quality new applications possible (e.g. road/building constructions) Aim of the treatment: final Zn-content in the slag: < 1 wt.-% final Pb-content in the slag: < 0,1 wt.-%

4 Composition of Investigated Slags Slags with varying zinc and lead contents have been deliberately produced (average values) wt.-% Pb Zn Fe Fe 2+/ Fe ges SiO 2 CaO MgO Al 2 O 3 IS 1,1 5,1 25,5 0, ,4 7,9 BSR I 7 11,8 25 0, ,5 2,4 BSR II 55 6,8 9,8 0,6 7,3 3,2 0,3 0,8

5 Investigations Chemical slag characterisation X-ray diffraction analysis of granulated industrial slag identified phases: Pb (metallic), FeO, Fe 3 O 4, ZnS (if S is present) rest: amorphous phase thermogravimetry / differential thermal analysis S reacts with ZnO in a roasting reaction and thereby promotes the recovery of Zn thermochemical modelling of states of equilibrium FactSage-based modelling of states of equilibrium from 700 C to 1500 C favourable conditions for the slag treatment include addition of a reducing agent and temperatures of > 1400 C a complete recovery of Pb and Zn from the slags can be achieved

6 Thermodynamic Modelling: Stable Phases Olivine: (CaFe,Fe 2,Zn 2 )SiO 4 Clinopyroxene: (CaFe,CaMg)Si 2 O 6 Spinell: ZnAl 2 O 4 Sphalerite, Wurtzite: ZnS

Utilised Technique: SAF advantages: very flexible regarding feed materials operation mode process temperature heat generation in the melt easy process control small units sufficient low off gas

7 Utilised Technique: SAF advantages: very flexible regarding feed materials operation mode process temperature heat generation in the melt easy process control small units sufficient low off gas volume possible cleaning by superheating (easy removal of precipitates) disadvantages: high demand of electrical energy comparably low volatilisation rates intensification by hollow electrode technique and coke injection tapping of the SAF at the IME

8 Investigations laboratory scale SAF-test work 44 tests with 8 to 12 kg slag in a DC EAF development of a hollow electrode technique for coke addition best results: recovery of 97 % of Pb and 98 % of Zn semi-pilot scale SAF-test work transfer of the results of preceding test work in semi-pilot scale 25 test runs with different industrial slags Duration of each experiment: 2 2,5 h In total 6,5 t of treated slag addition of coke through hollow electrode as standard technique setup of a pneumatic coke injection facility (used in 6 tests) for comparison 2 tests with premixed coke/slag-mixture

Semi-Pilot Scale SAF at IME Technical data: Max.

voltage: 110 V Power used in experiments: 150-350 KW

Electrode hole diameter: 65 mm Hollow electrode

9 Semi-Pilot Scale SAF at IME Technical data: Max. current: 5,3 ka DC Max. voltage: 110 V Power used in experiments: KW Total volume: 250 l Electrode diameter: 150 mm Electrode hole diameter: 65 mm Hollow electrode charging system Water cooled current supply Offgas system Tap holes Water cooled Cuelectrode

continuous operation injection lance: IME-development (steel tube

10 Pneumatic Coke Injection Unit Main characteristics: up to 3 bar outlet pressure 45 l storage bin loss in weight feeding (± 0,1 kg) continuous operation injection lance: IME-development (steel tube and SiC immersion piece) injection lance support coke injection unit

11 Semi-Pilot Scale Test Work: Key Figures and Procedure Procedure: preheating of the SAF with approx. 200 kg steel scrap melting of kg slag (Charging time ~ 1 h) adjustment of bath temperature C if required coke addition by hollow electrode or pneumatic injection holding time for homogenization and completion of reactions tapping of whole melt (metal and slag simultaneously) after solidification weighing and sampling of products slag

Coke Injection: Observations strong reaction in furnace and off gas (re-oxidation of reduced and evaporated Zn) only little emission of coke particles

12 Coke Injection: Observations strong reaction in furnace and off gas (re-oxidation of reduced and evaporated Zn) only little emission of coke particles reaction easily controllable (intensity of reaction and off gas temperature) heavy wear of immersion piece and furnace lining furnace wall electrode furnace bottom

of tests thereof < 0,1 % Pb in final slag thereof < 1 % Zn in final slag max Pb

13 Semi-Pilot Scale Test Work: Results Pb and Zn in resulting product phases (averages) technique for coke addition no. of tests thereof < 0,1 % Pb in final slag thereof < 1 % Zn in final slag max Pb recovery rate max Zn recovery rate hollow electrode ,5% 99,2% premixed 2 / / 93,9% 82,3% injection 6 / / 94,4% 78,1%

14 Zn-content in slag in wt.-% Mechanisms and final slag composition Pb-content in slag in wt.-% Duration in min Pb: Zn: to flue dust with avg. 25 % Pb, max > 50 % Pb for slags with high initial Pb content (> 50 %): formation of a lead bullion with > 90 % Pb exclusively to flue dust with avg. 50 % Zn, max 78 % Zn

15 Summary and Outlook Slags from pyrometallurgical zinc and lead winning contain significant contents of lead and zinc A process integrated treatment should be applied for economical, legislative and ecological reasons SAF-technique is very utilizable for recycling and treatment processes best case community values for Pb 0,1 wt.-% & Zn 0,1 wt.-% The treatment of slags in a SAF has been investigated in laboratory and semi-pilot scale SAF Coke injection not optimized yet but holds potential for process intensification Final mineral product reaches typical composition of NF metallurgy

4th Slag Valorisation Symposium, 15-17 April 2015 Thank you for your attention!

16 4th Slag Valorisation Symposium, April 2015 Thank you for your attention! IME Process Metallurgy and Metal, RWTH Aachen University Prof. Dr.-Ing. Dr. h.c. Bernd Friedrich

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

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 Motivation for