Development of a CaO-CaF 2 -slag system for high rare earth contents

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1 Development of a CaO-CaF 2 -slag system for high rare earth contents T. Müller; B. Friedrich IME Process Metallurgy and Metal Aachen University, Germany Prof. Dr.-Ing. Bernd Friedrich

2 Source for Rare Earth: Battery Design Types Nickel-Metalhydride battery composition (wt-%) Ni Co La, Ce, Nd, Pr Application 3-4 today 8-10 Fe H 2 +O 2 plastic Further application: TOYOTA MOTOR CORPORATION Prius,110,000 sold Hybrid Vehicles since 1998

3 Flowsheet of the intended recycling process Ni-MH-batteries Mechanical processing Can scrap Organic/separators NiMH Ni(OH) 2 Ni mass partly with carbon black and organics Flux Melting RE-rich slag Return slag Slag processing Pyromet. refining Ni-Co-alloy Molten salt electrolysis Mischmetal Ni-MH battery production

4 Flowsheet of the intended recycling process Ni-MH-batteries Mechanical processing Can scrap Organic/separators NiMH Ni(OH) 2 Ni mass partly with carbon black and organics Flux Melting RE-rich slag Return slag Slag processing Pyromet. refining Ni-Co-alloy Molten salt electrolysis Mischmetal Ni-MH battery production Concentrate after mechanical processing, w% Ni Co La, Ce, Nd, Pr Fe Mn C 2-3

5 Required slag properties Liquid at 1500 C (melting point of NiCo-alloy) Low evaporation pressure of slag components Low viscosity High density difference of slag and metal High solubility for RE respectively poor solubility for Ni and Co Suitable for slag processing

6 Slag development (I) First scan Slag system No flux added SiO 2 -CaO -MgO SiO 2 -CaO -Al 2 O 3 CaF 2 -CaO SiO 2 Result No phase separation Sufficient, but difficult phase separation Sufficient From very good to unsuccessful depending on added amount Unsuccessful CaCl 2 No phase separation

$refractory 4 water inlet 5 bag filter 6 spark shield 6 5$

7 Slag development (II) Lab-scale el. arc melting Experimental set up 1 graphite electrode (cathode) 2 copper electrode (anode) water cooled 3 refractory 4 water inlet 5 bag filter 6 spark shield T... thermo couples water outlet

8 Slag development (III) Lab-scale el. arc melting Results Slag system Composition (wt%) NiMH/flux Result CaF 2 CaO CaO, CaF from insufficient to very good SiO 2 - CaO MgO 45 SiO 2, 40 CaO, 15 MgO 3-9 from poor to very good CaF 2, SiO 2 -CaO -Al 2 O CaO, all insufficient Al 2 O 3 Due to unexpected results in repeated trials basic investigation of slag systems required: Investigation of density, surface tension and viscosity

9 Density determination Experimental procedure No information about RE-influence on CaO-CaF 2 systems were found Decided to determine some basic properties Lab-facilities for measurement of density, viscosity, surface tension, wetting angle available at IME Start with density measurement using hydrostatic weighing method: Derived equation for measurements with different bobs: m a1, m m1, m a2, m m2 : V 1, V 2 : ρ m ρ Weights of bob in air and in the melt Volumes of bob a = ( m - m ) ( m - m ) a1 ( V V ) ( 1+ ε ) 3 1 m1 2 a2 m2

10 Density determination Experimental setup Balance Scale Pt-Rh Pt-Wire wire Thermocouple to PC Pt-Sphere Mo bob to PC Frame Crucible Melt Furnace Furnace Controller Transformer

11 Density determination Results ρ min ρ max Arithmetic mean Standard deviation Trial Trial Trial Trial 1 Trial 2 Trial 3 3 2,5 Propability density 2 1,5 1 0,5 0 4,05 4,10 4,15 4,20 4,25 4,30 4,35 4,40 4,45 4,50 4,55 4,60 Density, g cm -3

12 Pilot plant tests Experimental set-up tapping operation Charging velocity kg/h Average tapping weight 245 kg Power during operation app.150 kw (max. 480) Average tapping temperature 1680 C

13 Pilot plant tests Input composition Nr. Material Flux composition Charge Pouring composition temperature SiO 2 CaF 2 CaO Flux Ni-MH C 1 Anode scrap 65 % 35 % 10 % 90 % Production scrap 65 % 35 % 10 % 90 % Spent batteries 65 % 35 % 10 % 90 % Pyrolysed spent batteries 65 % 35 % 10 % 90 % Pyrolysed spent batteries 65 % 35 % 5 % 95 % Pyrolysed spent batteries 65 % 35 % 5 % 95 % Mixture 65 % 35 % 5 % 95 % Mixture 65 % 35 % 5 % 95 % Polluted Mixture 65 % 35 % 5 % 95 % 1520 Material preparation Pellets Powder Similar smelting behaviour of different scraps Successful separation of NiCo and RE Required flux amount reduced to 5 % Both slag systems are suitable CaF 2 -CaO-system is easier to handle

14 Pilot plant tests Slag composition Nr. Material RE-Oxide Ca Mg Fe Al Co Ni Mn SiO 2 F 1 Anode scrap Production scrap Spent batteries Pyrolysed spent batteries Pyrolysed spent batteries Pyrolysed spent batteries Mixture Mixture Polluted Mixture RE content varies from 53 % to 69 % Low Ni and Co content Only part of Fe and Mn were slagged Mg originated from furnace refractory Focus on CaF 2 -CaO-system

15 Summary Objective of the project is the development of a closedloop recycling process for NiMH batteries Scan delivered possible suitable slag systems In more than 50 Lab-scale trials two possible slag systems were determined (CaF 2 -CaO and CaO-SiO 2 ) Start of basic information investigation (density, surface tension, viscosity) Pilot plant trials: Transfer from 5 kg to 300 kg successful conducted Next steps: Further trials for densiy, surface tension and viscosity determination

16 Thank you for your attention Acknowledgements: The authors are thankful to the Federal Ministry of Education and Research (BMBF) for financial support of this project. IME Process Metallurgy and Metal University of Technology, Aachen, Germany Prof. Dr.-Ing. Bernd Friedrich

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