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Recycling Aluminum Salt Cake

Recycling Aluminum Salt Cake

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Recycling Aluminum Salt Cake

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  1. Recycling Aluminum Salt Cake J.N. Hryn and E.J. Daniels Process Engineering Section Energy Systems Division Argonne National Laboratory

  2. About U.S. Department of Energy (DOE) • Maintains 5 major National Laboratories • Argonne, Oak Ridge, Sandia, Livermore, Brookhaven • 19 smaller laboratories and technology centers • Mission includes: • Advance the national, economic, and energy security of the United States • Promote scientific and technological innovation

  3. Founded in 1943, designated a national laboratory in 1946 Managed by The University of Chicago for the Department of Energy ~4000 employees and 4000 facility users ~$500M budget 1500-acre site in Illinois 800-acre site in Idaho Broad R&D portfolio Argonne partners with DOE, other federal labs, academia, and the private sector About Argonne National Laboratory

  4. About Process Engineering Section • Part of Energy Systems Division • Interdisciplinary, focus on applied research • Three R&D areas: • Recycling and separation process development • Aluminum and Magnesium • Automotive Shredder Residue • Plastics (recycled appliances and automotive) • Glass • Process modeling and simulation • Glass and aluminum melting furnaces • New materials applications • Diamond coatings • Thin films (atomic layer deposition)

  5. Recycling Aluminum Salt Cake • Opportunity: • Aluminum recycling generates salt cake by-product • Aluminum metal • Sodium chloride and potassium chloride salt • Non-metallic product (mainly aluminum oxide) • Salt cake is disposed in landfills • Only a few companies use responsible disposal methods • Environmental concern • Project Objective: • to develop a cost-effective salt cake recycling technology • recover aluminum, salts, and non-metallic product (NMP) • NMP is converted to value-added oxide products

  6. Recycling Aluminum Salt Cake – Overview Aluminum Refractory Feedstock Recovery of Salt Cake Constituents Ironmaking Feedstock Salt Conversion to Value-Added Products Salt Cake Steelmaking Feedstock Non-Metallic Product

  7. Project Summary • History: • 1990: US DOE-sponsored assessment study • 1994: bench-scale work begins at Argonne • 1996: Argonne & Alumitech begin collaboration • 1998: Argonne begins pilot-scale tests • 2001: Experimental work suspended • Preliminary conclusions: • Many technical solutions possible • No economical solutions yet for salt cake recycling • Best option is maximize aluminum recovery and disposal of residues in controlled landfill • Economic and environmental analysis suggested that recycling salt cake is not desirable

  8. Non-Metallic Product66% Aluminum6% Salt28% Average Salt Cake Composition

  9. crusher salt cake digester water aluminum (to smelters) screen filter NMP (to market) condenser steam salt (to smelters) evaporator Suggested Approach to Recycling Salt Cake

  10. Salt Cake Recycling Barriers in U.S. • salt recovery by evaporation is too expensive • high energy and capital costs, low product value

  11. Salt Cake Recycling Barriers in U.S. • no market for recovered NMP • high levels of impurities, variable composition

  12. 40 to 80% up to 40% up to 10% up to 5% up to 8% up to 10% alumina (a-Al2O3) spinel (MgAl2O4) magnesia (MgO) aluminum hydroxide (Al(OH)3) aluminum impurities (silicates, iron oxides,calcium fluoride, aluminum nitride) NMP Composition • In addition, “washed” NMP can contain up to 2% salt • Detrimental to many potential products

  13. Best Practice – Recycling Aluminum Salt Cake • Recycling in US is driven by business opportunities • U.S. best practice is to maximize Al recovery and dispose of residues (salt and NMP) in controlled landfills • Recycling salt cake in Europe is driven by legislation • No economically viable solution yet • Best practice is to maximize Al recovery with minimum salt flux, and dispose residues in controlled landfills

  14. Environmental Impact of Salt Cake Recycling • In all cases: • Salt recovery consumes more energy than can be recovered from the energy value of the recycled salt • Salt recovery generates more waste than would normally be generated if it was disposed in controlled landfills • NMP recovery becomes an environmental hazard when washed • Entrained aluminum becomes excessively reactive • Excessive energy and water consumption if dilute salt solutions are generated • Best environmental solution: • Do not recover salt, NMP • Maximize aluminum recovery • Use controlled landfills (RCRA C)

  15. Project Conclusions • Many technical solutions possible for recycling salt cake • None economical yet ($35/t landfill) • Best economic option is to maximize aluminum recovery and disposal of residue in controlled landfill • Use best process technology • TTRF furnace, quality flux, energy efficient process • Keep salt cake dry • Crush and recover metallic aluminum by screens and/or eddy-current magnetic separators • Best environmental option is to minimize salt cake generation • Maximize Al recovery, minimize salt use, minimize aluminum nitride, and dispose residue in controlled landfill