A U.S. Department of Energy Office of Science Laboratory Operated by The University of Chicago Office of Science U.S. Department of Energy Recycling Aluminum.
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A U.S. Department of EnergyOffice of Science LaboratoryOperated by The University of ChicagoOffice of Science
U.S. Department of Energy
Recycling Aluminum Salt Cake
J.N. Hryn and E.J. DanielsProcess Engineering SectionEnergy Systems DivisionArgonne National Laboratory
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
About Argonne National Laboratory
• Founded in 1943, designateda 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
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Pioneering Science andTechnology
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)
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
Recycling Aluminum Salt Cake – Overview
Salt Cake
Aluminum
Salt
Non-Metallic Product
Refractory Feedstock
Ironmaking Feedstock
Steelmaking Feedstock
Recovery ofSalt Cake
Constituents
Conversion to Value-Added
Products
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
Average Salt Cake Composition
Non-Metallic Product66%
Salt28%
Aluminum6%
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Pioneering Science andTechnology
digester
screen
filter
evaporator
aluminum (to smelters)
NMP (to market)
salt (to smelters)
crusher
condenser
water
steam
salt cake
Suggested Approach to Recycling Salt Cake
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Pioneering Science andTechnology
Salt Cake Recycling Barriers in U.S.
• salt recovery by evaporation is too expensive- high energy and capital costs, low product value
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Pioneering Science andTechnology
Salt Cake Recycling Barriers in U.S.
• no market for recovered NMP- high levels of impurities, variable composition
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Pioneering Science andTechnology
40 to 80%
up to 40%
up to 10%
up to 5%
up to 8%
up to 10%
alumina (-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
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Pioneering Science andTechnology
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
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Pioneering Science andTechnology
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)
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Pioneering Science andTechnology
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
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