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Recycling Aluminum Salt Cake J.N. Hryn and E.J. Daniels Process Engineering Section Energy Systems Division Argonne National Laboratory About U.S. Department of Energy (DOE) Maintains 5 major National Laboratories Argonne, Oak Ridge, Sandia, Livermore, Brookhaven

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Recycling aluminum salt cake l.jpg

Recycling Aluminum Salt Cake

J.N. Hryn and E.J. Daniels

Process Engineering Section

Energy Systems Division

Argonne National Laboratory


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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


About argonne national laboratory l.jpg

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


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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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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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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


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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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Non-Metallic Product66%

Aluminum6%

Salt28%

Average Salt Cake Composition


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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


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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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Salt Cake Recycling Barriers in U.S.

  • no market for recovered NMP

    • high levels of impurities, variable composition


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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


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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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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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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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