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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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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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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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

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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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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Average Salt Cake Composition

Non-Metallic Product66%

Salt28%

Aluminum6%

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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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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 (-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