EVALUATING THE SECONDARY RESOURCE POTENTIAL OF CHROMIUM RICH SLAGS FROM STAINLESS STEEL PRODUCTION

Dr. Andrea Winterstetter

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CONTENT

• Background • Goal & Motivation • New evaluation procedure under UNFC: ECLAR Methodology • Evaluating the secondary resource potential of stainless steel

slags• Conclusions & Outlook

1. BACKGROUNDStainless Steel Slags

STAINLESS STEEL PRODUCTION

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• Global stainless steel production steadily increasing (~ 50 % in China)

• Per 5 t of produced stainless steel: ~ 1 t of slag

• Slags contain up to 4 wt.% Chromium (Cr)

• Lower concentrations of valuable Ni, Mo, and V are present, embedded in an alkaline matrix Source: Statista 2017

CR (IV) – A HAZARD FOR HUMAN HEALTH & THE ENVIRONMENT

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Most of the slags landfilled or stockpiled for long periods at steel plants, leading to: • Waste of land / landfill space • Loss of valuable resources• Hazard to human health & the environment:

• Due to Cr (VI) leaching: Contamination of soil, surface & ground water

• Inhaled Cr (VI): Human carcinogen

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RECYCLING STAINLESS STEEL SLAGS ?

Two major problems regarding re-using / recycling slags:1) High Cr concentrations & leaching

potential put constraints to slag utilization as aggregate replacement in construction (e.g. in road engineering)

2) Slag use often hampered by volume instability, leading to a loss of strength over time

2. GOAL & MOTIVATION

GOAL & MOTIVATION

• Evaluate the socioeconomic viability of recycling stainless steel slags as a function of different technology choices Cr recovery: Comparison of 3 different selected lab scale leaching

approaches Valorizing remaining slag as building materials (CARBSTONE®)

• Decision support regarding technology development

3. New evaluation procedure under UNFC: Evaluation (E) and CLassification (CL) of

Anthropogenic Resources (AR) ECLAR

ECLAR: Decision Guidelines for Anthropogenic Resources I

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4. Evaluating the secondary resource potential of stainless steel slags

1. Hypochlorite assistedalkaline leaching approach1

2. Alkaline roasting followed by water leaching2

3. NaOCl assisted alkaline heap leaching3

Maturity Cr leaching approaches: Lab scalePrecipitation / recovery: Lab scale in this specific combinationCarbonation of matrix materials4: Commercial plant available since 2017

Cr leaching efficiency Medium 68 % High 90 % Low 11 %

Heating requirement Medium High Low

Cost for chemical reagents input High, due to use of NaOCl Medium

Low,due to leachate recirculation

Cost for water input High, due to use of ultrapure water

Medium

Cost for waste water treatment High High

Sources: Kim et al., 20161, Kim et al., 20152, Spooren et al., 20163, Quaghebeur et al., 20104

THREE CR LEACHING METHODS

WORK IN PROGRESS

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Done for lab scale experiments using STAN software: Material Flow Analysis Energy Flow Analysis Money Flow Analysis to quantify cost

To Do: Upscale cost Discounted Cash Flow (DCF) Analyis (if needed: Cut-off values) Life Cycle Impact Analysis (LCA) Uncertainty & Sensitivity Analysis Classification under UNFC : F-Axis criteria for technical feasibility will be fine-tuned

& developed into an aggregated indicator.

EXPECTED RESULTS - KEY PROJECT PARAMETERS

• Markets & prices for Cr products & building materials• Process costs depending on energy input & chemical reagents• Avoided costs for disposal alternatives of slags, e.g. landfilling

1. Alkaline roasting followed by water leaching o Medium cost o High Cr leaching efficiency2. Heap leaching o Low cost: Leachate incl. reagents recirculated, no heating involvedo Low Cr leaching efficiency3. Hypochlorite assisted alkaline leachingo High cost: Use of ultrapure water, NaOCl as leaching agent, high amount of

heating energy requiredo Medium Cr leaching efficiency

6. CONCLUSIONS

CONCLUSIONS

• New technologies & approaches for comprehensive resource extraction & valorization needed • to protect human health & the environment • to conserve resources & land

• ECLAR methodology under UNFC allows for • An iterative evaluation • To monitor the impact of new technology related to resource recovery, • by comparing costs dep. on process inputs, revenues as a function of marketable

outputs & recovery efficiencies as well as environmental impacts.

Contact:Dr. Andrea Winterstetter

Postdoctoral Researcher

Tel: +3214335151 andrea.winterstetter@vito.be

Thank you!

LITERATURE

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• KIM, E., SPOOREN, J., BROOS, K., HORCKMANS, L., QUAGHEBEUR, M. & VRANCKEN, K. 2015. Selective recovery of Cr from stainless steel slag by alkaline roasting followed by water leaching. Hydrometallurgy, 158, 139-148.

• KIM, E., SPOOREN, J., BROOS, K., NIELSEN, P., HORCKMANS, L., VRANCKEN, K. & QUAGHEBEUR, M. 2016. New method for selective Cr recovery from stainless steel slag by NaOCl assisted alkaline leaching and consecutive BaCrO 4 precipitation. Chemical Engineering Journal, 295, 542-551.

• QUAGHEBEUR, M., NIELSEN, P., LAENEN, B. & NGUYEN, E. 2010. Carbstone: sustainable valorisation technology for fine grained steel slags and CO 2. Refractory Worldforum, 2, 75-79.

• SPOOREN, J., KIM, E., HORCKMANS, L., BROOS, K., NIELSEN, P. & QUAGHEBEUR, M. 2016. In-situ chromium and vanadium recovery of landfilled ferrochromium and stainless steel slags. Chemical Engineering Journal, 303, 359-368.

• WINTERSTETTER, A. 2016. Mines of Tomorrow: Evaluating and Classifying Anthropogenic Resources: A new Methodology Doctor of Science in Civil Engineering PhD Thesis Vienna University of Technology.

• WINTERSTETTER, A., LANER, D., RECHBERGER, H. & FELLNER, J. 2015. Framework for the evaluation of anthropogenic resources: A landfill mining case study–Resource or reserve? Resources, Conservation and Recycling, 96, 19-30.

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