A probabilistic model for reconciling circularity and climate performance in steel-slag processing
DOI:
https://doi.org/10.33271/crpnmu/86.378Keywords:
steel slag, circularity, environmental safety, environmental impact assessmentAbstract
Purpose. To develop a probabilistic model for reconciling circularity with corporate Scope 1–3 emissions accounting and consequential assessment of changes in greenhouse gas emissions for legacy steel-slag processing, and to determine the conditions under which returning the material to use delivers climate benefits.
The methods. The functional unit was defined as 1 t of legacy slag delivered to the processing installation. The data were compiled from a publicly available environmental impact assessment report for a facility with a capacity of 800,000 t/year, emission factors, and industrial benchmarks. Three separate accounting ledgers were established: gross operational Scope 1–3 emissions, effective circularity, and the comparative change in emissions relative to virgin-aggregate supply. Uncertainty in the main technological, market, and logistical parameters was assessed using Monte Carlo simulation, with 100,000 iterations for each of the triangular, uniform, and beta-PERT distributions.
Findings. The calculated gross operational footprint is 1.569 kg CO₂-eq/t of slag, of which 72.8% is attributable to Scope 1, while the reported yield of potentially useful products is 96.1%. With verified use of the mineral fraction, the deterministic break-even additional transport distance is 49.4 km. For the triangular distribution, the 5th percentile, median, and 95th percentile of this threshold are 16.7, 30.8, and 49.0 km, respectively. The conservative threshold, robust to the form of the distribution, is 10.2 km. At an additional distance of 50 km, high circularity coincides with a climate burden in 76.3–93.0% of model realizations.
The originality. The break-even additional transport distance was found to depend linearly on the functional substitution coefficient for virgin aggregate and to be inversely proportional to transport carbon intensity, with all other parameters held constant. Conditions under which high circularity coincides with increased emissions were identified. A method was proposed for determining a conservative transport distance threshold for a specified probability of achieving a climate benefit, with robustness tested across different forms of input probability distributions.
Practical significance. The model enables climate screening using incomplete publicly available data, prioritization of evidence collection, and prevention of the deduction of avoided emissions from Scope 1-3 inventories. A qualified claim requires confirmation of end use, functional equivalence, transport routes, and energy consumption.
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