A Critical Evaluation of Methodological Discrepancies in Quantifying Steel Slag CO2 Sequestration

Steel slag, rich in free CaO/MgO, calcium silicates, and calcium ferrites, suits engineering, boosting alkaline solid waste and carbonating CO2 minerals. However, studies interpret CO2 sequestration capacity differently. Metrics like CO2 sequestration capacity, mass gain, and carbonate content are lumped as capture measures, blocking cross-study comparison and inconsistent carbonation assessments. The study rigorously evaluates seven conventional measurement techniques: thermogravimetric analysis, mass gain measurement, gas consumption monitoring, acid digestion method, elemental analysis, combustion-infrared absorption spectrometry, and X-ray diffraction, thoroughly discussing their quantifiable targets, relevant scopes, systematic biases, and failure scenarios. Representative data show 7-day CO2 sequestration values of 6.5–10.2 g CO2/100 g initial sample across four analytical routes; stepwise-TG, tangential-TG, combustion-infrared AD-TIC, and acid-digestion HT-TIC gave 9.0, 6.5, 10.2, and 9.7 g CO2/100 g, respectively, corresponding to a highest-to-lowest spread of 3.7 g CO2/100 g (36.3% of the highest value). Analytical findings indicate that variances among testing techniques arise not only from arbitrary measurement errors but mainly from differences in specific carbon pools, protocols for sample pre-treatment, criteria for identifying carbonate species, categorization of gas–liquid–solid phase limits, and methods for assessing statistical uncertainty. Consequently, this document suggests a quadruple-tiered evidence chain structure, encompassing the material background, process mass equilibrium, product-associated carbon measurement, and statistical fusion layers. An array of functional standards has been formulated, encompassing the removal of background baselines, confirmation of mass closure, four-point cross-validation, and broadened reporting of uncertainties. The suggested model converts the measurement of steel slag’s carbon capture ability from isolated, singular measurements to a system that is traceable, confirmable, and verifiable with multiple evidence sources. This offers strong methodological backing for large-scale lab experiments, expanding processes, confirming carbon emission reductions, and developing uniform testing procedures. To improve operational clarity, the framework explicitly distinguishes background solid inorganic carbon, newly mineralized stable solid carbon, liquid-phase dissolved inorganic carbon, physically retained CO2, and crystalline carbonate carbon; it also introduces quantitative decision bands for mass closure and cross-method agreement and demonstrates reconciliation using a published multi-method BOF steel-slag dataset.