This study investigates the carbon sequestration potential of fine-grained expansive soils treated using electrokinetic (EK) stabilisation. It identifies the physicochemical conditions that promote gravimetrically inferred calcium carbonate \(\:\left({\text{C}\text{a}\text{C}\text{O}}_{3}\right)\) precipitation, based on stoichiometric and gravimetric evidence, as a mechanism for laboratory-scale \(\:{\text{C}\text{O}}_{2}\) immobilization potential. EK tests were conducted using a five-factor face-centered central composite design with 48 experimental runs, and routine measurements of pH, salinity (Sal), total dissolved solids (TDS), electrical resistivity ( \(\:\rho\:\) ), and electrical conductivity (σ) were recorded to quantify their relationship with gravimetrically inferred \(\:{\text{C}\text{a}\text{C}\text{O}}_{3}\) formation. A quadratic Response Surface Methodology (RSM) model incorporating linear, interaction, and quadratic terms was developed to predict \(\:{\text{C}\text{O}}_{2}\) sequestration potential. Experimental data from calcium chloride and sodium carbonate \(\:\left({\text{C}\text{a}\text{C}\text{l}}_{2}-{\text{N}\text{a}}_{2}{\text{C}\text{O}}_{3}\right)\) electrolytes applied to EK-treated soil blocks were analyzed with multivariate regression and ANOVA to identify governing parameters. The model demonstrated near-perfect statistical agreement within the validated experimental design space ( \(\:{\text{R}}^{2}\) = 1.000; adjusted \(\:{\text{R}}^{2}\) = 1.000; predicted \(\:{\text{R}}^{2}\) = 0.9997; p < 0.001). ANOVA confirmed the statistical significance of all model terms (p < 0.0001), with TDS, ρ, and σ as significant main effects. Interaction analysis further revealed significant contributions from Sal × σ, ρ × σ, pH × Sal, TDS × ρ, and Sal × TDS. An empirical calibration constant, \(\:{\text{K}}_{{\text{C}\text{O}}_{2}|\:\sigma\:}\) = \(\:0.12\:\) g \(\:{\text{C}\text{O}}_{2}.\text{k}\) g⁻1·(S·m⁻1)⁻1 was derived by regressing gravimetrically measured \(\:{\text{C}\text{a}\text{C}\text{O}}_{3}\) contents against measured σ values and applying stoichiometric conversion. Optimal EK conditions for maximum model-predicted \(\:{\text{C}\text{O}}_{2}\:\) sequestration potential were achieved at pH ≈ 9.2, TDS ≈ 7.0 kg·m−3, Sal ≈ 4.0 g·kg−1, ρ < 0.1 Ω·m, and σ > 7.9 S·m−1. The model predicts an in-domain \(\:{\text{C}\text{O}}_{2}\) sequestration potential of approximately 2.0 g \(\:{\text{C}\text{O}}_{2}\) \(\:{\text{k}\text{g}}^{-1}\) of EK-treated soil under optimal laboratory conditions. Within the validated experimental design space and EK-treated soil–electrolyte system, these findings provide a data-driven framework linking routine EK measurements to model-predicted \(\:{\text{C}\text{O}}_{2}\) immobilisation potential. The model is intended for laboratory optimisation and future pilot-scale validation rather than immediate field application.
