<p>This study investigates the dispersion behavior of carbon blacks with different pH values in an alkaline Na₂CO₃ slurry used for continuous-casting mold flux preparation. Variations in surface functional groups of carbon black induce distinct interactions with Na⁺ ions, thereby altering the dispersion of carbon black in the slurry and ultimately influencing the melting uniformity of the mold flux. Through dynamic light scattering, copper bath experiments, Fourier transform infrared spectroscopy (FTIR), and molecular dynamics simulations, the study characterized the dispersibility of carbon black in alkaline Na₂CO₃ solution slurry, the melting uniformity of mold flux, surface chemical properties, and the interaction mechanism between functional groups and Na⁺ in the slurry. The results show that as the carbon black pH increases from 2.73 to 9.45, the aggregate particle size in the slurry decreases, zeta potential increases, dispersion performance improves, and mold flux melting uniformity increases. FTIR analysis indicates that with increasing carbon black pH, the contents of –COOH and –OH functional groups decrease, whereas –C=O and –C–O increase. Low pH carbon black (pH&#xa0;=&#xa0;2.73–3.18) rich in –COOH and –OH surface functional groups, after deprotonation forming –COO^– and –O^–, firmly binds Na⁺ to the surface through strong chemisorption (extremely negative binding energy, extremely low Na⁺ diffusion coefficient), leading to electrical double-layer compression, increased aggregate particle size, and poor dispersibility. In contrast, high pH carbon black (pH&#xa0;=&#xa0;7.48–9.45) with –C=O and –C–O as main functional groups only underwent weak physisorption with Na⁺ (higher binding energy, free Na⁺ diffusion), which helps maintain a thicker electrical double-layer structure and improves carbon black dispersibility. Selecting high pH carbon black rich in –C=O and –C–O surface functional groups during mold flux preparation can improve carbon black dispersibility, thereby enhancing the melting uniformity of the mold flux.</p>