The efficient processing of nepheline ores and red mud requires mineralogical preconditioning strategies that enhance aluminum recovery while controlling the potassium behavior in alkaline systems. In this study, carbonate–hydrothermal activation of a nepheline ore–red mud mixture (1:1 mass ratio) was investigated as a targeted approach for phase redistribution prior to alkaline leaching. Thermochemical activation in NaHCO₃ solution at 260 °C resulted in the partial destabilization of primary aluminosilicate phases and the formation of secondary carbonate-bearing and hydroxide phases. Quantitative phase analysis revealed the formation of cancrinite (~19 wt.%) and boehmite (~2.8 wt.%), indicating dissolution–reprecipitation processes accompanied by aluminum redistribution and carbonate incorporation. A two-stage alkaline leaching process with controlled calcium addition was applied to evaluate the effect of phase transformation on the extraction performance. The activated material exhibited enhanced reactivity, resulting in an alumina recovery of 92%–94% and selective potassium removal of 82%–87%. The results demonstrate that carbonate–hydrothermal activation acts as an effective mineralogical preconditioning strategy, transforming structurally stable aluminosilicates into more reactive phases. The proposed approach provides a basis for improving the efficiency and selectivity of integrated alumina recovery from complex aluminosilicate raw materials and industrial waste.

Carbonate thermochemical activation is a promising approach for modifying the mineralogical structure of nepheline–red mud mixtures prior to subsequent alkaline processing. However, quantitative statistical relationships between activation parameters and phase transformation remain insufficiently explored. In this study, Response Surface Methodology (RSM) combined with a Central Composite Design (CCD) was employed to develop and experimentally validate a quadratic regression model describing the influence of activation temperature, activation time, and NaHCO₃ concentration on cancrinite formation. Quantitatively determined cancrinite content obtained by X-ray diffraction (XRD) phase analysis was selected as the mineralogical response variable, enabling direct statistical evaluation of cancrinite-forming transformation. The developed quadratic model was statistically significant (F = 21.24, p < 0.0001) and explained 95.5% of the variability in the measured response (R² = 0.9550). Activation time exerted the strongest statistical influence on cancrinite formation, while activation temperature and NaHCO₃ concentration also showed statistically significant effects; the investigated interaction terms were not statistically significant. Numerical optimization identified a favorable region for cancrinite formation, with a predicted maximum response of 22.75 wt.%. Three independent validation experiments performed at practically selected operating conditions of 260 °C, 4 h, and 110 g/L NaHCO₃ yielded an average cancrinite content of 20.0 ± 1.0 wt.%. The principal novelty of the study lies in the use of quantitatively determined cancrinite content as the response variable in RSM, providing a direct statistical description of mineralogical transformation rather than optimization based solely on conventional technological responses. The developed model provides a quantitative framework for evaluating factor effects and identifying favorable activation conditions within the investigated experimental domain.