Abstract: To address the activity deterioration, increased disposal costs, and potential environmental risks associated with long-term landfilling of coal ash, hybrid alkaline cements based on landfilled coal ash (LHACs) were prepared using high-replacement (≥70%) landfilled ash and low-replacement (≤30%) clinker as precursors. Mechanical-chemical grinding activation was employed, followed by the incorporation of weak-alkaline sodium salts (sodium sulfate and sodium citrate) to synthesize the binders under ambient curing conditions. The workability, mechanical performance, hydration behavior and kinetics, hydration mechanisms, as well as the associated economic and environmental benefits were systematically evaluated through flowability and setting-time tests, compressive strength measurements, X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), Fourier-transform infrared spectroscopy (FT-IR), ²⁹Si MAS-NMR, and isothermal calorimetry. The results show that the SC-LHACs system activated by the sodium citrate/sodium sulfate combination exhibits favorable basic properties, with a flowability of 99.8 mm, initial and final setting times of 82 and 147 min, and compressive strengths of 19.4 MPa at 2 d and 38.7 MPa at 28 d, meeting the requirements of P.O. 32.5 cement and approaching those of P.O. 42.5 cement. Microstructural analyses reveal that C-LHACs mainly form C-(A)-S-H gels, whereas S-LHACs and SC-LHACs predominantly generate (N,C)-(A)-S-H gels. The incorporation of sodium sulfate decreases the proportion of chain-structured to network-structured gels derived from clinker hydration and ash activation, thereby promoting continuous ash hydration and matrix densification. In terms of hydration heat evolution and kinetics, weak-alkaline sodium salts elevate the first exothermic peak, advance the main hydration peak, shorten the induction period, and increase the fraction of early heat release. The hydration process evolves from the typical nucleation–growth/interfacial/diffusion (NG-I-D) regime of ordinary cement to an interface-reaction/diffusion (I-D) dominated combined kinetic mode, which is well described by the Kondo kinetic model. Mechanistically, sodium citrate complexes Ca²⁺ while sodium sulfate induces precipitation and ion exchange reactions, synergistically regulating the pore-solution chemistry, mitigating the dilution effect caused by low clinker content, and enabling coupled clinker hydration and ash activation with continuous gel polymerization. Economic and environmental assessments further indicate that, compared with P.O. 42.5 cement, the production costs of S-LHACs and SC-LHACs are reduced to 29.1% and 43.8%, while their carbon emissions decrease to 34.2% and 42.6%, respectively. Overall, LHACs demonstrate good engineering applicability together with significant cost and carbon reductions, showing strong potential for high-volume utilization of landfilled coal ash and low-carbon functional materials for underground coal mine applications.