Preparation and performance study of a new type of dual-ion dual-network gel for mining

To address the limitations of coal mine fire prevention and extinguishing gels—such as pipeline clogging, transport losses, and weak adhesion to coal surfaces—this study developed a dual-ion, dual-network gel (CMC–Fe–AlCit/PAM–PVA) system. Sodium carboxymethyl cellulose (CMC) served as the primary network, polyacrylamide (PAM) as the secondary network, and Fe-AlCit as a bimetallic crosslinking agent. The gel was synthesized under pH-modifying conditions provided by gluconic acid-δ-lactone (GDL). Response surface analysis (Design Expert) determined the optimal formulation ratio of CMC: Fe-AlCit: GDL: PAM: PVA as 3:7.5:2:3:4, achieving a gelation time of 4 min and 12 s—suitable for pipeline transport and goaf injection. FTIR analysis confirmed copolymerization and hydrogen bonding between PAM and CMC, as well as successful cross-linking polymerization forming a robust three-dimensional dual-network structure. Microscopic imaging revealed a compact porous morphology with grooves and crevices favorable for metal ion adsorption, thereby enhancing gel stability. Water retention tests showed a retention rate of 99.14% at 40 °C and 74.37% at 100 °C, indicating excellent thermal moisture retention. FTIR spectra of gel-treated coal confirmed effective inhibition of reactive hydroxyl, hydrocarbon, and carbonyl groups, and thermogravimetric analysis demonstrated superior thermal stability and suppression of spontaneous combustion. Cone calorimetry showed that, compared to raw coal, the peak heat release rate and total heat release decreased by 57.85% and 42.4%, respectively, demonstrating improved fire resistance. The maximum smoke suppression rate reached 95.4%, highlighting the gel’s efficacy in reducing toxic gas emissions and enhancing environmental safety. Rheological tests showed shear-thinning behavior between 25–75 °C temperature range, with shear stress remaining below 100 Pa, indicating stable deformation resistance. Flow simulations showed minimal influence of temperature on fluid behavior, although the consistency coefficient (K) slightly increased with temperature due to the reinforcing effect of the dual-network structure. The energy storage modulus (G′) exceeded the loss modulus (G″), indicating the gel’s elasticity dominance and superior mechanical resilience. Overall, the developed gel exhibits outstanding stability, water retention, and rheological properties, providing a reliable material for in-situ fire prevention and extinguishing in coal mines.