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In this study, geopolymers were prepared using ladle furnace slag (LFS) and fly ash (FA), and hydrothermal treatment was then used to synthesize bulk zeolite molecular sieves with gismondine, zeolite-P1, and sodalite phases. The effect of the synthesis conditions on the crystalline phases of the zeolite molecular sieves was investigated by XRD. The results showed that the best zeolite molecular sieves were prepared with an LFS: FA ratio of 4: 6, a curing temperature of 40 °C, a curing time of 12 h, a sodium silicate modulus (Ms) of 1.4, a NaOH concentration of 4 mol/L, a hydrothermal temperature of 120 °C, and a hydrothermal time of 12 h. On this basis, the products were analyzed by SEM, N2 adsorption, and FT-IR. The results showed that the synthesized zeolite molecular sieves had mesoporous properties, and the degree of polymerization and cross-linking of the silica-aluminate gel were enhanced after hydrothermal treatment. In addition, the formation mechanism of the zeolite molecular sieves was explored through the changes of the silica-alumina during zeolite formation. This paper is the first to use the hydrothermal conversion of zeolite molecular sieves from LFS-FA based polymers to provide some guidance for the resource utilization of LFS and FA.

Ladle furnace slag (LFS) can undergo hydration and carbonation reactions as cement. This article explores the effect of LFS hydration and carbonation reactions on cementitious substances at different temperatures and different LFS particle sizes, determining the effect of these varying conditions on the microstructure and formation mechanism of cementitious substances. The results show that in the early stages, C2S and C3S undergo hydration to generate C–S–H gel, which then undergoes decalcification and condensation to generate CaCO3 and Ca-deficient C–S–H gel; the hydration reaction and carbonation reaction promote and influence each other. The increase in temperature was found to hinder the formation of CaCO3 from Ca2+ and CO32−, thus reducing the efficiency of hydration carbonation. The increase in particle size was not conducive to the leaching of C2S and C3S to the surface of the reaction phase, which in turn reduced the degree of decalcification and polymerization of the C–S–H gel in the carbonation phase. It was concluded that the optimum LFS hydration and carbonation reactions were achieved at 20 °C and with a LFS particle sizes < 38 μm.

Activity models based on the ion and molecule coexistence theory have been widely used in the refining of metallurgical slags, with the SiO2 content of slag playing a crucial role in improving the mechanical properties of refining slag-based cementitious materials. In order to improve the reactivity of SiO2 in slag, this study established a SiO2 activity prediction model for the CaO-Al2O3-SiO2-MgO quaternary slag system based on the ion and molecule coexistence theory, validating the prediction results using reference values from the literature. Following this, the effects of w(SiO2), w(CaO), w(CaO)/w(Al2O3), and R(w(CaO)/w(SiO2)) on SiO2 activity were explored (where w and R represent content and alkalinity, respectively). The results show that the model could accurately predict the SiO2 activity of refining slag at 1873k. When the SiO2 content was increased from 10% to 30%, with 60% w(CaO) and a w(MgO)/w(Al2O3) ratio of 0.25, the SiO2 activity exhibited a trend of initially increasing and then decreasing, with a maximum activity value of 0.1359 reached at 17.5% w(SiO2). When slag contained 15% w(SiO2) and a w(MgO)/w(Al2O3) ratio of 0.25, the SiO2 activity decreased with increasing CaO content, reaching a maximum activity value of 0.1268 when 55% w(CaO) was present. Therefore, by controlling the ratio of w(CaO)/w(Al2O3) and w(CaO)/w(SiO2) in the slag to maintain a ratio of 3, the activity of SiO2 can be effectively increased.

Activity models based on the ion and molecule coexistence theory have been widely used in the refining of metallurgical slags, with the SiO2 content of slag playing a crucial role in improving the mechanical properties of refining slag-based cementitious materials. In order to improve the reactivity of SiO2 in slag, this study established a SiO2 activity prediction model for the CaO-Al2O3-SiO2-MgO quaternary slag system based on the ion and molecule coexistence theory, validating the prediction results using reference values from the literature. Following this, the effects of w(SiO2), w(CaO), w(CaO)/w(Al2O3) and R(w(CaO)/w(SiO2)) on SiO2 activity, were explored (where w and R represent content and alkalinity, respectively). The results show that the model could accurately predict the SiO2 activity of refining slag. When the SiO2 content was increased from 10–30%, with 60% w(CaO) and a w(MgO)/w(Al2O3) ratio of 0.25, the SiO2 activity exhibited a trend of initially increasing and then decreasing, with a maximum activity value of 0.1359 reached at 17.5% w(SiO2). When slag contained 15% w(SiO2) and a w(MgO)/w(Al2O3) ratio of 0.25, the SiO2 activity decreased with increasing CaO content, reaching a maximum activity value of 0.1268 when 55% w(CaO) was present. Therefore, by controlling the ratio of w(CaO)/w(Al2O3) and w(CaO)/w(SiO2) in the slag to maintain a ratio of 3, the activity of SiO2 can be effectively increased.