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Composition-controlled NaOH/Na2CO3 fusion activation of coal gasification slag: Structural reconstruction,
Xiaowei Gu1, Ziyang Hu1, Xu Wang1
1Liaoning Institute of Technological Innovation in Solid Waste Utilization, Northeastern University, Shenyang 110819, China; Science and Technology Innovation Center of Smart Water and Resource Environment, Northeastern University, Shenyang 110819, China; School of Resources and Civil Engineering, Northeastern University, Shenyang 110819, China.
Abstract:
Coal gasification slag (CGS) contains potentially reactive aluminosilicate phases, but its use in cement-based materials is limited by the low accessibility of Si- and Al-bearing species within its highly connected network. To overcome this limitation, a composition-controlled NaOH/Na2CO3 fusion strategy was adopted, in which the total alkali addition was fixed at 8 wt% of CGS for all alkali-containing formulations while the NaOH/Na2CO3 ratio was systematically varied to investigate the composition-dependent activation of CGS. The resulting changes were evaluated through strength activity index measurements, R3 calorimetry, elemental dissolution, phase evolution, structural characterization, and environmental and economic assessment. Among the investigated formulations, H6-C2 exhibited the highest activation efficiency. Its 28 d strength activity index reached 94.1%, representing an increase of 10.4% over H0-C0, while the cumulative heat release in the R3 test reached 285.39 J/g SCM. After 48 h of dissolution, the released Si and Al concentrations increased to 47.9292 and 26.7225 mg/L, respectively. Spectroscopic and phase analyses showed a decrease in the FTIR-derived polymerization degree to 0.5148 together with substantial phase redistribution toward Na-bearing silicate and aluminosilicate phases. These changes are consistent with reduced Si-O-T network connectivity and greater accessibility of Si- and Al-bearing constituents after fusion. The dissolution kinetic fitting further suggested contributions from both interfacial reaction and diffusion-related resistance to the observed Si and Al release. H6-C2 also reduced embodied energy, global warming potential, and production cost by 27.1%, 75.0%, and 46.5%, respectively, relative to ordinary Portland cement. Overall, the optimized NaOH/Na2CO3 ratio enhanced CGS reactivity while limiting environmental and economic burdens, supporting its value-added utilization as a lower-impact supplementary cementitious material.