Design of a full-solid-waste cementitious material using electrolytic manganese residue as a sulfate activator

With the rapid development of industrialization, electrolytic manganese residue (EMR), a solid waste generated from metal manganese smelting, urgently requires effective utilization. Based on the high sulfate content of EMR, this study investigated the feasibility of using EMR as a sulfate activator to prepare EMR-calcium carbide residue (CCR)-ground granulated blast furnace slag (GGBS) ternary full-solid-waste cementitious materials (ECGCM), with emphasis on hydration behavior and mechanical properties. Isothermal calorimetry, thermogravimetric analysis (TG), quantitative X-ray diffraction (QXRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) were employed to characterize the evolution of hydration products and microstructure. In addition, a life cycle assessment was conducted to evaluate the environmental and economic performance of different mix designs. The results showed that the optimal EMR content was 40 wt% (total SO₃ = 12.81 wt%), achieving compressive strengths of 19.7 MPa at 3 d and 35.7 MPa at 28 d. Increasing EMR content prolonged the induction period and delayed the hydration exothermic peak from 33 h (EMR10) to 58 h (EMR50). EMR also regulated hydration product formation throughout the hydration process. An appropriate EMR dosage promoted the synergistic formation of ettringite (AFt) and calcium aluminosilicate hydrate (C-(A)-S-H), thereby refining the microstructure. However, excessive EMR inhibited C-(A)-S-H formation, weakened the synergistic effect between hydration products, and deteriorated the pore structure. Toxicity characteristic leaching procedure (TCLP) results confirmed that ECGCM effectively immobilized heavy metals in EMR and significantly reduced environmental risks. Moreover, the sustainability index and economic index of EMR40 were 3.56 kg·CO₂-eq/t-MPa and 6.41 CNY-eq/t-MPa, respectively, representing reductions of 89.7% and 41.9% compared with Ordinary Portland Cement. These findings demonstrate the feasibility of using EMR as a sulfate activator to prepare sustainable ECGCM.