The primary magnesium production is accompanied by a large amount of magnesium slag (MS) discharge. The low hydration reactivity of γ-Ca₂SiO₄ (γ-C₂S) and MgO in MS results in the volume stability issue and low utilization rate of MS. To eliminate the issue, this study proposes to pre-autoclave the MS slurry to boost the hydration of γ-C₂S and MgO and then utilize their hydration products to prepare cementitious materials by carbonation curing. MgO from MS and prepared γ-C₂S are firstly employed as study objects respectively, for they are the main contents of magnesium slag. The results indicate that pre-autoclaving treatment can strongly elevate the hydration degree of MgO from MS, this can substantially solve the volume stability issue of MS. Meanwhile, the pre-autoclaving of γ-C₂S induces the generation of crystallized and amorphous C-S-H products, and both products could promote the carbonation reaction when compared to γ-C₂S. The carbonation degree of pre-autoclaved MS firstly increases and then decreases with the rising pre-autoclaving temperature, and the optimal pre-autoclaving temperature for MS carbonation is 160 °C, at this time, the powdered MS can be simply carbonated fully. The sample made of pre-autoclaved MS and then subjected to 4 h carbonation could achieve the compressive strength of 29 MPa. with good soundness. During volume stability testing, the volume expansion rate of a carbonated MS sample with pre-autoclaving was 0.07%, which is significantly lower than the normal requirement of 0.5%. This research offers a novel approach to utilizing magnesium slag in building materials and contributes to carbon reduction.

In the preparation of magnesium by Pidgeon process, the phenomenon slag pellets sticking on the wall of reduction pot always appear, and the glaze sticking on the inner wall of the reduction pot is difficult to remove. The mechanism of this phenomenon is studied in this work by X-ray fluorescence spectrometer (XRF) measurement, electron probe microanalyzer scanning (EPMA) analysis, differential scanning calorimetry (DSC) analysis, and thermodynamic calculations. The main components of the glaze are MgO, Ca₁₂Al₁₄F₂O₃₂, CaF₂, CaO, and a small amount of Ca₄Si₂O₇F₂. The solid-liquid transition temperature of Ca₁₂Al₁₄F₂O₃₂ and CaF₂ is close to the production temperature of Pidgeon process, which leads to the bonding between the slag pellets and the pot wall. The loss of CaF₂ in glaze layer will reduce the total amount of liquid phase and increase the temperature at which Ca₁₂Al₁₄F₂O₃₂ is completely transformed into liquid phase, which causes glaze layer sticking on the inner wall of the reduction pot.