A large amount of mineral-generated lithium slag will be produced after extracting lithium from spodumene. However, most lithium slag has not been well utilized. In this study, lithium slag was added to MOC, and its setting time, compressive strength, water resistance, phase composition, and microscopic morphology were studied. The results showed that although lithium slag prolonged the setting time and reduced the compressive strength of MOC, its water resistance improved. When the content of lithium slag was 20 wt%, the softening coefficient of the specimen reached a maximum value, and the softening coefficients at 3, 7, and 14 days were 1.47, 1.91, and 1.51 times that of MOC without lithium slag, respectively. A microscopic morphology analysis showed that the lithium slag transformed the MOC crystals from needle-like to column-like or block-like, the crystallization range expanded, and the binding force weakened. Magnesium oxychloride cement with excellent mechanical properties and good workability was combined with magnesium slag in this paper to provide the basis for the application of magnesium slag in building materials.

The composite gelling system of chlorine and magnesium thioxide was prepared by mixing different mass fractions of magnesium sulfate solution into MOC. Detailed studies regarding the influences of magnesium sulfate replacing magnesium chloride on the setting time, compressive strength, and water resistance of magnesium oxychloride cement (MOC) have been carried out in this paper. The phase composition and micro morphology of the hydration products in the mixed system were analyzed by XRD and SEM. The results show that the addition of magnesium sulfate prolongs the setting time and reduces the compressive strength of the mixed MOC. Compared with the primordial MOC system, the water resistance of the mixed system improved, with the mixed system exhibiting optimal water resistance when the mass fraction of magnesium sulfate was 30%. The phases of the mixed system were composed of 5Mg(OH)₂·MgCl₂·8H₂O and 5Mg(OH)₂·MgSO₄·7H₂O phases. The microscopic morphology shows that the interior of air-cured MOC was composed of a large number of needle-like crystals, and continuous crystal structures have close contact and a strong bonding force. Cracks and pores appear on the surface after submerging in water, and the crystallization state of the internal crystals becomes worse. The compressive strength and water stability of MOC were closely related to the crystal morphology.

This study investigates the effects of phosphoric acid (H₃PO₄), potassium dihydrogen phosphate (KH₂PO₄) and sodium dihydrogen phosphate (NaH₂PO₄) admixtures on the setting time, compressive strength and water resistance of magnesium oxychloride cement (MOC). MOC samples incorporating different admixtures are prepared, and their hydration products and microstructures are studied via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results indicate that the addition of H₃PO₄, KH₂PO₄ and NaH₂PO₄ reduces the initial and final setting times and decreases the compressive strength. However, the compressive strength of MOC is higher than 30.00 MPa with the addition of 2.0 wt.% phosphoric acid and its phosphate after 14 days of air curing. The water resistance of modified MOC slurries is significantly improved. The softening coefficient of MOC with 2.0 wt.% H₃PO₄ is 1.2 after 14 days of water immersion, which is 3.44 times higher than that of the neat MOC. The enhancement in water resistance is attributed to the formation of amorphous gel facilitated by H₃PO₄, KH₂PO₄ and NaH₂PO₄. Furthermore, the improvement in water resistance is manifested as H₃PO₄ > KH₂PO₄ > NaH₂PO₄.