Sustainable recovery and reutilization of molten salt from magnesium salt slag via supergravity separation

Magnesium salt slag is generated during the refining of crude magnesium and usually contains a large amount of soluble chloride salts, which will cause serious environmental problems. In this study, a new method was proposed for sustainable recovery and reutilization of molten salt from magnesium salt slag via supergravity separation. The phase transformation of molten salt with temperature was studied. The molten salt was in a fully molten state at 800–750 °C, while the NaCl precipitated at 750–700 °C, meantime combined with MgCl2 and tightly encapsulated the fine MgO particles. Therefore, recovery of molten salt was conducted at 800 °C enhanced by supergravity separation, where the molten salt and MgO-rich particles were efficiently recovered within 5 min with high recovery rates of 98.9 % and 99.5 %, respectively. Moreover, the recovered molten salt removed 98.6 % of oxide inclusions in the crude magnesium refining process. Meanwhile, the fine MgO-rich particles with w(MgO)=76.3 % and 1–10 µm was recovered from the magnesium salt slag, where the leaching amount of Cl- was decreased to 0.586 g/L, which was below the Chinese standard for chlorine ion content in solid wastes. Therefore, this manuscript provided a novel process for recovering molten salt from magnesium salt slag without additives and secondary pollution, meanwhile reducing the generation of solid waste and hazards.