Extraction of magnesium from mine tailings for carbon dioxide mineralization: A preliminary study of the effect of ammonium sulfate to tailings ratio on products and yield

Carbon capture and storage is needed to achieve deep cuts in industrial carbon dioxide (CO₂) emissions. One option for storing carbon dioxide is its mineralization, which is especially useful in regions with available mine tailings but no nearby geological formations suitable for carbon dioxide storage. A multi-step mineralization route has been developed at Åbo Akademi University. In this study the first step, thermal extraction of magnesium, was further improved for two magnesium-rich Finnish mine tailings as raw materials. In the experiments, the maximum yield of extracted magnesium was similar (57–65%) to that of previous studies for both tailings with a ratio of 1:3 of mine tailings to ammonium sulfate ((NH₄)₂SO₄), but only slightly better than with a ratio of 1:2 (55–58%). It was also found that increasing the average temperature from 410 to 460 °C slightly decreased the yield. Moreover, increasing the amount of the extracting agent, ammonium sulfate, can increase the possibility of obtaining efremovite ((NH₄)₂Mg₂(SO₄)₃) instead of magnesium sulfate (MgSO₄). This new knowledge of the effect of the reagent ratios on the formation of extraction products like efremovite could be exploited in further studies to minimize water consumption and thus energy use in ammonium sulfate recycling.