Abstract
Strontium is increasingly recognized as a strategically important element, used in functional ceramics, ferrite magnets, pyrotechnics, and emerging energy-storage technologies. Its primary production is largely derived from celestite (SrSO₄) deposits, and global production is highly concentrated, especially in China, which poses a risk to supply security. This criticality has generated growing interest in developing alternative recovery pathways, including secondary sources. Since strontium belongs to the alkaline earth group, it is often associated with calcium minerals.
In this work, the recovery of strontium from grey mud, mainly CaCO₃ residue generated during the aluminothermic reduction of pre-reduced manganese ore, is investigated. In the residue, 0.33% of SrO and 0.35% of BaO are present as minor but valuable components. The ratio of Ca/Sr is high (~102), and in order to separate Sr from the overwhelming Ca content, the large difference in solubility between alkaline-earth nitrates in organic solvents is exploited. The developed process first fumed the grey mud with concentrated nitric acid to convert all the carbonate species into their respective nitrates. The nitrated solid was then leached with acetone.
It was found that calcium nitrate preferentially dissolves in acetone, leaving a residue enriched in Sr and Ba nitrates with minor calcium content. In experimental trials, this workflow achieved about 70-75% strontium recovery and 90-95% barium recovery in the acetone-insoluble fraction, while limiting co-extraction of calcium to just 2–3.5%. .
This work demonstrates a low-energy, solvent-selective method for upgrading strontium from carbonate-bearing industrial residues. It opens a promising research route for strontium-bearing calcite minerals and by-products.