Sustainable synthesis of calcium and magnesium acetates from oil shale ash

As primary resources become increasingly scarce with global population growth, valorizing industrial side streams is essential. In Estonia, oil shale ash—the country’s most abundant industrial waste—offers a promising source of calcium and magnesium for producing snow and ice-melting agents. Conventional deicers, such as sodium chloride, pose severe environmental and infrastructural risks due to corrosion and ecological damage. Acetate-based deicers are less corrosive and more environmentally friendly, but their production typically depends on dolomitic lime, which requires mining and processing. Oil shale ash is already generated as a by-product of energy production, eliminating the need for additional extraction and reducing environmental impact. This study evaluated three synthesis methods: (1) conventional solution chemistry with magnetic stirring, (2) ultrasonic-assisted reaction, and (3) solvent-free mechanochemistry. Optimal conditions for solution-based synthesis—80 °C for 136 min with 3.4 equivalents of acetic acid—yielded over 96% for both calcium and magnesium. Ultrasonic-assisted reactions achieved comparable yields (>92%) but required longer times. Mechanochemistry proved most resource-efficient: a 5-minute milling with only one equivalent of acetic acid produced 78% calcium and 67% magnesium, while 30 minutes yielded 87% and 72%, respectively. The resulting salts were characterized for freezing point, effective temperature, and composition. Impurities such as gypsum and iron were detected, likely influencing ice-melting performance. Overall, mechanochemistry emerged as a rapid, sustainable method for producing acetate-based deicers with minimal reactant use, highlighting oil shale ash’s potential as a valuable resource for winter road maintenance. • Three methods to produce acetate salts from oil shale ash were evaluated. • 96% yields in solution with stirring at 80 °C, 136 min, 3.4 eq acetic acid. • Ultrasonic reaction was about 1.5 times slower than magnetic stirring. • Mechanochemistry was rapid and lowered needed reagent amount 2 times. • Products show promise; future work can improve de-icing performance.