From slag to structure: Formation of novel iron oxalate crystals via Cyrene™-driven microwave chemistry

Moving towards a circular economy, upgrading industrial waste products rich in metals and minerals into valuable materials essential for digital devices, catalysis, and environmental remediation is a key step. The procedures must be eco-friendly, efficient, and yield high production rates. In this work, we propose a microwave-assisted conversion process that transforms iron-rich oxide products (e.g., Fe 2 O 3 , Fe 3 O 4 ) into long iron oxalate crystals with mixed oxidation states using a green solvent mixture of water and Cyrene MT – a bio-derived solvent. Results show that an equal volume fraction of water and Cyrene MT enables uniform crystal growth with an average length of 71.5 ± 10.5 µm while achieving high conversion yields. The procedure is time- and energy-efficient, environmentally friendly, and potentially applicable to a wide range of industrial residues, as demonstrated in this work for steel slag.