LAUSR

Abstract In a world where the ubiquity of Co-Li batteries in smartphones, laptops and electric vehicles is giving rise to an increase of cobalt concentration in mining soils and landfill leachates, the absorption of Co 2 + ions by calcite provides a potential method to remove metal pollutants from aqueous media. Here, we show that the cobalt carbonates resulting from this process can be further recycled to produce lamellar Co 3 O 4 nanoparticles with sizes around 30 nm. The cores of the nanoparticles possess a Fd 3 ¯ m spinel crystal structure and order antiferromagnetically at a Neel temperature of T N ∼ 35 K . On the other hand, the loss of crystallinity in a 1–2 nm-thick surface shell leads to the appearance of magnetically disordered spins. Finally, the magnetic exchange coupling between the core and shell spins gives rise to a moderate exchange bias effect ( ∼ 500 Oe) at T = 5 K .