Investigation of ferronickel concentrate oxidation behavior and prevention strategies during drying

Ferronickel serves as an essential feedstock to produce stainless steel. A ferronickel concentrate assaying 28% Ni was obtained via two-stage thermal treatment of ultramafic Ni sulfide concentrate followed by direct grinding and sieving without magnetic separation. However, microstructural and compositional analysis revealed that post-upgrading oxidation led to the formation of a Ni-wustite phase, comprising up to 13% of the ferronickel concentrate and accounting for 7.3% of the total Ni. The oxidation behavior of ferronickel under different grinding and drying conditions revealed that the formation of Ni-wustite predominantly occurs during the drying stage rather than during early wet grinding. Excessive grinding accelerates oxidation even drying is conducted in a non-oxidizing atmosphere. Drying under a non-oxidizing atmosphere or after solvent immersion significantly suppresses Ni-wustite formation. Furthermore, rinsing ferronickel concentrate with Na2CO3 solution prior to drying is recommended, as it forms a passivation layer on the ferronickel surface, creating a physical and chemical barrier that prevents oxygen contact and thereby inhibits oxidation. The key findings of this study provide guidance for selecting appropriate ferronickel grinding and drying conditions, enabling the maximal recovery of ferronickel alloys liberated by direct grinding without magnetic separation.