Na₂SO₄-assisted reductive roasting for enhanced Ni and Co recovery from limonitic laterite: Mechanism and pilot-scale rotary kiln validation

The growing demand for Ni and Co in the new energy sector necessitates efficient extraction methods for limonitic laterite ores. This study demonstrated the effectiveness of sodium sulfate (Na₂SO₄) as an additive for enhancing the co-enrichment of Ni and Co during solid-state reduction. Na₂SO₄ promoted the formation of two distinct liquid phases, low-melting-point FeS–FeO–Fe and NaAlSiO₄–NaFeSiO₄, facilitating the migration and aggregation of Ni–Co–Fe alloy particles, leading to a high-grade alloy powder with 11.98wt% Ni and 0.88wt% Co and recoveries of 94.03% and 80.16%, respectively. Ni–Co–Fe particle growth was mainly driven by the FeS–FeO–Fe eutectic melt, aligned with a liquid-phase sintering mechanism. Pilot-scale rotary kiln experiments validated the industrial feasibility of this approach, which offers a promising solution for the sustainable extraction of these critical metals.