Effect of basicity on the structure characteristics of chromium-nickel bearing iron ore pellets

Abstract High MgO content and the dehydroxylation of laterite ore particles lead to poor compressive strength of fired chromium-nickel bearing iron ore pellets at natural basicity. For improving the compressive strength of the fired chromium‑nickel bearing iron ore pellets, burnt lime was applied as the additive to improve the pellet structure. Results showed that with an increase in quaternary basicity, the compressive strength of fired pellets was enhanced obviously. The optimum basicity of fired chromium-nickel bearing iron ore pellets is suggested at 1.15. Under the optimal test conditions, the compressive strength of fired pellets with natural basicity is only 607 N/pellet, but the compressive strength of fired pellets reaches 1991 N/pellet at basicity of 1.15. The structure of fired chromium-nickel pellets at 1.15 basicity greatly depends on the liquid bonding phases among chromite, hematite and enstatite particles, which are composed of kirschsteinite, SFCA and glass, and amount to 19.27% in fired pellets. The liquid bonding phases fill in the voids among mineral particles and interconnect them to form the intertwined structure, which increases the shrinkage and significantly improves the compression strength of fired pellets.