An integrated and efficient process for borax preparation and magnetite recovery from soda-ash roasted ludwigite ore under CO–CO2–N2 atmosphere

To realize the comprehensive utilization of ludwigite ore, an integrated and efficient route for the boron and iron separation was proposed in this work, which via soda-ash roasting under CO–CO_2–N₂ atmosphere followed by grind-leaching, magnetic separation, and CO₂ carbonation. The effects of roasting temperature, roasting time, CO/(CO+CO₂) composition, and Na₂CO₃ dosage on the boron and iron separation indices were primarily investigated. Under the optimized conditions of the roasting temperature of 850°C, roasting time of 60 min, soda ash dosage of 20wt%, and CO/(CO+CO₂) of 10vol%, 92% of boron was leached during wet grinding, and 88.6% of iron was recovered during the magnetic separation and magnetic concentrate with a total iron content of 61.51wt%. Raman spectra and ¹¹B NMR results indicated that boron exists as B(OH) ⁻₄ in the leachate, from which high-purity borax pentahydrate could be prepared by CO₂ carbonation.