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–CO₂–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 \rmB(\rm OH)_4^- in the leachate, from which high-purity borax pentahydrate could be prepared by CO₂ carbonation.