Recycling SiO₂ and Al₂O₃ from the Laterite Nickel Slag in Molten Sodium Hydroxides

Abstract

SiO₂ and Al₂O₃ in the metallurgical slag of nickel laterite ore have great recycling values. In this work, Si and Al were extracted from the slag in NaOH based molten salts through alkali roasting and water leaching process for preparing zeolite materials. The extraction ratio of SiO₂ increases with increased temperature and appropriately prolonged time, and more than 80% SiO₂ can be recycled from the slag after roasting at 550 °C. Si and Al from the slag are in the filtered liquor for producing zeolite materials, while Mg, Ca, Fe and other impurities remain in the leached residues. Adding Na₂CO₃ into the alkalin-slag roasting process can reduce the amount of pure NaOH used with minor decrease in extraction ratio of SiO₂, while make better separation of Ca to avoid it getting into the filtered liquor. Adding Al₂O₃ into the alkalin roasting process can replace part of more expensive NaAlO₂ addition that is required for preparing zeotite material, which may bring out a minor decrease in extraction ratio of SiO₂ due to formation of NaAlSiO₄ in the filtered residues. Quality X zeolite and 4A zeolite materials can be made from the starting liquor containing Si and Al recycled from the laterite nickel slag through alkali roasting and water leaching process.