Effects of cooling method on removal of sodium from active roasting red mud based on water leaching

- Cooling methods effects on roasted red mud for recovering Na+ were investigated.
- QXRD techniques were employed to characterize the variation of mineral phases.
- Morphology of samples cooled by different cooling methods is quite different.

Red mud cannot be directly employed as the raw material of iron-making and construction materials for the existence of sodium element. The effects of cooling methods of furnace, air, water and liquid nitrogen on roasted red mud for recovering Na+ with water leaching were investigated through the analyses of TG-DTA, QXRD, FTIR, SEM, etc. The faster cooling methods we used, the better leaching performance would be obtained. Liquid nitrogen cooling sample therefore displayed the best leaching result with concentration of 1202 mg·L− 1 Na+ at the first leaching stage (~ 25 wt.% total sodium recovery). Part of cancrinite known as desilication products transformed into NaCaHSiO4 and nepheline after the roasting process. In the fast cooling red muds, the new generation of Na2Ca(CO3)2 could dissolve directly into water; the increase of Ca(OH)2 concentration to ~ 4.8 wt.% was beneficial for the dissolution of cancrinite and NaCaHSiO4 during the leaching process; amorphous phase increasing from ~ 4.1 to ~ 13.5 wt.% made sodium be more easily leached out from sodium-containing amorphous phase than the same crystalline phase; fluey flakes or plate-shape particles weakened the aggregation behaviour; the increase of specific surface area from 1.898 to 2.177 m2·cm− 3 leaded to the contact area increasing between particles and leachant, implying that sodium could be more easily leached out from the fast cooling samples.