Sintering Optimisation and Recovery of Aluminum and Sodium from Greek Bauxite Residue

Abstract

Bauxite residue is treated for the recovery of aluminum and sodium by sintering with the addition of soda, metallurgical coke and other reagents such as CaO, MgO and BaO. A thorough thermodynamic analysis using Factsage 7.0™ software was completed together with XRD mineralogy of sinters with different fluxes and reagents additions. Through both thermodynamic interpretation and mineralogical confirmations, it was observed that the type of desilication product in bauxite residue influences the total aluminum recovery through the sintering process and formation of sodium aluminum silicate exists in equilibrium with sodium aluminate, unless silica is consumed by additives (such as CaO, MgO, BaO etc.) forming other more thermodynamically favorable species and liberating alumina. Addition of barium oxide improves the aluminum and sodium recovery to 75% and 94% respectively. Complex sinter product formation that are triggered due to high calcium content in the Greek bauxite residue reduces aluminum recovery efficiency. Optimised and feasible recovery of aluminum and sodium for Greek bauxite residue was proved to be 70% and 85% respectively, when sintered with 50% excess stoichiometric soda. It was observed that stoichiometric carbon addition in inert atmosphere only assisted recovery up to 75% of aluminum and 83% of sodium, though there are benefits gained from pre-reducing iron from hematite for downstream recovery.

Influence of Sodium Sulfate Addition on Iron Grain Growth during Carbothermic Roasting of Red Mud Samples with Different Basicity

“…A behavior of the Reactions (4) and ( 5) depends on chemical composition of the raw materials. In the system with red mud sample B (Figure 4) the Reactions (4) and ( 5 [59,60] that can complicate following extraction of aluminum from the tailings. In the system with red mud sample U (Figure 5) high content of calcium inhibits the Reaction (5) by calcium silicate 3CaO•2SiO 2 generation.…”

“…It is well-known that addition of CaO during sodium sintering of red mud (sinter leach process) leads to the formation of Ca 2 SiO 4 phase, which improves subsequent aluminum recovery by leaching [58][59][60]. On the other hand, CaO addition can decrease iron content in the magnetic concentrates obtained after solid phase reduction at low temperatures [61,62].…”

Separation of Scandium from Hydrochloric Acid–Ethanol Leachate of Bauxite Residue by a Supported Ionic Liquid Phase

“…However, several studies have been performed to recover major components of the BR. 10,53 Our results highlight the importance of the nature of lixiviants for designing an integrated process for metal recovery from the BR. It has been shown that the selectivity of the SILP is greatly affected by the solvent (water or ethanol).…”

“…Still, aluminum can be recovered beforehand from the BR, for instance, by sintering processes. 53 , 54 Several factors can have an impact on the selectivity of the sorption process from the mixture of aqueous–organic solvents, apart from the solvation and the formation of negatively charged complexes. They include the strength of the cation–organic solvent interactions, hydrogen bonding, the dielectric constant of the medium, and the standard molar free energies of transfer of single cations between different media.…”

Extraction of Valuable Elements from Red Mud with a Focus on Using Liquid Media—A Review

“…Wai et al [43] investigated the effect of CaO, MgO, and BaO addition on the aluminum and sodium recovery from red mud after sintering with Na 2 CO 3 . The mixtures of red mud, 25% of soda, and various additives in the amount of 20% were sintered at 900 • C for 2 h and then leached in 0.1 M NaOH solution.…”