The DSP concentrate sinter-leach process for aluminium and sodium recovery 1

Abstract

The combination Bayer sinter-leach process has been shown to be a technically viable method for reprocessing bauxite residue to recover lost caustic and alumina. However, this method suffers from high energy requirements and reagent consumption associated with processing the large volume of bauxite residue, the majority of which is gangue. To address this issue, processing a desilication product (DSP) concentrate derived from the novel Sandy Desilication Product process is studied. In the present study, critical processing parameters surrounding the sintering stage were investigated including the grade and particle size of the DSP concentrate, the limestone addition rate, using calcium oxalate as an alternative to limestone and reductive sintering. The DSP concentrate sinter mineral phases were specified using quantitative XRD and the sinter products were assessed for leachability. Maximising the silicate reaction extent during sintering was found to be important to ensure high leachability.

The DSP concentrate sinter-leach process for aluminium and sodium recovery 2: leaching behaviour

“…Two sinter products were produced based on the conditions that resulted highest sodium and aluminium recoveries in the study by Hodge et al (2020). The first of these used graphite powder to reduce Fe 2 O 3 during sintering (reductive sintering strategy/feed).…”

“…The other uses a high CaCO 3 dosage to fully react all Fe 2 O 3 to Ca 2 Fe 2 O 5 (high Ca strategy/feed). These sinter products were produced by forming a powdered mixture of reagent grade Zeolite A (as the DSP), Fe 2 O 3 and CaCO 3 and sintering at 1000°C for 1 h. The chemical compositions of these mixtures are presented in Table 1 and further details on the production of these materials can be found in Hodge et al (2020).…”

“…It should also be noted that 4% C addition is equivalent to approximately two times the stoichiometric requirement to reduce all Fe 2 O 3 to Fe. In Hodge et al (2020) it was shown that only reduction to magnetite is required and as such the C requirements would be lower in industry but were kept high for this work to ensure reduction occurred during sintering. Additionally it was shown in Hodge et al (2020) that the Ca:Fe molar ratio could be reduced to 0 if a reducing atmosphere was rigorously maintained.…”

“…Under reducing conditions, no reaction occurs between CaCO 3 and Fe 2 O 3 . Both strategies produced similar recoveries of approximately 85% for both sodium and aluminium (Hodge et al 2020). Additionally, it was found that the large particles produced during the modified predesilication stage are unsuitable for sintering.…”

“…The block flow diagram of the Sandy DSP process is presented in Figure 1. The sintering operation and conditions were described in Hodge et al (2020). It was found that to achieve a high sodium and aluminium recovery (greater than 80%), it was critical that complete reaction of DSP with CaCO 3 to occurred.…”