Bauxite residue sinter phase transformations

In the Bayer Process, between 2-35% aluminium (as wt. Al2O3%) is lost with bauxite residue (BR). This is primarily due to the inefficient dissolution of aluminium-bearing minerals during caustic leaching or from the formation of desilication product (DSP) that also constrains the recycling of caustic soda from the circuit. If these lost alumina and caustic can be recovered from BR, numerous potential processing options become available which could lead to zero-waste BR valorisation. Whilst the pyrometallurgical routes (lime soda and lime-soda sintering) have been extensively discussed in the literature for recovering alumina and sodium from BR, understanding of the mineralogical phase formation during sintering and the relationship to the thermodynamic driving forces are poorly reported .This paper presents the investigation of sintering tests conducted on two separate residues with different characteristics; Greek BR and Australian Br, and mineral phases present both before and after sintering for two distinctly different BRs. These mineral phases were characterised and quantified using XRD and XDB software. The Factsage thermodynamic software package was used to analyse reaction equilibria with potential sintering chemical reaction pathways being described

The EURARE Project: development of a sustainable exploitation scheme for Europe’s Rare Earth Ore Deposits

Numerous European industries are heavily dependent on imported rare earth element (REE) raw materials. This has created a need for the European Union (EU) to ensure a sustainable supply of REE minerals, as well as develop from the ground up the currently non-existent European REE extraction and processing industry. In order to support this, the European Commission, through the Seventh Framework Programme (FP7) scheme, funded the EURARE project which runs from 1st January 2013 to 31st December 2017. Through the EURARE project, selected European REE deposits have been researched and in certain cases identified resources were successfully processed for REE production. Several REE deposits across Europe have been the focus of detailed geological field and laboratory work. Mineral concentrates obtained from the Norra Kärr deposit in Sweden, the Kringlerne deposit in Greenland and the Kvanefjeld deposit in Greenland, Rødberg ore from Norway and bauxite residue from Greece were tested from laboratory to pilot scale by means of conventional and innovative metallurgical processing. The novel technologies developed provide efficiency and selectivity in various steps of the metallurgical processing, from ore beneficiation to metal production. A road map for sustainable REE production in Europe is now being developed, which includes an evaluation of the environmental benefits and risks of the EURARE technologies

Thermodynamics of Aluminothermic Processes for Ferrotitanium Alloy Production from Bauxite Residue and Ilmenite

Titanium oxide is a major component of bauxite residue (BR) with a high value, but it is often an unwanted element in common BR reuse options such as cement or iron production. Conventional carbothermic reduction smelting of BR produces a slag still containing a large amount of Ti. This study investigates an aluminothermic process for producing an FeTi alloy by combining BR, ilmenite ore, and fluxes. Based on thermodynamic calculations and batch experiments, the amounts of aluminum (reductant) and fluxes were investigated to achieve the optimum alloy production in parallel with a slag that could be further valorized in the cement industry. The mineralogical and chemical analysis of the metallic and slag phase agreed with the thermodynamic calculations. The results obtained by this study can lead to the development of a new process for the complete valorization of BR, paving the way for scaling up aluminothermic processes for producing ferroalloys from all iron-rich residues

A Study of the Occurrence of Selected Rare-Earth Elements in Neutralized-Leached Bauxite Residue and Comparison with Untreated Bauxite Residue

© 2019, The Minerals, Metals & Materials Society. This study investigates the chemical associations of the selected rare-earth elements (Sc, Y, Ce, La, and Nd) with major element phases in the postprocessed bauxite residues and compares them with the untreated bauxite residue. The treatment of bauxite residue considers our previous published process which involved the neutralization with CO 2 , followed by leaching with H 2 SO 4 . Neutralized bauxite residue resulted with larger aggregates than the untreated bauxite residue after making contact with CO 2 as the consequence of additional CaCO 3 formation. Neutralization with CO 2 , however, has a negligible effect on the distribution of the rare-earth elements (REEs) with respect to the untreated bauxite residue, but a large amount of rare earths remained unreacted after acid leaching. Electron probe microanalysis (EPMA) confirmed the chemical associations of Sc(III) and Ce(IV) with Fe(III)- and Al(III)-containing minerals in the postprocessed bauxite residues, i.e., bauxite residues subjected to CO 2 -neutralization and neutralization–acid leaching processes. The occurrence of Nd(III) is positively correlated to that of La(III) in the untreated bauxite residue, but both of them may be associated with the same mineralogical phase as Ce(IV) after processing. Y(III) may remain associated with the Al/Si-minerals, cancrinite and chamosite. Ergo, the extractability of Sc, Y, Ce, La, and Nd from neutralized bauxite residue is more difficult in H 2 SO 4 media due to the presence of coarser particles compared to those of the untreated bauxite residue, but also due to the formation of a solid product layer (i.e., CaSO 4 ) that is presumably adsorbed on the surface of Fe(III)-rich phases (hematite and goethite) and Al(III)-containing minerals (diaspore, gibbsite, boehmite, and chamosite).status: publishe

The EURARE Project: Development of a Sustainable Exploitation Scheme for Europe’s Rare Earth Ore Deposits

Numerous European industries are heavily dependent on imported rare earth element (REE) raw materials. This has created a need for the European Union (EU) to ensure a sustainable supply of REE minerals, as well as develop from the ground up the currently non-existent European REE extraction and processing industry. In order to support this, the European Commission, through the Seventh Framework Programme (FP7) scheme, funded the EURARE project which runs from 1st January 2013 to 31st December 2017. Through the EURARE project, selected European REE deposits have been researched and in certain cases identified resources were successfully processed for REE production. Several REE deposits across Europe have been the focus of detailed geological field and laboratory work. Mineral concentrates obtained from the Norra Kärr deposit in Sweden, the Kringlerne deposit in Greenland and the Kvanefjeld deposit in Greenland, Rødberg ore from Norway and bauxite residue from Greece were tested from laboratory to pilot scale by means of conventional and innovative metallurgical processing. The novel technologies developed provide efficiency and selectivity in various steps of the metallurgical processing, from ore beneficiation to metal production. A road map for sustainable REE production in Europe is now being developed, which includes an evaluation of the environmental benefits and risks of the EURARE technologies.status: publishe