Hematite (α-Fe2O3) – A potential Ce4+ carrier in red mud

Rare Earth Element Phases in Bauxite Residue

“…Nanoscale assessment discerned the existence of calcium ferrotitanate phases with several weight percent REEs concentrations, that also surpass REEs bulk concentration in bauxite residue. Current work does not provide support for the suggestion by Bolanz et al [55] who speculated that tetravalent cerium could theoretically be located in bauxite residue within hematite lattice. Neither does present work disprove the existence of such occurrence forms.…”

“…Hematite has been proven to be able to incorporate tetravalent cerium into its lattice. Based on that and the existence of cerium in hematite-enriched matrix of bauxite residue, hematite was suggested to contain cerium in its lattice as the potentially prevailing form of cerium occurrence in bauxite residue [55]. In the same study, the heavy minerals fraction was found to contain some sporadic grains of bastnäsite and monazite, but they were considered as negligible carriers of REEs.…”

“…The former comparison allows to suggest, that the observed LREE ferrotitanate phases presented in this study are not isolated cases for only AoG-s bauxite residue, but instead seem to be a more generic characteristic that occurs in bauxite residues originating from different alumina refineries. The exception presented by Bolanz et al, who hypothesize that the main carrier of cerium is hematite [55], indicates to the need of examining rare earth phases in relation to Bayer process conditions as well as in relation to bauxite feed and REE occurrence forms within bauxite.…”

“…In the same study, the heavy minerals fraction was found to contain some sporadic grains of bastnäsite and monazite, but they were considered as negligible carriers of REEs. Cerium was identified to occur in its tetravalent oxidation state in the bulk sample and therefore the common REE minerals (e.g., monazite) were excluded as the potential hosts of cerium [55]. The authors admitted that cerium location in hematite lattice remains hypothetical, but they insist that REEs occurrence in bauxite residue should be discussed in the context of main mineral phases rather than discrete REE phases [55].…”

“…Bayer process derived REE titanate compounds were mentioned in a patent describing the recovery of REEs from bauxite residue [51]. A recent contribution that investigated strictly the forms of cerium in bauxite residue, did not refer to any relations between cerium and titanium [55]. The former comparison allows to suggest, that the observed LREE ferrotitanate phases presented in this study are not isolated cases for only AoG-s bauxite residue, but instead seem to be a more generic characteristic that occurs in bauxite residues originating from different alumina refineries.…”