Naslov
REE potential of bauxite-related resources in the ESEE region: Focus to Croatia

Autori
Tomašić, Nenad ; Čobić, Andrea ; Fajković, Hana ; Miko, Slobodan ; Ilijanić, Nikolina ; Gizdavec, Nikola

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, stručni

Izvornik
ERES 2020 Abstracts / - , 2020

Skup
3rd European Rare Earth Resources Conference (ERES2020)

Mjesto i datum
Delfi, Grčka, 06.10.2020. - 09.10.2020

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
bauxite ; rare earth elements ; mineral composition ; leaching ; Croatia

Sažetak
REEBAUX is a projectfunded by European Institute ofInnovation andTechnology (EITRaw materials), whichdeals with the REE potentialofbauxite-related resources in the ESEE countries focusingto Croatia, Hungary, Montenegro and Slovenia. Although a great deal of bauxite-related industry has ceased in the region, some bauxite exploitable depositsand red mud accumulationshave been left behind. Theyrequirean assessmentin respect of critical raw materialspolicy in Europe, and in particular REE. So far, 47 bauxite deposits and 4 red mud landfillshave been addressed in this respectwithin the project activities.Apart of the project resultsachieved so farispresentedhere. Theyare collected by exploringbauxite deposits in Lika and Dalmatia regionsof Croatia.In general, bauxites are indirectly a potential source for REE ; after they are treated in Bayer process foralumina production, bauxite residueis commonlyleft behind with an increased REE content relative to the input bauxite raw material (usually twice the original REE content in bauxite1).The bauxite deposits in Lika and Dalmatia visited duringtheprojecttasks areof Triassic and Paleogene (Eocene) age2. In the area, bauxite deposits are numerous, however, mostlycontain low economic reserves.Several number of exploited, partially exploited and unexploited deposits have been evaluated.An average mineral composition of the collected bauxitesamplesis as follows: gibbsite, boehmite, hematite, anatase, in some cases goethite, kaolinite and rutilealso occur. X-ray diffraction (XRD)did not show any authigenic REE mineralisation, however, it does not exclude occurrence of REE minerals as accessory phases (low abundances). For aluminium industry, several deposits reach very favourable Al2O3/SiO2ratios (4.5 and up), with Al2O3topping values over 55%in some cases.REE abundances were determined using ICP-MS after lithium borate fusion and subsequent acid dissolution. Total REE content in the bauxite samples ranges from 380- 3495 ppm, with a usual inhomogeneous distribution withinindividual deposits. Mamutovac deposit near Oklaj (Šibenik-Knin County) wasstudied into more detaildue to interesting reserves still available for exploitation. A drilling operation was carried out downto the deposit footwall that is composed of Upper Cretaceous rudist limestone (sampled bauxite core up to adepth of 25.1 m). The samples were collected at 23 depth intervals. Total REE abundances range 312-772 ppm. Limited leaching experiments were performedfor selected bauxite samplesfrom several localities byusing a modified aqua regia dissolution technique (HNO3:HCl:H2O = 1:1:1). The leaching experiments showed a variable REE recovery from as low as 17% up to over 60% (Figure 1). Unleached REE are most likely contained in minerals like monazite and xenotime, whichwere not detected in the XRD patternsdue to low abundances. Among major constituents, Ca (47- 100%) and Fe (10-90%) are most significantly leached out. However, Ca absolute amounts are low, andonly calcite is sporadically observed in XRD patterns. On the other hand, iron concentrations are significant(8-25%), mostly accountingfor hematite and sometimes goethite. XRD data of theleached samples indicate dissolutionof hematite and goethite, but occurrence of magnetite in some cases. On the other hand, Fe leaching rates could be also partially related to amorphous iron oxyhydroxide phases.

Izvorni jezik
Engleski

Znanstvena područja
Geologija

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