Abstract
Karst bauxite deposits are currently investigated as a new resource for rare earth elements (REE) in order to avoid present and future supply shortfalls of these critical metals. The present work focuses on the geochemistry and mineralogy of the REE in karst bauxite deposits of the Catalan Coastal Range (CCR), NE-Spain. It is revealed that the studied bauxitic ores have a dominant breccia and local ooido-pisoidic and pelitomorphic texture. The bauxitic ores are mostly composed of kaolinite and hematite, as well as of lesser amounts of boehmite, diaspore, rutile and calcite. The mineralogy and major element composition indicate incomplete bauxitization of an argillaceous precursor material possibly derived from the erosion of the Mesozoic Ebro massif paleo-high. The studied bauxites are characterized by ∑REE (including Sc, Y) between 286 and 820 ppm (av. 483 ppm) and light REE to heavy REE (LREE/HREE) ratios up to 10.6. REE are mainly concentrated in phosphate minerals, identified as monazite-(Ce) and xenotime-(Y) of detrital origin and unidentified REE-phosphates of a possible authigenic origin. REE remobilization presumably took place under acidic conditions, whereas REE entrapment in the form of precipitation of authigenic rare earth minerals from percolating solutions was related to neutral to slightly alkaline conditions. During the bauxitization process no significant REE fractionation took place and the REE distribution pattern of the bauxitic ores was governed by the REE budget of the precursor material. Finally, adsorption as a main REE scavenging mechanism in the studied CCR bauxite deposits should not be considered, since the presented data did not reveal significant REE contents in Fe-and Mn-oxyhydroxides and clay minerals.
Highlights
According to the International Union of Pure and Applied Chemistry (IUPAC) rare earth elements (REE) are a group of 17 elements with a similar geochemical behavior comprising the lanthanides, yttrium (Y) and scandium (Sc) [1]
The European Commission has categorized these elements as critical raw materials, because of their high economic importance coupled to possible supply shortfalls [8] partly caused by a monopolization of the supply chain by China [4]
It is proven that fractionation of major, minor and trace elements does occur during bauxitization [26,29,58,61], it is widely accepted that the study of immobile elements is a powerful tool to unravel the parental material and the genetic history of karst bauxites [30]
Summary
According to the International Union of Pure and Applied Chemistry (IUPAC) REE are a group of 17 elements with a similar geochemical behavior comprising the lanthanides, yttrium (Y) and scandium (Sc) [1]. Traditionally exclude Sc or both Sc and Y and group REE into. Technological developments have dramatically increased the use of REE in the defense, aerospace, medical and automotive industries. Among others, they are essential components of catalysts, high-strength magnets (mainly NdFeB), super-alloys, display technology and lasers [1,4,5,6,7]. Achieving an undistorted and sustainable access to REE is of increasing concern in Europe, and across the globe. The European Commission has categorized these elements as critical raw materials, because of their high economic importance coupled to possible supply shortfalls [8] partly caused by a monopolization of the supply chain by China [4]
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