Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of production and political issues, most notably a near monopoly in supply from China. Red mud, the waste product of the Bayer process that produces alumina from bauxite, represents a potential secondary resource ofREE. Karst bauxite deposits represent the ideal source material forREE-enriched red mud as the conditions during formation of the bauxite allow for the retention ofREE. TheREEpass through the Bayer Process and are concentrated in the waste material. Millions of tonnes of red mud are currently stockpiled in onshore storage facilities across Europe, representing a potentialREEresource. Red mud from two case study sites, one in Greece and the other in Turkey, has been found to contain an average of ∼1000 ppm totalREE, with an enrichment of light over heavyREE. Although this is relatively low grade when compared with typical primaryREEdeposits (Mountain Pass and Mount Weld up to 80,000 ppm), it is of interest because of the large volumes available, the cost benefits of reprocessing waste, and the low proportion of contained radioactive elements. This work shows that ∼12,000 tonnes ofREEexist in red mud at the two case study areas alone, with much larger resources existing across Europe as a whole.

Approximately 300 million tonnes of bauxite are processed annually, primarily to extract alumina, and can contain moderate rare earth element (REE) concentrations, which are critical to a green energy future. Three bioleaching techniques (organic acid, reductive and oxidative) were tested on three karst bauxites using either Aspergillus sp. (organic acid bioleaching) or Acidithiobacillus ferrooxidans (reductive and oxidative bioleaching). Recovery was highest in relation to middle REE (generally Nd to Gd), with maximum recovery of individual REE between 26.2% and 62.8%, depending on the bauxite sample. REE recovery occurred at low pH (generally < 3), as a result of organic acids produced by Aspergillus sp. or sulphuric acid present in A. ferrooxidans growth media. Acid production was seen when A. ferrooxidans was present. However, a clear increase in REE recovery in the presence of A. ferrooxidans (compared to the control) was only seen with one bauxite sample (clay-rich) and only under oxidative conditions. The complex and varied nature of REE-bearing minerals in bauxite provides multiple targets for bioleaching, and although the majority of recoverable REE can be leached by organic and inorganic acids, there is potential for enhanced recovery by bioleaching.

Rare earth elements (REE) are essential raw materials used in modern technology. Current production of REE is dominated by hard-rock mining, particularly in China, which typically requires high energy input. In order to expand the resource base of the REE, it is important to determine what alternative sources exist. REE placers have been known for many years, and require less energy than mining of hard rock, but the REE ore minerals are typically derived from eroded granitic rocks and are commonly radioactive. Other types of REE placers, such as those derived from volcanic activity, are rare. The Aksu Diamas heavy mineral placer in Turkey has been assessed for potential REE extraction as a by-product of magnetite production, but its genesis was not previously well understood. REE at Aksu Diamas are hosted in an array of mineral phases, including apatite, chevkinite group minerals (CGM), monazite, allanite and britholite, which are concentrated in lenses and channels in unconsolidated Quaternary sands. Fingerprinting of pyroxene, CGM, magnetite and zircon have identified the source of the placer as the nearby Gölcük alkaline volcanic complex, which has a history of eruption throughout the Plio-Quaternary. Heavy minerals were eroded from tephra and reworked into basinal sediments. This type of deposit may represent a potential resource of REE in other areas of alkaline volcanism.

A light REE (LREE)-bearing mineral called chevkinite (Ce, La, Ca, Th)₄(Fe²⁺, Mg)₂(Ti, Fe³⁺)₃Si₄O_22, originating from a heavy metal placer deposit Aksu Diamas in Turkey, previously assessed for potential REE extraction as a by-product of magnetite production, was studied using scanning electron microscopy with energy and wavelength-dispersive spectrometers (SEM EDS-WDS). This mineral exhibits analytical challenges associated with severe X-ray energy overlaps between the REE, titanium, and barium. Here, we present an iterative process, showing that SEM EDS-WDS is a viable technique for obtaining good quality quantitative data. SEM EDS-WDS is an in situ, non-destructive, and relatively non-expensive technique, but operator’s experience is essential to obtain good quality data. In cases where the peak fitting remains challenging, in particular, and where the constituents have large differences in abundance, an assessment of the X-ray spectrum to qualitatively assign all peaks is essential prior to quantitative analysis.

The Çanakli deposit, part of the Aksu Diamas project in Turkey, is a potentially important source of European Rare Earth Element (REE) supply. It has an inferred resource of 494 million tonnes at a...

The major share of raw materials needed to sustain our present lifestyle and even more importantly, required for the crucial green transition, are sourced outside Europe. The European Commission aims to enhance Europe's resilience and strengthen domestic sourcing. Although Europe has a long tradition of mining and extractive activities, it is acknowledged that there are several challenges to achieve European sourcing of certain raw materials such as the critical raw materials. A basic prerequisite to enable access to domestic raw materials is information on raw material occurrences, current and past mining activities, resources and reserves. The Geological Survey organizations (GSOs) of Europe play a key role in generating, compiling, gathering and storing the most up-to-date information as well as long-term data series on raw materials at national and regional levels. Over the last decade, the GSOs have joined forces and taken essential steps to harmonize and share data on raw materials. The results of this co-operation are illustrated as interactive maps on the European Geological Data Infrastructure (EGDI). This paper describes the data compiled in co-operation between the GSOs, and analyses the strengths and weaknesses of, as well as opportunities for and threats towards, the data.