Detection of Rare Earth Elements (REEs) in mine waste applying destructive and spectral techniques: a chance to overcome the rising worldwide REEs demand?

he increasing demand of Rare Earth Elements (REE) in the industry and their economic relevance plays a crucial role in the mining exploration. In order to cover the worldwide demand unconventional deposits such as dumps and tailings from abandoned mines are being considered as a new source to recover REE bearing minerals. Purwadi et al. (2018) have investigated the concentration and visible and near-infrared reflectance spectroscopy of REEs-bearing tailings of a closed tin mine located on the Bangka Island (Indonesia) but detected no REEs bearing minerals due to their low abundance (<1wt.%). Our study investigates the sediments (quartz rich tailings) from this tin mine by means of Electron Microprobe (EMP). The measurements on 12 tailing samples have shown the occurrence of zircon ZrSiO4 and abundant REE bearing minerals such as monazite (Ce,La)PO4 , xenotime YPO4 , thorite (Th,U)SiO4, and uranite UO2. REEs bearing phases occur in quartz or at the grain boundaries, are approximately 5 to 50 μ large, and form relatively fresh (poorly altered) un-to subhedral grains providing suitable surfaces for EMP point analyses. Plotting the concentration of the REEs of monazite and xenotime in the chondrite normalized diagram they show the typical monazite decreasing and xenotime increasing pattern with no obvious anomaly. Chemically monazites are characterized by high thorium (up to 18% ThO - mainly as huttonite component) and very high yttrium and xenotime component (up to 3.5 wt. % Y2O3) indicating a high monazite formation temperature. More analyses including ICP-OES on selected samples are planned in the near future to investigate REE distribution in these type of deposits e.g. depleting and or enrichment triggered by fluids, weathering and alteration. The integration of spectral techniques and mineralogical-chemical investigations such as EMP and ICP-OES should play a crucial role in the future to characterize dumps, for the recovery of REEs and their signature in the deposits leading to a sustainable and economical extraction.