Abstract
The present research represents an approach toward the recycling of extractive waste inspired by circular economy and sustainability that is developed in accordance with Goal 12 of the United Nations 2030 Agenda for Sustainable Development Goals. A new procedure for the recovery of REEs from fluorite–barite–galena ores with calcite gangue from the Silius mine (Sardinia, Italy) is presented. The considered samples are waste materials of Silius mineralization, collected in the old processing plant of Assemini (near Cagliari). In this orebody, REE minerals consist of prevailing synchysite (a REE-bearing fluorocarbonate) and subordinate xenotime-Y (a Y-bearing phosphate). REE fluorocarbonates are extracted using 50% K2CO3 as the leaching solution, at 100 °C. Using a solution (mL)/sample (g) ratio of 25, about 10% of the total REE content of the considered sample is extracted within 1 h. At the laboratory scale, such alkaline leaching of REE from the waste materials allows the recovery of the CO2 produced as K2CO3 from concentrated KOH, in accordance with a circular flow. Further work is ongoing to scale up the process into a pilot plant, to prove that the method developed within this research can be economically feasible, socially suitable, and environmentally respectful.
Highlights
A great variety of metals and minerals have an increasing importance for human development
Rare earth elements (REEs) belong to the European Union (EU) list of critical raw materials (CRMs) [1], which are important for high-tech products and emerging innovations
scanning electron microscopy (SEM)-energy dispersion spectrometry (EDS) data indicate, in accordance with recent literature [19,20], that the bulk samples representing the Assemini waste material contain REE minerals finely included within the carbonate minerals and, to a lesser extent, in quartz and fluorite (Figures 5 and 6)
Summary
A great variety of metals and minerals have an increasing importance for human development. Critical metals and minerals, which are those of increasing economic importance that might be susceptible to future scarcity, are a particular worry, being vulnerable to politically or economically driven fluctuations in supply [2]. Sustainability 2021, 13, 14000 elements (REEs), Sc, Ti, V, Co, Ga, Ge, Nb, platinum group metals (PGMs), Hf, Ta, and W [3]. Rare earth elements (REEs) are a group of 17 elements (lanthanide elements plus scandium and yttrium), which have similar physical properties and are often found in the same ore deposits. REEs belong to the European Union (EU) list of critical raw materials (CRMs) [1], which are important for high-tech products and emerging innovations. The European Commission formulated in the year 2008 an integrated policy [4], i.e., the EU Raw Materials Initiative, based on three pillars, i.e., (i) ensuring a level playing field in access to resources in third countries, (ii) fostering a sustainable supply of raw materials from European sources, and (iii) boosting resource efficiency and promoting recycling
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