Estimating Volumes and CRM Recovery Potential from Granite Wastes in the Buddusò–Alà dei Sardi District (Sardinia, Italy)

Starting from May 2024, the Critical Raw Materials Act entered into force in the European Union with the purpose of ensuring access to a secure, resilient, and sustainable supply of Critical Raw Materials (CRMs), including by enhancing efficiency and circularity throughout the entire value chain. Within this regulation, particular emphasis is devoted to the recovery of CRMs from extractive waste. Equal importance is given to the inventory of waste facilities, which must be carried out by Member States in order to obtain a clear framework in geographic, legal, volumetric, and compositional terms.

In Italy, the Sardinia Region is characterized by a remarkably high number of waste deposits originating from ornamental granite extraction. These materials have potential for the recovery of some CRMs such as Rare Earth Elements, due to the presence of allanite, as well as feldspars for the ceramic industry [1–2]. However, the decline of the ornamental granite sector in Italy has resulted in a lack of updated data, making it impossible to estimate either the total amount of granite waste or its potential as a source of CRMs. In this context, the present study aims to estimate the volumes and potential CRMs supply associated with granite waste deposits in the Buddusò–Alà dei Sardi extractive district (Sardinia, Italy).

Using QGIS software and available spatial datasets, extractive areas within the district were identified, and waste dumps were mapped based on satellite imagery. Given the absence of detailed Digital Elevation Models (DEMs) for the study area, these were reconstructed from satellite data, enabling the estimation of dump volumes. The resulting volumes showed a Root Mean Square Error (RMSE) of approximately 27% compared with more accurate DEMs. Subsequently, based on literature data concerning the composition of local granites and potential concentration processes for CRMs described by Aquilano et al. [1] and Vaccaro et al. [2], the potentially recoverable quantities of CRMs were calculated.

Although the results are characterized by relatively high uncertainty, this approach provides a preliminary dataset for extensive areas where significant data gaps currently exist and where achieving high-accuracy estimates in the short term appears unrealistic. Moreover, extending this framework to the entire Region of Sardinia could support the identification of the most promising areas for more detailed investigations, ultimately improving data quality and targeting zones with the highest potential for CRMs recovery.

[1] Aquilano, A.; Marrocchino, E.; Vaccaro, C. Gravity and Magnetic Separation for Concentrating Critical Raw Materials from Granite Quarry Waste: A Case Study from Buddusò (Sardinia, Italy). Resources 2025, 14, 24.
[2] Vaccaro, C.; Aquilano, A.; Marrocchino, E. Alternative Sources of Raw Materials for the Ceramic Industry through Granite Waste Recycling: A Case Study from Buddusò, Sardinia, Italy. Appl. Sci. 2024, 14, 7967.