Comprehensive characterization of secondary sources originating from Turkey in terms of rare earth elements and scandium

Highlights: • REE potential of hazardous waste incineration plant ash was demonstrated. • The correlation between total REE and Sc concentrations was exhibited. • REE concentrations were evaluated for their potential to be a secondary source. • E-waste and fly ashes were evaluated as more critical secondary sources. REEs are essential materials for modern technology due to their unmatched physical and chemical properties. This paper reviews the potential and types of rare earth elements (REE) in 32 different secondary sources that contain water, wastewater, and slime/solid wastes originating from Turkey. Secondary sources were classified into five different categories as mining wastes (M), combustion residuals (C), sediments and sludges (S), e-waste (E), and wastewater (WW). After pre-processing and acidic digestion of solid samples, elemental concentrations of wastewaters and acidic leachates were measured. The highest total REE (REE_total) concentration was obtained in a combustion residue sample coded as C5 with 379 mg/kg. Besides, the highest critical REE (REE_critical) content was found in an e-waste sample including 346 mg/kg total REE and 76% critical REE. In addition, boron mine wastewater (W5) with a total REE concentration of 110 μg/L was evaluated as a significant important secondary source in terms of yttrium. The association, between scandium and total REE concentrations of category M and S, was evaluated and correlation coefficients of 0.86 and 0.69, respectively were calculated. E-waste and thermal power plant (TPP) ashes were evaluated as the secondary sources with the highest REE potential among the whole type of waste/wastewater.