Investigation on Li Recovery from Greek Coal Fly Ash Under a Circular Economy Framework: An Experimental Study

Lithium is classified as a critical element and is widely used in a variety of high-tech applications. Within the framework of a circular economy, demand is rising for technologies capable of recovering high-tech metals from waste materials and industrial byproducts. Coal fly ash (CFA) has attracted significant attention as a promising secondary resource for this purpose. Effective recovery requires the assessment of both metal enrichment levels and the underlying binding and leaching characteristics. The present study aims to contribute to advancing lithium recovery technology using coal fly ash as a secondary resource, thereby promoting waste valorization. Fourteen samples of coal fly ash from different power plants were collected and their mineralogy was studied by X-ray powder diffraction (XRD), their major constituents were analyzed by X-ray fluorescence spectroscopy (XRF), and their Li content was determined by inductively coupled plasma mass spectrometry (ICP-MS). Leaching experiments were conducted for selected samples using mineral acids (HCl and HF) and citric acid. Lithium concentrations in the analyzed samples ranged from 80 to 256 mg/kg, indicating enrichment relative to both global ash averages (enrichment factor > 1) and the Earth’s crust (enrichment factor > 2). Li in the samples, could be mainly associated with the amorphous fraction present in the samples. Leaching behavior across the samples follows a consistent trend, with hydrofluoric acid exhibiting the highest lithium extraction efficiency—reaching up to 79.9%.