Characterization of Phosphogypsum from Cartagena and Huelva, Spain<i></i>

Phosphogypsum (PG), a by-product of phosphoric acid production, is recognized as a Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) due to its enrichment in uranium-series radionuclides. In Spain, particularly in Huelva and Cartagena, large PG stacks raise growing environmental concerns related to soil and groundwater contamination. This study presents a mineralogical and preliminary environmental assessment of PG samples from these regions using X-ray diffraction (XRD) and energy-dispersive X-ray fluorescence (EDXRF). Gypsum (CaSO4 · 2 H2O) was identified as the dominant crystalline phase in all samples. Variations in peak intensity and preferred orientation suggest mineralogical heterogeneity linked to source rock properties and processing conditions. Subtle peak shifts and broadening indicate co-hydration with H2O and D2O, consistent with isotopic fractionation during crystallization. EDXRF analysis also revealed the presence of heavy metals such as chromium (Cr), nickel (Ni), lead (Pb), and zinc (Zn), as well as trace elements like strontium (Sr) and barium (Ba), which may influence environmental risk. No discrete phases of uranium, thorium, or radium were detected by XRD, supporting their probable incorporation at trace levels through substitution or adsorption, a finding confirmed by EDXRF elemental analysis. This mineralogical and chemical data forms the baseline from which a further comprehensive material characterization will be drawn, integrating gamma spectrometry, ICP-MS and SEM to evaluate the chemical speciation and environmental risk of PG. Based on Web of Science data, over 300 peer-reviewed articles on PG were published globally between 2020 and 2025, with China, Morocco, and Brazil leading in scientific output. The growing research interest underscores the strategic relevance of detailed PG characterization for informing safe reuse, regulatory decisions, and circular economy applications.