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Phosphogypsum (PG), a by-product of phosphate fertilizer production, is generated in large quantities in Morocco and worldwide and is classified as a naturally occurring radioactive material (NORM). Moroccan phosphogypsum contains minor impurities such as residual phosphoric acid, heavy metals, and rare earth elements; however, the presence of radionuclides remains the principal barrier to its reuse, particularly in construction materials. Among these radionuclides, radium-226 (Ra²²⁶) is the most radiologically significant, with specific activity exceeding 500 Bq/kg 1,2, surpassing internationally recommended limits for building materials 3 and posing potential radiological risks due to its mobility and decay products.
Numerous phosphogypsum purification methods have been investigated to reduce both minor impurities and radionuclide content 4–6. These approaches include physical and chemical treatments such as washing, neutralization, granulometric separation, and acid leaching. While these methods are generally effective in removing soluble impurities such as residual phosphoric acid, phosphates, fluorides, and certain metals, their ability to reduce Ra²²⁶ activity remains limited. In most cases, radium is strongly associated with the calcium sulfate matrix or present as sparingly soluble RaSO₄, resulting in low removal efficiency and limited radionuclide mobility under conventional treatment conditions.
In this study, we evaluate a purification strategy inspired by the work of Kovler et al. 7, focusing on the reduction of Ra²²⁶ activity in Moroccan PG through a combined radiochemical treatment approach. The process involves an initial treatment using calcium chloride (CaCl₂) to enhance radium mobility via sulfate–chloride ion exchange, followed by acid leaching using hydrochloric acid (HCl). Previous studies have shown that radium and other PG-associated contaminants, such as sulfates and phosphates, exhibit low solubility in aqueous media, limiting their mobilization. However, chloride complexation can significantly increase radium solubility, facilitating its subsequent extraction during acid leaching. Various experimental parameters—including CaCl₂ concentration, temperature, contact time, stirring speed, and solid-to-liquid ratio—were investigated to determine the optimal treatment conditions for Moroccan PG, aiming to maximize Ra²²⁶ reduction while preserving its physicochemical properties for potential use in construction applications.
Acknowledgments: Mohammed VI Polytechnic University (UM6P) and OCP collaborate as partners in advancing research and innovation through the Flagship Program: PHOSPHOGYPSE (OCP/UM6P) under the Research Grant (No. 127DOPR007-3). This partnership, supported by OCP SBU Manufacturing, underscores a shared commitment to the successful realization of the Flagship and all related projects.