What is Phosphogypsum?

Phosphogypsum (фосфорен гипс) is a by-product of phosphate fertilizer production, rich in calcium sulfate but also containing naturally occurring radionuclides such as uranium and radium. While it may superficially resemble ordinary gypsum, its origin, chemical composition, and potential risks make it a very different material. The aim of this post is to present to a general Macedonian audience what phosphogypsum is, where it comes from, what health-radiation risks it may carry, and how researchers study and analyze it.

By drawing on recent Macedonian research and technical literature, this post gives an overview of the origins of phosphogypsum, its key properties, its radiological risks, and how it is analyzed in the laboratory. This information is important for understanding whether phosphogypsum can be safely reused, managed, or monitored, as well as what decisions should be made about it in policy and environmental management.

Why these studies matter

Phosphogypsum represents one of the most important industrial wastes associated with the fertilizer industry. Despite being chemically similar to gypsum, its radioactivity makes it a special case: the radionuclides contained in it can pose both environmental and health risks if not properly managed. At the same time, phosphogypsum has the potential to be reused in construction or agriculture, but only under strict control and understanding of its composition.

In the Macedonian context, these studies help fill a knowledge gap: they explain how phosphogypsum forms, what radionuclides it may contain, and how different sources of phosphate ore influence its purity.

What the researchers found

Researchers report the following key findings:

• The radioactivity of phosphogypsum comes mainly from uranium-238 (U-238) and its decay chain. The uranium concentration in phosphates (from which phosphogypsum is produced) can vary widely depending on the raw material, from 0.010 to 0.400 g U/kg of phosphate.
• Radium-226 (Ra-226) and other radionuclides can be enriched in the phosphogypsum during the production of phosphoric acid.
• The researchers emphasize that radon gas (a decay product of radium) is one of the main radiological risks, especially if phosphogypsum is used in closed or poorly ventilated spaces.
• According to the technical research methods described in the e-print document, the specific activities of radionuclides like U-238, Ra-226 and Pb-210 are relatively high, indicating that a significant fraction of uranium remains in the waste.
• Importantly, the researchers note that the choice of the phosphate rockused in fertilizer production strongly influences how much uranium ends up in the phosphogypsum: for example, volcanic phosphates contain much less uranium.
• They suggest that using more “pure” phosphate or applying combined production methods (dihydrate / hemihydrate) could reduce the radioactivity of the phosphogypsum.
• Before any reuse (especially in construction), the phosphogypsum needs a preliminary purificationstep to lower the concentration of radionuclides.

How the work was carried out

The researchers applied a set of scientific methods to analyze phosphogypsum:

1. Sample collection:They collected samples from industrial sites (or piles) to ensure representativeness.
2. Mineralogical analysis:They used X-ray diffraction (XRD) to identify the mineral phases, revealing that the material is largely calcium sulfate, along with minor minerals.
3. Microscopy:SEM-EDS was used to examine morphology and elemental composition.
4. Geochemical analysis:They measured major oxides and trace elements, including rare-earth elements and uranium.
5. Radiochemical analysis:They determined the activity concentrations of radionuclides such as U-238, Ra-226, Pb-210, and others.
6. Risk estimation:Based on the measured activity, they evaluated possible radiation doses (especially external dose) and assessed whether reuse is realistic under safe conditions.

What it means for Veles

Although these sources were not written only for the Veles pile (фосфогипс депонија), they have important implications for Veles

• They show that the radioactivity in phosphogypsum is directly related to the raw materialsused in the fertilizer plant.
• The risk estimates (radionuclide activities, potential radon) indicate that if phosphogypsum from Veles were to be reused, it would need strict radiological control.
• The techniques the researchers used provide a roadmap for how to monitor and analyze the material in Veles (or any similar site): mineralogy, geochemistry, and radiochemical testing should be part of any environmental management plan.
• These studies support the idea that, w.ith proper planning, phosphogypsum from Veles (or similar sites) could be reused, but only after purification and treatment as in FICfighters project the scientists are researching, and not simply dumped or used in construction without assessment.

Want to know more?

If you would like to dive deeper into the science of phosphogypsum — its composition, analysis, and risk — these are the key references from Macedonian-language sources, or read more posts in the FICfighters Virtual Forum.

• Goce Delčev University, University Bulletin No. 290 (January 2022)– contains detailed discussion of the origins of phosphogypsum, radiological risk (radon, uranium), and implications for reuse. (Универзитет „Гоце Делчев“ – Штип)
• Natural Resources & Technology, Goce Delčev University (e-print document, December 2018)– detailed methodological description (XRD, ICP-MS, SEM-EDS, radiochemistry) and preliminary data on radionuclide activities.