Phosphate rock, that is used to produce mineral fertilizers, is among the fifth most mined materials on earth making phosphate rocks one of the most relevant unconventional uranium resource. The recovery of uranium during fertilizer production has the added advantage that the radiotoxic heavy metal will largely be removed from the final fertilizer product and not be dissipated on agricultural soils from where it might leach into waterbodies (Bigalke et al., 2017; Hill et al., 2024; Mwalongo et al., 2024). Worldwide it is estimated that uranium recovered from the more than 400 fertilizer plants operating around the world could theoretically substitute some 8%–15% of global uranium mining (Gabriel et al., 2013; Ulrich et al., 2014; Haneklaus, 2021) with Morocco, one of the largest phosphate rock producing countries in the world, being (theoretically) able to shoulder 1.5% of this singlehandedly (Qamouche et al., 2021).

The global potential for uranium recovery from phosphate rocks can be estimated using production data and phosphate rock reserve data as it is for instance reported annually by the USGS (USGS, 2023) as well as average concentrations of uranium in the considered phosphate rocks. Table 1 provides estimated amounts of uranium associated with phosphate rocks globally using 2021 production data of the USGS. The average uranium concentrations in phosphate rock by country were estimated using the dataset provided by Van Kauwenbergh (1997).

The quantitative assessment featured in Table 1 is a straightforward and simple analysis that provides insights concerning the amount of uranium linked to phosphate rock production and reserves globally. According to this simple assessment nearly 14,000 t of uranium are mined with phosphate rocks every year worldwide. Out of these 14,000 t, approximately 9,000 t have been observed as being connected to phosphate rocks with more elevated uranium concentrations of at least 90 ppm. Such phosphate rocks, or a cut-off grade of 90 ppm has been introduced in earlier analysis (Haneklaus, 2021) and it was proclaimed that such phosphate rocks might allow for commercial uranium recovery, while the rocks with lower uranium concentrations might not. The estimate in Table 1 provides a brief overview about the potential that uranium recovery from phosphate rocks could have on a global scale. In this context it is noteworthy that the uranium production in 2021 was approximately 47,500 t (NEA/IAEA, 2022; WNA, 2023c).

If uranium is recovered during phosphate rock development to mineral fertilizer using the historically proven solvent extraction process, approximately 95% of the uranium present in the WPA can be recovered and it can be estimated that 90% of this uranium transfers to the WPA. The amount of uranium that could theoretically be recovered from phosphate rock production in 2021 would thus be approximately 7,691 t or roughly 16% of the uranium production that year considering phosphate rocks with a uranium content of at least 90 ppm and Equations 1–3 that are provided below. Uranium  content  in  phosphate  rock : U p h o s p h a t e    r o c k = C i × P i (1) Uranium  content  in  WPA : U W P A = 0.90   C i × P i (2) Recoverable  uranium  content  from  WPA : U r e c o v e r a b l e = 0.95   U W P A (3) Where C_i (ppm) is the country specific uranium concentration in phosphate rock and P_i (t) is the corresponding quantity of imported phosphate rock. U_WPA is the concentration of uranium in the WPA and U_recoverable is the quantity of uranium that can be recovered from the WPA using best available technology (BAT), such as industrially proven solvent extraction.

It is noteworthy that it is extremely unlikely that there will be large scale recovery of uranium at the more than 400 mineral phosphate fertilizer plants operational worldwide at the moment. The very brief calculation provided here does, however, indicate the relevant potential that uranium recovery from phosphoric acid has as an additional raw material source.

Detailed country-specific assessments of annual uranium recovery potentials are accessible for Argentina (19 t uranium in 2017) (Lopez et al., 2019), China (648 t uranium in 2016) (Shang et al., 2021), the EU (334 t uranium from phosphate rock imports in 2017) (Tulsidas et al., 2019), the Philippines (14–26 t uranium annually from phosphate rock imports in 2020–2022) (Diwa et al., 2023), the United Republic of Tanzania (30–40 t uranium annually as byproduct from local Minjingu phosphate rock mining and processing) (Haneklaus et al., 2024) and the United States of America (2,116 t uranium in 2014) (Kim et al., 2016; Steiner etal., 2020).

For the Kingdom of Saudi Arabia such an assessment has to the best of our knowledge not been performed yet. In this context, the International Atomic Energy Agency (IAEA) estimated that some 187,100 t uranium are associated with phosphate rocks in Saudi Arabia (NEA/IAEA, 2022) (a slightly higher estimate than the one in Table 1) and Al-Eshaikh et al. (2016) recommended the consideration of phosphate rocks and desalination concentrate as potential domestic sources of uranium in the Kingdom of Saudi Arabia. Since 2011, Saudi Arabia is a major phosphate rock producer (see Figure 2) and the USGS estimated that the country produced 9.2 million t phosphate rocks in 2021 and 8.0 million t in 2020 respectively (USGS, 2023). The average concentration of uranium in phosphate rocks in Saudi Arabia is probably in the order of 60–80 ppm with maximum local concentrations of 100–150 ppm (Khater et al., 2016; Mehboob et al., 2021), so that in 2021 some 447–596 t uranium could have theoretically been recovered during phosphate rock processing in Saudi Arabia if 90% of the uranium in the phosphate rock transfers to the WPA from where recovery usually takes place, and this recovery happens at an overall efficiency of 95%. It is noteworthy that previous studies (Haneklaus, 2021) have set the cut-off grade for (potentially economic) uranium recovery from phosphate rock at 90 ppm so that it needs to be investigated if uranium recovery from phosphates might at all make sense in Saudi Arabia. The set cut-off grade is obviously an oversimplification that does not consider specific rock types ore processing methods. There is a good chance that the artificially introduced cut-off grade can be revised if more innovative processing methods are used for uranium recovery, other impurities are better understood that could increase uranium recovery efficiencies or the throughput of the fertilizer plants are increased, resulting in advantages economics of scale. The historic potential uranium recovery from phosphate rocks for the Kingdom of Saudi Arabia is depicted in Figure 2 using USGS phosphate rock production data.

Uranium is also naturally present in seawater in concentrations as low as 3.3 parts per billion or 0.0033 ppm. As a result of the very large potential quantities of uranium in seawater that are estimated to be in the order of 4.5 billion metric t or 500 times of all identified terrestrial reserves, uranium recovery from seawater is actively researched. The uranium concentration in desalination concentrates or brine from desalination plants, basically concentrated seawater, can be approximately two times higher than the uranium concentration in regular seawater and can show far fewer impurities than the seawater itself (Loganathan et al., 2017; Zhang et al., 2021; Altay et al., 2022). There have been several different approaches for uranium recovery from seawater and/or desalination concentrate. The used approaches are usually based on adsorption, ion-exchange, coagulation and coprecipitation, solvent extraction, membrane filtration, biological separation, and foam separation. Among these methods, adsorption is often considered to be the most convenient, efficient, and low-cost technique (Sodaye et al., 2009; Loganathan et al., 2017). The Kingdom of Saudi Arabia has depended on desalinated water since the 1950s and has since then come to be the major desalinated water producer in the world. As of 2023, sixty percent of the country’s water comes from desalination, with groundwater accounting for less than 40 percent. As of 2023, the Kingdom of Saudi Arabia had a total of 33 desalination plants in seventeen locations run by the SWCC, responsible for approximately 69 percent of desalination in the Kingdom and 20 percent of the worldwide desalination capacity (ArabNews, 2023). Data on the water desalination per year in Saudi Arabia was sourced from the SWCC. In 2021 a total of 2,154 t of seawater was desalinated in the Kingdom of Saudi Arabia. Approximately 6.46 t uranium were associated with this seawater and could have (theoretically) been recovered. Figure 3 provides an overview of the uranium quantities associated with seawater used for desalination in the Kingdom of Saudi Arabia.