**5. Tentative economic analysis**

The next step of the work was a selection of extracting agents appropriate for the membrane process. Tributyl phosphate (TBP), triethylamine (TEA), di(2-ethylhexyl)phosphoric acid (DEHPA), tri-n-octylamine (TnOA) and trioctylphosphine oxide (TOPO) (see **Figure 4**) were considered as a potential extracting agents. The extraction efficiency (%E) was calculated by

After preliminary experiments comprising determination of extraction efficiency, di(2-ethylhexyl)phosphoric acid (DEHPA) was found to be most favorable. The tests were performed using both model and real solutions. The results of experiments carried out using the model

ics of membrane extraction is similar for different concentrations of uranium. However, the fastest extraction occurred for solutions with low concentrations of uranium. For concentration of 0.1 g/L, extraction efficiency reached a constant value after less than 1 h, while for concentration of 0.3 g/L equilibrium state was reached after about 2 h. It was also proved that an initial uranium concentration has great importance for extraction efficiency. The highest efficiency of the extraction process, reaching over 90%, was achieved in case of the solution

The integrated process of extraction and stripping conducted in continuous mode was also investigated. This process includes two membrane modules, one for extraction and the other for back extraction. It was proved that in case of extraction/stripping process of real post-leaching solutions the high values of stripping and recovery of uranium were obtained. Using this process, it is possible to remove some metallic components from post-leaching liquors like Cu, Co and Ni. Such metals like Zn, Cr, Mo and Sb present in the ores were removed at the acid leaching stage. Application of the membrane processes in the technology of the uranium recovery is very beneficial. The membrane contactors can be applied for recovery of uranium and associated metals from uranium ores as well as for the extraction of uranium from the post-leaching solutions.

Extraction with the use of membrane contactors has many advantages over conventional methods of the extraction of uranium, like no fluid/fluid dispersion, no emulsion formation, no flooding at high flow rates, low solvent holdup, known and constant interfacial area, easy

**Figure 9.** Efficiency of the extraction of uranium in the membrane contactor depending on the initial concentration of

are summarized in **Figure 9**. They show that the kinet-

SO4

with a concentration of 0.1 g/L, while the lowest with a concentration of 0.3 g/L.

Eq. 6 (see above).

uranium in the feed solution.

solution of uranyl nitrate in 5% H<sup>2</sup>

80 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

In the case of low-grade uranium ores it is important to carry out a detailed geo-economic analysis, which will be aimed at reliable estimation of the cost of ore extraction. The costs of further technological processes of uranium recovery from the extracted ore in the initial phase are less important, because they can be very different, taking into account technological progress. While the cost of the mine construction and extraction of rocks on the surface, even in the long term, are not subject of significant changes.

In the case of the so-called Rajsk deposit, detailed geological and geochemical data were available. This allowed the development of a detailed mine model. Moreover, because the structure and form of uranium concentration of Lower Ordovician dictyonema Shales are similar to the Zechstein copper deposits exploited on a large scale on the Fore-Sudetic Monocline, there was a possibility to apply current costs of mining excavations, machinery and equipment as well as human labor.

In developing the model of mine adopted a number of assumptions resulting from the analysis of geological data and technology as well as the assumed concept of mining operation.

The deposit has an area of 16 km<sup>2</sup> , occurs at a depth of 400 to 550 m, the average thickness of the uranium-rich rocks is 2.88 m, and the average uranium content is 69 ppm. Recovery of uranium from the ore was assumed at 65% [12]. Based on these parameters of deposits, it was assumed that the operating time of the potential mine will be 24 years, with an annual production capacity of the mine about 4 million Mg/year, which will allow uranium mining about 270–300 Mg per year, and taking into account the uranium recovery from the ore will allow the uranium production of approximately 200 Mg/year [40]. This quantity is necessary for the operation of 1 GWe nuclear power plant.

Taking into account all the above assumptions, it was calculated that the cost of extraction of the ore needed to production of 1 kg yellow cake (commercial product of uranium) will be about \$ 800. This cost does not include the cost of technological processing of the ore, which will be quite high due to the low uranium content in the ore and its occurrence mainly in the form of organometallic compounds, which significantly reduce the uranium recovery. To assess the economic value of this occurrence of uranium ore, it should be compared to the price of a commercial product on the world market. Historically, the highest price of yellow cake at the turn of 2007/2008 was around \$ 175/kg and was extremely speculative. The price of this product in 2015 was about \$ 80/kg. The developed model of the exploitation of the deposit and based on it the evaluation of the cost of obtaining uranium ore from Lower Ordovician dictyonema shale (Podlasie Depression) justifies the statement of unprofitable extraction of uranium from this rock formation in a very long time perspective [3].
