**4. Novel methods of uranium extraction by using membrane methods**

Membrane processes and effective separation techniques can be applied in uranium technology. The first of proposed applications of membrane techniques was leaching of uranium from the ores with separation of solid and liquid phases in a helical membrane contactor equipped with rotor. [37]. The second one was recovering of uranium from post-leaching solutions by using solvent extraction with application of the membrane contactors with polypropylene porous membranes [38].

#### **4.1. Leaching of uranium using membrane contactor**

**Figure 5.** Set of two columns with strongly basic anion exchanger (DOWEX1 X8) and strongly acidic cation exchanger

(DOWEX50 WX8).

76 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

**Figure 6.** Precipitation of precursors of yellow cake.

As an alternative method of uranium leaching from the ores, the membrane contactor was proposed. The main advantage of using the membrane contactor is a possibility of combining two processes: leaching and separation of the solid phase from post-leaching solutions in one apparatus. Such an approach results in the reduction of total cost of operation with no consequences to the separation efficiency. Another advantage of using the membrane contactor is the possibility of conducting the leaching process at room temperature, which results in less energy consumption.

In the experiments, the membrane module with helical flow generated by rotating part, equipped with a tubular metallic membrane with the pore size of 0.1 μm, was applied. The scheme of the experimental set-up is presented in **Figure 7**. The sample of uranium ore with manganese dioxide, and a solution of 5% sulfuric acid, was placed in the stirred feed tank. Then, the suspension of uranium ore (feed) was transferred with a gear pump to the membrane contactor where the process of leaching was proceeded. The leaching process was conducted in a closed system, which means that permeate and retentate streams were recycled to the feed tank. The process parameters were as follows: velocity of the feed flow (QS ) was changed in the range of 1.1 × 10−5–2.2 × 10−5 m<sup>3</sup> /s and rotation frequency of the rotor (Ω) from 0 to 2500 rpm.

The results of uranium leaching conducted in the membrane contactor were compared with those obtained in experiments carried out using mixer-settler system. Leaching process using mixer-settler system was described in detail elsewhere [12]. The process was conducted in the stirred tank at 80°C for 8 h, using 10% sulfuric acid. The results of the experiments are collected in **Table 5**. As can be observed results of experiments conducted in the membrane contactor were comparable to those obtained by leaching process conducted in the mixer-settler

**Figure 7.** Experimental set-up for uranium leaching using membrane contactor.

system. The conducted experiments also have shown that both considered process parameters: velocity of the feed flow (QS) and a rotation frequency of the rotor (Ω) had an influence on the leaching efficiency of uranium and associated metals. When the velocity of the feed flow is considered, it can be noticed that an increase of this parameter results in an increase in the leaching efficiency of all analyzed metal ions. The increase in the rotation frequency of the rotor led to an increase in the leaching efficiency. However, this relation is clear only for the lower velocity of the feed flow (QS = 1.1× 10–5 m3 /s). In case of higher feed velocity, a visible improvement in leaching efficiency with increasing the rotation frequency was not observed.

#### **4.2. Extraction of uranium using membrane contactor**

The new approach for the liquid–liquid extraction of uranium involves the membrane contactor which enables effective contact of two phases engaged in the process. The two phases are separated by the membrane and species are transferred from one phase to the other by the diffusion mechanism. During the extraction in the membrane contactor, ions are received by the organic phase from the feed (aqueous phase) until thermodynamic equilibrium is reached.

In the experiments, an installation for extraction of uranium equipped with the membrane Liqui-Cel® Extra-Flow contactor produced by CELGARD was used. The scheme of the installation is presented in **Figure 8**.

hydrodynamic conditions in the membrane contactor eliminated the possibility of wetting the membrane and allowed stable working conditions of the apparatus. After a series of preliminary studies, it was found that a proper flow rate for the aqueous and organic phase (feed) is 98.11 and 5.95 L/h, accordingly. The flow of two phases in the system was arranged in co-current mode.

**Figure 8.** The scheme of the installation for extraction of uranium using membrane contactor.

**Leaching in the membrane contactor**

Leaching in the mixer and settler system

QS , [m<sup>3</sup>

**Process parameters Leaching efficiency, %**

80°C, 8 h 73.0

/s ] Ω, [rpm] U La Th V 1.1 × 10−5 0 49.2 21.2 57.9 14.2 1.1 × 10−5 1000 54.6 64.9 57.4 16.9 1.1 × 10−5 1500 53.9 67.0 62.5 18.2 2.2 × 10−5 0 67.5 75.9 75.9 21.8 2.2 × 10−5 1000 68.9 77.9 64.6 25.6 2.2 × 10−5 1500 56.7 65.5 65.5 18.0 2.2 × 10−5 2000 45.7 61.0 59.7 16.7 2.2 × 10−5 2500 63.9 94.1 25.8 25.1

Uranium in Poland: Resources and Recovery from Low-Grade Ores

http://dx.doi.org/10.5772/intechopen.72754

79

Process conditions Uranium leaching efficiency, %

**Table 5.** Leaching efficiency of uranium and accompanied metals obtained by two different methods of leaching.

The module contains microporous hollow fiber membranes made of a polypropylene (PP). The experimental set-up consists also of thermostat, two micropumps, flow meter and temperature sensor. The first stage of the work was a selection of process conditions. Appropriate selection of


**Table 5.** Leaching efficiency of uranium and accompanied metals obtained by two different methods of leaching.

system. The conducted experiments also have shown that both considered process parameters: velocity of the feed flow (QS) and a rotation frequency of the rotor (Ω) had an influence on the leaching efficiency of uranium and associated metals. When the velocity of the feed flow is considered, it can be noticed that an increase of this parameter results in an increase in the leaching efficiency of all analyzed metal ions. The increase in the rotation frequency of the rotor led to an increase in the leaching efficiency. However, this relation is clear only for the

improvement in leaching efficiency with increasing the rotation frequency was not observed.

The new approach for the liquid–liquid extraction of uranium involves the membrane contactor which enables effective contact of two phases engaged in the process. The two phases are separated by the membrane and species are transferred from one phase to the other by the diffusion mechanism. During the extraction in the membrane contactor, ions are received by the organic phase from the feed (aqueous phase) until thermodynamic equilibrium is reached.

In the experiments, an installation for extraction of uranium equipped with the membrane Liqui-Cel® Extra-Flow contactor produced by CELGARD was used. The scheme of the instal-

The module contains microporous hollow fiber membranes made of a polypropylene (PP). The experimental set-up consists also of thermostat, two micropumps, flow meter and temperature sensor. The first stage of the work was a selection of process conditions. Appropriate selection of

/s). In case of higher feed velocity, a visible

lower velocity of the feed flow (QS = 1.1× 10–5 m3

lation is presented in **Figure 8**.

**4.2. Extraction of uranium using membrane contactor**

**Figure 7.** Experimental set-up for uranium leaching using membrane contactor.

78 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

**Figure 8.** The scheme of the installation for extraction of uranium using membrane contactor.

hydrodynamic conditions in the membrane contactor eliminated the possibility of wetting the membrane and allowed stable working conditions of the apparatus. After a series of preliminary studies, it was found that a proper flow rate for the aqueous and organic phase (feed) is 98.11 and 5.95 L/h, accordingly. The flow of two phases in the system was arranged in co-current mode.

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 Eq. 6 (see above).

upscaling, etc. However, some drawbacks also exist, among others concentration polarization and fouling [39]. There is also the risk of wetting the membranes during long-term operation of the module resulting in mixing of the two phases. For the proper operation of membrane contactors, it is important to maintain appropriate hydrodynamic conditions for flow of solu-

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 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 equip-

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.

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

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

, occurs at a depth of 400 to 550 m, the average thickness

Uranium in Poland: Resources and Recovery from Low-Grade Ores

http://dx.doi.org/10.5772/intechopen.72754

81

tions over the membrane surface in order to eliminate such unfavorable phenomena.

**5. Tentative economic analysis**

ment as well as human labor.

The deposit has an area of 16 km<sup>2</sup>

for the operation of 1 GWe nuclear power plant.

uranium from this rock formation in a very long time perspective [3].

in the long term, are not subject of significant changes.

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 solution of uranyl nitrate in 5% H<sup>2</sup> SO4 are summarized in **Figure 9**. They show that the kinetics 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 with a concentration of 0.1 g/L, while the lowest with a concentration of 0.3 g/L.

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 uranium in the feed solution.

upscaling, etc. However, some drawbacks also exist, among others concentration polarization and fouling [39]. There is also the risk of wetting the membranes during long-term operation of the module resulting in mixing of the two phases. For the proper operation of membrane contactors, it is important to maintain appropriate hydrodynamic conditions for flow of solutions over the membrane surface in order to eliminate such unfavorable phenomena.
