**3. Uranium extraction from low-grade and secondary resources: From ore to yellow cake**

Uranium, more common element in the Earth's crust occurring in rocks, soil, rivers and ocean waters, has to be extracted from the raw material in a complex hydrometallurgical process [2]. The effect of ore mineralogy and mineral liberation of solid materials on the leaching behavior of uranium is not well defined. Uranium usually is accompanied by other valuable metals, e.g. V, Mo, Ag, Co and lanthanides that can be recovered in the technological process to improve the economics of the whole venture [9]. The procedure of uranium extraction must be designed to fit specific characteristics of the source material; however, the general procedure is similar for most of the ores and involves many separation steps. The basic stages are crushing and grinding, leaching, solid–liquid separation, ion exchange or solvent extraction and finally precipitation of the product, yellow cake – U3 O8 (**Figure 1**) [10, 11]. In the beginning, the mined ores must be crushed and ground to make the uranium ores more susceptible to uranium extraction by leaching. The optimal particle size in leaching process is 0–0.2 mm. So small particles can be readily suspended to expose the uranium minerals on the action of lixiviant. Such a pre-prepared material could be leached with acidic (sulfuric acid, hydrochloric acid, etc.) or alkaline (carbonate) solutions [6, 12]. Tetravalent uranium has low solubility in both types of solutions. For this reason, the first step in uranium leaching process is oxidation of uranium(IV) to uranium(VI) form. The use of oxidants, e.g. manganese oxide, potassium permanganate, sodium chlorate or hydrogen peroxide, increases the leaching ability of uranium in water. In acidic leaching, uranium oxidation requires the presence of ferric ion, regardless of used oxidizing agents [10]. The oxidizing agent oxidizes ferrous ion to ferric ion that is oxidant for the uranium as shown in Eqs. 1, 2 and 3.

$$\text{LIO}\_{2\text{(o)}} + 2Fe^{3+} \rightleftharpoons \text{LIO}\_{2\text{(aq)}}^{2+} + 2Fe^{2+} \tag{1}$$

not calcinated in the oven. The post-leaching solution is separated from the ores residue by filtration. The concentration of uranium and other elements in post-leaching solution may be determined using ICP-MS analyses [13]. The leaching efficiency is defined as the ratio of the amount of the metal in post-leaching solution to the amount of the metal in the ore sample

\_\_\_ *m*

Many factors influence the leaching process among others, the kind and concentration of leaching medium, size of ore particles, liquid to solid ratio, temperature, pressure and the

The predominant process for recovery of uranium from rocks is the leaching with sulfuric acid [14–16]. The efficiencies of leaching in sulfuric acid environment reach 85–95%. However, this method is not appropriate for the leaching of uranium from carbonate rocks due to high acid consumption [17, 18]. It is worth to note that the alkaline leaching is more selective for uranium in comparison with acid processing. Uranium was selectively leached by the mixture of

where m is the total mass of the metal recovered in post-leaching solution and mo

*<sup>m</sup>*0) <sup>∙</sup> 100% (5)

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is the total

according to the formula (Eq.5):

**Figure 1.** Treatment of uranium ores.

mass of the metal in the ore sample.

type of oxidizing agent.

*E* = (

$$2Fe^{2+} + MnO\_2 + 4H^+ \rightleftharpoons 2Fe^{3+} + Mn^{2+} + 2H\_2O \tag{2}$$

$$\text{LUO}\_{2(\text{q})} + 2Fe^{3+} \rightleftharpoons \text{LUO}\_{2(\text{q})}^{2+} + 2Fe^{2+} \tag{3}$$

In alkaline leaching, the oxidizing agent oxidizes directly uranium as shown in Eq. 4.

$$\mathrm{LIO}\_{20\text{s}} + \mathrm{H}\_{2}\mathrm{O}\_{2} + \mathrm{3CO}\_{3}^{\text{-}} \rightleftharpoons \mathrm{LIO}\_{2}\mathrm{(CO}\_{3}\mathrm{)}\_{3\text{aq}}^{\text{-}} + \mathrm{2OH}^{\cdot} \tag{4}$$

If uranium is closely associated with the organic compounds, the efficiency of leaching is low. The ores that contain the organic matter, e.g. dictyonema shales, have to be pre-treated by calcination. The samples of sandstones that contained less organic matter (below 0.1%) are

**Figure 1.** Treatment of uranium ores.

(geometric mean): Th 6 [mg/kg], Cu 24 [mg/kg], La 31 [mg/kg] and V 195 [mg/kg]. Uranium related to Triassic sandstones showed the strongest correlation with lead (0.92), yttrium (0.92),

Uranium, more common element in the Earth's crust occurring in rocks, soil, rivers and ocean waters, has to be extracted from the raw material in a complex hydrometallurgical process [2]. The effect of ore mineralogy and mineral liberation of solid materials on the leaching behavior of uranium is not well defined. Uranium usually is accompanied by other valuable metals, e.g. V, Mo, Ag, Co and lanthanides that can be recovered in the technological process to improve the economics of the whole venture [9]. The procedure of uranium extraction must be designed to fit specific characteristics of the source material; however, the general procedure is similar for most of the ores and involves many separation steps. The basic stages are crushing and grinding, leaching, solid–liquid separation, ion exchange or solvent extraction

ning, the mined ores must be crushed and ground to make the uranium ores more susceptible to uranium extraction by leaching. The optimal particle size in leaching process is 0–0.2 mm. So small particles can be readily suspended to expose the uranium minerals on the action of lixiviant. Such a pre-prepared material could be leached with acidic (sulfuric acid, hydrochloric acid, etc.) or alkaline (carbonate) solutions [6, 12]. Tetravalent uranium has low solubility in both types of solutions. For this reason, the first step in uranium leaching process is oxidation of uranium(IV) to uranium(VI) form. The use of oxidants, e.g. manganese oxide, potassium permanganate, sodium chlorate or hydrogen peroxide, increases the leaching ability of uranium in water. In acidic leaching, uranium oxidation requires the presence of ferric ion, regardless of used oxidizing agents [10]. The oxidizing agent oxidizes ferrous ion to ferric ion

O8

(**Figure 1**) [10, 11]. In the begin-

2+ + 2*Fe*2+ (1)

2+ + 2*Fe*2+ (3)

4− + 2*OH*<sup>−</sup> (4)

*O* (2)

**3. Uranium extraction from low-grade and secondary resources:** 

silver (0.76), copper (0.75), antimony (0.7) and cobalt (0.44) [8].

68 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

and finally precipitation of the product, yellow cake – U3

that is oxidant for the uranium as shown in Eqs. 1, 2 and 3.

2*Fe*2+ + *MnO*<sup>2</sup> + 4*H*<sup>+</sup> ⇄2*Fe*<sup>3</sup><sup>+</sup> + *Mn*2+ + 2*H*<sup>2</sup>

In alkaline leaching, the oxidizing agent oxidizes directly uranium as shown in Eq. 4.

<sup>2</sup><sup>−</sup> ⇄*UO*<sup>2</sup> (*CO*3)3(*aq*)

If uranium is closely associated with the organic compounds, the efficiency of leaching is low. The ores that contain the organic matter, e.g. dictyonema shales, have to be pre-treated by calcination. The samples of sandstones that contained less organic matter (below 0.1%) are

*O*<sup>2</sup> + 3*CO*<sup>3</sup>

*UO*2(*s*) + 2*Fe*<sup>3</sup><sup>+</sup> ⇄*UO*2(*aq*)

*UO*2(*s*) + 2*Fe*<sup>3</sup><sup>+</sup> ⇄ *UO*2(*aq*)

*UO*2(*s*) + *H*<sup>2</sup>

**From ore to yellow cake**

not calcinated in the oven. The post-leaching solution is separated from the ores residue by filtration. The concentration of uranium and other elements in post-leaching solution may be determined using ICP-MS analyses [13]. The leaching efficiency is defined as the ratio of the amount of the metal in post-leaching solution to the amount of the metal in the ore sample according to the formula (Eq.5):

$$E = \left(\frac{m}{m\_o}\right) \cdot 100\% \tag{5}$$

where m is the total mass of the metal recovered in post-leaching solution and mo is the total mass of the metal in the ore sample.

Many factors influence the leaching process among others, the kind and concentration of leaching medium, size of ore particles, liquid to solid ratio, temperature, pressure and the type of oxidizing agent.

The predominant process for recovery of uranium from rocks is the leaching with sulfuric acid [14–16]. The efficiencies of leaching in sulfuric acid environment reach 85–95%. However, this method is not appropriate for the leaching of uranium from carbonate rocks due to high acid consumption [17, 18]. It is worth to note that the alkaline leaching is more selective for uranium in comparison with acid processing. Uranium was selectively leached by the mixture of sodium carbonate, sodium hydroxide and hydrogen peroxide from hydrous oxide Egyptian monazite [19] and from Polish ores [6, 12]. The leaching test using deionized water as a leaching solution (pH = 5.7) was also performed on Jordania carbonate rocks [20]. The leaching efficiency was 9% using deionized water as a leaching solution.

#### **3.1. The leaching of Polish domestic ores**

In Poland, as it was said earlier, there are occurred mainly two types of uranium ores: dictyonema shales and sandstones. The content of metals in post-leaching solution is very depending on the initial composition of the ore and the used procedure of extraction. The effect of ore mineralogy and mineral liberation on the leaching behavior of uranium and other metals is not well defined. For this reason, the prediction of results of the treatment of ores is not possible and it was necessary to make an experimental work. It showed that sandstones were more readily leachable in comparison with the dictyonema shales. In the leaching by acid, all metals accompanying uranium in the ores were also present in acid post-leaching solutions [6]. The best results of acid leaching of dictyonema shales were obtained in the leaching with 10% H<sup>2</sup> SO4 during 8 hours at 80°C. The efficiencies of uranium leaching from different ore materials were in the range of 64–81%. Other metals were leached with the following efficiencies: Th 67–80%, V 25–52%, Mo 33–78%, Cu 28–52% and La 31–66%. The leaching of sandstones with 10% sulfuric acid was carried out at 60°C. Uranium was leached with efficiency 71–100%; efficiencies of leaching other metals were: Th: 13–62%, Cu: 10–67%, Co: 8–57%, La: 24–60%, V: 28–58%, Yb: 26–67% and Fe: 11–47%.

In the case of alkaline leaching, only three or two metallic components of the ores were detected in post-leaching solution: U, Mo and V (dictyonema shales) or U and small amounts of V (sandstones). U from calcinated samples of dictyonema shales was extracted with 42% efficiency, molybdenum with 24% and vanadium with ca. 8% efficiency. In the case of sandstones, 57–92% of uranium and 2–22% of vanadium were leached with a mixture of sodium carbonate and bicarbonate. The comparison of uranium leaching efficiencies depending on lixiviant and leaching method is presented in **Figures 2** and **3**.

#### **3.2. Recovery of uranium from the post-leaching solution**

The above-described process, the solid–liquid extraction, is a very important stage in the technology of uranium production from the uranium ores. The separation of solid residue from liquid leaves the post-leaching solution that is a mixture of different metal ions. Uranium and other metals can be recovered from post-leaching solutions by solvent extraction [21–24] followed by stripping to aqueous phase [25, 26] or by ion exchange [27, 28].

#### *3.2.1. Recovery of uranium by solvent-solvent extraction*

Solvent extraction is a comprehensive technique for separation of ionic solutes. The uranyl ion (UO2 2+) forms complexes with various extracting agents, among them tributylphosphate (TBP), di(2-ethylhexyl)phosphoric acid (DEHPA), triethylamine (TEA), tri-n-octylamine (TnOA), trioctylphosphine oxide (TOPO) and calixarenes, e.g. hexasodium 37,38,39,40,41,42-hexa(carbo xymethoxy)calix[6]arene-7-5,11,17,23,29,35-hexasulfonate (**Figure 4**, calix[6]arene: R1 = SO3 Na, R<sup>2</sup> = CH<sup>2</sup>

(**A**) 10% H<sup>2</sup>

Na2 CO<sup>3</sup> SO4

lixiviant: 10% H<sup>2</sup>

lixiviant: 5%Na<sup>2</sup>

SO4

CO<sup>3</sup>

/5%NaHCO3

cure": 2 g of ground uranium ores were treated with 95% H<sup>2</sup>

of 10% NaCl at 840°C during 3 h than leaching with 5% H<sup>2</sup>

with the appropriate groups R1

, oxidizing agent: 30% H<sup>2</sup>

, oxidizing agent: MnO<sup>2</sup>

O2

COOH). Calixarenes are a well-known family of macrocyclic molecules with broad

/5% NaHCO3

. The calixarenes are applied for UO2

O2

, oxidizing agent: KMnO4

2+ complexation

, 60°C, 1 h. (**C**). 8% NaOH/18%

, 60°C, 1 h.

, 80°C, 8 h. (B) Calcinated sample,

for 18 days, 25°C, 8 h. (D) Sintered sample with addition

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71

, 80°C, 8 h. (C) "acid-

field of potential applications in chemical, analytical and engineering materials area [29]. The reason of growing interest in these macrocycles is not only their easy synthesis through wellestablished and simple methods but also the possibility of shaping through functionalization

**Figure 3.** Efficiency of leaching uranium from sandstones by various lixiviants, liquid/solid ratio of 8:1 (vol./wt. basis).

CO<sup>3</sup>

, 60°C, 1 h. (**B**) 10% HCl, oxidizing agent: 30% H<sup>2</sup>

**Figure 2.** Efficiency of leaching uranium from dictyonema Shales using different methods. (A) Calcinated sample,

SO4

SO4 , MnO2

, liquid/solid ratio of 8:1 (vol./wt. basis), oxidizing agent: MnO<sup>2</sup>

, 80°C, 8 h.

, liquid/solid ratio of 8:1 (vol./wt. basis), oxidizing agent: MnO<sup>2</sup>

and R<sup>2</sup>

, 60°C, 1 h. (**D**) 5% Na<sup>2</sup>

with high efficient results in terms of stability and selectivity [30].

sodium carbonate, sodium hydroxide and hydrogen peroxide from hydrous oxide Egyptian monazite [19] and from Polish ores [6, 12]. The leaching test using deionized water as a leaching solution (pH = 5.7) was also performed on Jordania carbonate rocks [20]. The leaching

In Poland, as it was said earlier, there are occurred mainly two types of uranium ores: dictyonema shales and sandstones. The content of metals in post-leaching solution is very depending on the initial composition of the ore and the used procedure of extraction. The effect of ore mineralogy and mineral liberation on the leaching behavior of uranium and other metals is not well defined. For this reason, the prediction of results of the treatment of ores is not possible and it was necessary to make an experimental work. It showed that sandstones were more readily leachable in comparison with the dictyonema shales. In the leaching by acid, all metals accompanying uranium in the ores were also present in acid post-leaching solutions [6]. The best results of acid leaching of dictyonema shales were obtained in the leaching with

materials were in the range of 64–81%. Other metals were leached with the following efficiencies: Th 67–80%, V 25–52%, Mo 33–78%, Cu 28–52% and La 31–66%. The leaching of sandstones with 10% sulfuric acid was carried out at 60°C. Uranium was leached with efficiency 71–100%; efficiencies of leaching other metals were: Th: 13–62%, Cu: 10–67%, Co: 8–57%, La:

In the case of alkaline leaching, only three or two metallic components of the ores were detected in post-leaching solution: U, Mo and V (dictyonema shales) or U and small amounts of V (sandstones). U from calcinated samples of dictyonema shales was extracted with 42% efficiency, molybdenum with 24% and vanadium with ca. 8% efficiency. In the case of sandstones, 57–92% of uranium and 2–22% of vanadium were leached with a mixture of sodium carbonate and bicarbonate. The comparison of uranium leaching efficiencies depending on

The above-described process, the solid–liquid extraction, is a very important stage in the technology of uranium production from the uranium ores. The separation of solid residue from liquid leaves the post-leaching solution that is a mixture of different metal ions. Uranium and other metals can be recovered from post-leaching solutions by solvent extraction [21–24] fol-

Solvent extraction is a comprehensive technique for separation of ionic solutes. The uranyl ion

2+) forms complexes with various extracting agents, among them tributylphosphate (TBP), di(2-ethylhexyl)phosphoric acid (DEHPA), triethylamine (TEA), tri-n-octylamine (TnOA), trioctylphosphine oxide (TOPO) and calixarenes, e.g. hexasodium 37,38,39,40,41,42-hexa(carbo xymethoxy)calix[6]arene-7-5,11,17,23,29,35-hexasulfonate (**Figure 4**, calix[6]arene: R1 = SO3

Na,

during 8 hours at 80°C. The efficiencies of uranium leaching from different ore

efficiency was 9% using deionized water as a leaching solution.

70 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

**3.1. The leaching of Polish domestic ores**

24–60%, V: 28–58%, Yb: 26–67% and Fe: 11–47%.

lixiviant and leaching method is presented in **Figures 2** and **3**.

lowed by stripping to aqueous phase [25, 26] or by ion exchange [27, 28].

**3.2. Recovery of uranium from the post-leaching solution**

*3.2.1. Recovery of uranium by solvent-solvent extraction*

10% H<sup>2</sup>

(UO2

SO4

**Figure 2.** Efficiency of leaching uranium from dictyonema Shales using different methods. (A) Calcinated sample, lixiviant: 10% H<sup>2</sup> SO4 , liquid/solid ratio of 8:1 (vol./wt. basis), oxidizing agent: MnO<sup>2</sup> , 80°C, 8 h. (B) Calcinated sample, lixiviant: 5%Na<sup>2</sup> CO<sup>3</sup> /5%NaHCO3 , liquid/solid ratio of 8:1 (vol./wt. basis), oxidizing agent: MnO<sup>2</sup> , 80°C, 8 h. (C) "acidcure": 2 g of ground uranium ores were treated with 95% H<sup>2</sup> SO4 for 18 days, 25°C, 8 h. (D) Sintered sample with addition of 10% NaCl at 840°C during 3 h than leaching with 5% H<sup>2</sup> SO4 , MnO2 , 80°C, 8 h.

**Figure 3.** Efficiency of leaching uranium from sandstones by various lixiviants, liquid/solid ratio of 8:1 (vol./wt. basis). (**A**) 10% H<sup>2</sup> SO4 , oxidizing agent: MnO<sup>2</sup> , 60°C, 1 h. (**B**) 10% HCl, oxidizing agent: 30% H<sup>2</sup> O2 , 60°C, 1 h. (**C**). 8% NaOH/18% Na2 CO<sup>3</sup> , oxidizing agent: 30% H<sup>2</sup> O2 , 60°C, 1 h. (**D**) 5% Na<sup>2</sup> CO<sup>3</sup> /5% NaHCO3 , oxidizing agent: KMnO4 , 60°C, 1 h.

R<sup>2</sup> = CH<sup>2</sup> COOH). Calixarenes are a well-known family of macrocyclic molecules with broad field of potential applications in chemical, analytical and engineering materials area [29]. The reason of growing interest in these macrocycles is not only their easy synthesis through wellestablished and simple methods but also the possibility of shaping through functionalization with the appropriate groups R1 and R<sup>2</sup> . The calixarenes are applied for UO2 2+ complexation with high efficient results in terms of stability and selectivity [30].

TBP, neutral organophosphorus extractant, is probably the most known chelating agent. It was used on the commercial scale for the recovery of uranium (VI) not only from its ores but also from the spent nuclear fuel [31]. The selectivity of TBP is not high, similarly as its radiolytic stability. For this reason, other organophosphorus extractants, among them DEHPA, are applied in the technology of uranium production. DEHPA saponifies in stripping phase and wherefore the third phase is formed between the organic solvent and the aqueous phase. It can be prevented with a modifying agent, a suitable non-ionic surface active substance. The modifying agent like long-chain alcohols, alkyl phosphonates, alkyl phosphates and alkyl phosphine oxides have also a beneficial synergistic effect on the distribution ratio of uranium. One of such agents is TBP. The very good results were obtained in the extraction of uranium from the solutions resulting from leaching Polish uranium ores by using the mixture of DEHPA and TBP (0.2 M: 0.2 M) [32]. Before the solvent extraction, the post-leaching solutions were acidified to pH 1. This especially applied to the liquors from carbonate leaching. However, sometimes it was also necessary to adjust appropriate pH of the solution from acidic leaching. During the extraction process, uranium passes from the aqueous solution to the organic solution by using an extracting agent. The metal ions that have been extracted by the organic phase should be stripped by an aqueous phase in the stripping (re-extraction) process. A number of reagents are known in the literature to strip uranium from loaded extracting agents such as carbonates, acids, nitrates, chlorides, sulfates and hydroxides. In this study, the best results were obtained when stripping experiments were carried out with sodium carbonate or ammonium carbonate solutions. The extraction efficiency (%E) was calculated by the Formula (6):

$$\%E = \frac{100\,\% \cdot D\_{\varepsilon}}{D\_{\varepsilon} + \frac{V\_{\omega}}{V\_{\text{eq}}}} \tag{6}$$

where Dc is the distribution ratio, defined as the ratio of concentration of metal in organic phase over its concentration in aqueous phase, Vaq is the aqueous phase volume, and Vorg is the organic phase volume [33].

The stripping percentage, %S was determined by the relationship (7):

$$\% \mathcal{S} = \frac{100 \,\% \cdot D\_s}{D\_s + \frac{V\_{\ast q}}{V\_{\ast q}}} \tag{7}$$

**Figure 4.** The extracting agents using for the separation of uranium from the solution.

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where Ds is the distribution ratio of metal in stripping phase over its concentration in organic phase [33].

%R percent of the recovery of uranium in extraction/stripping process was determined by the relationship (8):

## 1

relationship (8):

$$\%R = \frac{\text{metal in the stripping phase}}{\text{metal in post-}leaching liquid} \cdot 100\% \tag{8}$$

The obtained results were satisfying; the overall recovery (%R), extraction efficiency (%E) and stripping (%S) reached even 98%. Apart from uranium, the other elements were also analyzed. The results of extraction/stripping processes of alkaline and acidic post-leaching solutions are reported in **Tables 3** and **4**, respectively. The purification of uranium from accompanying metals from acid leaching solution was only in part. The efficiency of recovery of uranium Uranium in Poland: Resources and Recovery from Low-Grade Ores http://dx.doi.org/10.5772/intechopen.72754 73

TBP, neutral organophosphorus extractant, is probably the most known chelating agent. It was used on the commercial scale for the recovery of uranium (VI) not only from its ores but also from the spent nuclear fuel [31]. The selectivity of TBP is not high, similarly as its radiolytic stability. For this reason, other organophosphorus extractants, among them DEHPA, are applied in the technology of uranium production. DEHPA saponifies in stripping phase and wherefore the third phase is formed between the organic solvent and the aqueous phase. It can be prevented with a modifying agent, a suitable non-ionic surface active substance. The modifying agent like long-chain alcohols, alkyl phosphonates, alkyl phosphates and alkyl phosphine oxides have also a beneficial synergistic effect on the distribution ratio of uranium. One of such agents is TBP. The very good results were obtained in the extraction of uranium from the solutions resulting from leaching Polish uranium ores by using the mixture of DEHPA and TBP (0.2 M: 0.2 M) [32]. Before the solvent extraction, the post-leaching solutions were acidified to pH 1. This especially applied to the liquors from carbonate leaching. However, sometimes it was also necessary to adjust appropriate pH of the solution from acidic leaching. During the extraction process, uranium passes from the aqueous solution to the organic solution by using an extracting agent. The metal ions that have been extracted by the organic phase should be stripped by an aqueous phase in the stripping (re-extraction) process. A number of reagents are known in the literature to strip uranium from loaded extracting agents such as carbonates, acids, nitrates, chlorides, sulfates and hydroxides. In this study, the best results were obtained when stripping experiments were carried out with sodium carbonate or ammonium carbonate solutions. The extraction efficiency (%E) was calculated by the Formula (6):

> 100 % ∙*Dc Dc* + *V* \_\_\_*aq Vorg*

> 100 % ∙*Ds Ds* + *V* \_\_\_*aq Vorg*

where Ds is the distribution ratio of metal in stripping phase over its concentration in organic

%R percent of the recovery of uranium in extraction/stripping process was determined by the

%*<sup>R</sup>* <sup>=</sup>*metal in the stripping phase* \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ *metal in post <sup>−</sup> leaching liquor*<sup>∙</sup> 100% (8)

The obtained results were satisfying; the overall recovery (%R), extraction efficiency (%E) and stripping (%S) reached even 98%. Apart from uranium, the other elements were also analyzed. The results of extraction/stripping processes of alkaline and acidic post-leaching solutions are reported in **Tables 3** and **4**, respectively. The purification of uranium from accompanying metals from acid leaching solution was only in part. The efficiency of recovery of uranium

where Dc is the distribution ratio, defined as the ratio of concentration of metal in organic phase over its concentration in aqueous phase, Vaq is the aqueous phase volume, and Vorg is the

(6)

(7)

%*E* = \_\_\_\_\_\_\_\_

72 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

%*S* = \_\_\_\_\_\_\_\_

The stripping percentage, %S was determined by the relationship (7):

organic phase volume [33].

phase [33].

relationship (8):

**Figure 4.** The extracting agents using for the separation of uranium from the solution.


a Ca —concentrations of metals in post leaching solution,

b Cb —concentrations of metals in organic phase from extraction process,

c Cc ,Cd—concentrations of metals in stripping phase.

**Table 3.** Extraction and stripping efficiencies of metals from acidic post-leaching solution, [DEHP]:[TBP] 0.2 M:0.2 M, temperature: 22°C, pH 1, phase ratio (*organic/aqueous*) 1:1.

ores, especially the lanthanides. They can be separated from the effluent from anion exchange column by using the second column filled with strongly acidic cation exchanger (DOWEX50 WX8) (**Figure 5**) [5]. The efficiencies of recovery of metals were almost quantitative: 93% for uranium and 99% for lanthanides were recovered. The other metals accompanying uranium

**Table 4.** Extraction and stripping efficiencies of metals from alkaline post-leaching solution, [DEHP]:[TBP] 0.2 M:0.2 M,

**0.5 M (NH4**

U 20 ± 1 20 ± 1 100 19.8 ± 1 99 99 19.8 ± 1 99 99 V 0.63 ± 0.06 <0.01 — — — — — — — Mo 0.72 ± 0.07 0 0 — — — — — —

**)2 CO3**

The solvent extraction and ion exchange processes were a part of the research on the possibility of uranium extraction from domestic resources in Poland. The next step was the precipi-

the form of ammonium or sodium diuranate, uranium peroxide and uranium trioxide by the addition of neutralizers such as sodium hydroxide, magnesium oxide or aqueous ammonia (**Figure 6**) [34, 35]. In all cases, the final product is yellow uranium salt, commonly known as

in 2 M H<sup>2</sup>

10). As was proved, the influence of temperature and concentration of uranyl ions in the solution was significant. The precipitation of ammonium diuranate was carried out in the temperature range of 40–90°C, at pH 9–11. The concentration of uranium was between 0.3 and 0.7 mg/L. The obtained yield was really high 83–98% [36]. It is significant that this salt was precipitated from solutions containing a low concentration of uranium (0.3–0.5 mg/mL). The precipitation step

> 2 *U*2

This procedure was used for obtaining "yellow cake" from the effluent from anion exchanger,

Uranium peroxide hydrates can be synthesized by dropping hydrogen peroxide to the acidic solution of uranyl ions, as it is shown in Eq. 8. Uranium peroxide can be precipitated from

*O*7↓ + 4*NH*<sup>4</sup>

SO4

. From acidic solutions, uranium is precipitated in

) 2 U2 O7

O8

<sup>+</sup> + 3*H*<sup>2</sup>

and UO<sup>4</sup>

**Stripping phase**

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**CO3**

75

**0.5 M Na2**

[ppm]c %S %R Cd [ppm]c %S %R

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

) were performed (respectively, Eqs. 9 and

was formed.

*O* (9)

⋅2H<sup>2</sup>

O from

in their ores were not separated and were present in the effluent from columns.

O8

The studies of precipitation of uranium as two different salts: (NH4

was followed by calcination step at temperature 750°C, in which U3

Dowex 1, that was described above. The yield was ca. 92% [28].

2+ + 6*NH*<sup>3</sup>(*aq*) → (*NH*4)

(NO<sup>3</sup> ) 2

**3.3. Precipitation of uranium yellow cake**

**Post-leaching solution Extracting phase Stripping phase**

—concentrations of metals in organic phase from extraction process,

[ppm]b %E Cc

[ppm]a Cb

—concentrations of metals in post leaching solution,

, Cd—concentrations of metals in stripping phase.

temperature: 22°C, pH 1, phase ratio (*organic/aqueous*) 1:1.

tation of precursors of yellow cake - U3

the model uranium solution (UO2

*UO*<sup>2</sup>

yellow cake.

Metal Ca

<sup>a</sup> Ca

bCb

<sup>c</sup> Cc

was high, but the final solution was contaminated by iron and small amounts of other metals: vanadium and ytterbium. On the other hand, the purification of uranium from alkaline postleaching solution was almost complete (**Table 4**). The extraction, followed by stripping step gave pure uranium solution. It is worthy to mention that the single, one-stage extraction of uranium from acidic post-leaching liquors is not sufficient to separate pure uranium. Further purification and separation of uranium from accompanying metals could be performed by ion exchange chromatography or a sequence of ion exchange/extraction treatments.

#### *3.2.2. Recovery of uranium by ion exchange*

The ion exchange is a very efficient method that can be used for separation of uranium from other metals. The separation of uranium from acid pregnant leach solution obtained from Polish uranium ores, using commercially available, strongly basic anion exchanger, Dowex 1 was investigated [28]. The feed solution was introduced into the column. The complexes of uranium, vanadium and molybdenum were adsorbed on Dowex 1 and then they were eluted with 0.15 M H<sup>2</sup> SO4 , followed by 1 M sulfuric acid. The first eluent removed the vanadium complex from the column. The second eluent allowed to obtain fraction of uranium complexes. The molybdenum complexes are very strongly fixed in anion exchange resin. They can be eluted only in part by 1 M H<sup>2</sup> SO4 . Wherefore the uranium fraction can be contamined with molybdenum. It is worth to note that the purification of the acid pregnant solution from leaching of sandstones that does not contain the molybdenum gave a pure uranium fraction. In this work, there was also considered the recovery of other valuable metals present in uranium


<sup>a</sup> Ca —concentrations of metals in post leaching solution,

bCb —concentrations of metals in organic phase from extraction process,

<sup>c</sup> Cc , Cd—concentrations of metals in stripping phase.

**Table 4.** Extraction and stripping efficiencies of metals from alkaline post-leaching solution, [DEHP]:[TBP] 0.2 M:0.2 M, temperature: 22°C, pH 1, phase ratio (*organic/aqueous*) 1:1.

ores, especially the lanthanides. They can be separated from the effluent from anion exchange column by using the second column filled with strongly acidic cation exchanger (DOWEX50 WX8) (**Figure 5**) [5]. The efficiencies of recovery of metals were almost quantitative: 93% for uranium and 99% for lanthanides were recovered. The other metals accompanying uranium in their ores were not separated and were present in the effluent from columns.

#### **3.3. Precipitation of uranium yellow cake**

was high, but the final solution was contaminated by iron and small amounts of other metals: vanadium and ytterbium. On the other hand, the purification of uranium from alkaline postleaching solution was almost complete (**Table 4**). The extraction, followed by stripping step gave pure uranium solution. It is worthy to mention that the single, one-stage extraction of uranium from acidic post-leaching liquors is not sufficient to separate pure uranium. Further purification and separation of uranium from accompanying metals could be performed by

**Table 3.** Extraction and stripping efficiencies of metals from acidic post-leaching solution, [DEHP]:[TBP] 0.2 M:0.2 M,

**0.5 M (NH4**

U 25 ± 1.25 25 ± 1.25 100 24.7 ± 1.2 99 99 24.7 ± 1.2 99 99 Th <0.1 — — — — — — — — Cu 14 ± 1.4 0 0 — — — — — — Co 0.5 ± 0.05 0 0 — — — — — — Mn 27 ± 2.7 0 0 — — — — — — La 0.2 ± 0.02 <0.001 <0.5 — — — — — — V 3 ± 0.3 0.75 ± 0.08 25 0.23 ± 0.02 31 8 0.23 ± 0.02 31 8 Mo 0.8 ± 0.08 0 0 — — — — — — Yb 0.2 ± 0.03 0.2 ± 0.03 100 0.19 ± 0.03 99 99 0.17 ± 0.03 85 85 Fe 230 ± 23 74 ± 7.4 32 21 ± 2.1 28 9 24 ± 2.4 32 10

**)2 CO3** **Stripping phase**

**CO3**

**0.5 M Na2**

[ppm]c %S %R Cd [ppm]c %S %R

The ion exchange is a very efficient method that can be used for separation of uranium from other metals. The separation of uranium from acid pregnant leach solution obtained from Polish uranium ores, using commercially available, strongly basic anion exchanger, Dowex 1 was investigated [28]. The feed solution was introduced into the column. The complexes of uranium, vanadium and molybdenum were adsorbed on Dowex 1 and then they were eluted

complex from the column. The second eluent allowed to obtain fraction of uranium complexes. The molybdenum complexes are very strongly fixed in anion exchange resin. They can

molybdenum. It is worth to note that the purification of the acid pregnant solution from leaching of sandstones that does not contain the molybdenum gave a pure uranium fraction. In this work, there was also considered the recovery of other valuable metals present in uranium

SO4

, followed by 1 M sulfuric acid. The first eluent removed the vanadium

. Wherefore the uranium fraction can be contamined with

ion exchange chromatography or a sequence of ion exchange/extraction treatments.

*3.2.2. Recovery of uranium by ion exchange*

—concentrations of metals in post leaching solution,

,Cd—concentrations of metals in stripping phase.

temperature: 22°C, pH 1, phase ratio (*organic/aqueous*) 1:1.

—concentrations of metals in organic phase from extraction process,

**Post-leaching solution Extracting phase Stripping phase**

74 Uranium - Safety, Resources, Separation and Thermodynamic Calculation

[ppm]b %E Cc

[ppm]a Cb

Metal Ca

a Ca

b Cb

c Cc

SO4

be eluted only in part by 1 M H<sup>2</sup>

with 0.15 M H<sup>2</sup>

The solvent extraction and ion exchange processes were a part of the research on the possibility of uranium extraction from domestic resources in Poland. The next step was the precipitation of precursors of yellow cake - U3 O8 . From acidic solutions, uranium is precipitated in the form of ammonium or sodium diuranate, uranium peroxide and uranium trioxide by the addition of neutralizers such as sodium hydroxide, magnesium oxide or aqueous ammonia (**Figure 6**) [34, 35]. In all cases, the final product is yellow uranium salt, commonly known as yellow cake.

The studies of precipitation of uranium as two different salts: (NH4 ) 2 U2 O7 and UO<sup>4</sup> ⋅2H<sup>2</sup> O from the model uranium solution (UO2 (NO<sup>3</sup> ) 2 in 2 M H<sup>2</sup> SO4 ) were performed (respectively, Eqs. 9 and 10). As was proved, the influence of temperature and concentration of uranyl ions in the solution was significant. The precipitation of ammonium diuranate was carried out in the temperature range of 40–90°C, at pH 9–11. The concentration of uranium was between 0.3 and 0.7 mg/L. The obtained yield was really high 83–98% [36]. It is significant that this salt was precipitated from solutions containing a low concentration of uranium (0.3–0.5 mg/mL). The precipitation step was followed by calcination step at temperature 750°C, in which U3 O8 was formed.

$$\mathrm{LIO}\_{2}^{2+} + 6\mathrm{NH}\_{3\mathrm{(aq)}} \rightarrow \left\{\mathrm{NH}\_{4}\right\}\_{2}\mathrm{L}\_{2}\mathrm{O}\_{7} \big| + 4\mathrm{NH}\_{4}^{\*} + 3\mathrm{H}\_{2}\mathrm{O} \tag{9}$$

This procedure was used for obtaining "yellow cake" from the effluent from anion exchanger, Dowex 1, that was described above. The yield was ca. 92% [28].

Uranium peroxide hydrates can be synthesized by dropping hydrogen peroxide to the acidic solution of uranyl ions, as it is shown in Eq. 8. Uranium peroxide can be precipitated from

eluted solution with concentration of uranium 0.5–0.9 g/L with high yield, almost quantitatively. It was found that optimal pH of the solution was between 9 and 11. The yield of the process provided at temperature 60°C was rather low, 17% for the solution with 0.5 g/L of uranium and 63% for the solution with 0.9 g/L of uranium. Increasing the temperature up to

*O* → *UO*<sup>4</sup> ∙ 2 *H*<sup>2</sup>

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 poly-

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

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

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

/s and rotation frequency of the rotor (Ω) from 0 to 2500 rpm.

tank. The process parameters were as follows: velocity of the feed flow (QS

*O*↓ + 2 *H*<sup>3</sup>

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

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

77

*O*<sup>+</sup> (10)

) was changed in the

90°C definitely improved efficiency, 93 and 99%, respectively.

2+ + *H*<sup>2</sup>

*O*<sup>2</sup> + 4 *H*<sup>2</sup>

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

*UO*<sup>2</sup>

propylene porous membranes [38].

energy consumption.

range of 1.1 × 10−5–2.2 × 10−5 m<sup>3</sup>

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

**methods**

**Figure 5.** Set of two columns with strongly basic anion exchanger (DOWEX1 X8) and strongly acidic cation exchanger (DOWEX50 WX8).

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

eluted solution with concentration of uranium 0.5–0.9 g/L with high yield, almost quantitatively. It was found that optimal pH of the solution was between 9 and 11. The yield of the process provided at temperature 60°C was rather low, 17% for the solution with 0.5 g/L of uranium and 63% for the solution with 0.9 g/L of uranium. Increasing the temperature up to 90°C definitely improved efficiency, 93 and 99%, respectively.

$$\rm{UIO\_2^{2+} + H\_2O\_2 + 4 \, H\_2O \to \rm{UIO\_4 \cdot 2 \, H\_2O \downarrow + 2 \, H\_3O^\*}}$$
