Extraction and Separation of Some Naturally Occurring Radionuclides ...

Arab Journal of Nuclear Science and Applications, 47(3), (48-60) 2014

Extraction and Separation of Some Naturally Occurring Radionuclides from Rare Earth Elements by Different Amines E. H. Borai*a, A .M. Shahr El-Dina, E .A. EL-Sofanya, A. A. Sakra, G. O. El-Sayedb a) Hot Lab. Center, Atomic Energy Authority, Cairo 13759, Egypt b) Chemistry Department, Faculty of Science, Benha University, Benha, Egypt

Received: 10/10/2013

Accepted: 26/11/2013 ABSTRACT

Uranium (U), thorium (Th) and rare earth elements (REEs) are important elements not only in environmental concern but also in industrial applications. In this endeavor, new extraction and separation procedure for U and Th from REEs has been developed. The parameters affecting U and Th extraction using different amines such as contact time, pH of the aqueous phase and metal ion concentration as well as amines concentration in the organic phase were investigated. Comparison between the results of using three different amines (primary, secondary and tertiary amines) as organic extractants has been reported. It was observed that the primary amine (Octylamine) is more effective for extraction of U, Th and REEs rather than the other two amines. On the other hand, the secondary and tertiary amines are more selective for extraction of U and Th rather than REEs. In a single element system, the extraction of U and Th are preferably with Octylamine. The results indicated the possibility of extracting 90% of U by 0.1 mol/l Octylamine at pH 4 for 2 hrs at 25 oC, while Th extraction efficiency reached faster to 97% by 0.005 mol/l Octylamine after 15 min., at pH 3 and 25 oC. In multielements system, the separation of U and Th from REEs was mainly carried out by tertiary amine. It was found that, 80% of Th could be efficiently separated by 0.01M N,N-dimethyl aniline at pH 4 for 15 min., while 66% of U was then separated by 0.1M N,Ndimethylaniline at pH 7 for 30 min., leaving REEs in the aqueous solution.

Keywords: Solvent extraction, REEs, Uranium, Thorium, Amines. INTRODUCTION The major sources for rare-earths (REs) are the classical ores such as monazite, xenotime, and bastnasite. Monazite is a rare earth phosphate containing thorium and uranium as associated metals (13) . Egyptian monazite (purity 97%) has been analyzed and was found to assay 5.9% ThO2, 0.44% U3O8, 26.55% Ce2O3, and 34.35% other rare earths (RE2O3) (4). Uranium and thorium are important elements in industry especially as energy sources in nuclear reactors. Thorium has not been used extensively as power reactor fuel because it has some inherent limitations in the fuel cycle which ultimately operates on 233U (5). Monazite sand possesses thorium of 10-11% concentration of ThO2 in the amount 2×105 tones of thorium and can be extracted satisfactorily from monazite by NaOH leaching and further purified with tertiary butyl phosphate. Thorium exists with only one natural isotope 232Th and is not very rare. Most of it is obtained as a byproduct in a process of complex phosphate extraction method of rare earths during the processing of monazite (6). Uranium is more abundant in earth crust than mercury and is present in the same amount as that of tin and molybdenum and is widely distributed. Natural uranium is a mixture of three isotopes, 238U (99.276%), 235U (0.718%) and 234U (0.004%). Uranium is a naturally occurring, ubiquitous, lithophilic metal found in various chemical forms including abiotic and biotic environmental forms, e.g. in soils, rocks, seas, oceans and microorganisms (7). 238U is an alpha emitter, decaying through the 18-member uranium natural decay series into 206Pb.

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Recovery of uranium and thorium metal ions is a challenging task because of the high acidic environment associated with them (8, 9). Various methods were adopted for separation of actinides, which include precipitation (10) and co-precipitation (11) and ion-exchange chromatography systems (12). But over the years, solvent extraction (SE) has been proved to be promising in this aspect because of simple operation and using this technique several extractants have been developed with various organic ligands like phosphonic acid based ligands (13), N,N-dialkyl amides (14), crown ethers (15), diketones (16), picolinamides (17), calixarenes (18). Amongst them, octyl(phenyl)- N,Ndiisobutylcarbamoyl-methylphosphine oxide (CMPO) is regarded as one of the best ligand for extraction of transuranium elements and used in TRUEX (Trans Uranium Extraction) process (19, 20). In the nuclear waste treatment, the radioactive solids are usually dissolved in nitric acid because nitric acid is compatible with the stainless steel equipment. This requires the development of radiationresistant extractants which could efficiently separate actinide elements (thorium, uranium, plutonium, and other heavy actinides) at high concentration of nitric acid in highly radioactive fields. The Amex process (21, 22), which is the core of most the processes utilized in the industry, was first described a process where thorium and uranium are extracted in two solvent extraction cycles. In this process, thorium is extracted in the first cycle with a primary amine, while uranium is extracted in the second cycle using secondary or tertiary amine. According to Amex process, the extraction coefficient of thorium obtained from the sulfuric medium can be as high as 1000 for 0.1 mol/L primary amine solution and practically null for tertiary amines. In this paper, trials to separate U, Th from REEs have been investigated by solvent extraction method using three different amines (primary, secondary and tertiary amines). Parameters affecting U and Th extraction and separation such as the contact time, pH and the metal ion concentration in the aqueous phase as well as amines concentration in the organic phase were investigated. EXPERIMENTAL Chemicals and Reagents: All chemicals and reagents used were analytical reagent grade and their solutions were prepared with distilled water. Uranyl sulfate and thorium sulfate were obtained from Fluka. Cerium chloride heptahydrate and other rare earth elements were obtained from Sigma Aldrich (99.9%). Octylamine, N-methylaniline, N,N-dimethylaniline and PAR were supplied by Merck. Also ascorbic acid, petroleum ether, formic acid, sodium hydroxide and arsenazo III were supplied from Fluka. The pH of the solutions was readjusted using 0.1M H2SO4 and 0.1M NH4OH. Instruments: All the pH values of different solutions were measured by using microprocessor–based pH meter type HANNA combined with temperature probe. All pH measurements were done at room temperature 25 ± 1oC. All samples in this work were weighed using an analytical balance produced by Bosh (Germany), having maximum sensitivity of 10-4 g and accuracy of ± 0.01 mg. Spectrophotometric Measurements of U, Th and REEs: The concentration of U, Th and REEs in the aqueous phase was determined spectrophotometrically using a Cintra UV-visible spectrophotometer model Cintra 2.2(Australia). This apparatus is a double beam recording spectrophotometer and has a scanning UV-visible range from 300 to 1100 nm. The scanning speed used during this work was 3200 nm/min. In all measurements, two matched 5.0 cm3 quartz cells with path length of 1.0 cm were used for the sample and blank solutions. Initial concentration of uranium and some REEs in the aqueous phase were determined by spectrophotometric method using a mixture of 0.4 mM PAR, 3 M NH4OH and 1 M CH3COOH, adjusted at pH 9.7. To 1 ml of uranium or REEs samples, 2 ml of the PAR mixture was added, and

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then diluted with water to 5 ml. The absorbance against a reagent blank solution was measured at 530 nm for U and 520 nm for REEs. For sensitive determination of thorium, Arsenazo III was used as a reagent (23). To 0.05 ml of thorium samples, 0.2 ml of 1 % ascorbic acid was added. After that 0.1 ml of the formate buffer and 0.4 ml of Arsenaso (III) solution were added. The absorbance against a reagent blank solution was measured at 620 nm. Experimental Procedure: Three different amines (primary, secondary and tertiary amines) was dissolved separately in petroleum ether then used for extraction process. Petroleum ether is a mixture of volatile aliphatic hydrocarbons consists primarily of pentane and isohexane and contains no aromatics. Petroleum ether was used as a diluent through this work for economic and practical reasons. Firstly, in normal precipitation experiments, different samples (10 ml each) containing of 50 ppm of U (VI) or 100 ppm Th (IV) were prepared individually at different pH values ranged from 2 to 12. After 30 min., shaking time, the concentrations of dissolved U (VI) and Th (IV) at each pH value were measured spectrophotometrically to calculate the percentage of U (VI) and Th (IV) at each pH. Secondly, using single system for extraction of U (VI) and Th (IV), different samples containing equal volumes from the organic phase of the investigated extractants (the different amines soluble in petroleum ether) and an aqueous phase containing 50ppm U (VI) or 100ppm Th (IV) were shaken individually in a water bath at different parameters such as the effect of contact time, the effect of pH values, the effect of amine concentration and the effect of metal ion concentration. Thirdly, using multielements system for separation of U (VI) and Th (IV) from REEs, different samples containing equal volumes from the organic phase of the investigated extractants (the different amines soluble in petroleum ether) and an aqueous phase containing 50 ppm U (VI), 100 ppm Th (IV), 100 ppm Ce(III), 100 ppm Y (III), 100 ppm Eu(III) and 100 ppm Yb (III) were shaken individually in a water bath for 15 and 60 min., at pH 4 with different amine concentrations at 25 ±1 oC. Finally, in selective separation of U(VI) and Th(IV) from REEs in monazite sample, two grams of monazite ore were mixed with 10 ml conc. H2SO4 (95%) for 2 h at 200 oC, then poured in 20 ml cooled distilled water and filtrated, then diluted to 50 ml with distilled water (considered as original solution). Representative aqueous sample solution of the sample was mixed with 50 ml of the organic phase containing of 0.01 M of N,N-dimethylaniline soluble in petroleum ether and shaked for 15 min, at pH 4 and at 25 oC. After separation of the organic phase from the aqueous phase, 10 ml of the aqueous was taken for measuring by inductive coupled plasma (ICP). 30 ml of the remaining aqueous phase from the previous experiment, was mixed with 30 ml of the organic phase containing of 0.1 M of N,N-dimethylaniline soluble in petroleum ether and shaked for 30 min., at pH 7 and at 25 oC. Also after separation of the organic phase from the aqueous phase, 10 ml of the aqueous was taken for measuring by ICP. The metal extraction (%) at any instant time was determined by the following equations: Extraction (%) = [(Co- Ce) / Co] x100 (1) Where Co is the initial concentration of metal ions and Ce is the concentration of metal ions in the aqueous after extraction process. Distribution coefficient (Kd ) was determined at different concentrations based on the equation. Kd = [(CO- Ce) / Ce] x V1/V2 (2) Where V1 is the volume of the aqueous phase (ml), and V2 is the volume of the organic phase (ml). The maximum isothermal capacity (qe) of the three investigated amines was determined by the following equations: qe = (Co- Ce) x V1/V2 (3) 05


RESULTS AND DISCUSSION Precipitation process: The main extraction processes of each of U (VI) and Th (IV) by different amines are mainly affected by the side reaction that may be occurred due to the normal precipitation during the metal hydrolysis which mainly depends on solution pH. In this respects, series of experiments have been tested separately to evaluate the degree of contribution of each of the two reaction mechanisms (extraction and precipitation). The results for normal precipitation of 50 ppm U (VI) and 100 ppm Th (IV) are shown in table (1). It can be seen that U (VI) starting precipitation at pH 10 and Th (IV) at pH 7. Table (1) Normal precipitation of U(VI) and Th (IV) at different pH values. pH values

2

3

4

5

6

7

8

9

10

11

12

U(VI) Precipitation % Th (IV) Precipitation %

Zero

Zero

Zero

Zero

Zero

Zero

Zero

Zero

45

67

89

Zero

Zero

Zero

Zero

Zero

47

63

88

94

97

99

Extraction process: The extractions of U and Th from aqueous solution using the three amines under investigation were studied individually. The different parameters affecting the extraction process were studied. Effect of contact time: One of the main factors affecting the uranium and thorium separation process is the contact time. The effect of the contact time was studied by mixing 10 ml of 50ppm U(VI) or 10 ml of 100ppm Th (IV) at pH 4 with 10 ml of the organic phase containing 0.1M of the investigated amine extractants at different times and at room temperature. According to Fig. (1), it was observed that octylamine is the strongest and fastest extractant for both of U (VI) and Th (IV) than the secondary and tertiary amines. Using octylamine, the extraction process reached to equilibrium after 15 and 120 min., for Th (IV) and U (VI), respectively. This means that the rate of extraction of Th (IV) ions is higher than that of U (VI) ions at the same experimental conditions. This is also reflects the separation possibility of these two ions based of the rate of extraction process. N-Methylaniline N,N-diMethylaniline Octylamine

100

N-Methylaniline N,N-diMethylaniline Octylamine

100

90 80

80

60

Extraction,%

Extraction, %

70

50 40

U(VI)

30 20

60

40

Th(IV) 20

10

0

0 -10 0

50

100

150

200

250

0

300

50

100

150

200

250

300

Time (min)

Time (min)

Fig.(1) Effect of contact time on extraction of U (VI) and Th (IV) ions.

05


Effect of pH: An important variable affecting the uranium and thorium separation is the pH of the aqueous solution. The effect of pH was examined by mixing 10 ml of 50ppm U (VI) or 10 ml of 100ppm Th (IV) with 10 ml of 0.1M of the different extractants at different pH values then shaked at room temperature for 30 or 15 min., respectively. As shown in tables (2, 3), it was observed that octylamine preferably extracts both Th(IV) and U(VI) and the extraction percent reach to equilibrium at pH 3 and 7 respectively. Plotting the logarithmic values of the distribution coefficients of U(VI) and Th(IV) against the pH values, Fig. (2), showed that the distribution coefficients of U(VI) and Th(IV) increases with increasing pH of the aqueous solution. The obtained results are in good agreement with the previously published results (24). Table (2) Effect of pH on the extraction percentage of U (VI) ions.

Amines

N-methylaniline

N,N-dimethylaniline

Octylamine

pH 2

Zero

Zero

42%

3 4 5 7 8

10% 20% 48% 62% 70%

11% 30% 52% 66% 78%

49% 60% 80% 84% 89%

Table (3) Effect of pH on the uptake percentage of Th(IV) ions.

Amines

N-methylaniline

N,N-dimethylaniline

Octylamine

pH 2

14%

21%

92%

3 4 5

56% 92% 93%

66% 93% 99%

97% 98% 99%

1.0

2.0

0.8 0.6

1.5

0.4

1.0

0.0

N-Methylaniline N,N-diMethylaniline Octylamine Linear Fit of N-Methylaniline Linear Fit of N,N-diMethylaniline Linear Fit of Octylamine

-0.2 -0.4

U (VI)

-0.6 -0.8

Log Kd

Log Kd

0.2

0.5

N-Methylaniline N,N-diMethylaniline Octylamine Linear Fit of N-Methylaniline Linear Fit of N,N-diMethylaniline Linear Fit of Octylamine

0.0

Th(IV)

-0.5

-1.0

-1.0 2

3

4

5

6

7

2.0

8

2.5

3.0

3.5

4.0

4.5

5.0

pH

pH

Fig. (2) Effect of pH on the distribution coefficients of U(VI) and Th(IV) ions.

05


Based on the chemical structure of the three investigated amines, Fig. (3), it could be observed that octylamine is more basic than both of N-methylaniline and N,N-dimethylaniline, this is due to: 

+I effect of the long chain alkyl groups in octylamine (C8H17NH2) which will increase the electron density on the N-atom. The lone pair electrons on the N-atom in both of N-methylaniline (C6H5NHCH3) and N,Ndimethylaniline [C6H5N(CH3)2] are delocalized over the benzene ring by the−R effect of – C6H5 group. At the same time [C6H5N(CH3)2] is more basic than (C6H5NHCH3) due to the presence of two electron-donating –CH3 groups in [C6H5N(CH3)2].



This explains why aliphatic amines are stronger bases than aromatic amines. Hence, the order of increasing basicity of the given amines is given as follows: C8H17NH2 > C6H5N(CH3)2 > C6H5NHCH3 Also, it is known that the higher the basic strength, the lower is the pKb values, where the pKb values increase in the order: C6H5NHCH3 > C6H5N(CH3)2 > C8H17NH2

Octylamine

N-Methylaniline

N,N-Dimethylaniline

Fig. (3) The structure of the three investigated amines. Effect of amine concentration: The concentration of amine extractants is one of the operating parameters that significantly influence the final recovery process of uranium and thorium. The effect of amine concentration was examined by mixing 10 ml of 50ppm U(VI) or 100ppm Th(IV) with 10 ml of different amine concentrations at pH 4 and shaked for 30 or 15 min., at room temperature. According to tables (4, 5), it was observed that the extraction efficiency of both U(VI) and Th(IV) increases linearly by increasing the extractant concentration of the three investigated amines. The results are in a good agreement with those reported (25, 26). They stated that the extraction% for uranium by secondary, tertiary and quaternary amines are nearly directly proportional to the amine concentration in the organic phase. The extraction percent of thorium against respective amine concentration showed the increase in extraction with extractant concentration. Moreover, the extraction efficiency of octylamine is preferably for both U(VI) and Th(IV) over the other two amines. Using octylamine, the extraction equilibrium reached to the maximum values by 0.005M (93%) and 0.15 M (78%) for Th(IV) and U(VI) respectively. Table (4) Effect of amine concentration on the extraction percentage of U(VI) ions. Amine

N-methylaniline

N,N-dimethylaniline

Octylamine

0.005

Zero

Zero

38%

0.025

8%

17%

42%

0.05

13%

29%

54%

0.1

20%

30%

0.15

56%

64%

Conc.

05

60% 78%


Table (5) Effect of amine concentration on the extraction percentage of Th(IV) ions. Amine

N-methylaniline

N,N-dimethylaniline

Octylamine

0.001 M

38%

49%

84%

0.005 M

66%

70%

93%

0.01 M

78%

80%

95%

0.025 M

83%

86%

96%

0.05 M

87%

90%

97%

0.1 M

92%

93%

98%

0.15 M

95%

98%

100%

Conc.

Effect of metal ion concentration: The effect of metal ion concentration of uranium and thorium was investigated to evaluate the maximum isothermal capacity of the three investigated amines. 10 ml of different U(VI) concentrations was mixed individually with 10 ml of 0.1M of the three amines at pH 4 and shaking for 30 min., at room temperature. Similarly, 10 ml of different Th(IV) concentrations was mixed individually with 10 ml of 0.005M of the three amines at pH 4 and shaking for 15 min., at room temperature. As shown in Fig. (4), it was observed that by increasing the initial metal ion concentration, the corresponding loading capacity increases till it reached to the maximum loading capacity (saturation capacity, qe). The revealed data clarified that the octylamine exhibited a higher extraction capacity compared with other amines while the lowest values were obtained by Nmethylaniline. The highest maximum capacity of U(VI) and Th(IV) were calculated as shown in table (6).


70

320 300


280

60

260 240

50

220

U(VI)

200

40

qe

qe

180 160 140

30

Th(IV)

120 100

20

80 60

10

40 20 50

100

150

200

250

0

300

200

400

600

800

1000

1200

1400

[M] (mg/l)

[M] (mg/l)

Fig. (4) The effect of metal ion concentration on the loading capacity of different amines.

08


Table (6) The maximum loading capacities of U(VI) and Th(IV) ions.

N-methylaniline

qe

N, N-dimethylaniline

Octylamine

U

Th

U

Th

U

Th

14

150

25

190

63

330

The higher loading capacity of Th(IV) than that of U(VI) ions is mainly depends on the capacity of the metallic ions to create anionic or neutral species in the aqueous phase; these species are then extracted through adduct formation. In sulphate medium, thorium is extracted preferably by primary amines, while uranium is extracted by tertiary amines (21, 27). Mechanisms for thorium and uranium extraction by amines were proposed (22), according to Eq. (4) and (5). 4RNH2H+HSO4−(org) + [Th(SO4)4]4−(aq) = (RNH2H+)4[Th(SO4)4]4−(org) + 4HSO4−(aq)

(4)

4R3NH+HSO4−(org) + [UO2 (SO4)3]4−(aq) = (R3NH+)4[UO2 (SO4)3]4−(org) + 4HSO4−(aq)

(5)

Selective separation of U(VI) and Th(IV) from REEs: Series of experiment was oriented to separate Th from U followed by subsequent separation of REEs. These experiments were performed based on the previously optimized conditions for extraction of U(VI) and Th(IV). As shown in table (7), using low amines concentration (0.005 M), Th(IV) could be only extracted efficiently by the three investigated amines while U(VI) and REEs could not extracted by either N-methylaniline (secondary amine) or N,N-dimethylaniline (tertiary amine). By increasing the concentration of the three amines from 0.005 to 0.05M, the extraction percentage of U (VI) increases gradually and reached to 11, 25 and 49% using N-methylaniline, N,N-dimethylaniline and octylamine respectively. On the other hand, REEs extraction remained at zero % even at 0.05 M of the secondary and tertiary amines, but for primary amine the extraction percentage of REEs increase gradually from Y(III) to Yb(III). Further increasing of the amines concentration to 0.1M and the shaking time to 1 hr leads to increases the extraction efficiency of U (VI) to 33, 45 and 77% by N-methylaniline, N,Ndimethylaniline and octylamine respectively. The results are in a good agreement with many previously published results. According to Kim et al. (28), zero percent extraction was observed for all rare-earths at all pH values studied using 1 mol/L Alamine 336 (tertiary amine) or Aliquat 336 (quaternary ammonium salt). Similarly, Amaral et.al (29), proved that Primene JM-T (primary amine) can extract thorium with concentration not exceed 0.15 mol/L, in which increasing concentration of Primene JM-T causes an increase in extraction of rare earth elements, but this fact was not observed for Alamine 336 (tertiary amine for uranium extraction) in the concentration range investigated which confirm that REEs can be extracted by primary amines not by tertiary amines. Also, as shown in table (7), the extraction percent for REEs increase in the following order: Y(III) < Ce(III) < Eu(III) < Yb(III) at the same condition.

00


The behavior is in consistency with the observations obtained by Jia, et.al (30) for some rare earth elements with D2EHPA. The increasing order of the extraction of metallic ions from Th(IV) to Ce(III), is in accordance with the increasing of the charge to radius ratios (z/r). The relationship between extraction percent and charge to radius ratio is against the Born equation (31), which indicates that for the same ligands, with constant structural effects, the stability constants of the cations are related to (z/r). Finally, secondary and tertiary amine could be efficiently used for separation of Th from U and REEs. Firstly, 80% of Th(IV) has been separated from U(VI) and REEs using 0.01M N, Ndimethylaniline at pH 4, 15 min. Secondly, 66% of U(VI) was then separated from REEs using 0.1M N,N-dimethylaniline at pH 7 for 30 min. The process of selective separation of Th(IV) from U(VI) and REEs could be represented as shown schematically in Fig. (6)

Fig. (6): Flowchart for selective separation of Th(IV) from U(VI) and REEs.

05


Table (7) Selective separation of Th(IV) from U(VI) and REEs.

Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III) Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III) Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III) Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III) Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III) Th(IV) U (VI) Y (III) Ce (III) Eu (III) Yb (III)

N-methylaniline N,N-dimethylaniline 0.005 M, 15 min. 66% 70% Zero Zero Zero Zero Zero Zero Zero Zero Zero Zero 0.01 M, 15 min. 78% 80% Zero Zero Zero Zero Zero Zero Zero Zero Zero Zero 0.015 M, 15 min. 81% 84% 8% 4% Zero Zero Zero Zero Zero Zero Zero Zero 0.025 M, 15 min. 83% 86% 7% 11% Zero Zero Zero Zero Zero Zero Zero Zero 0.05 M, 15 min. 87% 90% 11% 25% Zero Zero Zero Zero Zero Zero Zero Zero 0.1 M, 60 min. 92% 93% 33% 45% Zero Zero Zero Zero Zero Zero Zero Zero

Octylamine 93% 32% 18% 43% 67% 88% 95% 40% 27% 52% 71% 89% 96% 42% 35% 64% 75% 90% 96% 44% 44% 72% 80% 92% 97% 49% 62% 75% 83% 93% 98% 77% 75% 80% 87% 95%

The concentration of Th, Y, Ce, Eu and Yb was 100 ppm while the concentration of U was 50 ppm, and all above experiments were carried out at pH 4.

05


Selective separation of U(VI) and Th(IV) from REEs in monazite sample: The data represented in table 8, showed that thorium and uranium are highly separated (Uptake 70% and 55% respectively). The data is slightly deviated from the previous obtained for the simulated solution (Uptake 80% and 66% respectively) which attributed to the matrix effect of real monazite sample. These matrix effects may be attributed to the presence of high phosphate and sulfate concentration in real monazite sample. Furthermore, REEs are successful separated from thorium and uranium elements. Table (8): Selective separation of U(VI) and Th(IV) from REEs in monazite sample. Th(IV)

U(VI)

Ce (III)

Eu(III)

Y(III)

Original sample

7000ppm

500 ppm

28960ppm

166ppm

3125ppm

Residue after 15 min.

2100 ppm

500 ppm

28960ppm

166ppm

3125ppm

Residue after 30 min.

Zero

225 ppm

28960ppm

166ppm

3125ppm

The process of monazite opening could be represented as shown schematically in Fig.7.

Fig. (7): Flowchart for selective separation of of U(VI) and Th(IV) from REEs in monazite sample.

04


CONCLUSION Based on the above results, it could be concluded that octylamine, N-methylaniline and N,Ndimethylaniline in petroleum ether could be efficiently used to extract both U and Th, while only octylamine can extracts REEs. Both secondary and tertiary amines poorly extract REEs. Therefore, U and Th ions could be efficiently separated from REEs by gradient concentration of N, Ndimethylaniline. REFERENCES (1) (2)

(3)

(4) (5) (6) (7) (8)

(9)

(10) (11) (12) (13)

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