Extraction of Trivalent Americium and Europiumfrom Nitric Acid Solution with Di(2-ethylhexyl)dithiophosphinic Acid†

doi:10.7503/cjcu20180133

Abstract

Abstract:

The extraction of Am³⁺ and Eu³⁺ from HNO₃ solution with di(2-ethylhexyl)dithiophosphinic acid(D2EHDTPA) were investigated using n-dodecane as diluent. Influences of acidity, ligand concentration, N $O 3 -$ concentration and saponification on the extraction of Am³⁺ and Eu³⁺ were evaluated. The distribution ratio values of both Am³⁺ and Eu³⁺ increased with increasing pH values from 2.5 to 4.5, and also with increasing the ligand concentration from 0.10 mol/L to 0.50 mol/L. The maximum value of separation factor(SF_Am/Eu) can reach 4000 at pH=3.65. Slope analyses indicated the main formation of 3:1 and 2:1 complexes of D2EHDTPA with Am³⁺ and Eu³⁺, respectively. The nitrate ion did not take part in the extraction reaction of D2EHDTPA with Am³⁺ or Eu³⁺. The extractability of D2EHDTPA was significantly enhanced through the saponification with NaOH solution. SF_Am/Eu values could be improved to the magnitude of 10⁴, and the extraction capacity was approximately 60% of the theoretical value. Furthermore, the complexation behaviors of D2EHDTPA with Eu³⁺ were also investigated by electrospray ionization mass spectrometry(ESI-MS), Fourier transform infrared(FTIR) and isothermal titration calorimetry(ITC). The composition and stability constants(lgβ) of the complex of D2EHDTPA with Eu³⁺, as well as the thermodynamic parameters(ΔH, ΔS and ΔG) were obtained.

Key words: Di(2-ethylhexyl)dithiophosphinic acid, Am³⁺, Eu³⁺, Extraction, Selectivity

CLC Number:

O615.11

TrendMD:

ZHANG Lirong,WANG Zhipeng,LIU Ying,XU Chao,CHEN Jing,DING Songdong. Extraction of Trivalent Americium and Europiumfrom Nitric Acid Solution with Di(2-ethylhexyl)dithiophosphinic Acid^†[J]. Chem. J. Chinese Universities, 2019, 40(1): 1.

Figures/Tables 13

Fig.1 Chemical structures of purified Cyanex 301 and D2EHDTPA

Fig.2 Influence of contact time on the distribution ratio of Am3+ and Eu3+Organic phase: 0.50 mol/L D2EHDTPA in n-dodecane; aqueous phase: trace amount of 241Am3+ or 152,154Eu3+ in 1.0 mol/L NaNO3 solution with pH of 3.35 and 4.05 for Am3+ and Eu3+, respectively.

Fig.3 Influence of pH on the distribution ratio of Am3+ and Eu3+Organic phase: 0.50 mol/L D2EHDTPA in n-dodecane; aqueous phase: trace amount of 241Am3+ or 152,154Eu3+ in 1.0 mol/L NaNO3 solution with various pH.

Fig.4 Influence of D2EHDTPA concentration on the extraction of Am3+ and Eu3+Organic phase: various concentration of D2EHDTPA in n-dodecane; aqueous phase: trace amount of 241Am3+ or 152,154Eu3+ in 1.0 mol/L NaNO3 solution with pH of 3.24 and 4.40 for Am3+ and Eu3+, respectively.

Fig.5 Influence of NO3- concentration on the extraction of Am3+ and Eu3+Organic phase: 0.10(A), 0.30(B) or 0.50(C) mol/L D2EHDTPA in n-dodecane; aqueous phase: trace amount of 241Am3+ or 152,154Eu3+ in various concentration NaNO3 solutions with pH of 3.24 and 4.40 for Am3+ and Eu3+, respectively.

Table 1 Apparent extraction equilibrium constants for Am3+ and Eu3+ by D2EHDTPA at 25 ℃

c_L /(mol·L^-1)	lg $K ex, Am a$	lg $K ex, Eu b$	c_L /(mol·L^-1)	lg $K ex, Am a$	lg $K ex, Eu b$
0.10	-7.22	-9.00	0.35	-7.21	-9.16
0.15	-7.17	-9.11	0.40	-7.19	-9.19
0.20	-7.22	-9.19	0.45	-7.20	-9.18
0.25	-7.21	-9.15	0.50	-7.20	-9.09
0.30	-7.24	-9.15	Average value	-7.21	-9.14

Table 1 Apparent extraction equilibrium constants for Am3+ and Eu3+ by D2EHDTPA at 25 ℃

c_L /(mol·L^-1)	lg $K ex, Am a$	lg $K ex, Eu b$	c_L /(mol·L^-1)	lg $K ex, Am a$	lg $K ex, Eu b$
0.10	-7.22	-9.00	0.35	-7.21	-9.16
0.15	-7.17	-9.11	0.40	-7.19	-9.19
0.20	-7.22	-9.19	0.45	-7.20	-9.18
0.25	-7.21	-9.15	0.50	-7.20	-9.09
0.30	-7.24	-9.15	Average value	-7.21	-9.14

Fig.6 Influence of the saponification degree of D2EHDTPA on the distribution ratio of Am3+ and Eu3+

Table 2 Influence of the saponification degree of D2EHDTPA on the separation factor*

Saponification degree(%)	0	1	3	5	10	15	20
SF_Am/Eu	5.55	5.05	1.34×10⁴	2.51×10⁴	1.34×10⁴	4.86×10³	5.07×10³

Table 3 Eu3+ concentration in organic phase after extraction by D2EHDTPAa

$c Eu i b$ /(mol·L^-1)	0.1	0.2	0.3	0.4	0.5
$c Eu o c$ /(mol·L^-1)	0.022	0.022	0.022	0.023	0.022

Table 3 Eu3+ concentration in organic phase after extraction by D2EHDTPAa

$c Eu i b$ /(mol·L^-1)	0.1	0.2	0.3	0.4	0.5
$c Eu o c$ /(mol·L^-1)	0.022	0.022	0.022	0.023	0.022

Fig.7 HRESI(+)-MS spectra of the organic phase loaded with Eu3+

Fig.8 FTIR spectra of D2EHDTPA(a) and the organic phase loaded with Eu3+(b)

Fig.9 Microcalorimentric titration of Eu(ClO4)3 with D2EHDTPA in EtOH-H2O(volume ratio 99:1)(A) and the observed and fitted cumulative heat and the speciation of Eu3+ along the titration(B)Initial conditions: [Eu3+]=1.0×10-3 mol/L, volume=1.40 mL; Titration conditions: [D2EHDTPA]=1.0×10-2 mol/L, 30 additions of 0.01 mL each.

Table 4 Thermodynamic parameters for the complexation of Eu3+ with D2EHDTPA at 25 ℃

Reaction	lgβ	ΔH/(kJ·mol^-1)	ΔS/(J·mol^-1·K^-1)	ΔG/(kJ·mol^-1)
Eu³⁺+L^-=EuL²⁺	3.56	12.7	72.3	-8.85
Eu³⁺+2L^-=Eu $L 2 +$	6.57	16.6	113	-17.2
Eu³⁺+3L^-=EuL₃	9.52	18.5	162	-29.8

Table 4 Thermodynamic parameters for the complexation of Eu3+ with D2EHDTPA at 25 ℃

Reaction	lgβ	ΔH/(kJ·mol^-1)	ΔS/(J·mol^-1·K^-1)	ΔG/(kJ·mol^-1)
Eu³⁺+L^-=EuL²⁺	3.56	12.7	72.3	-8.85
Eu³⁺+2L^-=Eu $L 2 +$	6.57	16.6	113	-17.2
Eu³⁺+3L^-=EuL₃	9.52	18.5	162	-29.8

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