4th International Nuclear Chemistry Conference 14-19 September 2014, Maresias, Brasil Decomposition of uranyl peroxo-carbonato complex ions in the presence of metal oxide in carbonate media Sep. 19, 2014 Dong-Yong Chung*, Min-Sung Park, Keun-Young Lee, Eil -Hee Lee, Kwang-Wook Kim, Jei-Kwon Moon Contents 1 Introduction 2 Experiment 3 Results and Discussion 4 Summary 1 1. Introduction COL(Carbonate-based Oxidative Leaching-precipitation) Process A uranium recovery process from a spent fuel Oxidative leaching and a precipitation of U in high-alkaline carbonate media Dissolution of uranium oxide Uranium oxides can selectively be dissolved to form uranyl peroxocarbonato complex ions, UO2(O2)x(CO3)x2-2x-2y, with a high solubility in carbonate solutions that contain hydrogen peroxide, H2O2 A number of metal ions have a very limited solubility in carbonate solution and, unlike uranium, do not form complex ions 2 u COL(Carbonate-based Oxidative Leaching-precipitation) Process Ref.: Nucl. Technol. (2009) 166:170 Ø U leaching from spent nuclear fuel Ø Precipitation removal of environmentally-detrimental elements among the impurity elements co-leached together with U Ø Recovery of U by precipitation using pH-control Ø Recycles of all inorganic salts used in the system by salt-free methods 3 Stability characteristics of hydrogen peroxide and uranyl peroxocarbonato complex ion The uranium in uranyl peroxo-carbonato complex ions can be precipitated as the uranium peroxide, UO4•xH2O - UO4•xH2O : very low solubility of approximately 10-3~10-5 M at pH 2–3 - Uranyl peroxo-carbonato complex ion must not change. Decomposition of hydrogen peroxide and uranyl peroxo-carbonato complex ions in aqueous solution is catalyzed both homogeneously and heterogeneously. - dissolved ions - Metal oxides, hydroxides and metals - pH, temperature Stability characteristics of a uranium peroxo-carbonato complex ion - Decomposition of uranyl peroxo-carbonato complex to uranyl tricarbonato complex - Temperature à in previous study (Ref.: J. Hazard. Mater. (2012) 233-234 : 213) - Metal oxides à in this study (using absorption spectroscopy) 4 2. EXPERIMENTAL Particle size distribution Various metal oxides Metal oxides Vol. mean particle size(µm) CeO2 1.71 Gd2O3 5.29 La2O3 3.05 Nd2O3 3.11 PrO2 12.38 Sm2O3 3.16 MoO2 19.09 PdO 1.95 RuO2 5.68 ZrO2 2.16 Experimetal method Instruments • Dissolution of UO2 in a 0.5M Na2CO3+1.0M H2O2 sol’n • UV-vis absorption spectrum : HP-8453 spectrophotometer • Addition of metal oxides into dissolution solution • Particle size measurement : Microtrac S3500 • Absorption spectrum of solution with time • H2O2 conc. measurement : Reflectoquant (Merck RQflex plus 10) 5 3. Experimental Results [Na2CO3] Decomposition peroxide in a carbonate solution k of hydrogen [H2O2] 0.5 0.292 PJ 1.0 Decomposition of H2O2 0.5 in aqueous0.5 solution 0.252 H2O2(l) 0.192 0.299 → H [H2O2]/[H2O2]o=exp(-kt) 0.1 1.0 1.0 1.0 2O(l) + 1/2O2(g) d [ H 2O2 ] dt log([H2O2]/[H2O2]o) 1 0.1 0 k[ H 2O2 ] k : Rate constant Rate constants (hr-1) for the decomposition of hydrogen per oxide in a carbonate solutions [Na2CO3] (M) [H2O2] (M) Initial pH k (h-1) 0.5 1.0 10.3 0.292 0.5 0.5 10.8 0.252 0.1 1.0 10.0 0.192 1.0 1.0 10.6 0.299 Avg. 0.259 [Na2CO3] [H2O2] (M) (M) 0.5 1.0 0.5 0.5 0.1 1.0 1.0 1.0 1 2 3 4 Time (hour) 5 6 7 Fig. First order plots for decomposition of hydrogen peroxide in a carbonate solution ※ in the acid solution k=0.2 hr-1 ([H+] < 2 M) =0.2+0.34([H+]-2) ([H+] > 2 M) Ref.: J. Radioanal. Nucl. Chem Lett. (1995) 201:495 6 정동용-논문\₩논문-Catalyzed decomposition of H2O2 MetalO.opj Alloxides3 Decomposition of H2O2 in the presence of metal oxides in a carbonate solution No metal -1oxide H2O2 concentration ([H2O2]/[H2O2]o) 1 (k=0.29 hr ) 0.1 MoO2 ZrO2 Gd2O3 CeO2 SrO Nd2O3 PdO RuO2 La2O3 Sm2O3 PrO2 PdO RuO2 0.01 Rate constants (hr-1) for the decomposition of hydrogen peroxide for each metal oxides 0 1 MoO2 [Na2CO3]=0.5M [H2O2]o=1.0M Exp. vol.=100ml oxide =0.05g 2 3 Time (hour) 4 5 Fig. Variation of hydrogen peroxide concentration w ith a change of time in the presence of various metal oxides Metal oxides Rate constants, k (hr-1) MoO2 0.561 PdO 15.97 Gd2O3 0.413 CeO2 0.225 SrO 0.386 RuO2 115.1 Nd2O3 0.344 ZrO2 0.312 La2O3 0.283 Sm2O3 0.344 PrO2 0.281 Influence of metal oxides on rate constants RuO2 >>> PdO >> MoO2 > other oxides (Nd, Gd, Pr, La, Sm, Ce, Zr, Sr)No metal oxide 7 Absorption Spectrum of UO2(CO3)34- and UO2(O2)(CO3)34- in a 0.5M Na2CO3 solution 50 Molar Absorptivity in a 0.5M Na2CO3 solution -1 -1 Molar absorptivity (M cm ) 40 340nm 4- UO2(O2)(CO3)2 1000 448 30 800 435 600 462 20 400 § 10 200 4- 0 300 UO2(CO3)3 350 Uranyl triscarbonato complex ion, UO2(CO3)34: 28 M-1cm-1 at 448 nm : bright yellow 1200 § 400 450 500 Wavelength (nm) 550 0 600 Uranyl peroxo-carbonato complexion, UO2(O2)(CO3)24 - : 1082 M-1cm-1 at 340 nm, 142 M-1cm-1 at 500 nm : orange-red • Charge transfer complex • High molar absorptivity • Asymmetric molecule Fig. UV-visible spectra of UO2(CO3)34- and UO2(O2)(CO3)34complexes in a 0.5M carbonate solution 8 Dissolution of UO2 in Na2CO3-H2O2 solution UO2 (O2 ) x (CO3 ) 2y UO2 (s) yNa2CO3 xH2O2 2x 2y 2xH 4yNa 2e (1) (x/y=1/2, 2/1) Absorption spectra of UO2(O2)(CO3)24- complex 우라늄혼합물저감화\₩실험-우라늄혼합물 peroxo_stability\₩spectra ST1-spectra.opj GraphST1 2.0 Time (day) 1.0 0.5 1.0 0.8 1.0 0.8 540 550 [H2O2] (C/Co) Absorbance 1.2 560 Dissolution condition • Solution : 0.5M Na2CO3 + 1.0 M H2O2 • UO2 7.5g/L (U conc.=27.8mM) [Na2CO3]=0.5M [H2O2]=1.0M Decomposition of free H2O2 0 5 12 16 1.5 -2 [U]=6.6g/l=2.773x10 M UO2.18 1.5g/ 200ml UO2 용 해 시 H2O2 농 도 변 화 측 정 0.6 k=0.65 hr-1 0.4 0.2 0.0 400 500 600 Wavelength (nm) 700 0.0 0 1 2 3 Time (hour) Fig. Variation of the absorption spectra and peroxide with a change of time in a solution obtained from the dissolution of 7.5 g/L UO2 powder in a mixed solution of 0.5 M Na2CO3 + 1M H2O2. 4 • Complete dissolution of UO2 in 10 min • Dissolution of UO2 as a uranyl peroxo-carbonato c omplex, UO2(O2)(CO3)24• Absorption spectrum at 550 nm with time (high m olar absorptivity) - [UO2(O2)(CO3)24-] declined 14% after 16 days. T he rate constant for the decomposition of UO2(O2)(CO3)24- ion : 0.01 day-1(4.17x10-4hr-1) 9 Stability uranyl peroxo-carbonato complex in the presence of metal oxides Decomposition of uranyl peroxo-carbonato complex ion 우라늄혼합물저감화\₩실험-우라늄혼합물 peroxo_stability\₩spectra ST1-spectra ST1-1.opj ST11-spectra, Graph-day 우라늄혼합물저감화\₩실험-우라늄혼합물 peroxo_stability\₩spectra ST1-spectra-2 UO 2 (O 2 )( CO 3 ) 42 [U]=6.6g/l=2.773x10 ST1-2.opj M ST12-spec tra metal oxide/exp. vol.=0.02g/30ml Nd2O3 2.0 CO 32 H UO 2 (CO 3 )34 -2 [U]=6.6g/l=2.773x10 M metal oxide/exp. vol.=0.02g/30ml RuOx 2.0 Time (hour) Time (day) time increase 1.0 Nd2O3 0.5 우라늄혼합물저감화\₩실험-우라늄혼합물 peroxo_stability\₩spectra ST1-spectra ST1-3.opj 0.0 ST13-spectra, Graph-13-day 400 500 MoO2 time increase 1.0 700 500 [U]=6.6g/l=2.773x10 M metal 600oxide/exp. vol.=0.02g/30ml 700 PdO Wavelength (nm) 2.0 Time (day) Time (day) time increase 1.0 MoO2 0.5 0.0 400 500 600 Wavelength (nm) 700 1.5 Absorbance Absorbance 1.5 0 1.0 4.2 7.0 11 15 1.0 time increase 0 1.0 4.2 7.0 11 15 PdO 0.5 0.0 Experimental condition • [UO2(O2)(CO3)24-]=27.8 mM in a 0.5M Na2CO3 • Metal oxide conc. = 0.5 g/L • Metal 0xides : Nd2O3, RuO2, MoO2, PdO -2 400 Wavelength (nm) 2.0 (2) RuO2 0.5 우라늄혼합물저감화\₩실험-우라늄혼합물 peroxo_stability\₩spectra ST1-spectra -2 [U]=6.6g/l=2.773x10 M ST1-4.opj 0.0 ST14-spec tra, Graph-14-day metal oxide/exp. vol.=0.02g/30ml 600 0 2 4.3 7.7 24 32 100 1.5 Absorbance Absorbance 1.5 0 1.0 4.2 7.0 11 15 HO 2 400 500 600 • Nd oxide : 21 % of UO2(O2)(CO3)24- was decomposed • Ru oxide : Typical spectrum of uranyl tricarbonato complex ion after 100 hours. • Pd oxide : UO2(O2)(CO3)24- was completely decomposed to UO2(CO3)34- after 15 days. • Mo oxide : Partial decomposition of UO2(O2)(CO3)24- 700 Wavelength (nm) Fig. Variation of the absorption spectra in the presence of various metal oxides with a change of time. 10 Stability uranyl peroxo-carbonato complex in the presence of metal oxides UO2(O2)(CO3)4concentration (C/Co) 2 Decomposition of uranyl peroxo-carbonato complex ion 0.01 day-1 1 0.032 day-1 0.016 day-1 No oxide Nd2O3 MoO2 PdO RuO2 0.1 k=2.31 day-1 0.4 day-1 0.01 0 5 Time (day) 10 [UO2(O2)(CO3)24-]=27.8 mM in a 0.5M Na2CO3 Metal oxide conc. = 0.5 g/L Metal Oxides : Nd2O3, RuO2, MoO2, PdO Metal oxid es Rate constants, k (d ay-1) No Oxide 0.01 Nd2O3 0.016 MoO2 0.032 PdO 0.4 RuO2 2.31 15 Fig. Variation of the uranyl peroxo-carbonato complex ion concentration in the presence of various me tal oxides with a change of time. 11 Stability uranyl peroxo-carbonato complex in the presence of metal oxides Uranyl peroxo-carbonato complex formation [U]=5x10 M 2010.9.16 [U]=5x10 M 우라늄혼합물저감화\₩실험-우라늄혼합물 Peroxo_stability\₩spectra ST2-spectra ST2-1 Graph-ST21-day [U]=0.0005M [H2O2]=0.0025M 우라늄혼합물저감화\₩실험 -4-우라늄혼합물 [U]=0.0005M Peroxo_stability\₩spectra [H2O2]=0.0025M ST2-spectrametal oxide/exp. vol.=0.02g/30ml ST2-2 Nd O 2 3 Graph-ST22-day UO2 (CO3 )34 HO2 pale yellow H (3) 0.6 0.4 -4 [U]=5x10 M Oxide conc.=0.5g/L 400 500 Wavelength (nm) 1.0 Experimental condition • [U(VI)]=5x10-4 M, [H2O2]=2.5x10-3 M in 0.5M Na2CO3 • Metal oxide conc. = 0.5 g/L [U]=5x10 M 2010.9.16 metal oxide/exp. vol.=0.02g/30ml • Metal 0xides : Nd2O3, RuO2, MoO2, PdO PdO 0.6 0.4 우라늄혼합물저감화\₩실험-우라늄혼합물 2010.9.16 -4 [U]=0.0005M [U]=0.0005MPeroxo_stability\₩spec tra [U]=5x10 M [H2O2]=0.0025M [H2O2]=0.0025M ST2-spectra metal oxide/exp. vol.=0.02g/30ml ST2-4 0.2 MoO Graph-ST2-4 2 0.0 300 Time (hour) 0 1 5 23 0.8 Absorbance Time (day) 0 0.9 1.1 4.0 8.0 0.8 Absorbance CO32 orange red Ru oxide Nd oxide 400 1.0 Wavelength (nm) 0.6 0.4 500 Pd oxide 600 Results § A UO2(O2)(CO3)24- complex in a carbonate solution w as decomposed to the UO2(CO3)34- complex in the p resence of metal oxides. § Order of decomposition rate : RuO2 >> PdO >> MoO 2 > Nd2O3 Time (hour) 0 1 3 5 6.3 22.5 25.8 30 0.8 Absorbance Time (day) 0 0.9 4.0 8.0 -4 0.0 600 300 Mo oxide 0.8 Absorbance UO2 (O2 )(CO3 )2 1.0 1.0 우라늄혼합물저감화\₩실험-우라늄혼합물 Peroxo_stability\₩spectra ST2-spectra 0.2 ST2-3 Graph-ST23-day 2010.9.16 -4 metal oxide/exp. vol.=0.02g/30ml 4 RuOx 0.6 0.4 0.2 0.2 0.0 300 400 500 Wavelength (nm) 0.0 600 300 400 500 600 Wavelength (nm) Fig. Variation of the absorption spectra in the presence of various metal oxides with a change of time. 12 Stability of uranyl peroxo-carbonato complex at different temperatures 0.5 Uranyl peroxo carbonato compelex solution -4 2- with about 5x10 M uranium in 0.5 M CO3 0.4 1.2 Initial Uranyl tris-carbonato complex solution U : 10 g/l Absorbance Absorbance 1.0 0.3 0.2 at 80℃ 0.8 0.6 0.4 0.2 4 day 0.0 350 400 8 day 450 500 550 600 Wave length (nm) 0.1 20 day 0.0 300 35 day 400 500 Wavelength (nm) 600 Fig. Change in the absorption spectra of uranyl peroxo carbonato compl ex at 80°C as a function of time. Ref.: J. Hazard. Mater. (2012) 233-234 : 213 13 Stability of uranyl peroxo-carbonato complex at different temperatures 0.4 Uranyl peroxo carbonato compelex solution o 25 C -4 2- with about 5x10 M uranium in 0.5 M CO3 after 35days Absorbance 0.3 o 40 C 0.2 o 60 C 0.1 o 80 C 0.0 300 400 500 600 700 Wavelength (nm) Fig. Change in the absorption spectra of uranyl peroxo carbonato complex at different tem peratures 35 days after dissolution of UO2 in a carbonate solution. Ref.: J. Hazard. Mater. (2012) 233-234 : 213 14 4. Summary Ø The heterogeneous catalytic decomposition of the hydrogen peroxide and the uranyl pero xo-carbonato complex ion, UO2(O2)(CO3)24-, in the presence of each 11 element oxide (CeO2 , Gd2O3, La2O3, Nd2O3, PrO2, Sm2O3, MoO2, PdO, RuO2, ZrO2, and SrO) was investigated in a carbonate solution using absorption spectroscopy. Ø The hydrogen peroxide and the uranyl peroxo-carbonato complex ion decomposed into w ater and uranyl tricarbonato complex ion, UO2(CO3)34-, in a carbonate solution. Ø The rate constants for decomposition of H2O2 and UO2(O2)(CO3)24- in a 0.5 M carbonate sol ution were 0.292 hr-1 and 0.01 day-1 (4.17x10-4 hr-1). Ø The decomposition of hydrogen peroxide and the uranyl peroxo-carbonato complex ion w as just a little catalyzed heterogeneously by other metal oxides except Ru, Pd, Mo oxide. Ø The rate constants for decomposition of UO2(O2)(CO3)24- were 0.032 (1.33x10-3), 0.40 (1.67x 10-2) and 2.31 day-1 (9.63x10-2 hr-1) for Mo, Pd and Ru oxide Ø As the solution temperature increased, the decomposition of the uranyl peroxo-carbonato complex increased. 15 Thank you for Your Attentions 16
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