서지주요정보
Reduction of uranium(Ⅵ) at titanium electrode in nitric acid hydrazine media = 티타늄 전극에서 질산-하이드라이진 계의 우라늄(Ⅵ) 환원 연구
서명 / 저자 Reduction of uranium(Ⅵ) at titanium electrode in nitric acid hydrazine media = 티타늄 전극에서 질산-하이드라이진 계의 우라늄(Ⅵ) 환원 연구 / Kwang-Wook Kim.
저자명 Kim, Kwang-Wook ; 김광욱
발행사항 [대전 : 한국과학기술원, 1994].
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소장정보

등록번호

8004288

소장위치/청구기호

학술문화관(문화관) 보존서고

DCHE 94006

SMS전송

도서상태

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초록정보

This work has investigated the electrochemical properties and kinetics on the reduction of uranium(VI) at titanium electrode in a simulated solution of nitric acid and hydrazine. The analysis of a system with the electro-reduction and the mass transfer of uranium(VI) from organic phase was simulated by a model. The reduction of uranium(VI) needed a very high activation overpotential at non-pretreated titanium electrode in nitric acid and non-neutralized hydrazine media. It was affected by the ratio of hydrazine mono-hydrate to nitric acid rather than by only absolute amount of hydrazine mono-hydrate. When the above ratio exceeded 0.5, the reduction current decreased rapidly due to decrease of solution conductivity and increase of iR drop which were caused by consuming proton in the solution by the hydrazine mono-hydrate. There is less effect on the uranium reduction by the hydrazine mono-hydrate when the ratio is less than 0.5. The reduction of uranium(VI) was governed by charge-transfer controlled mechanism. It also was totally irreversible below potential showing a limiting current in current-potential curves. The experiment was performed for the neutralization of hydrazine mono-hydrate by nitric acid at pH 4.25. The reduction peaks of uranium(VI) of the voltammograms measured by electrochemical non-pretreated titanium electrode was not clear enough to be used for the kinetic analysis of the reduction of uranium(VI). The existence of oxide film at the titanium electrode without non-electrochemical pretreatment was confirmed by EPMA and a chronoamperometry method. The oxide film was effectively removed by a cathodic polarization method. The time for the removal of the oxide film, $t_{pr}$, depended only on a supplying electrolytic potential, $E_{pr}$. $$t_{pr} = 15.8E_{pr}\,^{-3.1}(-0.55\le{E_{pr}}\le{-0.9}\;V)$$ The electrode pretreated by the cathodic polarization gave good reduction peaks of uranium(VI) in the voltammogram by which kinetic analysis could be done. Because the reduction peak current at the pretreated titanium electrode in the nitric acid- neutralized hydrazine media was higher and was shifted to positive direction from the hydrogen evolution region than one at non-pretreated titanium electrode, the more effective system efficiency could be gotten. The reduction of uranium(VI) was found to satisfy the characters of irreversible electroreaction well. It was found that the ordinary electrolytic polishing method should not be applied to this titanium electrode, because even week positive potential produced strong oxide at the titanium electrode. The reduction of uranium(VI) depended strongly on nitric acid concentration. At more than 3 M nitric acid, the reduction peaks of uranium(VI) of voltammograms were overlapped with the currents of vigorous side reaction of hydrogen evolution or the reduction of nitric acid. Hence, the peak analysis was not possible. The existence of hydrazine in the solution was important in the uranium reduction because of preventing the reoxidation of uranium(IV), but the concentration of hydrazine had no effect on the uranium reduction. The hydrazine concentration of 0.1 M was enough to prevent the reoxidation of uranium(IV). A possibility was found that a uranous hydroxide was adsorbed at the titanium electrode in nitric acid of less than 0.75 M and it hindered the electro-reaction. The kinetic parameter, $\alpha\mbox{n}_a$, depended on nitric acid but the k$_0$ didn't. The following electro-reduction rate constant was obtained $$k_f = A \exp\{ - [B+C ln(C_{HNO_3})]F/RT[E_{app} - E^{0'}]\}$$ where, A, B, C, and $C_{HNO_3}$ are $5.659\times10^{-8}$, 0.111, 0.021, and the concentration of nitric acid (M), respectively. The controlled-potential of -0.5 V(vs. SSE) was suitable to the electrolysis operation for the production of uranium(IV) at titanium electrode with the best current efficiency and safe operation. A model for an analysis of the mechanism of electro-reduction accompanying mass transfer of uranium(VI) was set up on the basis of the two film theory. It was found that an optimal nitric acid concentration existed in terms of maximum production rate of uranium(IV) in a given time. The produced uranium(IV) culminated at near 0.3 N of nitric acid and then decreased rapidly. The mass transfer depended on more strongly the production rate of uranium(IV) rather than the electroreduction. The composition of uranium(IV) in a final solution depended strongly on the electrode area, but little on the mass transfer area. It was recommended for the maximum production rate of uranium(IV) that the nitric acid concentration should be kept as low as possible, but more than 0.5 N. The optimal electrode areas were be estimated from the simulations, when production yields of uranium(IV) and production compositions of uranium(IV) were decided to meet specific conditions for the separation of uranium and plutonium in PUREX process and the production of uranium(IV) in two phase system, so on.

서지기타정보

서지기타정보
청구기호 {DCHE 94006
형태사항 xvii, 167 p. : 삽도 ; 26 cm
언어 영어
일반주기 Appendix : 1, Distribution coefficients of uranium to tri-butyl phosphate. - 2, Uranium-plutonium separation processes in PUREX proecss. - 3, Electro-reactions at cathode and anode. - 4, Reduction of plutonium(Ⅳ)by uranium(Ⅳ). - 5, Stability of uranium(Ⅳ)and plutonium(Ⅲ). - 6, Electro-reduction mechanism of nitric acid. - 7, Decomposition of nitrous acid by hydrazine. - 8,Irreversible stationary electrode voltammetry. - 9, Program lists
저자명의 한글표기 : 김광욱
지도교수의 영문표기 : Jong-Duk Kim
지도교수의 한글표기 : 김종득
학위논문 학위논문(박사) - 한국과학기술원 : 화학공학과,
서지주기 Reference : p. 116-122
주제 Uranium.
Nitric acid.
전기 화학적 환원. --과학기술용어시소러스
우라늄. --과학기술용어시소러스
질산. --과학기술용어시소러스
Electrolytic reduction.
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