第44卷第2期原子能科學(xué)技術(shù)Vol 44, No. 22010年2月Atomic Energy Science and TechnologyFeb.2010甲醛肟與Pu(Ⅳ)的還原動(dòng)力學(xué)肖松濤,葉國安,羅方祥,劉協(xié)春(中國原子能科學(xué)研究院放射化學(xué)研究所,北京102413)摘要:研究了甲醛肟(FO)與Pu(Ⅳ)的還原反應(yīng)動(dòng)力學(xué),其動(dòng)力學(xué)方程式為-dc(Pu(Ⅳ))/dr=kc(Pu(Ⅳ))c61(FO)c0(H+),在18.7℃時(shí),反應(yīng)速率常數(shù)k=(110.39±7.70)(mol/L)7/s,活化能為(68,82±3.00)kJ/mol研究了甲醛肟濃度、H+濃度、硝酸根濃度、Fe3+濃度、UO+濃度以及溫度對甲醛肟與Pu(Ⅳ)還原反應(yīng)速率的影響。結(jié)果表明:增加甲醛肟濃度、降低UO和H+濃度、增加Fe濃度以及升高溫度,均使Pu(Ⅳ)還原速度增加;硝酸根濃度對甲醛肟還原Pu(Ⅳ)的速率基本無影響關(guān)鍵詞:Pu(Ⅳ);甲醛肟;還原反應(yīng);反應(yīng)速率中圖分類號:TQ031.6文獻(xiàn)標(biāo)志碼:A文章編號:1000-6931(2010)02-0166-05Kinetics of Reaction Between Pu(l) and Formoximein Nitric Acid solutionXIAO Song-tao, YE Guo-an, LUO Fang-xiang, LIU Xie-chunChina Institute of Atomic Energy, P. O. Box 275-26, Beijing 102413, China)Abstract: The kinetics of reaction between Pu(v) and formoxime (FO) in nitric acidsolution was determined. The rate equation is found to be -dc( Pu(i))/dtkc (Pu(V))c6l(FO)c-088(H+)where k=(110. 39+7. 70)(mol/L)0.73/s at 18. CThe activation energy is found to be Ea=(6882+3.00) kJ/mol. Effects of c(FO)c(H+), c(Fe), c(UO2), c(NO3 and temperature on reduction rate of Pu(iv)wereinvestigated. Pu(Iv) can be rapidly reduced to Pu(lll by FO under normal conditions.The reaction rate can be accelerated by increasing concentration of formoxime, decrea-sing concentration of UO2 and H, increasing concentration of Fe t and rising temperature. The influence of NO, on reaction rate is negligible.Key words: Pu( IV); formoxime; reduction reaction; reaction rate在乏燃料水法后處理中,U/Pu分離及Pu為Np(V),而不生成Np(Ⅳ),可使進(jìn)入1AP的凈化濃縮是 Purex流程的重要部分。無中的Np與Pu同時(shí)進(jìn)入水相,使 Purex流程達(dá)鹽、高效的還原劑能快速將Pu(Ⅳ)還原為不被到簡化,提高經(jīng)濟(jì)性。因此,無鹽有機(jī)還原劑開TBP萃取的Pu(Ⅲ),選擇性地將Np(Ⅵ)還原發(fā)與研究一直是 Purex流程中的重點(diǎn)研究方收稿日期:200906-02;修回日期:2009-07-15基金項(xiàng)目:中國核工業(yè)集團(tuán)公司預(yù)先研究基金項(xiàng)目(61601090401中國煤化工作者簡介:肖松濤(1975—),男,北京人,工程師,乏燃料后處理專業(yè)CNMHG第2期肖松濤等:甲醛肟與Pu(Ⅳ)的還原動(dòng)力學(xué)167向2。其中, Koltunov等{36對無鹽有機(jī)還原1.3數(shù)據(jù)處理方法劑進(jìn)行了長達(dá)30年的研究,取得了一定的成動(dòng)力學(xué)數(shù)據(jù)處理方法詳見文獻(xiàn)[12]。果,也暴露了無鹽有機(jī)還原劑中存在的一些問題以及展示了它的發(fā)展方向;張先業(yè)也對無鹽2結(jié)果與討論有機(jī)還原劑進(jìn)行了深入的工藝研究,認(rèn)為無鹽2.1反應(yīng)對Pu(N)級數(shù)的確定有機(jī)還原劑可在對 Purex流程后續(xù)工藝基本無在18.7℃時(shí),c(H+)=1.0mol/L,影響的情況下,做到高效、經(jīng)濟(jì)的UNp和(NO)=2.5mol/L,p(Pu(Ⅳ)=0.952g/L,U/Pu分離1。在眾多的無鹽有機(jī)還原劑中,甲醛肟濃度分別為0.022、0.040、0.050乙醛肟被認(rèn)為最具應(yīng)用前景,其中, Koltunov0.061、0.071、0.085mol/L條件下,進(jìn)行甲醛和 Hangingzhen分別對乙醛肟進(jìn)行了基礎(chǔ)研肟與Pu(Ⅳ)反應(yīng),記錄反應(yīng)體系在不同時(shí)間下究和較深入的應(yīng)用研究,認(rèn)為它可快速還原Np的吸光度數(shù)據(jù)。以ln[(A-A)/(A0-A。)]和Pu,并可同時(shí)清除亞硝酸,不再需額外的支對t作圖,結(jié)果示于圖I。從圖1可看出,持還原劑,但通過對其應(yīng)用研究,也顯露出一些1n[(A-A)/(A。-A)]與t之間呈良好的問題,如在含Pu有機(jī)相反萃到水相時(shí)產(chǎn)生界直線關(guān)系,表明反應(yīng)對Pu(Ⅳ)是一級反應(yīng)。面污物12。因此,對其結(jié)構(gòu)相類似的甲醛肟進(jìn)行了一些基礎(chǔ)研究和較深入的應(yīng)用研究,以驗(yàn)證該類試劑在 Purex流程中應(yīng)用的可能性。0.4-0.8甲醛肟是一種中性的無鹽有機(jī)還原劑,其分子式為H2C:NOH;它是中性試劑(pH=R2=0.98R2=0.98c(FO:7.0),不需硝酸中和,因此,可降低鹽析效應(yīng)對=0.99Pu(Ⅲ)分配的影響。為系統(tǒng)研究 Purex流程中甲醛肟與0.00.51.0152.02.53.03.5Pu(Ⅳ)還原反萃行為,本工作擬在硝酸介質(zhì)中進(jìn)行甲醛肟與Pu(Ⅳ)還原反應(yīng)動(dòng)力學(xué)研究。圖1反應(yīng)對Pu(Ⅳ)為一級反應(yīng)的驗(yàn)證Fig. 1 First order plo1實(shí)驗(yàn)試劑與儀器甲醛肟,10%的水溶液,其它雜質(zhì)含量低于2.2反應(yīng)對甲醛肟級數(shù)的確定1%,日本化工株式會(huì)社;Pu(Ⅳ)溶液系Fe(Ⅱ)在18.7℃時(shí),c(H+)=1.0mol/L,還原、HNO2氧化、2606陰離子交換樹脂純化所c(NO)=2.5mol/…,p(Pu(Ⅳ)=0.952g/L得,以K邊界法及a計(jì)數(shù)法測定其濃度,其H+甲醛肟濃度分別為0.040、0.050、0.061、濃度用定pH值滴定法測定;硝酸和硝酸鈉,分0.071、0.085mol/L條件下,進(jìn)行甲醛肟與析純,北京化學(xué)試劑公司Pu(Ⅳ)反應(yīng),記錄反應(yīng)體系在不同時(shí)間下的吸S600型紫外可見分光光度計(jì),德國耶拿光度數(shù)據(jù)。以hn[(A,-A。)/(A-A.)]對t公司;DC1020型低溫恒溫水浴槽,寧波新芝作圖,所得直線的斜率為表觀速率常數(shù)k',以生物科技公司;PHS3C型酸度計(jì),上海雷磁Ink對lnc(FO)作圖(圖2),可求得斜率n為儀器廠。1.61,即甲醛肟的反應(yīng)級數(shù)n=1.61。1.2實(shí)驗(yàn)方法2.3反應(yīng)對H+濃度的確定取2.0g/LPu、1.0mol/LHNO3溶液1mL在18.7℃時(shí),c(FO)=0.051mol/L、及其它調(diào)節(jié)各物質(zhì)濃度的溶液1mL置于1cmA中國煤化工)=25ml1,確比色皿中,加入0.1mL甲醛肟的硝酸溶液,立即酸于476m處測定溶液中Pu(Ⅳ)的吸光度,以吸條CNMHG下反應(yīng)的表觀速光度A-時(shí)間t曲線確定反應(yīng)的進(jìn)程。率常數(shù)k,以Inc(H+)對Ink'作圖得圖3。168原子能科學(xué)技術(shù)第44卷NO濃度分別為1.0、1.5、2.0、2.5、3.0mol/L條件下,求出不同NO3濃度下反應(yīng)的表觀速率常數(shù)k,以lnc(NO3)對nk'作圖得圖4y=1.61x+469圖4為反應(yīng)對NO級數(shù)的驗(yàn)證。結(jié)果表明,NO3濃度對甲醛肟還原Pu(Ⅳ)的反應(yīng)速率基0.2本無影響。0.6y=0.043x-225圖2反應(yīng)與甲醛肟級數(shù)的關(guān)系-2.0Fig 2 Relationship between In k and In c(Fo)圖3即為反應(yīng)對H級數(shù)的驗(yàn)證,可見,隨著酸0.00.2040.60.81.01.2度的增加,甲醛肟與Pu(Ⅳ)反應(yīng)速度減慢In(c(NO,"(mol- L-)]nc(H+)與lnk'呈直線關(guān)系,直線的斜率是圖4反應(yīng)與NO級數(shù)的關(guān)系0.88,即反應(yīng)對H的反應(yīng)級數(shù)為-0.88Fig 4 Relationship between In k and In c(NO:綜上所述,可得到甲醛肟還原Pu(Ⅳ)的動(dòng)力學(xué)速率方程:y=0.88x-0.075dc(Pu(Ⅳ))/dtR2=0.99kc(Pu(Ⅳ))c1:61(FO)c0.8(H)0.6在18.7℃時(shí),反應(yīng)速率常數(shù)k=(110.39士7.70)(mol/L)-03/s0.6-0.30表1列出本實(shí)驗(yàn)條件下部分甲醛肟與In(c(H*ymol-L-)]Pu(Ⅳ)氧化還原反應(yīng)的k和k。圖3反應(yīng)與H+級數(shù)的關(guān)系2.5Fe3+濃度對Pu(N)還原速率的影響Fig 3 Relationship between In k' and In c(H+)后處理過程中,由于設(shè)備的腐蝕,料液中有Fe3+存在。實(shí)驗(yàn)測得的不同F(xiàn)e3濃度下甲醛2.4反應(yīng)對NO3級數(shù)的確定肟還原Pu(Ⅳ)的表觀速率常數(shù)列于表2。從在18.7℃時(shí),c(FO)=0.061mol/L,表2可看出,Fe3t的存在能加快甲醛肟還原c(H+)=1.0mol/L,p(Pu(Ⅳ))=0.952g/L,Pu(Ⅳ)到Pu(Ⅲ)的反應(yīng),說明Fe+的存在對表1本實(shí)驗(yàn)條件下部分甲醛肟與Pu(N)氧化還原反應(yīng)的k和kTable 1 Rate constants k and k of reaction between Fo and Pu(n)in HNO, solutionc(H+)/(mol·I-1)(FO)/(mol·Ic(NO3)/(mol·L-1)k/(mol·L-1)-.7·s-1)0.04010.05070.06120.0714112.130.08490.0507中國煤化工CNMHG 106.50.05070.63第2期肖松濤等:甲醛肟與Pu(Ⅳ)的還原動(dòng)力學(xué)169續(xù)表1c(H+)/(mol·-1)c(FO)/(mol·L-1)c(NO3)/(mol·L-1)k/((mol·L-1)-0.73·s-1)115.062.50.0507110.100.05070.0507110.37該反應(yīng)有催化作用,由于甲醛肟的氧化還原標(biāo)準(zhǔn)表3不同UO+濃度下電位為0.66V,Fe3+/Fe2+的氧化還原標(biāo)準(zhǔn)電位為甲醛肟還原PuN)的反應(yīng)速率0.771V,因此,其催化機(jī)理可認(rèn)為是Table 3 Effect of UO:*concentractionFe3++H2C:NOH→→Fe2++氧化產(chǎn)物on k and k of Pu( n)reduction with FoFe++Pu'c(Fe+)/(mol·1.-1)k/s-1k/(mol/L)-0.7·s-1)造成Fe3+濃度增加使Pu(Ⅳ)的還原速度108.44加快的原因可能是Fe2+對Pu(Ⅳ)的還原速度80.45大于甲醛肟還原Pu(Ⅳ)的速度。00084.74表2不同F(xiàn)e+濃度下的k'和kTable 2 Influence of Fe+ concentractionE:c(FO)0. 051 mol/L,c(H)=1.0 mol/L,c(NO)=on rate constants2.5mol/L-,p(Pu(Ⅳ))=0.952g/L,r=18.7℃c(Fe+)/(mol·L-1)k'/s-1k/(mol/L)-0.73·s-1)0.00001根據(jù) Arrhenius定理,以lnk'對1/T作圖105.040.0001(圖5),即可求得反應(yīng)過程的活化能E=122.41(68.82±3.00)kJ/mol0.005183.411.58192,38EE:c(FO)=0. 051 mol/L,, c(H+)=0. 1 mol/L, c(NO:y=-3931x+1437R2=0.992.5mol/L,p(Pu(Ⅳ)=0.952g/L,t=18.7℃2.6UO2+濃度對Pu(Ⅳ)還原速率的影響0.6在 Purex流程中,1BF料液中同時(shí)含有U和Pu,UO2+濃度對Pu(Ⅳ)還原速率的影響涉及到U-Pu分離的問題。因此,實(shí)驗(yàn)測定了不同UO濃度下甲醛肟還原Pu(Ⅳ)的反應(yīng)速圖5反應(yīng)與溫度的關(guān)系率。結(jié)果表明,UO2+的存在使甲醛肟還原Fig 5 Relationship between In k' and 1/TPu(Ⅳ)的反應(yīng)速率降低(表3)。27溫度對Pu(Ⅳ)還原速率的影響3結(jié)論對同樣的反應(yīng)物濃度和介質(zhì)條件,改變反通過對甲醛肟與Pu(Ⅳ)的動(dòng)力學(xué)基礎(chǔ)研應(yīng)體系的溫度,研究溫度對甲醛肟還原Pu(Ⅳ)究,生1)用醛肟還原Pu(Ⅳ)的的反應(yīng)速率的影響。隨著溫度的升高,Pu(Ⅳ)動(dòng)中國煤化工Pu(Ⅳ))/dt的還原速度明顯加快,溫度每升高10K,甲醛kc(CNMHG),在18.7℃肟還原Pu(Ⅳ)的速度增加約4倍。時(shí),k=(110.39士7.70)(mol/L)03/s,反應(yīng)170原子能科學(xué)技術(shù)第44卷過程的活化能E=(68.82±300)kJ/mol;Radiochem, 2001, 21(1):7-12(in Chinese)2)酸度升高,其反應(yīng)速率降低;3)升高溫度,[8]鄭衛(wèi)芳,劉黎明,常志遠(yuǎn),乙異羥肟酸改善 Purex其反應(yīng)速率加快;4)NO3濃度對反應(yīng)速率基流程鈾產(chǎn)品中U-Pu的分離[冂].原子能科學(xué)技本無影響;5)UO2·濃度增加,其反應(yīng)速率降術(shù),2000,34(2):110-115ZHENG Weifang, LIU Liming, CHANG Zhi-低;6)甲醛肟可快速將Pu(Ⅳ)還原為Pu(Ⅲ),yuan. 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