摘 要:采用恒界面池法研究了在NH4SCN-HCl介质中DIBK-TOPO(二异丁基酮-三辛基氧化膦)体系萃取分离锆和铪的动力学性质,在一定实验条件下分别考察了搅拌速度、温度和界面积对锆铪萃取速率的影响。实验结果表明:当搅拌速度小于135 r·min-1时,锆铪的萃取速率随着搅拌速度的增加而增加,DIBK-TOPO体系对锆铪的萃取类型为扩散反应控制;当搅拌速度在135155 r·min-1范围内时,锆铪的萃取速率分别出现一段与搅拌速度无关的坪区,但锆的萃取速率常数与比界面积无关,对锆的萃取类型为相内化学反应控制类型,其表观活化能为-11.963 k J·mol-1,铪的萃取速率常数随着比界面积的增加而线性增加,且直线不通过坐标原点,因而对铪的萃取类型则为混合控制类型,其表观活化能为-22.406 k J·mol-1;当搅拌速度超过155 r·min-1时,因搅拌速度过快,造成两相界面出现混乱而不稳定。升高温度不利于DIBK-TOPO体系对锆和铪的萃取。
采用恒界面池法研究了在NH_4SCN-HCl介质中DIBK-TOPO(二异丁基酮-三辛基氧化膦)体系萃取分离锆和铪的动力学性质,在一定实验条件下分别考察了搅拌速度、温度和界面积对锆铪萃取速率的影响。实验结果表明:当搅拌速度小于135 r·min-1时,锆铪的萃取速率随着搅拌速度的增加而增加,DIBK-TOPO体系对锆铪的萃取类型为扩散反应控制;当搅拌速度在135~155 r·min~(-1)范围内时,锆铪的萃取速率分别出现一段与搅拌速度无关的坪区,但锆的萃取速率常数与比界面积无关,对锆的萃取类型为相内化学反应控制类型,其表观活化能为-11.963 k J·mol~(-1),铪的萃取速率常数随着比界面积的增加而线性增加,且直线不通过坐标原点,因而对铪的萃取类型则为混合控制类型,其表观活化能为-22.406 k J·mol~(-1);当搅拌速度超过155 r·min~(-1)时,因搅拌速度过快,造成两相界面出现混乱而不稳定。升高温度不利于DIBK-TOPO体系对锆和铪的萃取。
Extraction Kinetics of Zirconium and Hafnium in DIBK-TOPO System
Zhao Jun Xu Zhigao Zhang Wenjie Li Panhong Chi Ruan Xu Yuanlai
Key Laboratory of Catalysis and Materials Science of the State Ethnic Affairs Commission & Ministry of Education,South-Central University for Nationalities
Key Laboratory for Green Chemical Process of Ministry of Education,Wuhan Institute of Technology
Abstract:
The extraction kinetics of zirconium and hafnium from NH_4SCN-HCl medium by the mixture of DIBK( diisobutyl ketone)and TOPO( tri-n-octyl phosphine oxide) was studied using a Lewis Cell. Under the given conditions,the effects of interfacial area,temperature and stirring speed on the extraction rate were separately investigated. The experiment results showed that when the stirring speed was less than 135 r·min~(-1),the extraction rates of zirconium and hafnium in the DIBK-TOPO system increased with the increase of stirring speed. When the stirring speed was in the range of 135 ~ 155 r·min~(-1),the extraction rates of zirconium and hafnium had a plateau region which did not vary with the stirring speed. But the extraction rate constant of zirconium was not related with the specific interfacial area,the type of extraction of zirconium was controlled by chemical reactions at bulk phase with the activation energy of-11. 963 k J·mol~(-1). While the extraction rate constant of hafnium increased linearly with the increase of the specific interfacial area and the line passed through the origin of coordinates,the type of extraction of hafnium was controlled by mixed-control with the activation energy of-22. 406 k J·mol~(-1). When the stirring speed was more than 155 r·min~(-1),the phase interface was chaotic and unstable because the mixing speed was too fast,and it was not conducive to extraction operation. Elevated temperature was not conducive to the extraction of zirconium and hafnium in DIBK-TOPO system.
在动力学研究中,扩散控制过程的表观活化能小于20.9 k J·mol-1,而化学反应控制过程的表观活化能大于42 k J·mol-1,混合控制过程的表观活化能在20.9~42 k J·mol-1[20] 之间。根据图5中直线斜率,结合阿累尼乌斯方程,可计算得出DIBK-TOPO体系萃取锆铪的表观活化能分别为-11.963和-22.406 k J·mol-1。综合图3和5的实验结果,可以初步判断当转速为135~155 r·min-1时,DIBK-TOPO体系对铪萃取为混合反应控制,而锆的表观活化能虽然较小,但并不能说明一定是扩散控制,还需要根据界面积进行确定。
图4 温度对锆铪萃取速率(RO)的影响Fig.4 Effect of temperature on extraction rate of zirconium and hafnium(RO)
图5 锆和铪的lnRO与T-1关系Fig.5Relationships between lnROand T-1of zirconium and hafnium