TODGA-DHOA体系从硝酸介质中萃取碱土金属

Extraction of Alkali Earth Metal Ions From Aqueous Nitric Acid Solutions With TODGA-DHOA in n-Dodecane

合成了新型酰胺类萃取剂N,N,N′,N′-四辛基-3-氧戊二酰胺(TODGA)和N,N-二己基辛酰胺(DHOA),研究了以正十二烷为溶剂时,该萃取体系在硝酸介质中对碱土金属的萃取行为,考察了萃取体系变化、酸度、金属离子强度、盐析剂离子强度及温度对萃取分配比的影响。同时对萃合物的化学组成及萃取机理进行了分析和讨论。研究结果表明:TODGA与M(Ⅱ)形成的萃合物分子为M(NO3)2.2TODGA(org);在293K时,TODGA萃取Sr(Ⅱ)的ΔG=(-2.08±0.06)kJ/mol,ΔH=(-24.30±1.45)kJ/mol,ΔS=(-75.80±4.74)J/(mol.K)。在萃取过程中没有形成三相,提出了从高放废液(HLLW)中分离回收Sr的初步方案。

A novel extraction reagent, N, N, N^1, N^1-tetraoctyl diglycolamide（TODGA） was synthesized. The influence of various factors on the extraction of alkali earth metal from aqueous nitric acid solutions with this amide （L） and N, N-dihexyl-octamide （DHOA） is studied, including extractant concentration in n-dodecane, extracted ions concentration, acidity of aqueous phase, ionic strength of salting out agent and temperature. The composi- tion of the extracted species and the mechanism of extraction were studied. The results sug- gest the extracted species to be M（NO3）2 · 2TODGA（org）. The enthalpy change for the extraction of Ca（I[）, Sr（l]） and Ba（[[） are （-38.85±1.37） kJ/mol, （-24.30± 1.45） kJ/mol and （- 9. 14 ± 2.01） kJ/mol, respectively. The ehtropy change are （ - 78. 26 ± 2.67） J/（mol · K）, （-75.80-4.74） J/（mol · K） and （-51.85±6.11） ]/（mol · K）, and the Gibbs energy change are （ - 9.88± 0.06） kJ/mol, （ - 2.08 ± 0.06） kJ/mol and （6.06 ± O. 22） kJ/mol at 293 K, respectively. No emulsification or third phase formation is observed during the extraction process. On the basis of the experiment results, the method of seperation and recovery of Sr from high-level liquid waste puts forward.