In order to develop a new partitioning process of trivalent Am and rare earth elements(RE) by solvent extraction based on the n-octyl(phenyl)-N,N-diisobutyl carbamoyl methyl phosphine oxide(CMPO) and tributyl phosphate(TBP) mixed solvent, a mutual-separation of Am and RE was studied in a 6-component solution system containing Am, Ce, Nd, Eu, Y and Dy. Experimental systems were composed of a co-extraction of Am and RE by CMPO/TBP, a selective stripping of nitric acid by NaNO3, a selective stripping of Am by diethylene triamine pentaacetic acid (DTPA)-NaNO3 mixed solution, and a stripping of RE by HNO3 in series. The co-extraction yields of Am, Ce, Nd, Eu and Y by 0.2M CMPO/30% TBP at 2M HNO3 and O/A=3, were 99%, 96.9%, 96.9%, 96.3% and 81.6%, respectively. Nitric acid was effectively stripped from loaded-organic phase containing the Am, RE and HNO3 during 3 contact times with 0.5M NaNO3 (pH=2). The stripping yields of Am increased with increasing the DTPA concentration and pH of aqueous phase, while they decreased with increasing NaNO3 concentration. Complex formation moral ratio of DTPA to trivalent metal ion was approximately 1. The stripping yield of Am was 47.1% at 0.05M DTPA/2M NaNO3 (pH=2). The separation factors of Ce, Nd, Eu and Y with respect to Am were 17.0, 14.3, 2.8 and 0.9 respectively. Here Y needed to be removed before the stripping of Am. On the other hand, the stripping yields of RE increased with decreasing the nitric acid concentration. RE was stripped more than 70% by 0.01M HNO3. From the results, a new partitioning flow sheet for the selective separation of Am in a process is suggested. This new process overcomes the demerit of existing CMPO/TBP process, which requires an additional process to selectively separate Am from RE.

CMPO/TBP 혼합추출제에 의한 3가의 Am과 희토류 원소(RE : rare earth element)를 상호분리하는 공정을 개발하기 위하여 Am과 Ce, Nd, Eu, Y, Dy 등이 함유된 6성분계 용액으로 (1) CMPO/TBP 혼합추출제에 의한 공추출, (2)NaNO3에 의한 질산 역추출, (3)DTPA/NaNO3 혼합용액에 의한 Am 역추출(4)질산에 의한 RE 역추출을 순차적으로 수행하였다. 0.2 M CMPO/30% TBP, 2M 질산 및 O/A=3에서의 Am, Ce, Nd, Eu, Y의 공추출율은 각각 99%, 96.9%, 96.9%, 96.3%, 81.6%였으며, 질산 0.5M NaNO3 용액(pH=2)으로 3회 정도 역추출하여 제거할 수 있었다. 한편 Am의 역추출율은 DTPA 농도 및 pH 증가에 따라 증가하였으나, NaNO3 농도 증가에 따라서는 감소하였다. DTPA와 3가 금속이온과의 착물은 약 1:1의 몰비로 형성되었다. 0.05M DTPA/ 2M NaNO3(pH=2)의 경우 47.1%의 Am이 역추출되었으며, 이때 Ce, Nd, Eu, Y에 대한 분리계수는 각각 17.0, 14.3, 2.8, 0.9로서, Y를 Am 역추출 전에 미리 제거시켜야 한다 한편 RE의 역추출은 질산농도 감소에 따라 증가하며, 0.01M 질산에서 70%이상이 역추출되었다. 이상의 결과로부터 기존의 CMPO/TBP에 의한 Am/RE 상호분리 시 이를 모두 공추출하여 공역추출한 후 추가의 상호분리 공정이 요구되는 단점을 극복하면서 동일 공정 흐름 내에서 Am을 선택적으로 분리할 수 있는 새로운 공정 흐름도를 제시하였다.