Development of novel extractants with amino acid structure for efficient separation of nickel and cobalt from manganese ions

The solvent extraction separation of nickel and cobalt from manganese is an important issue to be resolved. Novel amic acid type extractants with the glycine or sarcosine moiety N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]glycine (D2EHAG) and N-[N,N-di(2-ethylhexyl)aminocarbonylmethyl]sarcosine (D2EHAS) were synthesized to achieve this separation. These extractants were prepared by a simple two-step reaction and were readily soluble in aliphatic organic solvents. The extraction behavior of Ni²⁺, Co²⁺, and Mn ²⁺ with D2EHAG and D2EHAS in n-dodecane was investigated compared with that of conventional extractants. The novel extractants extracted Ni ²⁺ and Co²⁺ preferentially with a high selectivity to Mn²⁺. The metal ions could be back-extracted quantitatively using 1 mol dm^-3 sulfuric acid. The extraction mechanism of the three metal ions with D2EHAG and D2EHAS was investigated, and results suggest that one divalent metal ion is extracted with two extractant molecules.