A Comprehensive Extraction Study Using a Mono-alkylated Diglycolamic Acid Extractant: Comparison Between a Secondary Amide Group and a Tertiary Amide Group

Abstract

The extraction characteristics of N-dodecyldiglycolamic acid (C₁₂DGAA), with a secondary amide group, for 56 metal ions have been investigated, and compared with those of N,N-dioctyldiglycolamic acid (DODGAA) with a tertiary amide group. C₁₂DGAA is capable of quantitative transfer for a variety of metal ions through a proton-exchange reaction, and the extraction behavior as a function of the aqueous-phase pH is similar for C₁₂DGAA and DODGAA. Compared with DODGAA, C₁₂DGAA has a poor extraction performance and separation ability for rare-earth metal ions, except for Sc(III). However, C₁₂DGAA tended to provide better extraction for relatively small-sized metal ions than DODGAA. In addition, it was found that C₁₂DGAA enables the selective removal of Hg(II) from aqueous solutions containing various divalent metal ions (Hg(II), Pb(II), Cu(II), Cd(II), Zn(II), Mn(II), Co(II), and Ni(II)).