Comprehensive extraction study using N,N-dioctylthiodiglycolamic acid: effect of S donor on metal extraction

Area of Science:

• * Coordination Chemistry
• * Analytical Chemistry
• * Materials Science

Background:

• * Investigating novel ligands for selective metal ion extraction is crucial for advancing hydrometallurgy and recycling processes.
• * N,N-dioctylthiodiglycolamic acid (T-DODGAA), a sulfur-donor ligand, presents unique properties due to its thioether linkage.
• * Comparison with N,N-dioctyldiglycolamic acid (DODGAA), an oxygen-donor analog, provides insights into donor atom effects on extraction efficiency.

Purpose of the Study:

• * To comprehensively evaluate the metal ion extraction ability of T-DODGAA for 56 different metal ions.
• * To compare the extraction performance of T-DODGAA with DODGAA.
• * To assess the practical feasibility of T-DODGAA in selective separation of rare metal ions for hydrometallurgy and recycling.

Main Methods:

• * Potentiometric titration was employed to determine the acid dissociation constant (pK_a) of T-DODGAA in an aqueous solution.
• * Solvent extraction experiments were conducted using T-DODGAA in isooctane to extract various metal ions via a proton-exchange mechanism.
• * Selective separation tests were performed on mixed metal systems, including rare metal ions.

Main Results:

• * T-DODGAA was found to be a slightly weaker acid than DODGAA, with pK_a values of 3.71 and 3.54, respectively.
• * T-DODGAA demonstrated superior extraction performance over DODGAA for several metal ions, including Hf(IV), Cr(III), Fe(III), Ni(II), Cu(II), Pd(II), Ag(I), Au(III), Hg(II), Al(III), and Ga(III), especially for soft metal ions.
• * Successful selective separation of rare metal ions such as Sc(III), Ni(II), Co(II), Pd(II), Au(III), In(III), and Ga(III) was achieved in mixed-ion systems.

Conclusions:

• * T-DODGAA is an effective ligand for the extraction of a wide range of metal ions, exhibiting enhanced selectivity for soft metal ions.
• * The sulfur donor atom in T-DODGAA contributes to its superior extraction capabilities compared to the oxygen donor in DODGAA.
• * T-DODGAA shows significant potential for practical applications in hydrometallurgy and metal recycling due to its efficient and selective metal ion separation properties.