Stepwise Recovery of Molybdenum, Vanadium, and Tungsten with Amino-Type “Trident” Molecule by Stripping

Comparative Extraction of Aluminum Group Metals Using Acetic Acid Derivatives with Three Different-Sized Frameworks for Coordination

“…The ∆pH 1/2 values for three ions between 2 and 5 were much larger than those between 1 and 4 and those between 3 and 6. The extraction pH ranges of all aluminum group ions with 2 were much lower than those with 1 and 3, probably due not only to the "converging functional group effect", but also to the "size discrimination effect" [15][16][17] or high polarity of the alkenyl trimethylol framework. The ∆pH 1/2 values for the three ions between 3 and 6 were larger than those between 1 and 4, possibly due to the different coordinating geometries of calix [4]arene derivative 1 and tripodal derivative 3.…”

“…All extraction reagents contained acetic acid; hence, all acted by a proton/cation exchange mechanism, and the extraction of the three metal ions increased with increasing the pH values. The reagent based on the calix [4]arene and tripodal frameworks 1-3 clearly exhibited a "converging functional group effect" [15][16][17] and extracted the metal ions at lower pH values than those for their corresponding monomer and monopodal reagents 4-6. A comparison using extraction equilibrium constants was not possible because of the different extraction reactions for 1-3 and 4-6.…”

“…In contrast, the ∆pH 1/2 value between Ga 3+ and In 3+ for 2 was smaller than that for 5, indicating a reduced separation efficiency for 2. This observation may be as a result of a "negative structural effect" [16,47], and indicates that the coordination site of 2 provides a better fit for Ga 3+ , or rather is sized somewhere between the ideal sizes for Ga 3+ and In 3+ . The ∆pH 1/2 between Ga 3+ and In 3+ for 3 was larger than that for 6, representing a higher separation efficiency of 3.…”

“…Most macrocyclic compounds form very stable metal ion complexes, the stability of which depends on how well the cation fits into the cavity formed by the donor atoms [14]. The size-discriminating effect is also the most comprehensible example among the six proposed "structural effects" for host ionophores, like calixarene derivatives [15][16][17], although there are some more requirements to employ them as extraction reagents [18]. To investigate the size discrimination for a series of homologous metal ions, a well-considered research strategy is required, and the data systematically collected for ionophores of different sizes must be compared in order to contribute to future molecular designs for more effective metal separation.…”

“…Our group has synthesized various extraction reagents based on different framework types, namely calix [4]arenes [15,18,19], "trident" molecules as alkenyltrimethylols [16,[19][20][21][22], and 2,2 ,2 -trihydroxytriphenylmethane [23]. These frameworks provide unique properties for the synthesis of their derivatives and for metal extraction (Table 1).…”