ION-PAIR EXTRACTION OF MOLYBDENUM(VI) IN THE PRESENCE OF 3-HYDROXY-2-NAPHTHOIC ACID

The extraction of Mo(VI) from its aqueous solutions into chloroform, i n the presence of 3-hydroxy-2-naphthoic acid (HNA) and n-butyltripheny lphosphonium bromide (LBr), was investigated using 99-Mo tracer, and t he composition of extracted species was studied. The yellow extracts f rom diluted sulfuric acid solutions (0.5 mol dm-3 H2SO4 to pH 5) conta ined ion-associates of phosphonium cations (L+) with oligonuclear anio nic complexes of Mo(VI) and HNA. Whereas the mean nuclearity of the ex tracted species was increasing slightly from 2.6 to 3.0 with pH increa sing from 1.2 to 4.1, the content of HNA in the species increased simu ltaneously more than three times. The highest values of molybdenum dis tribution ratio were found at pH 3.0-3.2, where as much as 95% of the total amount of molybdenum was extracted at c(HNA) = 14.6 mmol dm-3, c (HNA)/c(Mo) = 147, in the form of the species with a mean composition expressed by a ratio L+:Mo:HNA = 3.1:2.7:1.4. A comparison with previo usly studied ion-pair extraction of Mo(VI), in the presence of 2,3-dih ydroxynaphthalene as a chelating reagent, is given.