Scandium solubility constant

There have been very few studies on the hydrolytic reactions of actinium(III). There is only one study on the solubility of Ac(OH)3(s) (Ziv and Shestakova, 1965). These authors studied the solubility in a medium of 0.001 moll NH4NO3 and at 22 "C. They corrected for the activities of the ions in the solution and obtained a solubility constant of log A jio = 21.10 0.05. This value appears consistent with the solubility constants obtained for scandium(lll), yttrium(III) and lanthanum(III), with actinium(III) hydroxide as expected being the most basic. The solubility constant obtained by Ziv and Shestakova is retained in the present study for zero ionic strength and 25 C, namely,... 

Figure 53 shows the isothermal section of the Sc-Nd-Si system at 600 C which was determined by Banakh and Kotur (1998). The binary silicides NdSi2 t and NdSi dissolve 15 and 7 at.% Sc, respectively. The solubility of the third component in other neodymium and scandium binary silicides does not exceed 2 at.%. Five ternary compoimds exist in this system (see table 19). One of them, (4) in fig. 53, has variable composition of Sc and Nd. Four other have practically constant composition. 

The hydroxide and oxide phases that exist for scandium(III) include scandium hydroxide, Sc(OH)3(s), which likely has both amorphous and crystalline forms, ScOOH(s), and scandium oxide. It would be expected that the amorphous hydroxide is the most soluble and Sc203(s) the least. There have been few studies that have examined the solubility of these phases. None of the hydroxide or oxide phases of scandium are known to form naturally, with scandium present, as a major component, in eight mineral phases only (Wood and Samson, 2006). Moreover, there is much conjecture over which phases have actually been studied as well as their crystallinity (Baes and Mesmer, 1976 Wood and Samson, 2006). This review has selected data for both the hydroxide and oxide phases, based largely on the similarity in the stabilities obtained for the phases studied. Baes and Mesmer (1976) provided a stability constant for ScOOH(s) on the basis of data provided by Schindler (1963), but it is believed that the phase actually studied was Sc(OH)3(s) given the similar solubility found in the studies of Feitknecht and Schindler (1963) and Shkolnikov (2009). 

Ivanov-Emin, Nisel son andIvolgina (1960) andIvanov-Eminetal. (1968) studied the solubility of well-crystallised scandium hydroxide in solutions of sodium and potassium hydroxide. They showed that the solubility increased linearly with an increase in the hydroxide concentration. The stability of the solubility reaction should only be slightly dependent on ionic strength and medium and, as such, Ivanov-Emin et al. found a very similar stability constant in both bases. The constant obtained should be similar to that at zero ionic strength and the average is... 

Ivanov-Emin, B.N., Borzova, L.D., Zaitsev, B.E., and Mekes Fisher, M. (1968) Solubility of scandium hydroxide in potassium hydroxide solutions. Russ. J. Inorg. Chem., 13, 1156-1157 (English translation). Ivanov-Emin, B.N., Egorov, A.M., Romanuk, V.I., and Siforova, E.N. (1970) Constants... 

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