AN EXPERIMENTAL STUDY OF HYDROXO COMPLEX FORMATION IN BASIC AND NEAR–NEUTRAL SOLUTIONS OF RARE-EARTH ELEMENTS AND YTTRIUM AT 25 oC
S.A. Stepanchikova, R.P. Biteikina, G.P. Shironosova, G.R. Kolonin
V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, pr. Akademika Koptyuga 3, Novosibirsk, 630090, Russia
Keywords: Rare-earth elements, hydrolysis, complex formation, tetrad effect
Abstract
We have studied the hydrolytic behavior of Y3+ and trivalent ions of rare earth elements in aqueous solutions at 25 oC. The stepwise stability constants of hydroxide complexes were measured by spectrophotometry, using m -cresol purple and 1-(2-pyridylazo)-2-naphthol as pH indicators at an ionic strength no more than 0.0005. The results showed that at pH ranging between 6.0 and 11.0 in freshly prepared solutions of REE trichlorides, lanthanides are presented as Ln 3+, Ln(OH)2+, Ln(OH)2+, and Ln(OH)30. The plots of the formation constants of monohydroxo complexes of 4 fn ions M3+ versus atomic number Z deviate from smooth ones and consist of four convex curves. This phenomenon is also observed in normalized spectra of REE concentrations in natural objects and is known as the tetrad effect. The obtained data give an insight into the relationship between REE complex formation and REE fractionation in geochemical processes and can be used for physicochemical modeling of geochemical systems.
DOI: http://dx.doi.org/10.1016/j.rgg.2014.07.002
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