8th Liquid Matter Conference September 6-10, 2011 Wien, Austria ...

P2.76Tue 611:23-14:00Regularities in the rare earths hydrolytic behaviourSophia Stepanchikova 11 Intitute of Geology and Mineralogy, pr. Koptyuga, 3, 630090, Novosibirsk, RussianFederationThe REE hydrolysis equilibria in natural waters, environmental and geochemical systems are theleast well understood. Values of the stability constants have significant dispersion and being obtainedin different experimental conditions, are often incomparable with each other. The experimentaldata are usually obtained at considerably ionic strength and no taking in account presencetogether with monohydroxides, higher-order complex species. The main goal of this study was tominimize the errors arising from extrapolation of stability constants to zero ionic strength. Equilibriuain near-neutral and alkaline aqueous solutions of REE series were studied by spectrophotometricmethod with m-cresol purple and 2-naphtol as pH indicators with intensive spectra in visibleand UV regions. Experiments have been obtained at ionic strength no more 0.0005 without of polymerforms, side reactions and hydroxide precipitations. Complex anions as Ln(OH) 2+ , Ln(OH) 2+and Ln(OH) 30 have been found in freshly prepared LnCl 3 solutions. Species Ln(OH) 4− have alsobeen detected for same of yttrium group elements. The stability constants of hydroxide complexesat zero ionic strength were obtained as parameters of linear regression characterized spectra ofindicators in the solution under study. The data confirm increasing of monohydroxide complexesstability in the direction from La to Lu according to concept of ”lanthanoide compression”. Atthe same time failure of monotonous dependence from atomic number is distinctly expressed andis explained by the ligand field and covalence effects. One another set of data suggesting that thechemical bonding in lanthanoide complexes is not purely ionic is presented.76