gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1992.056.384.09 Mineralogy Transformation of Chernikovite into Meta-Uranocircite II, Ba(UO2)2(PO4)2·6H2O and Study of Its Solubility Vochten R. F. * Van Haverbeke L. † Van Springel K. * Laboratorium voor Chemische en Fysische Mineralogie, Universiteit Antwerpen, Middleheimlaan 1, 2020 Antwerpen, Belgium Laboratorium voor Anorganische Scheikunde, Universiteit Antwerpen, Groenenborgerlaan 171, 2020 Antwerpen, Belgium 9 1992 56 384 367 372 10 7 1991 5 12 1991 Copyright © 1992, The Mineralogical Society 1992 Abstract

Chernikovite, (H3O)2(UO2)2(PO4)2, was synthesized and subsequently transformed into meta- uranocircite II, Ba(UO2)2(PO4)2·6H2O, by ion-exchange experiments. The crystals are lemon-yellow and strongly fluorescent. From solubility data a mean pKs value at 25°C was determined as 51.79 ± 0.21. For a cell volume of 16.31.7 Å3 and Z = 4 the density was calculated as 3.970 g/cm3 whereas the measured density is 3.964 g/cm3. The X-ray powder pattern shows the following strongest lines:3.609(60)(114),3.470(60)(1¯23),2.9272(90)(132)2.9006(90)(3¯12), 2.6065(80)(1¯16), 2.4581(75)(2¯33), 2.2015(100)(143 ; 1¯43), 2.1869(100) (241 ; 226 ; 2¯41).

 Keywords meta-uranocircite II uranylphosphate group thermal behaviour solubility product