Abstract
Genesis of metaautinute [Ca(UO2/PO4)2 · 7H2O] starting from curite hints at the existence of an intermediate hydrogen autunite stage [HUO2PO4 · 4H2O]. The substitution of protons in hydrogen autunite by Ca2+ ions is proved by electrokinetic measurements. As a consequence of the similarity between X-ray powder patterns of hydrogen autunite and meta-autunite a glycolation method has been applied in order to distinguish the two species.
The cell dimensions have been determined from Guinier X-ray diffraction patterns. Both minerals are tetragonal with a=6.981±0.005 Å and c=8.448±0.005 Å for metaautunite and a=7.084±0.005 Å and c=8.777±0.005 Å for hydrogen autunite.
For both minerals, the zeta-potential is mostly negative and is strongly influenced by temperature, pH and concentration of cations in the suspension. The surface conductivity has been calculated from the value of the zetapotential. The electrokinetic properties of metaautunite are very similar to those of metatorbernite.
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Vochten, R., Deliens, M. Transformation of curite into metaautunite paragenesis and electrokinetic properties. Phys Chem Minerals 6, 129–143 (1980). https://doi.org/10.1007/BF00311050
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DOI: https://doi.org/10.1007/BF00311050