On the solubility of radium sulfate and carbonate
Radium is one of the most toxic elements and its concentration in different human activities and migration from man-made wastes provokes a strong interest in environmental science. To be able to model the migration process, reliable experimental thermodynamic data of radium compounds are needed.
In this work details of the safe radium source disassembly which were previously used in brachytherapy are described and different methods for conversion of RaSO4 into aqueous solution are reviewed. The method of choice included three cycles of RaSO4 heating in 1.5 M Na2CO3 up to 85 oC, cooling and subsequent removal of supernatant. X-ray diffraction studies showed that the method allows the synthesis of amorphous RaCO3, which can be dissolved in mineral acid. Gamma spectrometric measurements showed that most of the initial RaSO4 was converted into solution and that 7 ± 1 % of the initial 210Pb was co-precipitated with RaCO3. Synthesized RaCO3 was dissolved in HCl to prepare a radium stock solution. 
The radium stock solution was used to determine the solubility of pure RaSO4 and RaCO3 from oversaturation using Na2SO4 and Na2CO3 as a source of sulfate and carbonate ions. The solubility was determined at 25.1 oC as a function of ionic strength using NaCl media. The concentration of radium was measured by gamma spectrometry after separation of the aqueous phase from the solid phase using ultracentrifugation. The extended specific ion interaction theory was used to extrapolate solubility product constants to zero ionic strength (log10 Ksp° = -10.16 ± 0.05 for RaSO4 and log10 Ksp° = -7.73 ± 0.56 for RaCO3) and to calculate ion interaction coefficients.
A comparison of the shapes of the radium solubility curves for both anions with the shapes of corresponding barium solubility curves demonstrates the similarity of the behaviour of radium and barium salts in saline solutions. It can be supposed that due to the similarity of the radium and barium effective ionic radii, and the same charge, these ions undergo similar specific ion interactions in NaCl media.
Radium and Radioactivity
The radiations longest known to us are those capable of acting directly upon our senses; such are the rays of sound and light. But it has also long been recognized that, besides light itself, warm bodies emit rays in every respect analogous to luminous rays, though they do not possess the power of directly impressing our retina. Among such radiations, some, the infra-red, announce themselves to us by producing a measurable rise of temperature in the bodies which receive them, while others, the ultra-violet, act with specially great intensity upon photographic plates. We have here a first example of rays only indirectly accessible to us.
AQUEOUS SYSTEMS AT HIGH TEMPERATURE. XI. EFFECT OF PRESSURE ON LIQUID- LIQUID IMMISCIBILITY IN THE SYSTEM UO$sub 2$SO$sub 4$-H$sub 2$O AND LIQUID-SUPERCRITICAL FLUID EQUILIBRIA IN THE SYSTEM UO$sub 2$SO$sub 4$-H$sub 2$SO$sub 4$-H$sub 2$O 290-430 C, 75-330 BARS
Abstract By making use of a visual method, the effect of hydrostatic pressures up to 320 bars in raising the temperature, in the vicinity of 300°C at saturation vapour-pressure, of second-liquid phase formation in the system UO2SO4H2O for solutions varying from 0·14 to 4·5 molal in UO2SO4 was found to be +0·082° per bar. One exploratory run each on a solution of UO2F2 and H2O, and of CuSO4, H2SO4 and H2O, both of which show liquid-liquid immiscibility near 320° gave values of ( ∂t ∂p ) at constant composition of ∼+0·10 and +0·11, respectively. Since ( ∂t ∂p ) at a constant density of 0·712 for liquid H2O at 300° is +0·093° per bar, the temperature of liquid-liquid immiscibility appears to show a strong dependency on solvent density. The effect of pressures up to 330 bars on the temperature of second-liquid phase formation from the supercritical fluid UO3SO3H2O near 400° was found also to correspond approximately to ( ∂t ∂p ) at constant density for H2O at the same initial pressure, the value being in the vicinity of +0·4° per bar. In some additional experiments the vapour-pressures for the deliquescence of solid UO2SO4 hydrate were found to vary from 120 bars at 345° to 305 bars at 425°.