STUDIES ON THE GROWTH, DISSOLUTION AND EQUILIBRIUM SOLUBILITY OF Sa, Pb AND Ra SULFATES IN AQUEOUS SULFATE MEDIA: WITH APPLICATIONS TO THE SULFURIC ACID LEACHING PROCESS FOR URANIUM MILLING

Abstract

<p>The formation of hetero-epitaxial deposits of Sa, Pb and<br />mixed Ba/Pb and Ba/Ra sulfates on quartz and mica surfaces<br />has been demonstrated. The kinetics of their growth and<br />dissolution has been established. The importance of the<br />formation and dissolution of these deposits is found in the<br />observation that they are all host solids for the formation of<br />solid solutions of 228-radium (and by extension 226-radium).</p> <p>Desorption studies caried out on Ba²⁺, Ca²⁺ and SO₄²⁻ from quartz and mica surfaces into water indicate that these<br />ions are strongly retained by mica surfaces, with retention<br />times which are of sufficient duration to permit the formation<br />of the potential host solids required by the National Uranium<br />Mine Tailings model.</p> <p>The equilibrium solubility of PbSO₄ in Na₂SO₄ solutions<br />and in H₂SO₄ solutions from 0 to 6m has been measured<br />experimentally at 60ºC with subsequent modelling by means of<br />the Pitzer formulation for ion activities at high ionic strength.<br />The equilibrium solubility of BaSO₄ in H₂SO₄ solutions from 0<br />to 6m has been measured experimentally at both 25ºC and<br />60ºC with subsequent modelling. Such data are a necessary requirement for the modelling of the evolution of uranium mill wastes by the National Uranium Mine Tailings model and for<br />understanding the fate of radium during the milling and<br />leaching processes.</p>