State of uranyl silicates MII(HSiUO6)2 ·6H2O (MII=Mn, Co, Ni, Cu, Zn) in aqueous solutions

Abstract

Uranyl silicates with formula MII(HSiUO6)2·6H2O (MII=Mn, Co, Ni, Cu, Zn) were investigated in aqueous solutions in the pH range of 0÷14. The pH interval was established where compounds preserve their composition and structure. It varies in the pH range of (3.5–4.0)÷(10.8–11.4) and depends on MII type. Out of this pH interval investigated uranyl silicates convert to the compounds of other composition and structure, such as amorphous silica, polyuranates and hydroxides of 3d-transition elements. The solubility of MII(HSiUO6)2·6H2O was determined, it’s value changes on the several orders of magnitude from 10−6 M in subalkali solutions to 10−3 M in acid and strongly alkaline media. Using obtained experimental data the solubility products and solubility curves of uranyl silicates were calculated by mathematical modeling. Also the speciation diagrams of uranium (VI), silicon (IV) and M (II) in solutions and solids were plotted.