Thorium Carbonate

The precipitate obtained by adding sodium carbonate to the solution of a thorium salt is a basic carbonate which dissolves readily in excess of carbonate solution, forming a complex salt. This property serves to distinguish and separate thoria from other rare earths whose carbonates do not so readily dissolve in excess of alkali carbonate. From this solution alcohol precipitates the complex salt Na₆Th(CO₃)₅.12H₂O as a crystalline powder; the following salts have also been obtained: K₆Th(CO₃)₅.10H₂O, (NH₄)₂Th(CO₃)₃.6H₂O, Tl₆Th(CO₃)₅.

According to Chauvenet thorium oxide absorbs carbon dioxide, forming orthocarbonates. Under ordinary pressure the compound 2Th(OH)₄.CO₂ is produced, but under 30-40 atmospheres the ortho-carbonate ThCO₄.2H₂O. Under this latter pressure the anhydrous oxide yields ThCO₄.6ThO₂. The addition of sodium carbonate to a thorium salt solution forms ThCO₄.8H₂O, which loses 6H₂O in a vacuum, and on heating to 120° C. forms the basic salt 2ThCO₄.2ThO₂.3H₂O.