Treatment of Uranium Minerals

The chief source of uranium compounds is uraninite, but at the present time the working up of all uranium minerals has for its main object the extraction of radium, and the uranium salts are merely produced as by-products. Treatment of Uranium Minerals in use vary according to the nature of the desired product, which may be ammonium or sodium diuranate, or uranyl nitrate.

The mechanically dressed ore is first roasted in order to remove sulphur, arsenic, and other volatile ingredients, and then heated in a reverberatory furnace with sodium carbonate or sodium sulphate. The product is extracted with warm dilute sulphuric acid, whereupon the uranium passes into solution, whilst the radium remains in the residue with calcium, barium, and lead. This residue, which is the starting material for the extraction of radium, also contains silica and small quantities of copper, bismuth, arsenic, antimony, iron, aluminium, manganese, zinc, nickel, cobalt, thallium, vanadium, columbium, tantalum, and rare earths.

The acid filtrate is treated with an excess of sodium carbonate solution, whereby basic carbonates of iron, aluminium, nickel, and cobalt are precipitated, while the uranium remains in solution as sodium uranyl carbonate. The solution is neutralised by adding sulphuric acid and boiling, and on evaporation, sodium diuranate, Na₂U₂O₇.6H₂O, separates as a heavy yellow precipitate. If ammonium carbonate is used instead of sodium carbonate, or if the solution of sodium uranyl carbonate is boiled with ammonium sulphate, ammonium diuranate is obtained. In order to obtain uranyl nitrate, UO₂(NO₃)₂.6H₂O, the ammonium diuranate may be heated and the residue dissolved in nitric acid; or the original ore after roasting may be dissolved in nitric acid and the solution evaporated to dryness, the residue then being digested with water, filtered, and allowed to crystallise. The uranyl nitrate is purified by recrystallisation from water.

Carnotite may be fused with potassium hydrogen sulphate and the residue extracted with water. From the solution the double sulphates of potassium with uranium and vanadium may be obtained by crystallisation. These are reduced by means of zinc and sulphuric acid, and the vanadium precipitated from the solution by means of ammonia and ammonium carbonate. Ammonium diuranate separates from the filtrate on boiling.