Leaching of uranium ores using alkali-metal or ammonium carbonate and bicarbonate

摘要

Uranium containing materials having a substantial proportion of the uranium in the tetravalent state are leached with a solution containing alkali metal or ammonium carbonate in the presence of alkali metal or ammonium bicarbonate and a gas containing free oxygen and carbon dioxide, the amount of carbon dioxide being sufficient to maintain a bicarbonate concentration of at least 10 grams per litre until extraction is completed and the amount of alkali metal or ammonium carbonate and bicarbonate being sufficient to form soluble uranyl tricarbonates. The necessary bicarbonate may be formed in situ in the case of sulphur containing ores by the reaction therewith of oxygen and sodium carbonate. The aerating gases are normally air containing for example 1 to 2 per cent or more carbon dioxide, for example a mixture of flue gas and air. The carbon dioxide may also be supplied when oxygen is employed as aerating gas, by recycling, when the recycled gases pick up carbon dioxide generated by bicarbonate decomposition. The leaching may be effected at 50 to 100 DEG C. at atmospheric pressure. As shown in the Figure, the ore is wet ground in a grinder a and fed to a filter b where the filter cake is washed by a recycle solution c, and the filter cake is then fed successively to agitators d1, d2, d3 and d4. The filter cake is diluted in agitator d1 to 50 per cent solid content by a sodium carbonate solution e and is successively agitated with the aerating gas entering the lowest agitator d4 at g, which gases pass upwardly counter-current to the descending stages of the pulp. With a sulphide ore no carbon dioxide need be added since the aeration generates sufficient carbon dioxide in the agitator d4 by decomposition of the bicarbonate arising from the reaction between the sodium carbonate and the sulphur of the ore. With an ore not containing sulphur, the necessary carbon dioxide would be added to the agitator d4 or d3. The contents of agitator d4 are discharged to a filter k and washed there with a recarbonated barren solution c from a scrubber j. The leach solution is collected in tank q and the uranium therein precipitated as uranate by the addition of caustic soda from tank u. The uranate formed is removed at r from a filter s and the barren solution is re-cycled through line y to a scrubber j where free caustic is destroyed by passing in carbon dioxide. The recarbonated barren solution is employed as a wash on the initial filter b, on filter k and is also used to repulp the filter cake from filter k in a repulper l and to wash the pulp so formed on a filter m. The wash filtrate from the filter m is passed to a scrubber f and from thence after treatment with carbon dioxide to the initial agitator d1 through pipe e. Specification 716,597 is referred to.