Uranium leaching efficiency

In-situ leaching in the seams themselves proceeds with sulfuric acid or carbonate solutions. The leaching agent is fed in via injection tubes into the rock seam and brought to the surface via a central tube. In situ uranium leaching efficiency is 60 to 85%. Currently ca. 5000 t of uranium are extracted in this way. 

In most ores, sufficient Fe is already present. For some ores, it is necessary to add metallic iron. In practice, the oxidation potential of the solution can be monitored and controlled using the Fe /Fe ratio. Very high leaching efficiencies with H2SO ate common, eg, 95—98% dissolution yield of uranium (39). If acid consumption exceeds 68 kg/1 of ore treated, alkaline leaching is preferred. The comparative costs of acid, sodium hydroxide, and sodium carbonate differ widely in different areas and are the determining factor. 

It has recently been discovered that the roasting of carnotite ore at 850°C in the presence of a few per cent of calcium sulphate, prior to carbonate leaching, enhances both the vanadium and uranium extraction efficiencies. A convenient way of achieving the desired conditions is to blend the ore with another carnotite ore with a high natural calcium sulphate content, when available, rather than waste the beneficial effect of the latter by treating it alone. 

The last reaction cited above as shown is very effectively catalyzed by bacterial action but is very slow chemically by recycling the spent ferrous liquors and regenerating ferric iron bacterially, the amount of iron which must be derived from pyrite oxidation is limited to that needed to make up losses from the system, principally in the uranium product stream. This is important if the slow step in the overall process is the oxidation of pyrite. The situation is different in the case of bacterial leaching of copper sulfides where all the sulfide must be attacked to obtain copper with a high efficiency. A fourth reaction which may occur is the hydrolysis of ferric sulfate in solution, thus regenerating more sulfuric acid the ferrous-ferric oxidation consumes acid. 

In the fuel fabrication process, uranium in the fuel compact is recovered by the bum-grind-leach method and basic data have been accumulated. In the recovery process, almost 100 % of crushing efficiency was obtained by selected cmshing gap and no additional adjustment of the gap was needed. 

One popular ettneept holds that the metals are progressively leached from the host rock as the roll front passes through it. Uranium districts are found in areas where the background levels of uranium are elevated. Based on the nature of the alteration, leaching trf the host rock on the oxidized side of a roll can be extremely inten.se. With the remarkable efficiency of the precipitating mechanism only a few parts per million of uranium have to be removed from the volume of oxidized rock associated with most roll-front deposits to account for the amount of uranium in the orebody. 

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