Variables of acid leaching of Uranium
4.2.1.1 Variables of acid leaching.
Finesse of grinding. In this type of leaching uranium is leached selectively and carbonates react weakly with gangue. The leaching agent has difficulties for penetrating the ore and the final product of grinding must be fine. Sometimes, the ground ore must be 70-80% minus 200 mesh.
Dosage. Reagents to be employed must maintain a pH value between 9 and 10.5. Generally, the dosage can be 40-50 g/l Na2CO3 and 10-20 g/l NaHCO3. Sodium carbonate consumption is in the range 7.5 to 40 kg/t.
Oxidant, temperature, time contact, and pressure. U6+ is leached easily by carbonates. U4+ needs oxidant conditions.
2UO2 + O2 = 2UO3
Leaching requires high temperatures, 70 to 80 oC, and long contact time such as 20 hours or four days. High pressures are required in certain cases.
Relation solid/liquid. Similarly to acid leaching, this relation has influence in selection of equipments to be used and the reagent consumption. The amount of liquid depends of the rheological conditions that allow good results. A relation 1/1 is the most convenient.
4.2.2.2 Secondary reactions.
Although alkaline leaching is very selective, there are some minerals that consume reagents.
Calcium sulphate. It is a great reagent consumer.
CaSO4 + CO32- = CaCO3 + SO42-.
Pyrites, silicates, and aluminates. Consume carbonate but generate bicarbonate ion.
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