Variables Affecting Uranium Acid Leaching

4.2.1.1 Variables of acid leaching:
Finesse of grinding. Leaching kinetic depends of particle surface conditions. Uranium minerals must be accessible to the leaching agent so that reactions can be done very fast. However, excessive grinding will dissolve more gangue and costs could be higher.

Dosage. The amount of sulphuric acid to be used is in the range 20 to 100 kg/t. It’s the main variable because represents approximately 70% total cost and 40% operative cost.

Oxidant. When is present U⁴⁺ is necessary an oxidant. It is required at least 0.5 g/l Fe³⁺ in order to assure oxidant conditions. Pulp potential must be -430 mV.

Temperature. Favors reaction kinetic. However, there some problems, some gangue minerals will be dissolved too, and the equipment can be corroded. The temperature must be selected considering economic aspects and leaching efficiency.

Retention time and temperature. Contact time of leaching solution has influence in uranium leaching. It is possible combine time and temperature: short times with high temperature and long times with low temperature.

Retention time and acid dosage. Shorter times with high dosages and long times with low dosages. Dissolution of hexavalent uranium is easy in good conditions of acidity and pulp potential. However tetravalent uranium has slow kinetic.

Relation solid/liquid. Has influence in the acid consumption and equipments to be used in the process. Its value depends of the best rheological conditions for the leaching process.

Pressure. It is useful because can reduce acid consumption. With the least practical conditions of pressure and temperature can be obtained acid sulphuric

FeS₂ + 14Fe³⁺ 8H₂O = 15Fe²⁺ + 2SO₄^2- + 16H⁺

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