Question

Describe how uranium ores can be leached in alkaline conditions. What at the chemical reactions that occur? What are the circumstances when you would use alkaline leaching rather than acid leaching to recover Uranium? How will the dissolved Uranium be recovered from the pregnant liquor solution?

Answer 1

1st part

Alkaline leaching is done by adding by reagent Sodiym carbonate and Sodium bicarbonate .The basis of the method is formation of stable uranyl tricarbonate complex ion. For dissolving in carbonate solution the uranium must be present in the hexavalent uranyl state.

at first efective oxidation of tetravalent uranium can be done by oxygen. high pressure is required as rate of oxidation depends on partial pressure of oxygen.

effective temperature of the process is 60 to 100^oc.

excess amount of reagent is needed.

the reactions are given below

2UO₂ + O₂ = UO₃

UO₃ + CO₃^2- + HCO₃^- = UO₂( CO₃)₃^4- + H₂O

UO₃ + 3 CO₃^2- + H₂O = UO₂(CO₃)₃^4- + OH^-

The hydroxyl ion is removed by adding excess bicarbonate ion.

2nd part

basic leaching is done when fewer impurities are present. and uranium oxide can also be directly precipitated without purification.

3rd part

Ion exchange process has been used to recover uranium from carbonate leach solution.