Secondary Reaction in Uranium Leaching Process

4.2.1.2 Secondary reactions.
Uranium can be insoluble or forms a precipitate if soluble gangue is dissolved by the acid and reacts with uranium.

Phosphates and arsenates precipitate uranium.

PO₄H^2- + UO₂²⁺ = PO₄HUO₂

AsO₄H^2- + UO₂²⁺ = AsO₄HUO₂

Reactions can be counteracted reducing pH value so that phosphates and arsenates can be in solution.

PO₄H^2- + UO₂^2- = PO₄H^2-

AsO₄H^2- + UO₂²⁺ = AsO₄H^2-

If there is good amount of Fe³⁺ in solution, the presence of free phosphate can be reduced.

Fe³⁺ + PO₄H^2- = FePO₄H⁺

Ion Fe+3 is insoluble at pH values higher than 3. If the pH value is in the range 1.5 to 2.0, ion Fe3+ will be soluble.

Phosphates are consumers of acid and its dissolution is a permanent competing against uranium leaching. They can inhibit the action of ferric ions and promote uranium reprecipitation when the pH value is higher than 2. Strong base resins are affected by phosphates.

Carbonates are leached by acids and consume high amount of acid. One kilogram of carbonate consumes one kilogram of acid. Its presence is an important factor in order to determine the right process of leaching (acid or alkaline). Amounts higher than 10% carbonate favor alkaline leaching.

Silicates consume acid at pH 1.8 to 2.0 and interfere in solid-liquid separation.

Iron oxides help uranium leaching because they favor uranium oxidation.

Sulphides consume acid and oxidant agent.

Carbonaceous minerals like graphite and carbonated shale are not reactive, but interfere in solid-liquid separation.

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