Uranium extraction from pitchblende (uraninite): which primary process step is used to bring uranium into solution for subsequent recovery?

Introduction / Context:
Processing uranium ores such as pitchblende (uraninite) involves crushing, grinding, and hydrometallurgical steps to solubilise uranium and separate it from gangue. Recognising the primary leaching chemistry is important for materials and nuclear fuel engineers.

Given Data / Assumptions:

• Host ore contains uranium oxides with associated minerals.
• Conventional acid leach flowsheets are considered.

Concept / Approach:
In acid leach circuits, sulphuric acid (often with an oxidant like MnO2, ferric iron, or oxygen) converts uranium oxides to soluble uranyl sulphate complexes. The pregnant leach solution is then clarified and uranium is recovered by solvent extraction or ion exchange, followed by precipitation (e.g., as ammonium diuranate) and calcination to U3O8.

Step-by-Step Solution:
1) Crush and grind ore to liberate uranium minerals.2) Leach with H2SO4 and oxidant to dissolve uranium as uranyl complexes.3) Separate solids/liquids; purify via SX or IX; precipitate and calcine to product.

Verification / Alternative check:
Some ores use alkaline carbonate leaching when acid-consuming gangue is high; the question points to sulphuric acid as the standard for many pitchblende deposits.

Why Other Options Are Wrong:
Froth flotation may upgrade ore but does not itself dissolve uranium.Smelting is not the common primary recovery route for uranium oxides.Uranium oxides do not dissolve in plain water.

Common Pitfalls:
Assuming a single universal flowsheet; failing to note the role of oxidants in acid leaching.

Final Answer:
Leaching with sulphuric acid