Sure! Let’s solve **Question 3** step-by-step, with clear explanations and final answers for each subpart. --- # 3.1 Uranium leaching from pitchblende (U₃O₈) concentrate using excess sulphuric acid ## 3.1.1 Chemical and Electrochemical Aspects of Leaching **Chemical Reaction:** When U₃O₈ is treated with H₂SO₄, it reacts to form soluble uranyl sulfate: \[ U_3O_8 + 8H_2SO_4 \rightarrow 3UO_2SO_4 + 4H_2O + 4SO_2 \] **Electrochemical Reactions:** - **Anodic Reaction:** Uranium(IV) is oxidized to Uranium(VI): \( UO_2 \rightarrow UO_2^{2+} + 2e^- \) - **Cathodic Reaction:** Oxygen is reduced, for example: \( O_2 + 4H^+ + 4e^- \rightarrow 2H_2O \) - **Overall Electrochemical Reaction:** The leaching process involves oxidation of U(IV) to U(VI) and reduction of oxygen. ## 3.1.2 Uranium Species in Solution and Ion Exchange Extractant The main uranium species in sulfuric acid leach solution is the **uranyl ion**, \( UO_2^{2+} \), which often forms complexes such as \( UO_2(SO_4)_2^{2-} \). A typical ion exchange extractant used is **quaternary ammonium salts** (e.g., Aliquat 336). ## 3.1.3 Possible Eluant Solutions and Their Purpose Common eluants for uranium from anion exchange resin are **sodium chloride (NaCl)** or **sodium carbonate (Na₂CO₃)**. These are used because they displace the uranium complex ions from the resin by providing competing anions (Cl⁻ or CO₃²⁻), which have higher affinity for the resin, thus releasing uranium into the solution. --- # 3.2 Sodium carbonate as an alternative leaching reagent ## 3.2.1 Flow Sheet for Solvay Process (Sodium Carbonate Production) 1. Ammonia and carbon dioxide are bubbled through brine (sodium chloride solution). 2. Sodium bicarbonate precipitates out and is filtered. 3. Sodium bicarbonate is heated to form sodium carbonate. **Flow Sheet:** Brine (NaCl) + NH₃ + CO₂ + H₂O → NaHCO₃ ↓ → (Heating) → Na₂CO₃ + CO₂ + H₂O ## 3.2.2 Reaction Equation for Sodium Carbonate Leaching of Uraninite \[ UO_2 + Na_2CO_3 + 1/2 O_2 + H_2O \rightarrow Na_2UO_2(CO_3)_2 \] ## 3.2.3 Mineralogical Condition Favoring Sodium Carbonate over Sulphuric Acid Sodium carbonate is favored when the ore contains **acid-consuming gangue minerals** such as calcite or dolomite. These minerals would react with sulphuric acid, consuming large amounts and increasing cost, but do not consume sodium carbonate as rapidly. --- # 3.3 Sulfonated polystyrene divinyl benzene copolymer (Na⁺ form) for hard water treatment ## 3.3.1 Resin Structure The resin is a polymer matrix of **polystyrene cross-linked with divinylbenzene**, with **sulfonic acid groups (-SO₃⁻)** attached, neutralized by sodium ions (Na⁺). (Sketch in answer book: Long-chain styrene with -SO₃⁻Na⁺ groups on the aromatic rings; cross-links between chains.) ## 3.3.2 Ion Exchange Reaction and Sorption Step The basic ion exchange reaction for water softening: \[ 2RNa + Ca^{2+} \rightarrow R_2Ca + 2Na^+ \] Here, R = resin matrix. Sorption step: Calcium ions in hard water are exchanged for sodium ions on the resin. ## 3.3.3 Ion Exchange Mechanism Responsible for Sorption The mechanism is **cation exchange**: divalent cations (like Ca²⁺ or Mg²⁺) displace two Na⁺ ions from the sulfonate groups on the resin due to higher charge and affinity. ## 3.3.4 Elution and Regeneration of the Resin To regenerate, the resin is treated with a strong sodium chloride (brine) solution: \[ R_2Ca + 2Na^+ \rightarrow 2RNa + Ca^{2+} \] This reaction replaces the Ca²⁺ on the resin with Na⁺ ions, restoring the resin to its original state. The underlying ion exchange mechanism is the same cation exchange process. --- # Final Summary You have the chemical and electrochemical reactions for uranium leaching, typical uranium species and extractants, eluants and their purposes, a flow sheet and reactions for sodium carbonate leaching, mineralogical preferences, resin structure and reactions for water softening, and regeneration mechanisms. This covers all the subparts with clear explanations and relevant chemical equations.