Le raffinage du cuivre par électrolyse

Electrolytic Refining of Copper

Introduction to Electrolysis

• The process of copper refining through electrolysis is introduced, highlighting its significance in metal purification.

• An electrolytic setup typically involves a container and two electrodes connected by a voltage generator.

Components of the Electrolytic Cell

• The anode is made from blister copper (98.5% pure), while the cathode consists of already refined copper (over 99% pure).

• A solution containing Cu²⁺ ions at a concentration of 45 grams per liter is used for the electrolysis process.

pH Influence on Copper Ions

• A predominance diagram indicates that at a pH below 5.4, Cu²⁺ ions dominate; above this pH, Cu(OH)₂ precipitates as a solid.

• Maintaining the pH below 5.4 is crucial to keep Cu²⁺ ions available for electrolysis; thus, sulfuric acid (H₂SO₄) is added to ensure an acidic environment.

Reactions at the Electrodes

• At the anode, oxidation occurs where copper loses electrons and transforms into Cu²⁺ ions in solution.

• Electrons flow through an external circuit from the anode to the cathode due to the action of the voltage generator.

Reduction Process at Cathode

• At the cathode, reduction takes place where Cu²⁺ ions gain electrons and revert back to solid copper.

• Over time, as copper dissolves from the anode and deposits onto the cathode, impurities settle at the bottom of the container.

Observations During Electrolysis

• The anode diminishes in size as it releases copper into solution while impurities fall out as sludge.

• The cathode grows larger with nearly pure copper accumulating over time due to continuous deposition from solution.

Current Intensity Calculations

• To determine current intensity during electrolysis, calculations are based on 350 kg of blister copper containing approximately 345 kg of actual copper.

Electrolysis of Copper: Key Concepts and Calculations

Understanding the Electrolysis Process

• A quantity of 5.43 x 10^3 moles of copper is discussed, emphasizing that for complete oxidation to Cu²⁺, two electrons must be exchanged per mole.

• The amount of electrons circulating in the electrolytic system is double that of the copper being oxidized, leading to a total of approximately 18.9 x 10^3 moles of copper involved in the process.

• Each mole of electrons carries a charge of approximately 96.5 x 10^3 coulombs (Faraday's constant), allowing for the calculation that around 1.05 x 10^9 coulombs are transported during this electrolysis.

Current Intensity Calculation

• The total charge is transported over a duration of 20 days, which converts to about 6.07 x 10^6 seconds, resulting in an extremely high current intensity calculated as Q/Δt.