Electrowinning Copper Chemistry Tutorial

Key Concepts

• Electrowinning refers to the process of using electrolysis to extract a metallic element from the compounds in its ore.
• Copper occurs on Earth both as native copper (the uncombined element, Cu), and in ores (copper compounds, or mixtures of compounds, from which copper metal can be extracted profitably).
• Copper ores are usually copper oxides, copper sulfides or copper carbonates.
• Most copper oxide ores do not contain a high enough percentage of copper to make direct smelting of the ore economically viable.
• Electrowinning can be used to extract the copper from these copper oxide ores.
• The process for extracting copper from copper oxide ores can be summarized as:

1. Mining : digging or blasting to obtain the ore from the surrounding rock.
2. Crushing : mined ore is crushed into very small pieces.
3. Grinding : crushed ore is ground into a powder.
4. Concentrating : adding water to the powder to create a slurry containing about 15% copper.
5. Leaching : sulfuric acid is added to the concentrated slurry to dissolve the copper producing an acidified aqueous solution of Cu²⁺.

   Sulfuric acid is an oxidizing agent (oxidant) but not a very strong one unless it is hot and concentrated.

   Copper metal is a reducing agent (reductant) but not a very stong one.

   Copper metal won't dissolve in nonoxidizing acids like HCl, but will dissolve in hot concentrated H₂SO₄:

   Cu_(s) + 3H₂SO₄ → Cu²⁺ + SO_2(g) + 2HSO₄^- + 2H₂O

6. Electrowinning : electrolysis of the Cu²⁺_(aq) solution to produce metallic copper, Cu_(s).

Electrowinning Copper

In the electrowinning stage of copper extraction, the solution containing the copper ions is pumped through a series of tanks.

Suspended in these tanks are sheets of lead alloy (anodes) alternating with cathodes made of either thin copper starter sheets or stainless steel blanks.

An external power supply is used to pull electrons out of the anode and push them to the cathode.

The animation below represents one of these electrolytic cells using copper starter sheets.

Anode (positive electrode) lead alloy plates Oxidation occurs at the anode. Water is oxidized at the anode. H2O(l) → 2H+(aq)+ ½O2(g)+ 2e- Water is consumed at the anode. Oxygen gas and protons are produced at the anode. Electrons are produced at the anode. Electrons flow from anode to cathode.		Cathode (negative electrode) thin copper sheets (starter sheets) or stainless steel sheets (blanks) Reduction occurs at the cathode. Copper ions migrate to the cathode. Copper ions are reduced at the cathode. Cu2+(aq) + 2e- → Cu(s) Solid copper is deposited at the cathode.
	Note: H+ is not reduced to H2(g) at the cathode. Cu2+ lies below H+ in the table of standard reduction potentials. Cu2+ is a stronger oxidant than H+. Cu2+ is more easily reduced than H+.
anode reaction: H2O(l) → 2H+(aq) + ½O2(g) + 2e- cathode reaction: Cu2+(aq) + 2e- → Cu(s) overall reaction: Cu2+(aq) + H2O(l) → Cu(s) + 2H+(aq) + ½O2(g) or using only integers (whole numbers): 2Cu2+(aq) + 2H2O(l) → 2Cu(s) + 4H+(aq) + O2(g)