Q.How is leaching carried out in case of low grade copper ores?

The ore is treated with dilute $H_2SO_4$ (sometimes assisted by bacteria that oxidise sulphide minerals) so that copper dissolves as $Cu^{2+}$ in solution. This leach solution is then treated with scrap iron, which displaces metallic copper: $Fe + Cu^{2+} \rightarrow Fe^{2+} + Cu$. …

Step 1 – Why leaching is used for low-grade ore

When copper ore is too low-grade (too dilute in copper) to be economically processed by roasting/smelting (pyrometallurgy), a hydrometallurgical (leaching) route is used instead, since it can work efficiently even on dilute, large-tonnage material without the fuel costs of a furnace.

Step 2 – The leaching step

The crushed low-grade ore is treated with a dilute sulphuric acid solution (in the presence of air/oxygen), which dissolves the copper content, bringing it into solution as $Cu^{2+}$ ions:

In many modern operations this is assisted or driven by bacterial action (bioleaching), where naturally occurring bacteria oxidise the sulphide minerals and accelerate the release of copper ions into solution.

Step 3 – Recovery of copper by displacement

The resulting copper-bearing leach solution is then treated with scrap iron, which — being more electropositive than copper — displaces metallic copper from solution:

$Fe(s) + Cu^{2+}(aq) \rightarrow Fe^{2+}(aq) + Cu(s)$ …

Describe the two-step hydrometallurgical sequence: dissolve copper into solution using dilute acid (± bacteria) in air, then displace metallic copp …

• Describing only the leaching (dissolution) step and forgetting the essential recovery step (displacement by scrap iron) that actually yields metallic copper. …