Alternative methods of extracting metals (HT only): Copper ores are becoming scarce and new ways of extracting copper from low-grade ores include phytomining, and bioleaching. These methods avoid traditional mining methods of digging, moving and disposing of large amounts of rock.

The idea

Copper is a finite resource; high-grade ores are depleting, making low-grade ores increasingly important. Traditional mining digs, moves and disposes of huge volumes of rock, which is energy-intensive and damages landscapes. Phytomining and bioleaching are alternative biological methods (assessed at Higher Tier only) extracting copper from low-grade ores without large-scale digging. Phytomining grows plants that absorb copper compounds; harvesting and burning them produces ash rich in copper compounds. Bioleaching uses bacteria to convert insoluble copper compounds into soluble ones. Both produce a leachate or ash from which copper is obtained, e.g., by displacement with scrap iron or electrolysis.

What earns the marks

• Copper ores are finite and high-grade ores are becoming scarce, so low-grade ores must be used.
• Traditional mining involves digging, moving and disposing of large amounts of rock, which is costly and environmentally damaging.
• Phytomining uses plants to absorb metal compounds from the soil; the plants are harvested and burned to produce ash containing metal compounds.
• Bioleaching uses bacteria to produce a solution (leachate) containing soluble copper compounds from insoluble copper compounds in low-grade ore.
• Copper can be extracted from the ash or leachate, for example by displacement using scrap iron or by electrolysis.

Common mistakes and how to put them right

• Thinking phytomining involves burning plants to release copper metal directly.

  Put it right: Burning produces ash containing copper compounds, and further processing is needed to obtain copper.

• Confusing bioleaching with phytomining.

  Put it right: Bioleaching uses bacteria to produce a copper-containing leachate, while phytomining uses plants and ash.

• Stating that these methods avoid all environmental impact.

  Put it right: They reduce digging, moving and disposal of rock but still require energy, land and processing, so some impact remains.

• Believing low-grade ores contain no copper.

  Put it right: They contain small amounts of copper compounds, which can still be extracted economically by these methods.

Exam tips

• Link scarcity of copper ores to the need for alternative methods when explaining why phytomining and bioleaching are used.
• Contrast traditional mining with the alternatives by naming the specific avoided processes: digging, moving and disposing of large amounts of rock.
• Use precise terms such as low-grade ore, leachate, ash and displacement, and avoid vague phrases like 'environmentally friendly' without explanation.
• Remember that phytomining and bioleaching are Higher Tier only topics.