MYP Chemistry 5.14 Extraction Notes

Why Do We Need to Extract Substances from Natural Resources?

Most metals and many useful substances are not found in a pure, elemental form in nature. Instead, they are usually present as:

1. Ores – rocks that contain enough of a metal compound to make extraction economical.
2. Minerals – naturally occurring compounds in the Earth’s crust.
3. Other compounds mixed with unwanted materials (called gangue).

To use these materials in manufacturing, construction, transport, electronics and medicine, we must first extract and purify them.

How Do Properties and Reactivity Influence Extraction Methods?

The method used to extract a substance depends on:

1. Its chemical reactivity.
2. Its position in the reactivity series.
3. Its bonding (how strongly it is combined with other elements).
4. Whether it is found as an element or in compounds.

Physical Separation

1. Some substances can be obtained using physical methods when they:
   1. Are already in their elemental (native) form, or
   2. Are mixed, but not chemically bonded, with other materials.
2. Methods include:
   1. Filtration
   2. Distillation
   3. Magnetic separation
   4. Panning or sluicing (for dense metals like gold)

Chemical Reduction (Using Carbon or Other Reducing Agents)

1. Many metals are found as metal oxides and must be chemically reduced to obtain the metal.
2. Metals that are less reactive than carbon can usually be extracted by reducing their oxides with carbon (or carbon monoxide): $$\text{Metal oxide} + \text{carbon (or CO)} \to \text{Metal} + \text{Carbon dioxide}$$

Electrolysis (For Very Reactive Metals)

1. Metals more reactive than carbon (e.g. aluminium, sodium, magnesium) form very stable compounds.
2. Carbon is not strong enough to reduce them economically, so we use electrolysis.
3. Electrolysis involves:
   1. Passing an electric current through a molten or aqueous ionic compound.
   2. Ions move to electrodes where redox reactions occur, separating the elements.

Displacement Reactions

Some metals can be extracted by displacement, where a more reactive metal or another reducing agent displaces a less reactive metal from its compound.

Balancing Benefits and Impacts of Extraction

1. Extracting materials gives us essential resources, but it also brings environmental and social challenges.
2. Chemists, engineers, governments and communities must balance benefits and costs.

Environmental Impacts

1. Habitat destruction
   1. Mining often requires clearing large areas of land.
   2. Leads to loss of biodiversity and disruption of ecosystems.
2. Pollution
   1. Air pollution:
      1. Smelting can release gases such as sulfur dioxide (SO₂) → contributes to acid rain.
   2. Water pollution:
      1. Mine runoff may contain heavy metal ions or acidic water that contaminates rivers and groundwater.
   3. Soil contamination:
      1. Toxic substances can remain in the soil long after mining stops.
3. Energy use and climate impact
   1. Processes like electrolysis require huge amounts of energy, often from fossil fuels.
   2. This leads to carbon dioxide emissions and contributes to climate change.

Social Impacts

1. Community displacement
   1. Large mining operations can displace local communities, including indigenous groups.
   2. Traditional livelihoods (farming, fishing, herding) can be disturbed or destroyed.
2. Health risks
   1. Workers may be exposed to dust, toxic chemicals, and unsafe conditions.
   2. Nearby residents can be affected by air and water pollution.
3. Economic benefits and dependence
   1. Mining can bring jobs and infrastructure (roads, schools).
   2. But regions may become economically dependent on a single industry.

Balancing Benefits with Impacts

To reduce negative impacts while still accessing important materials, we can:

1. Increase Recycling
   1. Recycling metals (like aluminium, copper, steel) reduces the need for new extraction.
   2. Example: Recycling aluminium uses up to 95% less energy than extracting it from bauxite.
   3. Reduces waste, energy use and environmental damage.
2. Use More Sustainable Practices
   1. Rehabilitation and reforestation of mined land.
   2. Careful water management to prevent pollution and conserve water.
   3. Using cleaner energy sources where possible (e.g. renewables) to power extraction.
3. Implement and Follow Legislation
   1. Governments can set rules and limits on pollution, land use and worker safety.
   2. Bans or restrictions on especially harmful practices or substances (e.g. certain toxic chemicals).
   3. Environmental impact assessments before major projects start.
4. Make Ethical Choices
   1. Industries and individuals can:
   2. Choose products made with recycled materials.
   3. Support companies that follow ethical and environmental standards.
   4. Encourage responsible sourcing of metals (e.g. avoiding “conflict minerals”).