Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe how mineral deposits form.
• Explain the chemistry of extracting minerals from ores.
• Discuss the environmental impacts of mining.
• Identify key energy resources from the lithosphere.
• Write balanced equations for energy production.

Lesson summary

The Earth's lithosphere, or the rocky outer part of the Earth, is a treasure trove of resources. In South Africa, mining and energy resources are central to our economy, culture, and society. Understanding the chemical systems within the lithosphere – how these resources are formed, extracted, processed, and their impact on the environment – is crucial for responsible resource management and sustainable development. Mining is a major employer, particularly in rural areas. Energy resources are essential for powering our homes, industries, and infrastructure.

However, these activities also pose significant environmental challenges, such as pollution and habitat destruction.

Lesson notes

2.1 Formation of Mineral Deposits: Mineral deposits are naturally occurring concentrations of minerals in the Earth's crust. The formation processes vary depending on the mineral and geological setting.

Magmatic Processes: As magma cools, different minerals crystallize at different temperatures. Early-forming minerals, like olivine and pyroxene, tend to settle to the bottom of the magma chamber due to their higher density (process called fractional crystallization). Later-forming minerals, rich in valuable elements such as gold or platinum, can become concentrated in residual magma. Examples include the Bushveld Igneous Complex in South Africa, a world-renowned source of platinum group metals (PGMs).

Hydrothermal Processes: Hot, chemically active fluids circulate through rocks, dissolving and transporting elements. These fluids can be of magmatic origin, heated groundwater, or metamorphic fluids. As the fluids cool or react with surrounding rocks, minerals precipitate out, forming veins or disseminated deposits. Gold deposits are often formed through hydrothermal processes.

Sedimentary Processes: Weathering and erosion break down rocks into sediments. These sediments are transported by water, wind, or ice and deposited in layers. Chemical precipitation from seawater or lake water can also form sedimentary mineral deposits. Banded Iron Formations (BIFs) are a prime example of sedimentary deposits.

Metamorphic Processes: Existing rocks are transformed by heat, pressure, and chemically active fluids. These processes can recrystallize minerals, concentrate elements, or form new minerals. Diamonds are formed under extreme pressure in the Earth's mantle and are brought to the surface in kimberlite pipes, which are volcanic conduits. 2.2 Extraction and Processing of Minerals: Mining: Ores are extracted from the Earth through surface mining (open-pit or strip mining) or underground mining. The choice of method depends on the depth, size, and grade of the ore body.

Crushing and Grinding: Ore is crushed and ground into fine particles to increase the surface area for subsequent processing.

Froth Flotation: This process separates valuable minerals from waste rock (gangue) based on their surface properties. The ground ore is mixed with water and chemicals called collectors, which selectively attach to the desired mineral particles, making them hydrophobic. Air is then bubbled through the mixture, and the hydrophobic mineral particles attach to the air bubbles, forming a froth that is skimmed off.

Example: Separation of copper sulfide minerals from silicate gangue.

Smelting: This is a high-temperature process used to extract metals from their ores. The ore is heated with a reducing agent, such as coke (carbon), to remove oxygen and other impurities.

Example: ``` 2Fe₂O₃(s) + 3C(s) → 4Fe(l) + 3CO₂(g) Iron(III) oxide + Carbon → Iron + Carbon Dioxide ``` This reaction represents the smelting of iron ore (hematite) in a blast furnace. The carbon reduces the iron oxide to elemental iron.

Leaching: This process uses chemical solutions to dissolve valuable minerals from the ore. For example, gold can be leached from ore using cyanide solutions: ``` 4Au(s) + 8NaCN(aq) + O₂(g) + 2H₂O(l) → 4Na[Au(CN)₂](aq) + 4NaOH(aq) Gold + Sodium Cyanide + Oxygen + Water → Sodium Tetracyanoaurate(I) + Sodium Hydroxide ``` The gold dissolves in the cyanide solution as a complex ion, which can then be recovered. 2.3 Environmental Impacts of Mining and Energy Resource Utilization: Acid Mine Drainage (AMD): This occurs when sulfide minerals (e.g., pyrite, FeS₂) are exposed to air and water during mining. The sulfide minerals oxidize, producing sulfuric acid and dissolved iron. The acidic water can contaminate surface and groundwater, harming aquatic life and damaging infrastructure. ``` 2FeS₂(s) + 7O₂(g) + 2H₂O(l) → 2Fe²⁺(aq) + 4SO₄²⁻(aq) + 4H⁺(aq) Pyrite + Oxygen + Water → Iron(II) ion + Sulfate ion + Hydrogen ion ``` The iron(II) ion can further oxidize to iron(III) ion, which precipitates as iron hydroxide (rust), giving the water a characteristic orange color.

Air Pollution: The combustion of fossil fuels (coal, oil, natural gas) releases air pollutants such as sulfur dioxide (SO₂), nitrogen oxides (NOx), particulate matter (PM), and carbon dioxide (CO₂). SO₂ and NOx contribute to acid rain, while CO₂ is a greenhouse gas that contributes to climate change. ``` S(s) + O₂(g) → SO₂(g) Sulfur + Oxygen → Sulfur Dioxide ``` Habitat Destruction: Mining and energy resource extraction can lead to habitat destruction, soil erosion, and water pollution, impacting biodiversity and ecosystem services.

Water Pollution: In addition to AMD, mining activities can release heavy metals (e.g., mercury, lead, arsenic) into the environment, posing risks to human health and ecosystems. 2.4 Energy Resources: Coal: A sedimentary rock composed primarily of carbonized plant matter. It is formed over millions of years from the accumulation and compression of plant remains.