Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define key terms like ore, gangue, and beneficiation.
• Describe the extraction process for a South African mineral.
• Explain the environmental impacts of mining and energy production.
• Compare fossil fuels and renewable energy sources.
• Evaluate the sustainability of these practices.

Lesson summary

The lithosphere, the Earth's solid outer layer, is a treasure trove of mineral resources and energy sources. South Africa is particularly rich in these resources, with mining and energy production forming a significant part of our economy.

However, the extraction and use of these resources have profound environmental and social consequences. Understanding the chemical processes involved in mining and energy production is crucial for making informed decisions about sustainable resource management.

Lesson notes

2. 1.

Mining and Mineral Resources Lithosphere: The rigid outer layer of the Earth, consisting of the crust and the uppermost part of the mantle. It is the source of most mined materials.

Ore: A naturally occurring solid material from which a metal or valuable mineral can be profitably extracted. An ore is a mixture of the desired mineral and unwanted materials.

Gangue: The commercially valueless material that surrounds, or is closely mixed with, a wanted mineral in an ore deposit. Examples of gangue minerals include quartz, calcite, and clay minerals.

Concentration: The process of increasing the proportion of the desired mineral in an ore. This involves separating the valuable mineral from the gangue.

Extraction: The process of removing the desired element or compound from the concentrated ore. This often involves chemical reactions.

Beneficiation: A general term for the processes used to improve the economic value of an ore by removing gangue minerals and concentrating the desired mineral. Beneficiation can include crushing, grinding, gravity separation, flotation, and magnetic separation. 2.

2. Processes in Mining South African mining activities are extensive and diverse. Let's focus on platinum mining as an example.

Example: Platinum Mining in South Africa Exploration: Locating platinum deposits through geological surveys and drilling.

Mining: Extracting the ore-bearing rock (often a type of igneous rock called Merensky Reef or UG2 Reef) from the ground.

This can be done through: Open-pit mining: Removing surface layers to access shallow deposits. Environmentally destructive, but cost-effective for large, shallow deposits.

Underground mining: Digging tunnels and shafts to access deeper deposits. More expensive and dangerous, but less environmentally disruptive on the surface.

Crushing and Grinding: The mined rock is crushed and ground into a fine powder to increase the surface area for subsequent processes.

Froth Flotation: This is a key concentration process. The powdered ore is mixed with water and reagents (chemicals) that selectively make the platinum-containing minerals hydrophobic (water-repelling). Air is bubbled through the mixture. The hydrophobic minerals attach to the air bubbles and float to the surface, forming a froth that is skimmed off. The gangue minerals, which are hydrophilic (water-attracting), remain in the water.

Chemical Principle: Selective adsorption of reagents onto the surface of platinum-containing minerals, changing their surface properties.

Smelting: The concentrated platinum-containing minerals are smelted (heated to high temperatures) in furnaces. This converts the platinum group metals (PGMs) into a molten alloy.

Refining: The molten alloy undergoes further refining processes to separate the individual PGMs (platinum, palladium, rhodium, ruthenium, iridium, and osmium). This can involve chemical leaching, solvent extraction, and other techniques.

Chemical Reactions: Various chemical reactions are used to selectively dissolve and precipitate different PGMs. For example, different metals will react with different acids, based on their reduction potentials.

Environmental Considerations: Mining activities generate tailings (waste material) that can contain harmful substances like heavy metals and cyanide (used in some gold extraction processes). Tailings dams are used to store tailings, but leaks or failures can cause significant environmental damage. Air pollution from dust and emissions from smelting is also a concern. Water pollution from acid mine drainage (AMD), formed when sulphide minerals are exposed to air and water, is a major problem in many mining areas. 2.

3. Energy Resources Fossil Fuels: Formed from the remains of ancient organisms over millions of years. Examples include coal, oil (petroleum), and natural gas. These are non-renewable resources.

Renewable Energy: Energy that is derived from natural processes that are replenished at a rate equal to or faster than their rate of consumption. Examples include solar energy, wind energy, hydroelectric energy, and geothermal energy. 2.

4. Energy Production and Environmental Impact Coal-fired Power Plants: South Africa relies heavily on coal for electricity generation. Coal is burned to heat water, producing steam that drives turbines connected to generators.

Chemical Reaction: Combustion of coal (mainly carbon) with oxygen: `C(s) + O2(g) -> CO2(g)` Environmental Impact: Burning coal releases greenhouse gases (CO2), contributing to climate change. It also releases air pollutants such as sulfur dioxide (SO2), which causes acid rain, and particulate matter (PM), which harms human health.

Solar Energy: Harnessing the sun's energy using photovoltaic (PV) cells, which convert sunlight directly into electricity.

Environmental Impact: Relatively clean, but the manufacturing of PV cells can involve hazardous materials. Land use can also be a concern for large-scale solar farms.