Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Define the lithosphere and its key resources in South Africa.
• Describe the chemical processes for extracting minerals like gold and coal.
• Explain the environmental impacts of mining and energy production.
• Differentiate between renewable and non-renewable energy.
• Discuss the move towards sustainable energy in South Africa.

Lesson summary

The lithosphere, Earth's rigid outer layer, is the source of many chemical systems crucial to South Africa's economy and energy security. Understanding mining and energy resources is vital for all South Africans, as these resources are central to our economic well-being, job creation, and industrial development.

However, resource extraction and energy production also have significant environmental consequences, demanding a balanced approach to sustainable development. This week, we will explore the chemical processes involved in extracting and processing these resources and the challenges associated with their sustainable utilization.

Lesson notes

2.1 The Lithosphere and its Resources: The lithosphere comprises the Earth's crust and the uppermost part of the mantle. It's the source of all minerals, rocks, and fossil fuels. Understanding the geological processes that concentrated these resources is crucial.

Minerals: Naturally occurring, inorganic solids with a definite chemical composition and crystalline structure. Examples in South Africa include gold, platinum, diamonds, coal, iron ore, and manganese.

Rocks: Aggregates of one or more minerals.

Ores: Rocks containing valuable minerals that can be economically extracted.

Fossil Fuels: Combustible geological deposits of organic matter, formed from decayed plants and animals that have been converted to crude oil, coal, natural gas, or heavy oils by exposure to heat and pressure in the earth's crust over hundreds of millions of years. 2.2 Mining and Extraction Processes: Mining involves extracting valuable minerals from the earth. Several methods are used, depending on the type and location of the ore.

Surface Mining (Open-Pit Mining): Used when ore deposits are near the surface. Large pits are dug to extract the ore.

Examples: Coal mining in Mpumalanga, Iron ore mining in the Northern Cape.

Underground Mining: Used when ore deposits are deep underground. Shafts and tunnels are constructed to access the ore.

Examples: Gold and platinum mining in Gauteng and North West provinces. 2.3 Chemical Processes in Mineral Extraction and Beneficiation: Beneficiation refers to the processes that improve the grade or quality of the ore. These processes often involve chemical reactions.

Flotation: Used to separate valuable minerals from waste rock (gangue). The ore is ground into a fine powder and mixed with water and chemicals (frothers and collectors). Air is blown through the mixture, and the valuable minerals attach to the air bubbles and float to the surface, forming a froth that can be collected. This is commonly used for gold and platinum extraction.

Leaching: A process where chemicals are used to dissolve valuable minerals from the ore. For example, cyanide leaching is used to extract gold.

Reaction: 4Au(s) + 8CN-(aq) + O2(g) + 2H2O(l) → 4[Au(CN)2]-(aq) + 4OH-(aq) Gold is oxidized and dissolved as the dicyanoaurate(I) complex, [Au(CN)2]-.

Smelting: A high-temperature process used to extract metals from their ores. For example, iron ore (Fe2O3) is smelted with coke (carbon) in a blast furnace to produce iron.

Reaction: Fe2O3(s) + 3C(s) → 2Fe(l) + 3CO(g)

Example 1: Calculating the mass of gold extracted using cyanide leaching Suppose a mining company uses cyanide leaching to extract gold from 1000 kg of ore containing 0.01% gold by mass. Assuming the leaching process is 90% efficient, calculate the mass of gold extracted.

Step 1: Calculate the mass of gold in the ore. Mass of gold = (0.01/100) 1000 kg = 0.1 kg Step 2: Account for the efficiency of the leaching process. Mass of gold extracted = 0.90 0.1 kg = 0.09 kg Answer: The mass of gold extracted is 0.09 kg. 2.4 Energy Resources: Fossil Fuels (Non-Renewable): Coal, oil, and natural gas. Formed from the remains of ancient organisms over millions of years. Burning fossil fuels releases energy, but also greenhouse gases, contributing to climate change. South Africa relies heavily on coal for electricity generation.

Renewable Energy: Solar, wind, hydro, and biomass. These resources are naturally replenished and have a lower environmental impact. South Africa has significant potential for solar and wind energy. 2.5 Environmental Impacts: Mining and energy production can have severe environmental impacts: Water Pollution: Acid mine drainage (AMD) is a major problem in South Africa. Sulfide minerals in the ore react with water and oxygen to form sulfuric acid, which contaminates water sources.

Reaction: FeS2(s) + O2(g) + H2O(l) → Fe2+(aq) + SO42-(aq) + H+(aq) (Simplified)

Air Pollution: Burning fossil fuels releases greenhouse gases and particulate matter, contributing to climate change and respiratory problems. Dust from mining operations also causes air pollution.

Land Degradation: Open-pit mining can destroy habitats and leave behind large, unstable landscapes.

Soil Contamination: Heavy metals and other pollutants from mining activities can contaminate the soil, making it unsuitable for agriculture. 2.6 Mitigation Strategies: Acid Mine Drainage Treatment: Neutralizing the acid with lime or other alkaline substances.

Rehabilitation of Mining Sites: Replanting vegetation and stabilizing the land.

Transition to Renewable Energy: Investing in solar, wind, and other renewable energy sources.

Improved Mining Practices: Reducing waste and using more efficient extraction methods.

Carbon Capture and Storage (CCS): Capturing CO2 emissions from power plants and storing them underground.

Example 2: Calculating the cost of AMD neutralization A mine produces 1000 m3 of AMD per day with a sulfuric acid concentration of 0.01 M.