Lesson Notes By Weeks and Term v5 - Grade 11
Chemical Systems: lithosphere (mining and energy resources) – Week 2 focus
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Chemical Systems: lithosphere (mining and energy resources) – Week 2 focus
Download the Lessonotes Mobile South Africa app for faster lesson access on Android and iPhone.
Subject: Physical Sciences
Class: Grade 11
Term: Term 4
Week: 2
Theme: General lesson support
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The lithosphere, the Earth's rigid outer layer, is a treasure trove of minerals and energy resources. South Africa’s economy and its history are inextricably linked to the mining and exploitation of these resources, particularly gold, diamonds, platinum group metals, coal, and iron ore. Understanding the chemistry and geological processes involved in the formation, extraction, and processing of these resources is crucial for informed decision-making regarding sustainable development, environmental protection, and economic growth in our country. For example, understanding the chemical processes in gold extraction can help to mitigate the environmental impacts of gold mining operations.
2.1 Mineral and Energy Resources in the Lithosphere The lithosphere contains a vast array of mineral and energy resources. Minerals are naturally occurring, inorganic solids with a definite chemical composition and crystalline structure. Energy resources are substances that can be used to produce heat, electricity, or other forms of energy. South African
Examples: Gold: Found in the Witwatersrand Basin, South Africa is historically one of the world's largest gold producers.
Platinum Group Metals (PGMs): South Africa holds the largest reserves of PGMs, crucial for catalytic converters in vehicles and various industrial applications.
Diamonds: Primarily found in kimberlite pipes, playing a significant role in South Africa's economy.
Coal: Abundant reserves used for electricity generation and export.
Iron Ore: Important for steel production, essential for infrastructure development.
Manganese: Crucial alloy for steel.
Chromium: Important component in stainless steel production.
Energy Resources: Coal: A fossil fuel formed from decayed plant matter. Primarily used for electricity generation.
Natural Gas: Typically found associated with oil deposits.
Uranium: Used in nuclear power plants. South Africa has uranium deposits, including some associated with gold tailings. 2.2 Chemical Processes in Resource Extraction and Processing 2.2.1 Gold Extraction: Cyanide Leaching Gold is often found in low concentrations within ore. Cyanide leaching is a common method for extracting gold from ore.
The Process: The gold ore is crushed and mixed with a cyanide solution (NaCN or KCN). The cyanide ions react with the gold to form a water-soluble gold cyanide complex.
Chemical Equation: `4Au(s) + 8CN-(aq) + O2(g) + 2H2O(l) → 4[Au(CN)2]-(aq) + 4OH-(aq)` Explanation: `Au(s)`: Solid gold. `CN-(aq)`: Cyanide ions in aqueous solution. `O2(g)`: Oxygen gas, required as an oxidizing agent. `H2O(l)`: Water. `[Au(CN)2]-(aq)`: The water-soluble gold cyanide complex (dicyanoaurate(I) ion). `OH-(aq)`: Hydroxide ions.
Recovery: The gold cyanide complex is then recovered from the solution, often using zinc. `[Au(CN)2]-(aq) + Zn(s) → Au(s) + [Zn(CN)4]2-(aq)` Explanation: `Zn(s)`: Solid zinc. `[Zn(CN)4]2-(aq)`: Zinc cyanide complex. The gold is reduced, plating out onto the zinc.