Metals and Non-metals · Lesson 9 of 13
Occurrence Of Metals And Extraction Of Metals
“Before a metal becomes useful, it has to be found, separated from gangue and matched with the right extraction route.”
• Define minerals, ores and gangue. • Distinguish free-state occurrence from combined-state occurrence of metals. • Relate natural occurrence to position in the reactivity series. • Explain why extraction methods differ for high-, middle- and low-reactivity metals. • Explain the purpose of enrichment of ores.
The earth's crust is a major source of metals, while seawater also contains dissolved salts. Whether a metal occurs free or combined is strongly related to its chemical reactivity.
Occurrence Of Metals
A Mineral is an element or compound that occurs naturally in the earth's crust.
An Ore is a mineral from which a metal can be extracted profitably because it contains a sufficiently high proportion of that metal.
Mineral Versus Ore
Every ore is a mineral, but not every mineral is useful as an ore. The key additional condition is that the metal can be extracted profitably.
Extraction Of Metals
Some metals occur in the free state and some mainly as compounds. Less reactive metals such as gold, silver, platinum and copper can occur free. Copper and silver can also occur as combined sulphide or oxide ores.
Highly Reactive Metals
Potassium, sodium, calcium, magnesium and aluminium are so reactive that they are not normally found free. They occur in combined form.
Moderately Reactive Metals
Zinc, iron and lead are moderately reactive and are commonly found as oxides, sulphides or carbonates.
Three Reactivity Groups For Extraction
Low-, middle- and high-reactivity metals require different extraction techniques. The reactivity series therefore acts as a guide for metallurgy.
Enrichment Of Ores
Gangue is unwanted earthy material such as soil or sand mixed with an ore.
Ores mined from the earth contain gangue. The impurities are removed before extraction using methods based on differences between the physical or chemical properties of the ore and the gangue.
Removing gangue reduces unwanted material before the energy-intensive chemical extraction steps begin.
Quiz
What is a mineral?
What makes a mineral an ore?
Which metals can occur free because of low reactivity?
What is gangue?
Why do extraction methods differ?
Practice Problems
- Define mineral, ore and gangue and explain how they are related.
- Explain why gold may occur free while sodium does not.
- Classify K, Mg, Fe, Pb, Cu and Au into high-, middle- or low-reactivity groups.
- Explain why many moderately reactive metals occur as oxides, sulphides or carbonates.
- Explain the purpose of enriching an ore before extraction.
- Describe how the reactivity series helps choose an extraction method.
Key Takeaways
• Minerals occur naturally in the earth's crust, while ores are useful minerals from which metals can be extracted profitably. • Low-reactivity metals may occur free, while highly reactive metals occur in compounds. • Middle-reactivity metals commonly occur as oxides, sulphides or carbonates. • Gangue is unwanted material such as soil or sand mixed with ore. • The extraction method is chosen according to the metal's reactivity.