3.3 Separating Metals from Metal Oxides Flashcards
What are ores?
Ores are rocks that contain enough metal to make it economically worthwhile extracting the metal from it. They often contain compounds of the metal, e.g. metal oxides. Before we can use the metals, they need to be extracted from their ores.
What is oxidation in terms of extracting metals?
The process of gainting oxygen
What is reduction in terms of extracting metals?
The loss of oxygen
Many metals can oxidise into metal oxides when exposed to oxygen. Why is this?
They are reactive
What is iron oxide?
Rust
Why are unreactive metals, like gold, often found as pure metals?
They are too unreactive to react with oxygen and form metal oxides
How does the metals place in the reactivity series determine how we can extract it?
If the metal is higher than carbon in the reactivity series, it will be extracted using electrolysis. If the metal is lower than carbon in the reactivity series, it will be extracted by reduction (using carbon).
Describe how metals below carbon in a reactivity series are extracted from metal oxides
To extract the metal, it will be heated with carbon at a high temperature. The carbon reduces the metal oxide by removing the oxygen, forming a vapour made of the metal and either carbon monoxide or carbon dioxide gas. The impure vapour is condensed in the absence of air (to prevent re-oxidation) and is then separated from the mixture and purified.
Scientists are developing biological methods to extract less reactive metals from their ores. Which type of ores can these methods extract metals from?
Low-grade ores (contain very little metal) and from the waste from other metal extraction processes.
What are the two types of biological methods to extract metals?
- Phytoextraction
- Bioleaching
Phytoextraction
This involves growing plants in soil that contains metal compounds. The plants can’t use or get rid of the metals so they gradually build up in the leaves. The plants can be harvested, dried and burned in a furnace. The ash contains metal compounds from which the metal can be extracted by electrolysis or displacement reactions. Plants will be better suited for phytoextraction if they are large, grow fast and can be grown in large quantities in a given area.
Bioleaching
This uses bacteria to convert insoluble metal compounds in the ore into soluble compounds, separating the metal from the ore in the process. The leachate (the solution that is produced) contains a dilute aqueous solution of metal ions, which can be extracted, e.g. by electrolysis or displacement with a more reactive metal.
What are the advantages of biological methods to extract metals? (3)
- They’re less damaging to the environment than traditional methods.
- They take less energy.
- They can extract metals from waste materials so less ‘new’ ores need extracting - this makes it a cheaper process. It also means that fewer toxic metals get sent to landfills so it reduces the risk of them contaminating our water supplies.
What is the disadvantage of using biological methods to extract metals?
They take much more time to produce large quantity of metal
What is important about the terms ‘oxidation’ and ‘reduction’?
They can be described either in terms of gain/loss of oxygen, or in terms of gain/loss of electrons.
