C14 - Resources Flashcards
Two methods of extracting copper
• Bioleaching
• Phytomining
What is phytomining?
• Involves growing plants in soil that contains copper. The plants can’t use or get rid of the copper so it gradually builds up in the leaves. The plants can be harvested, dried or burned in a furnace. The ash contains soluble copper compounds from which copper can be extracted by electrolysis or displacement using scrap iron.
What is bioleaching?
• bacteria are used to convert copper compounds in the ore into soluble copper compounds, separating out the copper from the ore in the process. The leachate (the solution produced by the process) contains copper ions, which can be extracted by electrolysis or displacement with a more reactive metal.
What is displacement?
• a redox reaction
• involves one metal kicking another one out of a compound
• if you put a reactive metal into the solution of a dissolved metal compound , reactive metal will replace the less reactive metal in the compound
Iron and copper sulfate displacement
• if you put iron in a solution of copper sulfate, the more reactive iron will displace the less reactive compound from the solution. You end up with iron sulfate solution and copper metal.
• in this reaction, iron loses two electrons to become a 2+ iron - oxidised
What is electrolysis?
• uses electrical current to cause a reaction
• an electric current is passed through an electrolyte (molten or dissolved ionic compound) ions move towards electrodes, where they react, and the compound decomposes.
• positive ions in the electrolyte will move towards the cathode and gain electrons (they are reduced)
• negative ions in the electrolyte will move towards the anode and lose electrons (they are oxidised).
• creates a flow of charge through the electrolyte as ions travel to the electrodes.
• as ions gain or lose electrons, they form the uncharged element and are discharged from the electrolyte
Describe how bioleaching is used to obtain copper.
• uses bacteria to produce solutions containing copper compounds / leachate solutions
• from which copper is obtained by electrolysis/displacement
Recycling key points
• There are social, economic and environmental issues associated with exploiting the Earth’s limited supplies of raw materials, such as metal ores.
• Recycling metals saves energy and our limited, finite metal ores (and fossil fuels). The pollution caused by the mining and extraction of metals is also reduced by recycling.
Recycling copper
Impure copper from recycling has to be purified for use in electrical wiring, unless it has been reclaimed solely from old electricity wires. High-quality copper from wires can be recycled by melting and/or reusing it.
Recycling aluminium
it is important to recycle aluminium to help conserve the Earth’s reserves of aluminium ore. Aluminium is extracted from molten aluminium oxide at high temperatures using electrolysis. The process requires huge amounts of electrical energy. Recycling saves energy, and therefore money, since recycling aluminium does not involve electrolysis.
When comparing recycled aluminium with aluminium extracted from its ore, there is a 95% energy saving.
Recycling steel/iron
Using recycled steel saves about 50% of the energy used to extract iron and turn it into steel. Much of the energy in the production of steel from iron ore is supplied by burning fossil fuels, such as natural gas used to heat the air entering a blast furnace. Therefore, recycling helps save the dwindling supplies of the non-renewable fuels.
Reverse Osmosis
• method of desalination (removal of salt from seawater)
• seawater is forced through a membrane at a high pressure
• membrane allows water molecules to pass through but prevents any other chemicals dissolved in the water from passing through
Thermal desalination
• salt water is heated or the water is allowed to evaporate
• water vapour is collected rather than being lost
• water vapour is condensed to form pure water
• salt is left behind
