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How do we obtain metals
I. Minerals
--Only a few metals (e.g. gold and platinum) are found as free, uncombined elements in
the earth.
--Most metals exist as compounds in nature.
--The individual chemical compounds that make up rocks are called minerals.
--Minerals from which we extract metals are called ores.
II. How long will metal resources last
The Earth’s metal resources are limited and cannot be replaced once they are used up.
III. Conservation of Metal Resources
Since the deposits of mineral (metals) are non-renewable and of limited amount,
we should conserve the metal resources by reuse, recycle and replace.
Reuse -- some manufactured items can be reuse rather than thrown away.
Recycle -- means melting down and using it again.
Examples : --aluminium in old soft drink cans.
--lead from old batteries
-- gold and silver in jewellery
Importance of recycling
a) Metal resources are _________
b) ______ is saved to conserve energy.
c) Increase the public awareness of conservation
d) Other resources (e.g. water) are saved.
e) Waste disposal problems and environmental problems are reduced.
Problems in recycling
a) The difficulty of getting people to save scrap metal
b) The difficulty of sorting the scrap metal.
c) The cost of _______ing the scrap waste
The cost of _______ing waste to the recycling plant.
The cost of ____ing and purifying the metal.
The cost of disposing waste from the recycling process.
iii) Replace -- Some new materials can be used to replace metals
Substitute (代用品)
Telephone wires
Optical fibres
Construction materials
Drink containers
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