Page 37 - Curriculum Visions Dynamic Book

Amalgams in metal refining
Mercury has long been used to extract gold, silver and the other noble metals from the small pieces of ore that are obtained from panning river beds.
The panning process – swirling rock and ore grain around on a shallow plate – cannot completely separate the metal from the rock. If mercury is added to the ore, it dissolves the metal from the rock, forming a paste-like amalgam. The unwanted rock can then be washed away.
To extract the gold or silver from the amalgam, advantage is taken of the low boiling point of mercury. The amalgam is heated over a fire and the mercury vaporises, leaving the pure silver or gold behind.
The mercury is collected by condensation and reused.
amalgam: a liquid alloy of mercury with another metal.
noble metal: silver, gold, platinum, and mercury. These are the least reactive metals.
 Small-scale prospectors first remove as
much sand and other waste materials as possible, concentrating their ore into the bottom of a pan
as shown here. A small amount of mercury is now added and the pan is heated, so that the amalgam can be run off. This picture was taken in the famous Serra Pelada prospecting area of Brazil.
Dental fillings
Dental amalgam is an alloy of
52% mercury, 33% silver, 12.5% tin, 2% copper and 0.5% zinc.
Fillings in the chewing surfaces
of teeth are made of wear-resisting amalgams. The silver, tin and mercury are mixed together and forced into the cavity. The mixture then slowly hardens.
Care has to be taken to carve the amalgam into the proper contour shape of the tooth as it is hardening but before it sets hard.
Plastic polymers (which can be white) are usually used in the front of the mouth, where amalgams would look unsightly.
 Dental amalgam on the end of a dental instrument about to be pushed into a cavity in a tooth.
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