Page 31 - Curriculum Visions Dynamic Book

Extraction and refining
Silver is present in small concentrations along with several other metals, such as copper, lead and zinc and it is usually extracted while these metals are being refined.
During electrical refining of copper, for example, the silver settles out at the bottom of the tank in which copper is being refined by electrolysis. The silver is dissolved out of the residue using concentrated nitric acid. The solution is then reacted with iron sulphate, and the silver comes out of solution as a precipitate. It is then further refined by electrolysis.
Silver also dissolves in solutions of sodium or potassium cyanide, and these substances can be used for chemical extraction. The reaction produces a solution containing silver cyanide to which zinc is added causing the silver metal to precipitate out. This method was developed just
in time to be used to extract silver from the Comstock Lode.
Because cyanide is so dangerous, the cyanide process is little used today. Instead, a flotation process is used (see page 10). Jets of water create bubbles in tanks of ore powder containing
a frothing agent. The silver is taken way in the froth and is then refined by electrical means.
Because so much silver is used in film-making, attempts are made to recover the silver on the film and recycle it during film processing. About one fifth of the silver used in film-making is recovered. This is done by burning the film and then refining the silver by electrical means.
gangue: the unwanted material in an ore.
hydrothermal: a process in which hot water is involved. It is usually
used in the context of rock formation because hot water and other fluids sent outwards from liquid magmas are important carriers of metals and the minerals that form gemstones.
lode: a deposit in which a number of veins of a metal found close together.
ore: a rock containing enough of
a useful substance to make mining it worthwhile.
vein: a mineral deposit different
from, and usually cutting across,
the surrounding rocks. Most mineral and metal-bearing veins are deposits filling fractures. The veins were filled by hot, mineral-rich waters rising upwards from liquid volcanic magma. They are important sources of many metals, such as silver and gold, and
also minerals such as gemstones. Veins are usually narrow, and were best suited to hand-mining. They
are less exploited in the modern machine age.
EQUATION: The use of cyanide to extract silver
Silver cyanide complex + zinc ➪ zinc cyanide complex + silver 2NaAg(CN)2(aq) + Zn(s) ➪ Na2Zn(CN)4(aq) + 2Ag(s)
Also...
The Comstock Lode was a zone nearly six kilometres long that included deposits of native silver. It was discovered in the Sierra Nevada mountains of Nevada, USA, in 1859. It was named after the prospector who found the lode, Henry T. P. Comstock.
The area produced one of the richest silver rushes in history, probably yielding some $300 million at 19th century values (many billions in today’s values). Virginia City was founded and grew up around the lode. When the silver was mined out, people moved away, and Virginia City is now a ghost town.
 The wealth of the town of Taxco in central Mexico was based on a silver lode discovered nearby. The lode is still worked, although most of the native metal has been removed in the past two centuries. The grand church and other buildings reflect the money that the exploitation of silver brought to this otherwise poor rural area.
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