Electrolysis of Copper
By Oliver Moody
Purification of copper
Copper is a good conductor of electricity, and is used extensively to
make electrical wiring and components. The extraction of copper
from copper ore is done by reduction with carbon. However, the
copper produced is not pure enough for use as a conductor, so it is
purified using electrolysis.
Electrolysis of copper
In this process, the positive electrode (the anode) is made of the
impure copper which is to be purified. The negative electrode (the
cathode) is a bar of pure copper. The two electrodes are placed in a
solution of copper(II) sulfate.
A rod of pure copper is used
as a cathode and the impure
copper is an anode. The
electrolyte (solution the ions
travel through) is a solution
of copper (II) sulphate
(CUSO4).
During electrolysis, copper
(II) ions leave the impure
copper anode and since they
are positive are attracted to
the negative cathode - here
they pick up the two
electrons that are needed to
form a copper metal and this
builds up pure copper.
Impurities from the anode collect at the bottom of the solution.
Anode sludge
The impurities found in copper anodes as well as the structure and
manner of dissolving of anodes, continuously cause. small quantities
of particulates and impurities to be generated. These go into the
plating bath. The black phosphorus.film which forms on
phosphatized anodes in copper sulphate baths winds up in the
plating solution as the anodes,.corrode and get smaller in the normal
plating process. Normal filtration practice removes these particulates
and precipitates without problem. This so called "sludge" formation
is normal and expected.