Improvements in and relating to the Desilverization of Lead and Simultaneous Manufacture of White Lead by Electrolysis of Argentiferous Lead.
Year: 1891

page_text: Date of Application, 9th Jan., 1891-Accepted, 7th Mar., 1891
COMPLETE SPECIFICATION.
Improvements in and relating to the Desilverization of Lead and
Simultaneous Manufacture of White Lead by Electrolysis of
Argentiferous Lead.
I, TURNER D. BOTTOME, of the Town of Hoosick, in the State of New York,
U.S., Electrician, do hereby declare the nature of this invention, and in what
manner the same is to be performed, to be particularly described and ascertained
in and by the following statement :-
This invention relates to an improved process for refining pig lead containing
silver as an impurity, and also to the simultaneous production of white lead, by the
use of electricity.
Heretofore lead has been desilverized principally by the cupellation process, but
it is now generally admitted that the said process cannot be economically carried on
in the case of lead which contains less than 8 ozs. of silver to the ton. For refining
lead containing only a small quantity of silver the usual process is to melt the lead
and then allow it to cool until crystals of lead form, these crystals are then removed
and the molten liquid that remains now contains the greater part of the silver, it is
It is
then cupelled in the ordinary way to obtain the silver in the free state.
obvious that methods similar to the above can only extract a certain proportion of
the silver and that they are attended with considerable expense in order to get out
the last traces of the silver.
The object of my invention is to completely desilverize lead, and to obtain the
silver pure in the solid metallic form ready for the market in one operation, and to
simultaneously produce basic lead carbonate from the remaining lead.
My objects are obtained in the following manner : It being known that lead
carbonate is insoluble in a dilute solution of ammonium carbonate while silver on
the other hand is soluble in the same, hence an electrolyte that will dissolve both
lead and silver by the use of an electric current and one that is synergistic to a
chemical such as ammonium carbonate will accomplish my purpose.
In order to carry my invention into practical effect, it is necessary that the
chemical solution or electrolyte shall be composed of chemicals that will not
decompose one another under the influence of the electric current, I have found
that a solution composed of one half a pound of ammonium nitrate and the same
quantity of ammonium carbonate dissolved in one gallon of water to best answer
my purpose, although, acetate of ammonium and the carbonate of ammonium in
similar proportions will answer as well. There are other solutions that may be
used for accomplishing the same result, but they all depend on a chemical that will
precipitate lead and yet dissolve silver in the presence of carbon dioxide, ammonium
compounds do this in the highest degree, although the soluble thio-sulphates have
the same action. Taking for example a solution composed as above described of
carbonate and nitrate of ammonia and immersing therein pigs of lead connected as
anodes to the terminals of an electrical generator, and having suitable cathodes
also electrically connected and immersed in the solution, upon the passage of an
electric current the leaden anodes are dissolved the silver and lead both going into
the solution, but the lead is immediately precipitated by the presence of free carbon
dioxide which is continually injected into the bath during the working of the
process, the silver instead of being precipitated is deposited in the metallic state
upon the cathodes. I do not limit myself to the exact proportions of the ingredients
used to prepare the electrolyte nor do I limit myself to any particular chemical
compounds in the preparation of the same.

page_text: Having now particularly described and ascertained the nature of my invention,
and in what manner the same is to be performed, I declare that what I claim is:-
:-
1. The process of refining lead, consisting in subjecting argentiferous lead to
electrolysis while immersed in an electrolyte composed of ammonium salts kept
saturated with carbon dioxide substantially as described.
2. The process of refining lead containing silver consisting in electrolytically
dissolving the said lead in an electrolytic solution composed of ammonium or
synergistic compounds dissolved in water and kept saturated with carbon dioxide,
whereby lead carbonate precipitates and silver deposits upon cathodes substantially
as described.
3. The process of desilverizing lead and forming white lead simultaneously,
consisting in electrolytically dissolving anodes of the said lead in a chemical
solution composed of solvents of silver and precipitants of lead compounds, while
saturated with carbon dioxide substantially as and for the purpose described.
4. The process of desilverizing lead, consisting in subjecting anodes of the said
lead to the electrolyzing action of an electric current, while they are immersed in a
solution having a chemical affinity for both silver and lead, but which precipitates
lead when saturated with carbon dioxide, substantially as described.
Dated this 29th day of December 1890.
TURNER D. BOTTOME.