A New or Improved Process for Obtaining, by Electrical Decom- position, Metallic Zinc from Solution of Sulphite of Zinc.
Year: 1890

page_text: Date of Application, 5th June, 1890
Complete Specification Left, 5th Mar., 1891-Accepted, 25th Apr., 1891
PROVISIONAL SPECIFICATION.
A New or Improved Process for Obtaining, by Electrical Decom-
position, Metallic Zinc from Solution of Sulphite of Zinc.
A communication to me from abroad by THEODOR LANGE, of Brieg, in the
Empire of Germany.
1, EDMUND EDWARDS, of the firm of Edwards and Co., Patent Agents and
Engineers, of 35, Southampton Buildings, Chancery Lane, in the County of
Middlesex, do hereby declare the nature of this invention to be as follows:-
Attempts have heretofore been made to produce metallic zinc from solution of
sulphate of zinc, by electrolysis, but such attempts have not been successful as the
deposit of metallic zinc from such solution has been imperfect and irregular.
The present invention consists in making use of a solution of zinc oxide in the
form of sulphite instead of sulphate the presence of sulphurous acid acting beneficially
with regard both to the chemical and electrical effects.
In the first place, a difficulty in the use of a solution of sulphate of zinc from
electrolysis is in keeping the bath constantly neutral, and preventing the collection
of acid mixture at the cathode causing polarization and the evolution of hydrogen,
and the consequent deposit of the zinc in an irregular and spongy state, with
oxidized parts, the zinc so produced not being capable of ready melting. In the
decomposition of sulphate of zinc by means of a current of electricity surplus
oxygen is set free which promotes the collection of acid at the cathode, and must
be neutralized or removed.
For this purpose the use of sulphurous acid instead of sulphuric acid serves,
owing to its property of being readily converted to sulphuric acid by the
absorption of the oxygen set free in the bath by the clectric current as just
described. The resulting sulphuric acid rises to the surface of the bath and may
be removed.
By the decomposition of sulphite of zinc (sulphurous acid and zinc oxide) the
metallic zinc is freed from its oxygen which passes to the sulphurous acid at the
cathode in the bath and converts it by its addition, to sulphuric acid.
In the second place, by the use of a combination of zinc with sulphurous acid,
the electricity required for the decomposition of the sulphite of zinc is economized.
The chemical combination of zinc with sulphuric acid shews a heat of combination
representing 103230 units of heat, and that of zinc for sulphurous acid only
71070 units so that there is a saving in the decomposition of the sulphite of
32160 units, or nearly one volt less current energy as compared with the decom-
position of the sulphate.
It follows therefore that the electrical deposition of zinc from its sulphite
requires 30 per cent. less power.
If therefore for the production of 1000 kilos. of zinc per diem from its sulphate,
at 2.5 volts about 170 horse power is necessary, then for the deposit of the same
quantity from the sulphite at 17 volts, only 120 horse power will be required.
If no sulphurous acid in the form of gas is available direct from the roasting
furnace of the ore, it can be obtained in a liquid form in suitable vessels and used
for the same purpose.
Dated this 5th day of June 1800
EDWARDS & Co.,
35, Southampton Buildings, Chancery Lane, London,
Agents for the Applicant.

page_text: COMPLETE SPECIFICATION.
A New or Improved Process for Obtaining, by Electrical Decom-
position, Metallic Zinc from Solution of Sulphite of Zinc.
A communication to me by THEODOR LANGE, of Brieg, in the Empire of Germany.
I, EDMUND EDWARDS, of the firm of Edwards & Co., Patent Agents and
Engineers, of 35, Southampton Buildings, Chancery Lane, in the County of
Middlesex, do hereby declare the nature of this invention, and the manner in which
the same is to be performed, to be particularly described and ascertained in and
by the following statement, that is to say :-
Attempts have heretofore been made to produce metallic zinc from solutions
of sulphate of zinc, by electrolysis, but such attempts have not been successful,
as the deposit of metallic zinc from such solution has been imperfect and irregular.
The present invention consists in making use of a solution of zinc oxide in the
form of sulphite instead of sulphate, the presence of sulphurous acid acting
beneficially with regard both to the chemical and electrical effects.
In the first place a difficulty in the use of a solution of sulphate of zinc for
electrolysis is in keeping the bath constantly neutral, and preventing the collection
of acid mixture at the cathode, causing polarization and the evolution of hydrogen,
and the consequent deposit of the zinc in an irregular and spongy state, with
oxidized parts, the zinc so produced not being capable of readily melting. In the
decomposition of sulphate of zinc by means of a current of electricity surplus
oxygen is set free which promotes the collection of acid at the cathode, and must
be neutralized or removed.
For this purpose the use of sulphurous acid instead of sulphuric acid serves,
owing to its property of being readily converted to sulphuric acid by the absorption
of the oxygen set free in the bath by the electric current as just described. The
resulting sulphuric acid rises to the surface of the bath and may be removed.
By the decomposition of the sulphite of zine (sulphurous acid and zinc oxide)
the metallic zinc is freed from its oxygen which passes to the sulphurous acid at
the cathode in the bath and converts it by its addition, to sulphuric acid.
In the second place, by the use of a combination of zine with sulphurous acid, the
electricity required for the decomposition of the sulphite of zinc is economized.
The chemical combination of zinc with sulphuric acid shews a heat of combination
representing 103230 units of heat, and that of zinc with sulphurous acid only
71070 units, so that there is a saving in the decomposition of the sulphite of
32160 units, or nearly one volt less current energy as compared with the decom-
position of the sulphate.
It follows therefore that the electrical deposition of zinc from its sulphite
requires 30 per cent. less power. If, therefore, for the production of 1000 kilos. of
zinc per diem from its sulphate, at 2.5 volts about 170 horse power is necessary,
then for the deposit of the same quantity from the sulphite at 1.7 volts, only
120 horse power will be required.
If no sulphurous acid in the form of gas is available direct from the roasting
furnace of the ore, it can be obtained in a liquid form in suitable vessels and used
for the purpose described.
Having now particularly described and ascertained the nature of the said
invention, and the manner in which the same is to be performed, I declare that
what I claim is :-
The process of obtaining metallic zinc from a solution of sulphite of zinc, by
electrolysis, whereby sulphuric acid is formed as a by product, substantially as
specified.