IMPROVEMENTS IN THE MANUFACTURE OF METALLIC ZINC AND OF SULPHURIC ACID
Year: 1877

page_text: LETTERS PATENT to Edward Andrew Parnell, of Swansea, in the County of
Glamorgan, for the Invention of "IMPROVEMENTS IN THE MANUFACTURE OF
METALLIC ZINC AND OF SULPHURIC ACID."
Sealed the 3rd August 1877, and dated the 28th February 1877.
COMPLETE SPECIFICATION filed by the said Edward Andrew Parnell at the
Office of the Commissioners of Patents on the 28th February 1877.
EDWARD ANDREW PARNELL, of Swansea, in the County of Glamorgan.
PROVEMENTS IN THE MANUFACTURE OF METALLIC ZINC AND OF SULPHURIC ACID."
My said Invention consists,―
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IM-
Firstly. Of a method of preparing or obtaining a material from the treatment of
blende or sulphide of zinc, which is well adapted for the manufacture of metallic
zinc.
And, Secondly. In the preparation of sulphuric acid from sulphate of zinc.
In carrying out my said Invention I first calcine ordinary blende (which has been
previously reduced to a state of powder) with exposure to air at a moderate heat,
whereby the sulphide of zinc becomes changed partly to sulphate of zinc and partly
to oxide of zinc. For this purpose any variety of blende may be used, but my said
Invention is especially adapted for the poorer or weaker varieties of the ore, which
contain so small a proportion of zinc as to be ill adapted for the ordinary mode of
obtaining the same by calcination in furnaces, and subsequent distillation in earthen
retorts. The calcination of such ground blende, as before mentioned, may be effected
in the ordinary open calcining furnace, but, I prefer to conduct this operation
without direct contact with the gases from the fire, so as to collect the sulphurous
acid disengaged during the calcination, and to make the same available for the
preparation of sulphuric acid in the usual manner.
A close oven may be used for the operation of calcination, but I prefer to use
what is known as "Oxland and Hocking's rotating cylinder" (for which Letters Patent
bearing date the Twenty-fifth day of September 1868, No. 2950, were granted), hot air
being caused to enter the cylinder at the lower end instead of employing the gases
from a fire-place. I conduct the calcination at a moderate heat, such as is
favorable to the production of sulphate of zinc, as will be well understood.
Dmine 37

page_text: To the calcined ore, which contains both oxide of zinc and sulphate of zinc,
associated with impurities, that is to say, oxide of iron, oxide and sulphate of lead
and quartz, I next add dilute sulphuric acid, consisting of about three parts of
water to one of concentrated acid in a sufficient quantity to unite with the oxide of
zinc in the roasted ore, and form neutral sulphate of zinc. The sulphuric acid
immediately combines with the oxide of zinc in preference to the oxide of iron, thus
affording a solution of sulphate of zinc containing a very small proportion of or no
sulphate of iron. The sulphate of zinc thus obtained is separated from the insoluble
portion by decantation, filtration, and washing in the usual manner, and then con-
centrated by evaporation in iron or leaden pans.
I next decompose the sulphate of zine by calcination, so as to obtain therefrom
oxide of zinc adapted for the preparation of metallic zinc, and sulphurous acid
available for the production or recovery of sulphuric acid in leaden chambers
and towers as well understood. I conduct this calcination in a close furnace
or oven so as to avoid direct contact with the gases from the fire-place.
At a high temperature sulphate of zinc is decomposed and resolved into oxide of
zinc and a mixture of sulphurous acid and oxygen gases, but instead of calcining
sulphate of zinc alone I prefer to mix it previously with a reducing agent, the most
suitable being sulphide of zinc or raw blende. I mix the ore in a state of fine
division with the concentrated solution of sulphate of zinc in such proportion that
the zinc in the blende amounts to about one-third of the zinc in the sulphate.
After being partially dried this mixture is heated in a close furnace or oven, the
sulphurous acid gas then produced being conveyed by a flue to sulphuric acid
chambers and towers.
The decomposition of the sulphate of zinc in the preceding mixture commences at
a temperature below redness, but it is desirable to bring the mixture to a dull red
heat before removing it from the furnace. When it ceases to disengage sulphurous
acid, it consists principally of oxide of zinc associated with a little oxide of iron, and
silica derived from the portion of blende used in the last operation. It is then fit
for use in the manufacture of metallic zinc by distillation with carbonaceous matter
in earthen retorts in the usual way. The proportion of zinc in the calcined product
varies from 60 to 70 per cent., according to the strength of the blende mixed with
the sulphate for the last operation.
Having thus declared and ascertained the nature of my said Invention, and in
what manner the same is to be performed, I wish it to be distinctly understood that
I do not claim the manufacture of sulphuric acid from the gaseous products of the
first calcination of raw blende, but what I do consider as being novel and original
and therefore claim as constituting my said Invention, are,-
"
First. The production or recovery of sulphuric acid from the gaseous products of
the calcination of sulphate of zinc, either alone or mixed with a reducing agent,
such as sulphide of zinc, either artificial or native, substantially as herein-before
described and set forth.
And, Secondly. The use and application for the manufacture of metallic zinc of
the product of calcination of a mixture of sulphate of zinc with sulphide of zinc,
either artificial or native, substantially as herein-before described and set forth.
In witness whereof, I, the said Edward Andrew Parnell, have hereunto set
my hand and seal, this Twenty-third day of February, in the year of our
Lord One thousand eight hundred and seventy-seven.