Improved Process of Manufacturing Lead-sulphate from Metallic Lead.
Year: 1891

page_text: Date of Application, 19th May, 1891-Accepted, 25th July 1891
COMPLETE SPECIFICATION.
Improved Process of Manufacturing Lead-sulphate from Metallic
Lead.
I, HEATON PENNINGTON, Manufacturing Chemist, residing at No. 915 Adams
Street, Chicago, in the County of Cook and State of Illinois, one of the United
States of America, do hereby declare the nature of my invention and in what
manner the same is to be performed to be particularly described and ascertained in
and by the following statement and accompanying drawings
It is well known from laboratory experiments that by treating litharge or sugar
of lead with sulphuric acid and separating the sulphate from the liquid and washing it,
a pure lead-sulphate is obtained. But the production of the litharge (by roasting
or otherwise), or the sugar of lead (by treating metallic lead with dilute acetic
acid and evaporating the liquid), is so expensive as to practically prohibit the use
of these processes at the present time for the manufacture of lead-sulphate in com-
mercial quantities for the purpose of a pigment.
The process heretofore industrially employed for producing lead-sulphate from
metallic lead, consists in submitting small feathers or flakes of metallic lead to the
alternate action of dilute acetic acid and of atmospheric air, whereby a solution of
lead-acetate is produced, to which sulphuric acid is added to precipitate the lead
as a sulphate. Such process, as it has been heretofore practised, has always pro-
duced a distinctly acicular crystalline sulphate, containing more or less lead-oxides,
etc., either mechanically mixed with the sulphate or occluded within the crystals or
aggregations of crystals, and therefore difficult if not impossible to separate by any
subsequent operation. By reason of the impurities and the acicular crystallization,
the product has been quite useless as a pigment, lacking density and opacity, and
having to be mixed and ground with zinc white, barytes, or other equivalent sub-
stances, to adapt it for use as a paint; and even when thus mixed and ground, the
resulting paint, besides being expensive, lacks proper opacity, requires too much oil
for grinding and thinning, and works poorly under the brush.
One object of my invention has been to produce a process by which there can
be industrially manufactured, from metallic lead, a pure lead-sulphate in condition
to be used for paints without the admixture of anything but oil; and another
object has been, to render my improved process more economical, convenient and
rapid, by improvements in the apparatus employed for carrying it into practice.
Any person skilled in the art as it has been heretofore known and practised, will
understand the nature of my several improvements from the following description
and statement.
I have discovered that the imperfect character of the product heretofore produced
by subjecting metallic lead alternately to the action of acetic acid and air and then
treating the acetate solution with sulphuric acid, has been due to two causes,
to-witFirst, the formation of obdurate lead-oxides during the alternate treat-
ment by acetic acid and air, and secondly, the formation of hard, acicular crystals
of lead sulphate during the treatment of the acetate solution with sulphuric acid.
My improved process prevents the first of these evils, by keeping the metallic lead
loose enough to be thoroughly pervious to the air, and it prevents the second of
them by agitating the solution, during the sulphuric acid treatment, so violently
that injurious acicular crystallization is practically unable to take place. My
improved apparatus accomplishes its special purposes by reason of being so con-
structed as to hold the metallic lead in a loose condition, permeable to the air,
during the process of aeration; by providing means for causing the air to

page_text: thoroughly permeate the mass of lead during the aerating step; by providing
means for removing the fine particles and pieces of partially dissolved lead that
might otherwise become so compacted as to obstruct the action of the air through
the mass and retain an injurious. amount of moisture by providing means for
closing the vessel during the action of the acetic acid; and by providing means for
drawing off the acetate solution from time to time, and charging-in fresh metallic
lead, so as to render the operation practically continuous. My mode of manufac-
ture is substantially as follows:
First I take metallic lead, reduce it, by any suitable means, to thin sheets,
shavings, filaments or flakes, and place it in the vats preferably without contact
with water or long exposure to air. In thus reducing it, I prefer to plane it into
thin shavings or filaments, which curl up and intertangle or lodge across each
other when aggregated together, forming ample air-spaces, and materially tending
to hinder it from subsequently settling into a compact mass. Substantially the
entire surface of the lead becomes thus freshly cut and in the best condition to be
vigorously attacked by the acetic acid, which is then applied as, in the old and well
known process.
In treating the metallic lead, thus prepared, to the alternate action of acetic acid
and air, I place the lead in a suitable vat; subject it, as usual to the action of
dilute acetic acid; draw off the liquid take care that the remaining lead be kept
lightened up so as to be permeable to the air; allow it to stand a sufficient length
of time to be properly acted upon by the air; then charge-in fresh lead, taking
care that it shall not press the old lead down, into a solid mass, but that the entire
charge, old and new, shall be loosened up thoroughly; then renew the dilute acetic
acid; and so on. With the old form of vat heretofore used, and which may be
employed in my process if preferred, the loosening-up of the lead must be per-
formed by manual labour, from time to time, as may be required.
I have discovered, however, that the lead can be kept in a sufficiently loose con-
dition without manual labour, by suspending it between downwardly converging
supports during the acetation and aeration, and, for reasons of convenience, economy,
and rapidity of operation, I prefer to employ a vat or "corroder constructed and
operating on that principle, and have shown the same in the accompanying drawing,
wherein :
off.
A is the body of the corroder, made in frusto-conical, or tapering polyhedral
form, preferably about 12 feet high, with a bottom diameter of about 2 feet and a
top diameter of about 8 feet, and having a charging-hole in the top, say 2 feet in
diameter, closed by a removable cover B, and an opening in the bottom, say, 1 foot
in diameter, provided with a gate C, which can be opened when desired, or closed
water-tight. I prefer to fill the lower corners, as shown at d. The walls of the
vessel are provided with a series of air-holes, aaa, which are plugged when the
corroder is charged with liquid, and opened, for aeration when the liquid is drawn
These holes should be about two inches in diameter, and should be arranged
at proper intervals throughout those portions of the walls with which the charge
of lead comes in contact during the treatment. The vessel should also be pro-
vided with a discharge-orifice a¹, having a suitable plug or spigot, to enable the
acetate solution to be drawn off from the lead whenever desirable. In operation
the corroder is to be charged with lead to a line slightly above the upper air-hole,
and then with acid liquor to cover the lead, and the top closed. As the lead contracts
in volume under the action of the acid, it does not leave the walls, so as to form a
space around it, but merely settles to a lower position where the downwardly
tapering walls receive and support it as before. The result is, that it does not
compact but remains loose and thoroughly pervious to the liquid, the action of
which consequently proceeds much more rapidly than in the old forms of corroder.
The liquid is then drawn off through the discharge orifice a', the top cover
removed, and the air-holes, a, opened; when the loose condition of the remaining
lead, and its contact with the tapering walls around it, enable the air to permeate

page_text: the whole mass and rapidly effect its complete aeration. During the process of
aeration the bottom gate C may be opened if desired; and it will be advisable to
open it occasionally in order to remove any fine particles of lead that may compact
themselves together on the gate or floor of the vessel. If more rapid work is
desired, a fan-blower or its equivalent may be employed to force or draw an air-
blast through the lead, instead of awaiting the slower action of the atmosphere ;
and if very rapid work is desired, a hot blast may be employed for such purpose.
Means for creating and supplying an artificial current of air whether hot or cold,
are so well known in the arts that I do not deem it necessary to describe them here,
but merely to say that any suitable means may be employed for the purpose-for
example, a fan-blower with an adjustable or detachable induction or eduction tube
running to any suitable opening in the corroder, so as to cause an artificial air-
current to pass through the latter during the process of aeration. When the fan-
blast is used it may be applied through the top or bottom holes of the corroder
and the lateral ventilating holes kept plugged or altogether dispensed with, if pre-
ferred, as the forced blast will fully compensate for them.
Coming now to the next step of my improved process-that of treating the
acetate solution with sulphuric acid-in this step the acid is applied in practically
the same proportions as in the old process, but it is advisable to sprinkle it into
the acetate much more rapidly than has been customary, say, about four times as
quickly, for the best results. During the action of the sulphuric acid upon the
acetate, the solution is to be violently agitated to prevent the formation of
deleterious acicular crystals. To this end, it should be subjected, in the sulphating
tank, to the action of a mechanical agitator having a sufficiently violent action to
accomplish the purpose referred to. If the old form of stirrer be employed, it
should be speeded up to at least about double its former number of revolutions per
minute. I prefer a form of rotary stirrer having both vertical and horizontal arms
or bars moving through the liquid. In any case, and whatever form of agitator be
employed, the agitation must be sufficiently violent to prevent the formation of
acicular crystals and render the sulphate practically amorphous and a microscopic
examination of the precipitate will show when the speed of the agitator is sufficient
to accomplish this result.
After the sulphate is formed, it is settled in the usual way, the liquid returned
to the corroders, and the sulphate precipitate thoroughly washed in pure water
and then separated therefrom in the usual way. Great care should be taken to
wash the precipitate thoroughly clean, or else it will be liable subsequently to
become slimy and then to harden in the keg.
The sulphate is then dried, and, when necessary, it may be ground or crushed to
break up any lumps, and is ready for use as a pigment, with oil, without the
addition of any other substance. The resulting pigment is much superior, in every
respect, to the product of the old process, as well as to all lead carbonate paints,
and to all paints made from a distinctly crystalline lead-sulphate, by whatever
process produced-the amorphous character of the sulphate giving the paint
exactly the density, opacity, body, and other qualities which best adapt it for
practical application with a brush, and the purity of the sulphate rendering it
unalterable by ordinary atmospheric agencies.
It will, of course, be understood by those familiar with the art, that the entire
process should be carried on in a room or building, heated to as high and uniform
a temperature as is practicable.
Having now particularly described and ascertained the nature of my said inven-
tion, and in what manner the same is to be performed I declare that what I
claim is :-
:―
The improved process herein set forth, distinguishable from prior processes by
the loose condition of the lead during the application of the acetic acid and air,
and by the violent agitation of the solution during its treatment with sulphuric

page_text: acid, whereby a pure and practically amorphous lead-sulphate is produced, sub-
stantially as described.
Dated this 16th day of May 1891
DUTTON & FULTON,
1, St. James' Square, Manchester, Agents.