Improvements relating to the Treatment of Lead and other Fumes in the Manufacture of Pigments, and to Apparatus therefor.
Year: 1889

page_text: Date of Application, 16th July, 1889-Accepted, 17th Aug., 1889
COMPLETE ‘SPECIFICATION.
Improvements relating to the Treatment of Lead and other Fumes
in the Manufacture of Pigments, and to Apparatus therefor.
I, FRANK LESLIE BARTLETT, Metallurgist, of Portland, in the County of
Cumberland, and State of Maine, United States of America, 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 :—
My invention relates to a process and apparatus for refining and whitening the
fume collected in the operation of treating lead, zinc and antimony ores by smelting
or roasting processes in the manufacture of paint pigment.
A further object of the invention is to condense and reduce the volume of such
fumes which are first collected in the form of an exceedingly light dust.
It is well known that such fume is often collected in condensers, bags or screens
which, by reason of its dark color must be resmelted or revolatilized in order to
render it white and pure.
The dark color of this fume arises from the presence of various substances such as
the rare metals cadmium, selenium, vanadium and tellurium, and also sulphur
compounds, carbonaceous matter and acids. The base of the fume or pigment is,
however, either lead, zine or antimony, or compounds of these metals in the form
of oxides, sulphurets, sulphides, or mixtures of the same.
Hitherto no other methods have been used for refining these products except the
usual ones of resubliming and resmelting in furnaces of various kinds, and these
methods of refining have been tedious and expensive, owing to the bulky and light
nature of the substances operated upon. It has also been difficult by the old methods
to obtain pigment of a uniform color and quality.
My invention is founded on the fact that when dark colored fume of the kind
specified is collected comparatively free from extraneous matter, as sand, grit, ash,
iron rust, etc., and is then caused to pass through a heated tube in the presence of
air and out of contact with the products of combustion, and is continually stirred
and scraped from the walls of said tube during its passage, the fume becomes white,
dense and soft, and it is found to be free from the volatile sulphur compounds, acids,
carbonaceous matter and such volatile metals as selenium, arsenic, etc. The fume
thus treated is fitted for a pure white pigment, has great covering power and
possesses great stability as to color, while it is condensed to one-fourth to
one-eighth of its original bulk.
My invention therefore consists of the above described process and of certain
apparatus which I have devised for putting the process into practical operation.
This apparatus consists essentially of a tube and a furnace for heating the same, a
coreless helical screw extending through said tube formed of a coiled bar having an
outer spiral edge conforming to the lower portion of the tube, and means for
rotating said screw, relative to said tube.
In the accompanying drawing I have illustrated an apparatus which is adapted to
carrying my process into effect and which embodies my invention.
In the drawing
Fig. is a central vertical longitudinal section showing the
connections in elevation.
Fig. 2. is a plan or top view, and
Fig. 3. is a cross section of the screw.
screw and its
A represents a furnace of suitable length having a hearth B and an outlet Auo D
connecting with a stack or chimney D. Between the hearth and the outlet flue
there is formed a chamber C through which the flame and the products of combustion
pass. Extending longitudinally through this chamber and passing through the end
walls at each end of the furnace is the tube E which I make preferably of iron.
At

page_text: one end I connect with the tube suitable means of supplying fume to it, here shown
as a hopper F and on the opposite end I place a cap i. In this cap is an opening
for the admission of air, and a slide 3 for closing the opening when desired. Another
opening for the discharge of tho fumo is provided in the lower portion of the cap i¹.
A hood G covers the top of the furnace and is provided with an outlet flue or pipe g.
The hood G is placed a short distance above the furnace whereby an air space is
formed and a pipe connects the tube E with this air space.
Extending through the tube E is the coreless helical screw conveyer I. This
screw I prefer to make of cast iron and it has the form of a flat bar coiled edgewise
whereby an outer spiral edge is formed which fits the surface of the tube accurately. 1
As here shown the screw fits the entire tube, but in practice it is only necessary for it to
fit the lower part as it is there that the fume is all conveyed. The screw is
strengthened by means of bars i which are preferably formed integral with it and
extend through the hollow core. Means are provided for rotating the screw.
here shown I use a pulley J¹ secured to a shaft J which is journalled in a suitable
frame-work J. It is obvious that any other suitable means may be employed to
rotate the screw.
As
In carrying my process into effect by means of the heroindescribed apparatus a
fire is built in the hearth B and the tube is kept preferably at a uniform low red
heat. The fume is fed in at the hopper, the screw being slowly revolved and a supply
of air is admitted through the aperture. The fume is supplied to the screw only
in such quantities that small portions will be carried along the bottom of the tube
by each flange of the screw, and care is taken that the portion conveyed by each
flange does not come above the top or inner edge of the flange whereby portions of
it would fall backward over the flange. As the fume is thus forced along in small
detached masses it is slowly and thoroughly stirred, it is subjected uniformly to a
slowly moving current of air which the open form of the screw admits freely to all
particles of fume, and the surface of the tube is continually scraped clear of any fume
which may have adhered.
As the fume is at first very light and easily blown, it is important, as pointed out,
that it should not be allowed to fall back over the flange as it is pushed along, since
the dust thus formed would be carried off by the current of air. At a certain point
The action
it becomes very sticky and tends to stick to both the tube and the screw.
of the spiral edge of the screw continually removes all that sticks to the tube and
to remove what sticks to the flange of the screw I occasionally introduce a rod into
the core of the screw and allow it to tumble until the adhering fume is shaken off.
If any fume is allowed to adhere long enough to become overheated, litharge is
formed, which discolors the product.
It will thus be seen that by the use of my apparatus the following things are
accomplished all of which are necessary to the success of my process, viz. :
All portions of the fume are evenly heated and subjected to the action of the air.
The stirring is effected so gently that no dust is carried away by the current of air.
The particles of fume are effectually prevented from sticking to the walls of the
tube and thus becoming over-heated and allowed to form litharge.
As before stated, the pigment when it comes from the end of the tube has given
off all its impurities and becomes dense and white and has a body sufficient to
produco a fine quality of paint.
It is obviously immaterial whether the screw is made to rotate within the tube
or the tube rotates above the screw; the relativo action of the parts would be the
same.
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
claim is
(1) The herein described method of refining fume which consists in passing i
through a heated tube in the presence of air, and continually stirring it and scraping
it from the walls of said tube during its passage, substantially as described.

page_text: (2) The herein described apparatus for refining fume, which consists of a tube, and
a furnace for heating the same, a coreless holical scrow within said tube having the
form of a coiled rod or bar with an outer spiral edge fitting the lower portion of
said tube, and means for rotating said screw relative to said tube, substantially as
shown.
Dated this 16th day of July 1889.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.