Improvements in the Manufacture of White Lead.
Year: 1893

page_text: Date of Application, 21st Nov., 1893-Accepted, 23rd Dec., 1893
COME LEIE DIECIFICATION.
Improvements in the Manufacture of White Lead.
I, ELWYN WALLER, of 33, West 15th Street, in the City and County of New
York, in the State of New York, one of the United States of America, Chemist, 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 the manufacture of white lead, for use as a pigment, from
the native lead carbonates or ores containing native lead carbonates.
In carrying out my invention, I heat an aqueous solution of ammonium acetate
in a suitable vessel, still or digester, in contact with native lead carbonate or ores
containing the same, preferably pulverized. The aqueous vapours evolved by such
boiling treatment are collected and condensed, and one obtains in this distillate, a
solution of ammonium carbonate. In the vessel in which the solution has been
heated will now be found a solution of lead acetate, either neutral or basic,
according to the proportion of ammonium acetate used, and mingled with this
solution will be found the undissolved portions of the ore. The solution of lead
acetate is separated from the solid matter by filtering, or other means known in the
arts, and the clear solution thus obtained is then mixed with the distillate, namely,.
the solution of ammonium carbonate. The effect of this mixing is to precipitate
lead from the solution in the form of lead hydrocarbonate or white lead, the
supernatant liquid in the precipitating tank or vessel being a solution of ammonium
acetate. Thus the ammonium acetate previously employed is regenerated in a form
suitable for the treatment of another portion of the lead carbonate ores, and the
operation above described may be carried on indefinitely with very slight loss of
the ammonium acetate employed.
The temperature at which the solutions are mixed is not altogether a matter of
indifference. In general terms, the higher the temperature of the solutions mixed,
the finer the quality of the product. The best temperature at which to work will
be regulated by the quality and quantity of product desired, the bulk of the
solutions employed, the extent of surface exposed for evaporation in the mixing
vessel, and other similar conditions.
If, as is sometimes the case, copper or silver exists in the ore treated in such a
condition that portions of these metals, or either of them, also pass into the lead
acetate solution in the preparation of the same as above described, the addition of
a small percentage of metallic lead, so comminuted as to present an extended
surface, may be added. This addition of metallic lead has the effect of precipitating
from the solution the copper or silver in a metallic form, a corresponding amount
of the lead passing into the solution in accordance with well-known chemical laws.
The surplus of metallic lead so introduced, if any, together with the copper or
silver which may be removed in a metallic form by this means, will of course
mingle with the undissolved residue of solid matters and be separated from the clear
solution of lead before proceeding to precipitation.
The proportions of the crude materials used in the process will depend upon the
richness of the ore and the perfection of the arrangements for condensing the
distillate. In theory, the reaction from the mixture of 154 pounds of ammonium
acetate with 207 pounds of lead as carbonate, or 267 pounds of lead carbonate, will
afford 325 pounds of neutral lead acetate and 96 pounds of ammonium carbonate.
If it be the object to obtain a basic lead acetate solution, the proportion of ore
must be increased, thereby increasing the proportion of lead presented for solution.
Twice the above-stated proportion of lead, as carbonate, will afford, theoretically,
the necessary proportion for the formation of a bi-basic lead acetate, the other

page_text: proportions remaining the same. Three times that proportion of lead, as carbonate
(621 pounds), will form a tri-basic acetate. Some allowance must however be
made for loss from imperfect condensation, which is inevitable when the process is
carried out on a commercial scale. Also, where the ores treated contain but small
amounts of lead carbonate, the proportion of water used for the solution may need
to be increased, comparatively, in order to give the required mobility to the mixture
of ore and solution. With rich ores, containing from 60 to 70 per centum of lead,
´it has been found practicable to use a solution of ammonium acetate containing
about one pound of the salt to a gallon of water. Of such solution, it is advisable
to use about 40 gallons to every 100 pounds of lead existing in the ore as carbonate,
the treatment being conducted in a closed vessel capable of being heated to the
temperature of ebullition and connected with a condenser in any manner found
convenient. The distillation is best conducted with a moderate heat so as to keep
the liquid gently boiling. When about one-half to two-thirds of the liquid has
been distilled off, the distilling vessel contains the lead in solution. The distillation
may then be stopped and this solution of lead separated from the undissolved residue
by any suitable means.
The precipitated lead hydrocarbonate, or white lead, may be washed and dried
for use by well-known methods.
The washings from the undissolved residue, or solid matter, may be employed to
bring the bulk of the solutions used up to the necessary volume; or, after
neutralizing with acetic acid, they may be evaporated to a point at which neutral
lead acetate will crystallize out, the product being thus prepared for market as lead
acetate.
The washings from the white lead may be economized in a similar manner, or
may be utilized in the works in other ways.
Any loss of strength of the ammonium acetate solution may be made good by
adding this salt.
The apparatus employed in carrying out my process forms no part of my present
invention; indeed, it is not material what form of apparatus is employed, so long as
it is adapted to the end sought.
I am aware that it is not new, in the manufacture of white lead, to utilize the
reaction of ammonium acetate on litharge or massicat, but processes dependent on
this reaction are entirely different from mine and necessitate the employment of
free carbon dioxide. None of these processes employ distillation and they are
usually carried out without the aid of heat.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I claim :-
1. In the process of making white lead, heating the native lead carbonate with
an aqueous solution of ammonium acetate, whereby lead acetate and ammonium
carbonate are formed, the latter being carried over with the aqueous vapour and
condensed, substantially as set forth.
2. The herein described method of making white lead, which consists in distilling
natural lead carbonate with an aqueous solution of ammonium acetate and
condensing the distillate which is a solution of ammonium carbonate, then
separating the resultant clear solution of lead acetate from the undissolved residue
from the distilling vessel, and then mixing together the said solutions of ammonium
carbonate and lead acetate, whereby lead hydrocarbonate is precipitated and a
solution of ammonium acetate yielded.
Dated the Plat dow of N1000
G. G. M. HARDINGHAM,
191, Fleet Street, London, E.C., Chartered Patent Agent.