Improvements in the Treatment of Lead Ores, and the Production therefrom of White Lead, Salts, and Colours of Lead, as also simultaneously Zino White.
Year: 1891

page_text: Date of Application, 30th Oct., 1891
Complete Specification Left, 30th Aug., 1892-Accepted, 1st Oct., 1892
PROVISIONAL SPECIFICATION.
Improvements in the Treatment of Lead Ores, and the Production
therefrom of White Lead, Salts, and Colours of Lead, as also
simultaneously Zino White.
I THOMAS HENRY COBLEY Manufacturing Chemist Albion Street Dunstable
Bedfordshire do hereby declare the nature of this invention to be as follows:-
My invention relates to the treatment of lead ores such as galena and native
carbonate of lead or other oxidisable ores of lead and preparing therefrom as herein-
after described white lead meaning carbonate or oxy carbonate of lead, oxide,
acetate or chromate and other combinations of lead and by such process to produce
at the same time zine white.
In carrying out my invention I proceed as follows. In the case of galena or
sulphide of lead I mix it in a fine state of division with a sufficient amount of lime
to combine with the sulphur in the ore preferably in the form of hydrate of lime
and to expedite the oxidation I add a small percentage of nitrate, this is most
effectually done by slakeing the lime with a strong solution of nitrate of soda.
The ore thus mixed is calcined in any convenient furnace at a dull red heat until
thoroughly oxidised it is then passed through a washing mill, or levigating machine
until the lime compounds are removed and the pure oxide remains and may then
be employed, for uses like and in place of litharge for all the ordinary applications
of the same.
The native carbonate requires simply careful roasting with the addition of
caustic lime to prevent peroxidation and silicification acting as a carrier of the
carbonic acid as eliminated.
After roasting it is also passed through a washing mill or levigating apparatus
to free the oxide of lead from extraneous matters.
The oxide of lead obtained in the manner as described for the production of
white lead is next attacked by an acid to form a salt of lead for the continuous
working of which I prefer to employ acetic acid and nitric acid.
A solution of the acetate or any other salt or combination of lead thus formed is
then decomposed by zinc cuttings or scraps and waste of metallic zinc into a metallic
lead sponge and corresponding salt of zinc. The spongy metallic lead is after
being washed brought into an oxidising drum cylinder or chamber through which a
current of warm air accompanied by steam or not is made to pass through at a
good speed or it may be left to free oxidation by exposure.
When sufficiently oxidised it is placed in a carbonating chamber or apparatus
where carbonic acid and steam is made to act upon it in order to convert it into an
amorphous oxycarbonate or true white lead or the lead solution may be precipitated
by an alkali or alkaline earth as neutral carbonate and the necessary equivalent of
corroded oxide as hereinbefore mentioned mixed and boiled with the same so as to
form in another way the oxycarbonate of lead above mentioned. The resulting
salt of zinc is precipitated by means of a soluble sulphide preferably in the case of
acetate with a special sulphur compound of calcium namely a so called polysulphide
of calcium made by dissolving finely divided sulphur with caustic lime or by any
other known means in the form of sulphide of zinc which will have to be furnaced
in the usual manner to give it necessary body and colour or it may be precipitated
as carbonate or oxide and reduced for new use as precipitant of lead. The colours
of lead are produced in the usual manner by the action of chromates and
bichromates upon the lead solutions as obtained in the manner herein set forth.
Dated this 29th day of October 1891.

page_text: COMPLETE SPECIFICATION.
Improvements in the Treatment of Lead Ores, and the Production
therefrom of White Lead, Salts, and Colours of Lead, as also
simultaneously Zinc White.
I THOMAS HENRY COBLEY of No. 1 Albion Street Dunstable in the County of
Bedford Manufacturing 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 treatment of lead ores such as galena and native
carbonate of lead or other oxidisable ores of lead and preparing therefrom as
hereinafter described white lead meaning carbonate or oxycarbonate of lead acetate
or chromate and other salts of lead and by such process to produce at the same
time zinc white.
In carrying out my invention I proceed as follows. When treating galena or
sulphide of lead I first mix the ore in a fine state of division with a sufficient
amount of lime to combine with the sulphur present in the ore varying according to
the percentage of the ore in lead sulphide which can easily be estimated by any
known test, the lime employed should be in the form of hydrate or slaked lime in.
powder or paste if desired the oxidising process may be accelerated by the addition
of a small quantity of nitrate of soda this is simply done by adding 2 or 3% more
or less of the nitrate to weight or percentage of ore dissolving it in the water with
which the lime is slaked and added to the ore. The ore thus mixed is then roasted
at a dull red heat until thoroughly oxidised that is the whole of the sulphide
decomposed which is readily ascertained when by the addition of an acid sul-
phuretted hydrogen ceases to be evolved from the mass.
The native carbonate of lead ore being well washed and reduced to a fine state
of division has also to undergo a careful roasting at a still lower temperature as it
readily parts with its carbonic acid and according to the degree of purity to which
it has been reduced by washing it should previous to roasting be intimately admixed
with from 2 to 3% of caustic lime or any cheap material which will make it
agglomerate so as to make it more convenient for the workmen to handle in
charging and discharging from the roasting furnace and prevent silicification with
any impurities present. The mixing may be conducted in an ordinary mortar mill
and the kind of furnace best adapted for ensuring a careful roasting would be a
revolving furnace both for the convenience of charging and discharging. Where
there is much impurity contained in the ores then it is advisable to pass the
roasted mass through a levigating mill to remove such impurities, but with well
washed and carefully roasted ore this may be dispensed with. The oxide of lead
obtained in this manner from either description of ore is next attacked by an acid
to form a salt of lead and the acid I prefer for the manufacture of white lead and
for the continuous or recuperative working of the same is acetic acid although
other acids may be employed for forming other salts of lead the operation of
dissolution is best carried out by mixing the roasted ore with sufficient acid to
form a thin paste and then allow it to digest the remaining acid requires to be
added to it until an acid reaction takes place this is done in a convenient receptacle
provided with means of agitation and warmed by means of steam or other
convenient means to further the action of the acid and formation of the lead salts.
The salt of lead thus formed is then washed out by the addition of warm water
and run into a settling tank or vat where it is allowed to settle and then it is
removed by decantation, syphoning or other convenient means to a precipitating
tank and for white lead it is precipitated in the first instance by introducing into it
metallic zinc in any form as zinc cuttings washed zinc ashes, recovered zinc old or
waste zinc previously cleansed by washing with dilute acid as is well known a

page_text: galvanic action is set up and the lead is deposited in the form of spongy lead while
the zinc remains in solution as a salt of zinc corresponding to the acid which has
been employed in this case ácetate of zinc-the spongy lead after being removed
from the precipitating tank drained and washed is then exposed to the air charged
with carbonic acid from any source in a chamber provided with shelves for
distributing the lead in thin layers. The carbonic acid may be very simply
introduced from the fumes of burning charcoal or washed flue gases.
This
operation may be more expeditiously carried out by introducing the spongy lead
into a revolving drum or cylinder and passing the vapours of carbonic acid diluted
with air or steam into the said drum or cylinder and causing it to revolve at a good
speed in either case when the lead is sufficiently corroded or the whole converted
into white lead it is then ground and levigated in the usual manner and afterwards
dried at a low temperature. The conversion of spongy lead into white lead may
also be effected in the ordinary way by substituting it for the prepared metallic
lead or litharge in use by known corrosive processes such as the Dutch and other
processes whereby a great economy will be effected from the readiness with which
it is converted into white lead. The spongy lead may also be converted into red
lead by calcination in a suitable furnace with or without the addition of an oxidising
agent such as nitrate of soda and from its great purity would be suitable for the
manufacture of glass and porcelain. The resulting salt or acetate of zinc when all
the lead has been removed is then treated for the recovery of both acid and zinc
the most advantageous method for carrying out this part of the process is instead
of precipitating by a soluble alkaline sulphide or polysulphide of calcium by double
decomposition it will be better to liberate the sulphur from these in the form of
sulphuretted hydrogen and passing the same into the zinc solution by this means
the sulphide of zine or zinc white will be precipitated and the acetic acid completely
recovered for reuse the operation is a simple one and based upon known chemical
reaction the liberation of sulphuretted hydrogen from the sulphides is readily
effected with an acid or the introduction of steam into the sulphides. The white
sulphide of zinc is filtered and then burnt in a kiln or furnace and treated afterwards
in the ordinary manner for employment as a pigment.
Another way of recovering the zinc is to precipitate it with lime and reduce the
zinc oxide thus obtained to metallic zinc by mixing it with carbonaceous matter
and other reducing agents and fireing it up to the point of reduction or by any
other known means. The acetate of lime remaining will yield by distillation with
If
an acid a fresh supply of acetic acid for treating fresh quantities of lead ore.
it is desirable to convert a portion of the lead solution into acetate and chromates
of lead this can be most economically done by taking off the strong solutions from
the dissolved ore and after careful filtration to evaporate them to the crystallising
point and use the mother liquor and weaker washing out liquors for the production
of various shades of chrome by precipitation with the chromates and bichromates
of lime, soda or potash, preferably of lime for economy's sake. The precipitates to
be washed and dried in the usual manner.
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--
1. The treatment of lead ores by oxydising roasting dissolution with acetic acid
and galvanic deposition of spongy lead by means of metallic zinc and the treatment
of this spongy lead by means of carbonic acid with or without the aid of steam and
thereby converting it into white lead or red lead and other products of lead
substantially as hereinbefore described.
2. The treatment of the waste acetate of zinc by sulphuretted hydrogen for the
recovery of the acetic acid for reuse and simultaneous production of zinc white
(white sulphide of zinc) as hereinbefore described.
3. The treatment of lead ores and the production therefrom of spongy lead

page_text: which is converted into white lead or other products of lead and the recovery of
acid used therein and the production of zinc white in the manner hereinbefore
described.
Dated this 29th day of Avonat 1909
THOMAS HENRY COBLEY.