IMPROVEMENTS IN DESILVERING LEAD
Year: 1874

page_text: LETTERS PATENT to Joseph Alexander Cicognani, of 20, Great
Winchester Street, in the City of London, Merchant, for the In-
vention of "IMPROVEMENTS IN DESILVERING LEAD."-A communication
from abroad by the Baron Andrea Podesta, of Genoa, in the
Kingdom of Italy, President of the Compagnia Generale delle
Miniere.
Sealed the 24th July 1874, and dated the 21st May 1874.
PROVISIONAL SPECIFICATION left by the said Joseph Alexander
Cicognani at the Office of the Commissioners of Patents, with
his Petition, on the 21st May 1874.
I, JOSEPH ALEXANDER CICOGNANI, of 20, Great Winchester Street,
in the City of London, Merchant, do hereby declare the nature of the
said Invention for "IMPROVEMENTS IN DESILVERING LEAD," to be as
follows:-
-
This Invention has for its object improvements in the desilvering lead
by means of zinc.
In the following description the process of desilvering lead is divided

page_text: These seven stages will be referred to by the numbers which precede
them.
Suppose lead containing about 1 kilogramme of silver to the ton is to
be operated upon, two pots, A and B, each capable of containing
about 20 tons of lead, are employed. Pipes from the bottom of these
pots communicate with a common reservoir C at a lower level. 20 tons
of lead are melted in pot A and the lead is skimmed to remove the
dross. Zinc is introduced at the bottom of the pot in any convenient
manner used in the well-known zinc processes for desilvering lead. A
scum containing zinc, silver, and lead rises to the surface. The scum
which first rises is not so rich in silver as that which subsequently rises.
This zinc scum is introduced into the pots over and over again, the
number of times that it can profitably be used depending upon the rich-
ness of the lead operated upon, and upon the quantity of silver that the.
scum has already extracted. The scum from the pot A is introduced
into the pot B, and a fresh quantity of zinc is introduced into pot A, the
resulting scum of which is carried to pot B and so on. For lead con-
taining 1 kilo. of silver to the ton about four charges of zinc will be
required, the total quantity of zinc used being less than 1 per cent. In
about twenty-four hours all the silver that can profitably be separated
will have been removed from the lead in pot A. This lead is then run
into the common reservoir C, and is taken to the calcination furnace,
and is there raised to a temperature sufficient to remove the last traces
of zinc, and is then cast into pigs.
A fresh charge of lead is now introduced into the pot A, and is

page_text: silverization of the lead in pot B is completed. The richest scum is
first used, and then the others in order of richness, and finally fresh zinc
is used to complete the desilverization. For lead of the above-mentioned
richness the scums will be used about three times before they are ready
for stage 4.
In the above description of stage 2 only two pots are mentioned, but
it is evident that three or a greater number of pots may be used. (if the
richness of the lead justifics it), and the zinc scums will be carried suc-
cessively from pot to pot in similar manner to that above described, the
richest scum being always used for the pot containing the richest lead,
and fresh zinc being used to complete the operation of desilvering.
The zinc scums obtained as above described are taken to a small
reverberatory furnace with an inclined sole, and are submitted to a heat
only just sufficient to melt the lead which is found mixed with the scum.
Care must be taken that the flame is not an oxidising one. As the lead
melts out and runs down the inclined sole the scum diminishes greatly
in bulk. Fresh scum is added from time to time as room is made for it,
so that the scum resulting from the desilvering of 100 tons or more of
lead can easily be treated at one operation. The lead which has run out
during this operation is comparatively poor. It is taken back to the pots
and recommences at stage 1. During the process of roasting the zinc
scum as above described it is intimately mixed with a certain quantity
of powdered coal, litharge, and burnt lime. The mass resting on the sole
of the furnace acquires a granular state, and is greatly subdivided, and
becomes fit, for the succeeding operation 5.
The separation of the silver from the zinc scum thus prepared is
effected in a reverberatory furnace. A small charge (say from to 1 ton)
of the rich lead produced in stage 7 is melted on the sole of this furnace
to form a bath. The current of air is then stopped, and a quantity of
zinc scum prepared, as described in stage 4, is introduced on to this bath,
and is covered with a stratum of litharge. Air is then admitted to the
furnace, and the fire is increased. The litharge begins to melt into the
richi scums, and a development of gases takes place which peculiarly
facilitates an intimate contact between the various materials on the sole
and the reactions which are to take place. If this operation is properly
conducted no flame rises on the surface, and no oxide of zinc is pro-
duced by contact with the air. If however a patch of the zinc scum

page_text: comes into contact with the air and is enflamed a shovelful of litharge
thrown on to the place is sufficient to extinguish it. This operation of
transferring the silver from the zinc to the lead occupies about six hours.
The litharge will have been reduced into lead, and from 95 to 98 per cent.
of the silver contained in the zinc scum will remain in the lead bath.
The remaining silver with the zinc and some lead floats in the slag at the
surface of the bath. If thought desirable further charges of zinc scum
can be introduced into the furnace to give up their silver to the lead in
a similar manner. The rich lead obtained in the stage just described is
submitted to cupellation and the silver separated from the lead in the
ordinary well-known manner.
The slag resulting from stage 5 containing zinc, lead, and some silver is
placed in a smelting furnace with the skimmings of the first melting
(stage 1), and the resulting lead, which is comparatively rich in silver, is
used as above described for the bath in stage 5.
:
SPECIFICATION in pursuance of the conditions of the Letters Patent,
filed by the said Joseph Alexander Cicognani in the Great Scal
Patent Office on the 20th November 1874.
TO ALL TO WHOM THESE PRESENTS SHALL COME, I, JOSEPH
ALEXANDER CICOGNANI, of 20, Great Winchester Street, in the City of
London, Merchant, send greeting.
WHEREAS Her most Excellent Majesty Queen Victoria, by Her
Letters Patent, bearing date the Twenty-first day of May, in the year
of our Lord One thousand eight hundred and seventy-four, in the
thirty-seventh year of Her reign, did, for Herself, Her heirs and
successors, give and grant unto me, the said Joseph Alexander
Cicognani, Her special license that I, the said Joseph Alexander
Cicognani, my executors, administrators, and assigns, or such others
as I, the said Joseph Alexander Cicognani, my executors, administrators,
and assigns, should at any time agree with, and no others, from time
to time and at all times thereafter during the term therein expressed,
should and lawfully might make, use, exercise, and vend, within the
United Kingdom of Great Britain and Ireland, the Channel Islands, and
Isle of Man, an Invention for "IMPROVEMENTS IN DESILVERING LEAD," a

page_text: of lead are melted in pot A, and the lead is skimmed to remove the
dross. Zinc is introduced at the bottom of the pot in any convenient
manner used in the well-known zinc processes for desilvering lead. A
scum containing zinc, silver, and lead rises to the surface. The scum
which first rises is not so rich in silver as that which subsequently rises.
This zinc scum is introduced into the pots over and over again, the
number of times that it can profitably be used depending upon the
richness of the lead operated upon, and upon the quantity of silver that
the scum has already extracted. The scum from the pot A is introduced
into the pot B and a fresh quantity of zinc is introduced into pot A, the
resulting scum of which is carried to pot B and so on. For lead con-
taining 1 kilogramme of silver to the ton about four charges of zinc will
be required, the total quantity of zinc used being less than 1 per cent.
In about twenty-four hours all the silver that can profitably be separated
will have been removed from the lead in pot A. This lead is then run
into the common reservoir C, and is taken to the calcination furnace,
and is there raised to a temperature sufficient to remove the last traces
of zinc, and is then cast into pigs.
.
A fresh charge of lead is now introduced into the pot A, and is treated
as before with the zinc scums from the pot B until the desilverization of 2
the lead in pot B is completed. The richest scum is first used, and then
the others in order of richness, and finally fresh zinc is used to complete.
the desilverization. For lead of the above-mentioned richness the scums
will be used about three times before they are ready for stage 4.
In the above description of stage 2 only two pots are mentioned, but 2
it is evident that three or a greater number of pots may be used (if the
richness of the lead justifies it), and the zinc scums will be carried suc-
cessively from pot to pot in similar manner to that above described, the
richest scum being always used for the pot containing the richest lead,
and fresh zinc being used to complete the operation of desilvering.
8
The zinc scums obtained as above described are taken to a small
reverberatory furnace with an inclined sole, and are submitted to a heat
only just sufficient to melt the lead which is found mixed with the scum.
Care must be taken that the flame is not an oxidizing one. As the lead
melts out and runs down the inclined sole the scum diminishes greatly 3
in bulk. Fresh scum is added from time to time as room is made for it,
so that the scum resulting from the desilvering of 100 tons or more of

page_text: lead can easily be treated at one operation. The lead which has run out
during this operation is comparatively poor. It is taken back to the
pots and recommences at stage 1. During the process of roasting the
zinc scum as above described it is intimately mixed with a certain
quantity of powdered coal, litharge, and burnt lime. The mass resting
on the sole of the furnace acquires a granular state, and is greatly
subdivided, and becomes fit for the succeeding operation 5.
The separation of the silver from the zinc scum thus prepared is
effected in a reverberatory furnace. A small charge (say from 4 to 1 ton)
of the rich lead produced in stage 7 is melted on the sole of this furnace
to form a bath. The current of air is then stopped, and a quantity of
zinc scum prepared as described in stage 4 is introduced on to this bath,
and is covered with a stratum of litharge. Air is then admitted to the
furnace and the fire is increased. The litharge begins to melt into the
rich scums, and a development of gases takes place which peculiarly
facilitates an intimate contact between the various materials on the sole
and the reactions which are to take place. If this operation is properly
conducted no flame rises on the surface and no oxide of zinc is produced
by contact with the air. If however a patch of the zinc scum comes
into contact with the air and is inflamed a shovelful of litharge thrown
on to the place is sufficient to extinguish it. This operation of trans-
ferring the silver from the zinc to the lead occupies about six hours.
The litharge will have been reduced into lead and from 95 to 98
per cent. of the silver contained in the zinc scum will remain in
the lead bath. The remaining silver, with the zinc and some lead,
floats in the slag at the surface of the bath. If thought desirable
further charges of zinc scum can be introduced into the furnace to give
up their silver to the lead in a similar manner. The rich lead obtained
in the stage just described is submitted to cupellation and the silver
separated from the lead in the ordinary well-known mannor.
The slag resulting from stage 5 containing zinc, lead, and some silver
is placed in a smelting furnace with the skimmings of the first melting
(stage 1), and the resulting lead, which is comparatively rich in silver, is
used as above described for the bath in stage 5.
Having thus described the nature of the said Invention, and the
manner of performing the same, I would remark that I am aware that
the use of zinc for the purpose of desilvering lead is not new, and to it

page_text: I make no claim; I am also aware that the treatment of the argenti-
ferous zino so obtained with litharge is not new, and to it I make no
claim; but what I claim is the means employed for desilvering lead,
substantially as herein described.
In witness whereof, I, the said Joseph Alexander Cicognani,
have hereunto set my hand and seal, this Nineteenth day of
November, in the year of our Lord One thousand eight hundred
and seventy-four.