IMPROVEMENTS IN SEPARATING THE PRECIOUS METALS FROM LEAD
Year: 1886

page_text: THOMAS JOHN GREENWAY 378 Ecclesall Rd, Sheffield, Yorkshire, Metallurgical
Chemist, do hereby declare the nature of my invention for IMPROVEMENTS IN
SEPARATING THE PRECIOUS METALS FROM LEAD to be as follows:-
My invention consists of a new method of dealing with the Lead-Zinc-Silver
&ctr Alloy produced when treating Lead containing the precious metals by the
Zinc desilverizing process. This Alloy which is commonly known to those who
carry on the said process as Zinc Skimmings, is the product into which. the precious
metals are concentrated. The composition of these Zinc Skimmings is ordinarily
as follows
Lead
Zinc
P
At the p-
which
Preciou
-
etals & impurities
-
50-80 %
10-20 %.
remainder.
these Zinc Skimmings are treated by various methods all of
separating the Zinc and the production of Lead rich in the
This rich Lead is then submitted to cupellation whereby the base
metals are separated leaving the precious metals in a marketable condition. A
portion of the Zinc contents of the Zinc Skimmings is recovered by some of these
methods, notably those which embrace the distillation of the Alloy; but the presence
of so much Lead renders the recovering of the Zinc by all of these methods very
costly, a large quantity of material having to undergo treatment in order to recover
a comparatively small quantity of Zinc. It is therefore evident that if this Lead
can be cheaply separated from the Zinc Skimmings the cost of recovering the Zinc
would be greatly reduced and the precious metals might be produced as coarse
bullion without undergoing cupellation.
I have found that by melting the Zinc Skimmings thoroughly under such
conditions as to avoid oxidizing it as far as practicable, a new Alloy consisting
chiefly of Zinc and the precious metals separates from the Lead present and floats
above it forming a well defined molten layer. As it solidifies at a temperature
much above the melting point of Lead, it can be readily separated from the latter
by allowing the whole to cool until the new alloy has formed a solid cake, when it
[Price 6d1

page_text: can be lifted away from the still liquid Lead. The composition of the new Alloy is
ordinarily as follows
Zinc
Precious metals
Lead
Copper and other impurities
50-60 %
-
20-30 %
-
2- 4%
-
remainder.
Practically I melt the Zinc Skimmings in an open deep cast iron pan, which
I call a separating pan. It may also be melted under certain fluxes or in a closed
pan containing a reducing atmosphere such as coal gas; but so far I have found
little if any practical advantage in employing any means of preventing the oxidation
of the Alloy beyond limiting its surface by using a deep pan in preference to a
wider shallow one. When the Zinc Skimmings are properly melted the contents
of the pan will be found to have separated into three distinct layers. The top one
consists of infusible powdery matter, which contains chiefly Oxides of Zinc & Lead
mingled mechanically with more or less metallic matter. The middle layer is the
new Alloy of Zine & the Precious metals. The lowest layer is the Lead which has
been separated from the other metals by this operation. A conveniently shaped
iron frame is now fixed below the surface of the molten metal, about or above
which the new alloy is allowed to solidify. After its solidification the frame is
lifted out of the separating pan carrying with it the new alloy together with the
layer of oxidized matter above it, and leaving the Lead still liquid and compara-
tively hot in the pan.
The Lead is allowed to cool still further, whereby a small quantity of Zinc
Skimmings crystallizes out; this is removed and treated with a succeeding charge
of Zinc Skimmings in the separating pan; while the Lead which contains a little
Zinc and also Silver is laded into the desilverizing pans and treated with a
succeeding charge of the original Lead.
The cake of the new Zinc & precious metal alloy is separated from the powdery
matter overlaying it, broken up & mixed with one or two percent of coal slack or
other carbonaceous material and submitted to distillation in any convenient
apparatus, various forms of which are now used for distilling Zino Skimmings.
A large proportion of the Zinc contents of the new alloy is thus recovered leaving
the precious metals associated with 15% to 40% of impurities which may be
either cast into bars and sold as refinable bullion or treated direct by well known
methods of separating and refining the precious metals.
The infusible powdery matter which constituted the top layer in the separating
pan is mixed with two to three per cent of coal slack or other carbonaceous matter
and distilled, producing Zinc and a residue of Lead rich in the precious metals
which is returned to the separating pan and there treated together with a new
charge of Zinc Skimmings.
T
1094

page_text: трогощеню ш борац
544LD
I, THOMAS JOHN GREENWAY of 378 Eccleshall Road, Sheffield in the county of
York, Metallurgical 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 consists, of a new method of dealing with the Lead, Zinc Silver
Alloy, produced, when treating Lead containing the precious metals, by the Zinc
desilverizing process. This alloy, is the product, into which the precious metals
are concentrated by this process, and is technically known, (& will be spoken of
hereafter), as "Zinc Skimmings."
When removed from the desilverizing pans, it usually contains upwards of 85%
of Lead, the remainder being chiefly Zine, associated with more or less of the
precious metals. In order to separate the Lead, and concentrate the precious
metals as far as posible, before proceeding to treat them for the recovery of the
Zinc, and precious metals, the Zinc Skimmings are now usually submitted to
liquation, which however, only partially eliminates the Lead, the liquated Zinc
Skimmings containing, even when the liquation has been carried to an extreme
limit, about 50%. Lead, and generally under 10% of the precious metals.
My said invention consists of a cheap, and simple method, of separating nearly
the whole of the Lead, from the liquated Zinc Skimmings, and thereby considerably
concentrating its Zinc and precious metal contents, by producing therefrom a new

page_text: On cooling the whole to a certain point this layer of alloy will solidify and may
be lifted off the surface of the still fluid & homogeneous mixture of Lead and
the alloy.
On cooling the latter still further a small quantity of Zinc Skimmings will
separate from the Lead as described above.
It follows from the described properties of the new alloy that the bulk of the
Zine and precious metals contained in Zinc Skimmings may be separated in this
form by simply melting the latter provided it can be obtained poor enough in Lead
to allow the new alloy to separate out in sufficient quantity. As this takes place
when the Zinc Skimmings contain as much as 75% of Lead the above mentioned
condition is always practically attainable for the Lead contents of the Zinc
Skimmings may be easily reduced to from 60 to 70%. by simple liquation.
Practically then, I obtain the new alloy by melting the Zinc Skimmings in a
deep cast iron pan which I call a separating pan.
The Skimmings may be melted under certain fluxes or in a closed pan containing
a reducing atmosphere such as coal gas or Carbonic Oxide in order to prevent
oxidation of the Skimmings at the high temperature employed, but so far I have
found little if any practical advantage in employing any means of preventing
oxidation, beyond limiting the surface of the metal exposed.
The cake of the new Zinc and precious metal alloy is separated from the powdery
matter overlaying it, broken up, mixed with one or two per cent of coal slack, or
other carbonaceous matter, and may be submitted to distillation in any of the
forms of apparatus, which are now used for the treatment of Zinc Skimmings.
A very large proportion of the Zinc contents of the alloy, is thus separated and
recovered, leaving the precious metals associated with 15% to 50% of impurities,
which may be refined and separated, by well known methods.
The infusible powdery matter, which constituted the top layer in the separating
pan, may be either distilled in the same manner as the alloy, or smelted with
the Lead dross and other products, for the production of Silver Lead for the
desilverizing pans.
Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, I declare that what
I claim is
An improved method of carrying on the "Zine desilverizing" process for the
treatment of Lead containing the precious metals, by melting the alloy known as
"Zinc Skimmings," obtained in that process in such a way as to avoid oxidizing it
to any great extent and to eliminate a great part of the Lead it contains and to
obtain from it a new alloy composed of Zinc, Precious Metals, and Lead, the Lead
forming a very small percentage (say 2° to 10°) of the same, thus concentrating
the precious metals and zinc to a much greater extent than heretofore, thereby
avoiding a great portion of the expenses attending the operation by which these
metals are subsequently separated and recovered, as herein explained & described.
18th Otahan 1000