IMPROVEMENTS IN TREATING CUPREOUS SOLUTIONS FOR THE PURPOSE OF SEPARATING SILVER
Year: 1877

page_text: LETTERS PATENT to Erhard Ludwig Mayer, of Glasgow, in the County of
Lanark, North Britain, Chemist, for the Invention of "IMPROVEMENTS IN
TREATING CUPREOUS SOLUTIONS FOR THE PURPOSE OF SEPARATING SILVER."
Sealed the 15th June 1877, and dated the 21st April 1877.
PROVISIONAL SPECIFICATION left by the said Erhard Ludwig Mayer at tlie
Office of the Commissioners of Patents on the 21st April 1877.
ERHARD LUDWIG MAYER, of Glasgow, in the County of Lanark, North Britain,
Chemist. "IMPROVEMENTS IN TREATING CUPREOUS SOLUTIONS FOR THE PURPOSE
OF SEPARATING SILVER."
This Invention relates to cupreous solutions containing silver, such as are obtained
in treating cupreous pyrites by what is known as the wet process for extracting
copper; and it has for its object to separate the silver in an improved, rapid, and
convenient manner.
The Invention consists in mixing a solution of glue and a solution of an iodide
with the cupreous solution. A precipitate is formed containing silver, glue, and
iodine. The larger portion of the compound of silver, glue, and iodine is rapidly
deposited, and can be separated by decantation or filtration, whilst any of the glue
or compound of silver, glue, and iodine that remains in solution can be precipitated
by means of tannin or any suitable substance containing tannin.
The substances added are proportioned to suit the various strengths and consti-
tuents of the cupreous solutions, as ascertained by chemical tests; and for the glue
any suitable nitrogenous substance, such as blood, albumen, gluten, or the like, which
is found to act in an analogous manner, may be substituted.
It is an advantage of the improved process that the solutions may be treated in
a highly concentrated state.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Erhard Ludwig Mayer in the Great Seal Patent Office on the
20th October 1877.
ERHARD LUDWIG MAYER, of Glasgow, in the County of Lanark, North Britain,
Chemist. "IMPROVEMENTS IN TREATING CUPREOUS SOLUTIONS FOR THE PURPOSE
OF SEPARATING SILVER."
My said Invention relates to the treatment of cupreous solutions containing silver,
and such as are obtained in treating cupreous pyrites by what is known as the
"wet" process for extracting copper; and it has for its object to separate the silver
in an improved, rapid, and convenient manner.
My Invention is based on the discovery by me of the use, as herein described, of
a new compound or compounds, in which silver, certain nitrogenous substances, and
iodine are chemically combined, and are not separable by any process which does
not involve chemical decomposition. The nitrogenous substances which may be
used are of the class of organic substances to which glue and albumen belong.
Practically I find that glue is the most suitable substance.
"
The Invention consists essentially in adding glue or its substitute and an iodide
or a suitable compound of iodine to the cupreous solution or copper liquor" in
such a manner that the glue or its substitute and the iodine may combine with the
silver present in the cupreous solution, and so form the new chemical compound or
compounds which separates from the cupreous solution as a precipitato.
Compared with processes previously employed for the same purpose my improved
process has the advantages, that it is practically applicable to cupreous solutions
which are highly concentrated, that the precipitates can be separated in a very
short time, and that the loss of iodine is comparatively slight. The larger portion
of the compound or compounds of silver, glue, and iodine is rapidly deposited, and
can be separated by decantation or filtration, whilst any of the glue or compound
of silver, glue, and iodine that remains in solution can be precipitated by means of
tannin or any suitable substance containing tannin.
And in order that my said Invention and the manner of performing the same
may be properly understood, I will proceed to particularly describe what I believe
to be the best mode of proceeding in the case of cupreous solutions, such as I have
generally to deal with.
I find that I can operate with great advantage upon cupreous solutions which
are made as concentrated as is conveniently possible when lixiviating the calcined
or furnaced materials as practised in the "wet" process of extracting copper. I
take, for example, a cupreous solution of which the following is an approximate
analysis :-
Sodium sulphate
Sodium chloride
Copper
Lead
Iron
9.66%
17.96
"
6.78
"
.506 "
.045
دو
Cobalt, nickel, manganese,
3.46
zinc, as oxides
Chlorine
"
10.89

page_text: ,
solution of potassium iodide or other convenient iodide containing about 12 ounces
of iodine. The glue and the iodide may be dissolved separately, and the solutions
be mixed, or one may be dissolved in the solution of the other, heat being employed
if necessary to produce the solution of the glue. The mixed or joint solution is
made with about as much water as to occupy a cubic foot. After the compound
Bolution of glue and iodide has been thoroughly mixed with the cupreous solution
the contents of the tank are transferred to a first settling tank, which is by prefer-
ence somewhat larger than the mixing tank. The liquor is left undisturbed in the
first settling tank for about an hour, during which time the larger portion of the
compound of silver, glue, and iodine settles to the bottom, and then the liquor is
drawn off at a point about one foot above the bottom of the tank, and is conveyed
to a second settling tank of still greater capacity than the first settling tank. In
the second settling tank a solution containing one-quarter to one-half pound of
tannin, or an infusion of galls or sumnach, or any infusion or solution containing
tannin, or any astringent principle having an analogous action and of equivalent
strength, is added to the liquor principally for the purpose of expediting the preci-
pitation of the remainder of the compound of silver, glue, and iodine formed in the
liquors. After the liquor has been left undisturbed for from one and a half to two
and a half hours in the second settling tank, it is drawn off at a point one and a half
to two feet above the bottom of the tank, and being then practically free from silver
can be treated in the usual way for the precipitation of the copper. Several fresh
quantities of cupreous solution may be similarly treated in the tanks without
removing the precipitates, which may accumulate for about a week or longer. The
precipitates taken from the mixing and first and second settling tanks are conveyed
to a fourth tank provided with a perforated bottom, which is covered with iron ore
or other suitable filtering material, this perforated bottom being two or two and a
half feet above the actual bottom of the tank. The precipitate is then covered with
dilute acid, which is pumped over it as often as may seem necessary, the pump
drawing from about eight inches below the perforated bottom. This arrangement
allows any precipitate which may go through the filter to settle and remain undis-
turbed at the bottom of the tank, whence it can be removed when convenient. The
acid used is the same as is employed in lixiviating the calcined materials, and its
purpose is to dissolve out any copper salts that are mixed with the precipitate.
When the acid no longer dissolves the copper rapidly from the precipitate, it can be
utilised and be saturated with copper salts by employing it for lixiviating the
calcined materials. Fresh dilute acid is repeatedly run through the precipitate
until all the copper salts are dissolved out. The washed precipitate which now
contains besides the compound of silver, glue, and iodine, chiefly lead salts and lime
salts, is removed, and the iodine recovered from it.
I treat the precipitate in the following manner for the recovery of the iodine:-
I place a quantity of the precipitate in a drum which is about four feet in diameter
and three feet in length, and can be turned about its axis, which is placed horizon-
tally. After neutralising any free acid in the precipitate with slaked lime or
otherwise, I add a solution of sulphides, taking by preference, where conveniently
obtainable, the solution of sulphides obtained by lixiviating oxidised alkali waste.
The sulphide solution having been added, the drum is turned slowly, and after it
has rotated for some time it will be found that all the sulphides have disappeared
from the solution, whilst sulphates, chlorides, and iodides have taken their place.
The liquor can then be removed and may be used, instead of fresh solution of
potassium iodide, for the precipitation of further quantities of silver from fresh
cupreous solutions with the aid of the proper proportion of glue or its substitute.
A fresh quantity of sulphide solution is next put into the drum and worked as
before, and the process is repeated until all the iodine has been recovered, as a
soluble iodide, from the silver precipitate, after which the precipitate, then consisting
principally of sulphides of heavy metals, is removed from the drum and a fresh
quantity of undecomposed precipitate is put into it.
The sulphides containing the silver inay be sold without further treatment or

page_text: they may be smelted or otherwise treated by known means to recover the silver in
the metallic state, in which it will be found to be mixed with lead, and also to
contain a part of the gold that was in the cupreous solutions.
The glue employed in carrying out my improved process may be of the least
expensive kind met with in commerce. The proportion of glue used may be varied
to some extent without affecting the results, and different qualities of glue or isin-
glass, or different kinds of nitrogenous substances substituted for the glue, may
require to be used in different proportions, which proportions will require to be
ascertained in each case by actual trial. The glue or its substitute should in every
case be somewhat more than sufficient to combine with all the silver ascertained to
be present in the cupreous solution to be treated. The proportion of glue or its
substitute does not require to be modified for different strengths of the cupreous
solutions, but only so as to correspond with the silver in such solutions.
Having thus particularly described my said Invention and the manner of
performing the same, I have to state that I do not restrict myself to the precise
details herein-before described, but that what I believe to be novel and original and
claim as the Invention secured to me by the herein-before in part recited Letters
Patent is,-
First. The process of separating silver from cupreous solutions by adding to such
solutions glue or other nitrogenous substance acting in an analogous manner, and an
iodide or other suitable compound of iodine, so as to form a precipitate comprising
a compound or compounds in which silver, glue, or its substitute and iodine aro
chemically combined, the iodine being recovered by treating the precipitates with
soluble sulphides, the whole process being carried on substantially in the manner
described.
Second. The use substantially as herein described of glue or albumen or other
analogous substances and iodine for the purpose of separating silver from cupreous
solutions in which that metal is contained.
In witness whereof, I, the said Erhard Ludwig Mayer, have hereunto set my
hand and seal, this Nineteenth day of October, in the year of our Lord
One thousand eight hundred and seventy-seven.
ERHARD LUDWIG MAYER. (L.S.)