proved Process for the Recovery of Gold and Silver from Solutions
Year: 1895

page_text: Date of Application, 30th Apr 1895-Accepted, 6th July, 1895
COMPLETE SPECIFICATION
Improved Process for the Recovery of Gold and Silver from
Solutions
I, EDWARD DWIGHT KENDALL of Sewaren, in the County of Middlesex and
State of New Jersey, United States of America, Gentleman, 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
In this application wherever I use the term zinc, I do not wish to be necessarily
understood as meaning zinc from which all impurities have been removed, but I wish
to be understood as referrin, also to commercial zinc which is really a zinc alloy
containing zinc in combination with a small percentage of various metals such as
antimony, arsenic and lead
I do not confine myself to any particular solvent in making the solutions of
precious metals from the ore, necessarily the precipitating agent must be such as
to be chemically active in the presence of such solvent, it is applicable to all
processes where a metallic precipitating agent is used, but as in the present_state
of the art, the solvent in general use is an aqueous solution of a cyanide, I will
explain my process as applied to that method
The cyanide solution charged with the precious metals bas heretofore been
subjected to various processes for the recovery of the gold and silver, and the
object of my invention is to furnish a rapid, exhaustive and comparatively
inexpensive process for the separation of the precious from the baser metals
contained in the solution, and primarily involves the use of a new and improved
precipitating ie-agent and a new and improved method of treating the resulting
precipitates
Heretofore in the so-called cyanide processes the solution has been made to
percolate through a precipitating agent of comminuted zinc, whereby the gold and
silver as well as the baser metals have been deposited together upon the zinc, but
in these processes the after-recovery of the gold and silver from the precipitate
is tedious and only partially effective
In my improved process I bring the charged solution into contact with a
pulverized amalgam of zinc and mercury, hereafter more fully described, either by
agitation or percolation A convenient form of apparatus for extracting the
precious metals from the solution is to confine the amalgam within a vessel having
flexible surrounding walls rubber such as is used in the manufacture of tubing
may be successfully used, the object of having the surrounding walls flexible
results from the fact that as the solution percolates through the pulverized
amalgam, the extracted precious metals bridge over, so to speak, between the
particles of amalgam and if the process be long enough continued, will ultimately
obstruct the flow of the solution and prevent the deposition of the precious metals
except in that part of the chamber adjacent to the point where the solution enters
the chamber By compressing the sides of the chamber at intervals, the subjacent
mass of filtering amalgam is broken up and the solution flows without inter ruption
Preferably there should be a series of filtering chambers arranged vertically the
flow of the solution being from the storage tank to the bottom of the first
chamber, thence upwardly through that chamber, thence by a connecting tube to the
bottom of the succeeding chamber and so on through the series to the sump tank
As a result of the chemical and electrolytical action which takes place and
which may be somewhat hatened by heating the solution, the gold and silver are
taken up by the mercury of the amalgam, an equivalent part of the zinc in the

page_text: amalgam takes the place of those metals in the solution and of the baser metals
which are separately precipitated The valuable precipitate will then consist of
gold and silver and the excess of zinc amalgam, this excess must always be
present because it is impossible to predetermine exactly how much of the zinc
amalgam the solution requires and therefore, to guard against all contingencies
and to secure the certain amalgamation of all the gold and silver contained in the
solution, it is practically necessary to supply the zinc amalgam in aquantity
greater than the preliminary assay of the ore might indicate, particularly so, as
by the next step in the process the zinc is readily separated from the other con-
stituent parts of the amalgam, this is accomplished by removing the valuable
precipitate to another vessel, covering it with granulated carbon-the ordinary
hard carbon such as is used in electrical batteries answers the purpose very well-
and then nearly filling the vessel with a solution of sulphuric or other suitable
acid and water in the proportion of about one part of acid to ten or twelve of
water, this combination constitutes the elements of an electrical voltaic pair
carbon in the presence of the amalgam is chemically inert but electrically active,
the electrolytic action which follows, causes the zinc to be rapidly oxidized,
dissolved and taken up by the dilute acid after the exhaustion of the zinc the
amalgam will consist of gold, silver and mercury only, and the precious metals are
recovered therefrom by the ordinary well known processes such as distilling off
the mercury
,
The zinc amalgam above referred to should of course be comminuted into
granules, turnings, filings or shavings, but to obtain the best and most economical
results, it should be pulverized
If metallic mercury should be added to zinc powder there would immediately be
formed a pasty, cohesive mass of amalgam, which would destroy the individuality
of the separate particles of the zinc powder and thus materially and unfavorably
affect the process
a
This cohesion of the particles may be prevented and their individuality retained
in the form of an amalgamated powder by agitating the powdered zinc in
solution of salt of mercury, such as a nitrate or sulphate
Another method of
producing the powdered amalgam is to melt the zinc and while fluid mix with it
about one pound of metallic mercury to three of zinc and after thorough mixing
and cooling grinding the amalgam thus formed, but I do not confine myself to any
particular proportion or method of producing the powdered amalgam, the essential
requirement being as applied to all processes that it shall be an amalgam of mercury
with that metal which may be properly used as a precipitant for the particular
solvent used in the original solution as above stated when the solvent is cyanogen
the precipitating agent is an amalgam of zinc and mercury, preferably in the form
of powder or granules
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
1 In the recovery of gold and silver from cyanide solutions, the process of
subjecting said solutions to the action of a pulverized amalgam composed of
mercury and zinc as described
2 In the recovery of gold and silver from solutions, the process of transferring
the gold and silver from said solutions to a mercurial amalgam, by first subjecting
them to the action of a pulverized oi granulated amalgam composed of mercury
and an appropriate metallic reagent and then treating the valuable precipitate to
the action of granulated carbon in a bath of dilute acid, substantially as
described
3 The process of the recovery of gold and silver from solutions which consists
of the following steps (1), the subjecting of the ore containing the precious
metals to the action of a solvent, thus obtaining an aqueous solution of the solvent 5
and the minerals contained in the oie, (2), subjecting the said solution to the

page_text: electro-chemical action of a mercurial amalgam, (3), subjecting the valuable
precipitate secured by the preceding process to the action of dilute acid in the
presence of carbon, (4), the recovery of the valuable metal from the result of the
preceding process substantially as described
Dated this 30th day of April 1895
BOULT & WADE,
Agents for the Applicant