Revivification of the Materials Used in such Treatment.
Year: 1888

page_text: Revivification of the Materials Used in such Treatment.
1 WILLIAM CROOKES, of Kensington Park Gardens in the County of Middlesex,
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 experimenting on various samples of auriferous ores, I have found it possible
to treat some efficiently by commercial perchloride of iron, but other ores require
a somewhat different treatment to prevent a large percentage of the gold being
lost in the tailings.
Now, the main object of the present invention is to secure the largest available
yield of gold, and this I do by subjecting crushed auriferous ores to the action of
a solution of perchloride of iron, with or without common salt, in the presence of
heat, either with the addition of nitrate of soda, nitrate of potash, or equivalent
nitrate, or peroxide of manganese, or free mineral acid.
When the ores contain only a small quantity of sulphurets or other minerals
attackable by perchloride of iron, I prefer to use a fairly strong solution of per-
chloride of iron, of about sp. gr. 1.150 [30 Twad.] (which solution should not be
neutral), and to this I add as much common salt, in crystals, as the solution of
perchloride of iron will dissolve in the cold. To this mixture, contained in a
suitable tank, I add the crushed ore which is to be operated upon. It should be
remarked that common salt need only be used when silver is present in the ore in an
appreciable percentage. To the mixture I add nitrate of soda or its equivalent, or
well-washed precipitated peroxide of manganese, (Weldon mud) in the proportion of
one part of the peroxide of manganeso to three parts of the perchloride of iron
present; or in the case of the nitrates, one part of such oxidising element to five parts
of the perchloride of iron, and I heat the whole to a temperature of 95° to 100° C.,
with continuous stirring by any suitable means.
The result of this mode of treatment will be appreciated from the fact that the
gold is not infrequently locked up in mineral matter that resists the action of the
perchloride of iron. In such a case, the addition of peroxide of manganese, or
nitrate of soda, puts the perchloride of iron into a kind of unstable equilibrium, leaving
the extra atom of chlorine available for the conversion of the gold to a chloride.

page_text: The action of the process is to reduce the perchloride of iron to the state of
protochloride, and it is the reconversion of this protochloride to perchloride which
constitutes the second head of my invention, the nature of which will be hereafter
explained.
In treating some ores in which the gold is comparatively free from sulphurets or
other mineralising ingredients, the peroxide of manganese need not be in such an
easily soluble form as Weldon mud, but native manganese may be used, although the
action is slower. Some ores will require more, and some less, peroxide of manganese,
or other oxidising element, than I have specified. This can easily be ascertained by
one or two experimental tests.
When the ores contain other metals worth extracting beside gold and silver, such as
copper, cobalt, antimony &c., I use an excess of the perchloride of iron solution as
above, together with the common salt and peroxide of manganese, and heat almost to
boiling.
When the ores contain gold and silver associated with mineral matters attackable
by perchloride of iron, and having bases of little or no commercial value, such as iron,
I use the solution of perchloride of iron as neutral as possible, and of sp. gr. about
1.100, with well washed precipitated peroxide of manganese (Weldon mud), and as
much common salt as the solution will take up in the cold, and work at a temperature
not exceeding 50° C.
After the action has proceeded to a sufficient extent, the mixture is allowed to
settle, and the clear liquor is drawn off, or the mixture may be clarified by filtration
in any well known manner. The residue should then be washed.
In precipitating the metals from the clear solution, I use copper for the gold,
silver &c.; iron to precipitate the copper &c.
Auriferous ores are of very various compositions, and it is consequently impossible
to give their approximate composition. I have chiefly worked on ores in which
sulphurets, arseniurets, &c., predominate.
may remark that the process will extract the gold from the gold ores in their
natural state, but when loaded with sulphurets and similar mineralised ores it will be
an advantage to roast them. The ores need not be roasted "sweet," although the
better they are roasted, the easier the precious metals are extracted.
The process may be employed on the gold ore as it comes from the mine (after
fine pulverisation), but in most cases when the gold is "free," and in that state
removable by amalgamation, it is best to subject the ore first to the ordinary treatment
for extracting the gold, and then to treat the concentrated sulphurets or tailings by
my process.
The process is especially useful where the gold is associated with mineral matters
which prevent the mercury from attacking the gold in the ordinary amalgamation
process, owing to its "flouring" or "sickening."
The action of the common salt is to dissolve out the chloride of silver, into which
the silver has been converted by the action of the perchloride of iron.
When using hydrochloric acid to dissolve the peroxide of iron in the ore and
convert the same into perchloride of iron, the acid should be added gradually, with
the aid of heat, until no more iron is dissolved easily, care being taken that no great
excess of acid is used. Different samples of ore will take different percentages
of acid.
I will now explain the mode of revivifying the spent solution of perchloride of
iron, so as to render it available for further use in the treatment of auriferous ores.
I take the spent solution of chloride of iron, and boil it up with an oxidising
agent, such as nitrate of soda or other nitrate, or peroxide of manganese, and a little
free mineral acid (say, sulphuric acid), and common salt (chloride of sodium) being
present, the acid, acting in the presence of the manganese or nitrate, will liberate
chlorine, which, uniting with the protochloride of iron, will convert it into perchloride.
By the addition of lime or chalk, and the application of air under pressure to the
liquor, the manganese will be thrown down in the form of peroxide.

page_text: Having now particularly described and ascertained the nature of my said
Invention, and in what manner the same is to be performed, 1 declare that what I
claim is :-
:-
1. In the treatment of auriferous ores for the extraction of gold therefrom, the
use of peroxide of manganese in combination with perchloride of iron as above set
forth.
2. The use, as an oxidising agent, in the treatment of auriferous ores by perchloride
of iron, of nitrate of soda, nitrate of potash, or an equivalent nitrate, alone or in
combination with peroxide of manganese.
3. The revivification of spent chloride of iron in the manner and for the purpose
above set forth.