Improvements relating to the Extraction of Precious Metals from Ores, Slicks, or Metalliferous Residues, and the like.
Year: 1898

page_text: Date of Application, 8th Sept., 1898-Accepted, 8th Sept., 1899
Improvements relating to the Extraction of Precious Metals from
Ores, Slicks, or Metalliferous Residues, and the like.
We, SIGISMUND KUROVSKY, of Zalathna, and GUSTAV GSCHWANDTNER, of
Selmeczbánya, Engineers, and Dr. HENRY SCHUSTER, of Arad, Physician, all in
the Empire of Austria-Hungary, 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:―
This invention relates to an improved method of treating precious metals, but
more especialy pyritous or cupriferous, non-pyritous or non-cupriferous ores,
slicks or metalliferous residues, which contain gold; the special object of the
invention is, to avoid the considerable losses of gold, which in all methods here-
tofore employed have been inevitable and which in most cases are due to the fact,
that in auriferous ores and mixtures, treated according to previous methods, the
gold contained therein, has not been opened up to a sufficient extent and that
consequently a considerable percentage of the gold is rendered inaccessible for the
cyanic solutions employed. Whereas heretofore it has been endeavoured to reduce
the losses of gold by perfecting the dissolving process, the main feature of this
invention lies in the treatment preceding the dissolving process, in view of the
recognized fact, that the yield in gold in the first place depends on the
circumstances: to what degree of completeness the elimination of the metals
occurring jointly with the gold has been effected, or how far the preliminary
treatment of the ores has been carried with the object of transforming them into
a state, in which the said metals were capable of being eliminated without
impeding the operation of eliminating the gold by means of cyanic solutions.
By none of the processes heretofore employed or suggested is it possible to
obtain a complete opening up of the gold, because, for the purpose of fixing the
sulphates, principally produced by the decomposition of the quartz, several
reagents have to be employed, in order to further the action of the cyanic
solutions; moreover, materials containing more than one per cent. of copper could
not heretofore be treated, especially by reason of the fact, that the operation of
washing out the gold by cyanic solutions was impeded by the sulphur, copper,
arsenic and lead, contained in the material treated: it is therefore necessary in
the first place, to render these said substances, contained therein, innocuous.
We attain this object by jointly roasting the raw product, treated, with sodium
chloride (common salt), this being effected in such a manner that the sulphur,
contained in the raw product is burnt and that the metallic constituents are
converted into chlorides or chlorurets respectively.
The roasting is effected, according to the percentage of sulphur contained in
the raw produce, either in self-heating or in flame furnaces. In self-heating
furnaces the roasting is effected without the use of an organic fuel; the amount
of heat generated by the combustion of the sulphur, contained in the roasted
raw product, being in this furnace utilized for the purpose of heating.
In the case of flame furnaces an organic fuel is used, wood, yielding a long flame

page_text: being preferably employed; furnaces of this kind are used in the case of treating
products poor in sulphur.
The roasting according to this invention, effected in self heating furnaces, is
preferably carried out in the following manner :.
The thoroughly disintegrated and dried raw-product is mixed with half the
amount of common salt required for the chlorination, then placed into the
uppermost working chamber of the furnace, where it is spread out evenly. The
sulphur contained in the raw product, will be ignited as it arrives in contact with
the previously heated walls of the furnace and, by its being burnt will change
into dioxide of sulphur which has the effect of decomposing the sodium chloride,
whilst the chlorine, thus set free, changes the metals into chlorides. The period
of this chlorination-roasting is of course dependent upon the amount of sulphur
contained in the raw product, so that in this respect it is even impossible to fix
the time within wide limits. Thus for instance, in roasting a raw product,
containing 45 per cent. of sulphur in a furnace provided with seven working
chambers, the inventors have found, that for the purpose of completely eliminat-
ing the sulphur and of completely chlorinating the raw product, about 42 hours
were required.
In describing the roasting process, we will use the following example:
After six hours roasting of the raw product brought into the furnace, the
product was shifted from the first working chamber into the second, in which the
said raw product again spread out in uniform layers, was roasted for six hours,
while fresh raw material was supplied to the first working chamber. After the
completion of a further six hour's roasting, the raw material located in the second
working chamber is moved into the third and that, located in the first working
chamber, is moved into the second chamber, while into the emptied first working
chamber fresh raw material is placed and so forth. On displacing the raw
product from the third to the fourth working space, the second half of the common
salt required for the chlorination is supplied to the raw product. During the
period in which the raw product, mixed with the common salt, is moved through
the seven working chambers of the furnace and roasted, a portion of all those
constituent parts which prevent or at least impede the elimination of the gold,
but more especially the sulphur is burnt and, after having produced its decompos-
ing effect upon the common salt, it is completely removed, whilst the silver, the
lead, the arsenic and copper and possibly also other metals, even a portion of the
gold are changed into such combination (chloride, chloruret) which are readily
soluble in hot water or preferably in a common salt lye, so as to admit of thus
being removed from the roasted material, whilst the main bulk of the residual
gold is perfectly opened up for the solution of cyanide of potassium and for other
cyanic solutions, that is to say, can be completely extracted by the action of
such solutions.
The period of roasting in flame furnaces is likewise dependent upon the amount
of sulphur contained in the raw material. Thus, for instance, a raw product
containing either no sulphur at all, or from one to two per cent. of sulphur, can,
when mixed with a quantity of common salt (sodium chloride) from eight to
fourteen per cent. of its weight; be completely chlorinated in eight hours.
When using a flame furnace provided, for instance, with two adjacent working
chambers and adapted for heating with wood, we can treat about 10 to 12 hundred-
weight of such raw material in each chamber. The raw material must also in
this case be thoroughly disintegrated and dried and, while well mixed with one
half of the previously fixed amount of common salt, be spread out in the working
chambers.
When, after the commencement of the heating, the raw product passes to dull
red heat, it is constantly stirred with iron rakes and the heating continued until
an intense red heat is reached. When using the amount of raw material above
mentioned, the heating is slightly reduced after three and a half hour's duration,
the raw material located in the constituent working chambers is heaped up and

page_text: the material located in the first working chamber (beside the fire bridge) is
brought into the second working chamber, while the material contained in this
latter space is raked or shovelled over into the first working chamber; after the
material having been evenly spread out in both working chambers, the other half
of the amount of common salt is added and the mixture then again constantly
stirred, while the heating is again increased. After further three hours the
roasting is completed.
The chemical process in this case is the same as in the case of roasting in a
self heating furnace.
The raw product roasted in self heating furnaces as well as in flame furnaces is
passed into wooden lixiviating tanks or boxes provided with a quartz filter and
formed either conical or cylindrical toward the bottom.
This lixiviating tank, which is shown in vertical section on the accompanying.
drawing, consists of the skeleton frame a, the box b fitted in this frame, supports c
for the bottom, perforated bottom d, quartz filter bed e, grating f and wedge
pieces K for retaining the grating. indicates the roasted material, the lye
and are the outlet openings for the lye. In these tanks or boxes the raw
product is, according to the nature of the chlorides or chlorurets-treated either
directly with cyanide of potassium or with other cyanic solution, or is previously
treated with hot water or, if found suitable, with a solution of common salt of
from 12 to 14° B.
The object of this preliminary lixiviation is, to free the metallic gold, con-
tained in the roasted material, from the metal compounds, especially from the
chlorurets and chlorides, in order to render the same metallic gold more accessible
to the action of the cyanic solutions.
The period of the preliminary lixiviation preferably extends to 24 hours, it
may, however, be considerably shortened, if stirring apparatus are used in the
lixiviation-vats, seing that the chlorurets and chlorides are thereby brought
into intimate contact with the solvent and consequently become far more rapidly
dissolved.
The lye saturated with the chlorides and chlorurets flows through a series
of vessels (preferably 6 to 8 in number) arranged stepwise, that is to say cach
succeeding vessel is at a lower level than that of the preceding one. These
vessels are filled with fragments of old iron, and the outflow openings are placed
at one third of the height of the vessel from the bottom. The lye passing through
such vessels is freed from its metal. by the fragments of oid iron in this manner
the gold, silver, lead and copper contained in the chlorides and chlorurets is
cemented. From the cement-after its having been removed from the iron-the
gold is climinated in the known manner, and if desired, by simple treatment with
lead. If the salts of the metals, opened up by the chlorination-roasting, are of
such a nature as not to reduce the elimination of gold by the cyanic solution,
then the preliminary lixiviation previously referred to becomes superfluous,
because in this case the roasted material may be immediately subjected to the
treatment with a cyanic solution.
pre-
In cases, however, where the processes heretofore usually employed have not
led to a good result for the reason that many metallic salts acting in the known
manner have prevented the action of the cyanic solution, the operation of
liminary lixiviation in connection with chlorination roasting will be found of
excellent service, because the mineralized gold and even the fixed gold which, in
the case of the former processes, was entirely inextractable and was consequently
considered as a pure loss, is, according to the present invention brought into a
state of perpetual solubility and can be obtained without any difficulty.
Upon the material, remaining after the preliminary lixiviation and containing
but gold, cyanide of potassium or another cyanide solution is directly introduced
in the known manner from below or from above, without the said material being
previously washed or subjected to any other preliminary treatment. Sinco
according to our detailed description; the gold, by the preliminary lixiviation,

page_text: is completely opened up and as each constituent part that might noxiously affect
the cyanic solution itself, in the least degree, is removed, we have now to deal
with pure metallic gold, so that, for the purpose of completely extracting the
same, a comparatively highly dilute cyanic solution may be employed. The
experiments made by the inventors in this direction, have shown that, if the raw
material does not contain more than thirty grammes of gold per ton then 0.5-1
and at most two kilogrammes of cyanic salt are required for extracting the said
gold from one ton of raw material,
It is advantageous that the raw material should be treated with two kinds of
cyanic solution, namely first with a solution containing 0.5 per cent. of cyanic
salt and subsequently with one containing 0.05 per cent. thereof; the period of
extraction which is dependent upon the quantity of gold contained in the raw
material, varies between 24 and 96 hours, of which 18 to 72 hours fall to the
treatment with the stronger cyanic solution and the remainder, to the treatment
with the weaker cyanic solution. As the extraction of the gold contained in
the raw material is almost completed already by the treatment with the first, the
stronger solution, the treatment with the second, weaker solution removes even
that portion of gold, that may perhaps have passed into a bicyanide-salt, and
the said second solution will have the effect of reviving the cyanic salt, that
may possibly have remained with the gold particles, in other words of increasing
its dissolving action. For the purpose of obtaining a more rapid extraction,
suitable stirring apparatus may be employed, in order to place the raw material
into a more intimate contact with the solvent.
After the removal of the two cyanic solutions from the material treated, either
by pouring them off or by withdrawing them by means of appropriate suction
apparatus, the remaining material is treated with pure water until it is ascer-
tained by analysis that the cyanic salts or in other words the goid fixed by
the said salts has been completely washed out. The remaining material then
is entirely worthless, seeing that it is void of any metallic contents.
The elimination of the gold from the two cyanic solutions as well as from
the wash may be effected in the known manner either by chemical or by electrical
Jeans.
It appears, however, advantageous to effect this elimination by the aid of
the boxes or tanks, recommended for carrying out the preliminary lixiviation
and arranged step-wise or at successively lower levels, the said boxes or tanks
being for this purpose filled with minute zinc chips or fragments upon which the
gold-containing solutions are separately poured through plates of zinc or lead
perforated like a sieve and arranged above the receptacles; the liquid is discharged
from the receptacles by means of pipes terminating at one third of the height
of these receptacles from the bottom, so that only one third of the zine chips
measured from below is in permanent contact with the liquid. According to
former methods of eliminating the gold by the aid of zine, the cyanic solution has
been in permanent contact with the whole amount of zinc, and consequently
a large quantity of cyanic salt was required for fixing the zinc, and moreover the
precipitation surface was so reduced by the metals cemented by the zine that the
zine had almost entirely lost its working effect especially upon the solutions con-
taining but a small quantity of gold cyanide. Therefore the simpler arrangement
above referred to, in which only one third (the lower) of the zinc is in permanent
contact with the cyanic solution, whilst two thirds are freed by the continuously
flowing liquid from the gold already cemented and deposited and consequently
offer to the liquid, constantly flowing in, a continually new precipitating surface,
must at all events act more advantageously than the precipitating apparatus
heretofore used or suggested.
The water employed for washing out the material treated with cyanic solutions,
s, after having passed the precipitation apparatus, either used for eliminating
the cyanic salts or is allowed to simply flow off. The cyanic solutions freed from

page_text: their contents of gold may be again utilized after the cyanic contents have been
substituted.
The gold cemented by the zinc is freed from the zinc in the known manner,
preferably by the aid of dilute acids, the residual metal is mixed with potash and
saltpetre in a graphite crucible and is put on the market in form of raw gold or
is sold prior to its being melted.
The metal obtained by electrolytical means is melted with the anode and may be
utilized as an alloy rich in gold.
The method just described may of course be carried out and modified in many
ways according to the nature of the raw material to be treated and to the
apparatus at disposal. The essential feature of the invention consists on effecting
the roasting of the raw material by the aid of common salt for the purpose of
burning and removing the sulphur and of converting the metals, occurring in
connection with the gold, into chlorides and chlorurets.
For the purpose of on the one hand rendering the products of combustion of
the sulphur of use and on the other hand eliminating and removing the chlorides
and chlorurets and of, moreover, eliminating the residual gold any process, either
known already or to be specially adopted for this purpose may be employed,
without the essential feature of the invention being thereby in any way impaired.
The mixing proportion and the degree of concentration of the reagents are,
of course, dependent upon the nature of the raw products to be treated."
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is :-
1. A process of treating precious metals, more especially ores, slicks, slags
and residues containing gold, presenting this characteristic feature, that the
products to be treated are mixed with common salt and are roasted either in
self-heating furnaces by way of the known use of the sulphur contained for
generating the required heat or in ordinary flame furnaces.
2. In the process described in the first claim, the operation of previously
lixiviating the roasted product by the aid of a solution of common salt or of hot
water, for the purpose of removing the metallic chlorides or chlorurets produced
as a consequence of the roasting.
3. In the process described in the first claim, the method of repeatedly passing
the liquid eliminated from the roasted material and containing the chlorides or
chlorurets, over iron chips or fragments, preferably in such a manner that the
said liquid leaves the cementing layers, formed of pieces of iron, at the lower
third of the said layers.
4. In the process described in the first claim, the method of washing out the
1oasted product, prior to the operation of the preliminary lixiviation, referred to
in the second claim, first by means of a stronger, then by means of a weaker
solution of cyanic salt and finally by means of water.
5. In the process, described in the first claim, the operation of repeatedly
passing the cyanic salt solutions-employed for washing out the roasted product
either before or after the preliminary lixiviation-and, if found suitable, also
the wash-water through zinc chips or fragments for the purpose of removing
the metal, this being preferably effected in such a manner, that the liquid
will leave the layers formed of these chips or fragments of zinc at the lower third
of their depth.
HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicants.