An Improved Method and Apparatus for Extracting Precious Metals from Slimes or other Finely Divided Material Containing the same.
Year: 1896

page_text: Date of Application, 18th Nov., 1895-Accepted, 6th Feb., 1897
COMPLETE SPECIFICATION.
An Improved Method and Apparatus for Extracting Precious Metals
from Slimes or other Finely Divided Material Containing the
same.
We, DAVID WHITE of Stawell, in the Colony of Victoria, Engineer, and
THOMAS MOORE SIMPSON also of Stawall, in the Colony of Victoria, Metallurgist,
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 is one which enables precious metais to be extracted from elimes
(a proportion of which is inevitably produced by wet stamping which is the almost
universal method in use for crushing gold ores) in a cheap and profitable manner.
We thereby solve a problem which has for a number of years engaged the earnest
attention of metallurgists and chemists. Amongst these is Schiedel who says
(October 1894): "The treatment of slimes.or of tailings pulp containing a high
percentage of slimes is still one of the unsolved problems of the cyanide process;
at present most of the slimes are washed away and with them a large amount of
gold is lost." In 1896 Park published the statements :-That one of the main
obstacles to the success of the cyanide process is the difficulty hitherto met with in
the treatment of slimes; that if slimes could be treated, finer crushing would be
adopted and more gold be thereby extracted; that slimes are extremely preju-
dicial to leaching, interfering with percolation and washing, are apt to be
irregular in distribution, conduce to the formation of channels through the ore,
and that so far no satisfactory process of treating them has been offered to the
public.
The principal attempts bithorto made to treat slimes on a large scale have been
by the use of mechanical stirrers, paddles, screws, or similar locally moving agitators,
in some cases supplemented by hand labor and other agencies crudely employed.
The wear and tear and other expenses attendant on the use of such appliances, have
however been a bar to practical success, notwithstanding the fact that the slimes
are often richer in gold than the sands which are successfully treated by ordinary
methods.
Our treatment by circulation takes hours as compared with days required
by percolation processes, and gives high extraction with marked economy of
cyanide.
The excessive disproportion (40 and even 60 to 1) between the theoretically
necessary (according to Elener's equation) and the actual consumption of cyanogen
in gold extracting is well known. The causes are not entirely ascertained but the
present mode of slow percolation in open vats is one cause, and we find that by our
invention the disproportion aforesaid is much reduced. Owing to the rapidity of
our treatment, a smaller and less costly plant than an ordinary percolation plant
will treat a greater quantity of ore in a given time.
In our invention the whole of the necessary agitation is produced by the passage
under special conditions of a gaseous body (hereafter defined) through the respective
vats in which the slimes, along with solvent solutions containing cyanide, are
placed.
Whilst this invention is intended specially for the cyanogen treatment of slimes
and alluvial sludges it is applicable also to the extraction of precious metals from

page_text: old battery sands, quartz tailings direct from the mill, whether orushed wet or dry,
or other finely divided material containing the said metale.
In order to further understand this invention reference should be made to the
accompanying drawings, in which the same letters of reference indicate the same parts,
and in which Figure 1 represents in side elevation (partly sectional) an apparatus
for carrying out the same. Figure 2 shows a plan view (partly sectional) of the
saine apparatus from above. Figure 3 shows a detail in plan view upon twice as
large a scale as the rest. In these drawings A A represent a series of fixed upright
vats or high tubs of enamelled iron, steel or other material not objectionably acted
upon by the chemicals employed, having each a removable gas tight lid B at
its large upper end, acd a discharge cock or door C at its small lowor end. Vats
of pear shaped or conical form, are particularly advantageous and therefore are
represented.
In Figure 2 one vat is shown in section on the liue 4 Figure 1, auother in section
on the line 5 Figure 1, and another in section on the line 6 Figure 1. Any number
of these vats may be used to forin the series according to the quantity of ore to be
treated in a given time, whilst the size of the vats and of the charges of material
placed within them may vary as desired to suit different classes of charge. The
more grauular and porous the ore the greater its bulk may conveniently be, whilst
if exceedingly tenacious and slimy comparatively small charges are employed.
When our invention is used fine crushing is not a drawback but au advantage
as the extraction of gold will often be then higher. It has indeed hitherto
often occurred in crushing ores for cyanide treatment that fine erushing has been
carefully avoided. The result in certain cases has been the production of coarse
free gold which the weak cyanide solution used failed to entirely dissolve; fine
gold also was left locked up in the gangue so that it could not be attacked by the
solvent.
D represents a receiver of compressed air or other gas or gaseous compound well
known to be suitable for the purposes of promoting oxidation and agitation. This
receiver is filled by means (as compressor or pump) not shown. A main E (or
mains) from D leads (or lead) the contents of the latter, bereafter called for shortness
"gas,
"into the base of each vat A as by branch pipes E, terminating in a number
of small jet holes within the bottom of the vat. These jet holes G (Figure 3) are
arranged suitably at short distances apart, for example, as gas burners are arranged,
round a tubular ring H. There is also a series of distinct connecting tubes J by
which each vat is connected with the next vat in the series, each said tube J leading
from the interior of the top of ouc vat to the interior of the base of the other or to
any suitable other or additional points, ending in for example a number of jot holes
shown by K and L arranged on rings M and N respectively within each vat.
O, P, represent partitions in the form of gratings, the first having apertures say of
one foot square each, the second apertures say of one to two inches square, the
sizes in each case being widely variable. Q shows a pressure gauge to each vat
head, and Ra device as a glass gauge to show the amount of sulution and extent
of agitation in each vat. S and T each represent a series of cocks for regulating
admission of "charged gas" from oue vat to another, U a series of cooks for regu
lating admission of "gas" from the supply main E into each vat, and V a series of
cocks for taking samples of the pulp from each vat for assay and for testing the strength
of the cyanide solution. A return main W from the last vat in the series commu-
nicates with a second receiver X into which "charged gas" passes and is drawn
therefrom in quantities as required by pipe Y which forms the intake of the
compressor or pump. Z is a cock for stopping circulation of "charged gas
through the returu main. Separate pipes to and from the respective vats may be
used instead of single mains, and cocks may be located wherever desired.
33
The receivers D and X are fitted with gauges and suitable valves to reduce
superabundant pressure, in the case of receiver X the entry of air being allowed
when the pressure within the receiver is below that of the atmosphere.
Without entering minutely into those details of (or iuto those immaterial

page_text: variations in the construction of our apparatus, which persons familiar with
processes of gold extraction by oyanide solutions will readily understand, the method
of extraction will now be oxplained.
In using our invention any suitable known solution containing cyanide (but not
restricted to that chemical pure and simple as admixtures are well known to be
advantageous in some cases) is first run into the vats A till they are partially filled.
The "gas" is turned on from main E sc as to agitate the solution, and then the
caked or pasty slimes, or sludge, wet tailings, or the dry finely divided auriferous
materials are introduced into the vats by suitable known means, still taking care to
only partially fill the vats. An even initial distribution of slimy ore is totally
unnecessary. Even when sludge is dumped in in large semi dried compact masses,
they soon, through the presence of the gratings and P (which also protect the
jet orifices from injury or choking) and under the influence of the agitation become
disintegrated. (If the ores require preliminary alkaline treatment the same may
be given in vats of the same construction by using alkaline solution instead of
cyanide solution, but in this description we shall continue to deal with the mode of
dissolution of the gold from the ore when it is ready for contact with solution
containing cyanide.) The vat covers are fastened on when the auriferous charge
has been introduced and circulation of "gas" and "charged gas" (through in
succession receiver D, any number of vats A, receiver X, the compressor or pump,
and then through D again and so on) is continued until the desired extraction of
gold from the ore has been accomplished, the pressure being increased or diminished
as required, and being supplied through the jets G, K, aud L, simultaneously or
through only some of them; for instance through G in the first vat of the series
(in the drawing showu nearest to the reservoir D), and through L only or L and K
only in the other vats.
The motion in the vats resembles boiling in appearance, and effectually removes
any films on the gold, and exposes surfaces for the cyanogen to attack. The
gratings increase the friction, diffuse the agitation, prevent the formation of
currents of small area, and cut up the lumps which may exist in the charge. As
the extraction under agitation proceeds the more homogeneous and loose the pulp
becomes.
When the gold extraction is complete the pulp may be discharged through the
doors or cocks C and filtered, additional wash water or weak cyanide solution being
introduced as desired. One main 7 for introducing cyanide solution is shown
having branch pipes 8. There may be several such mains, by one of which
water may be introduced when required. The pulp may however (if desired)
be ejected with the assistance of "charged gas" by closing the appropriate
cocks S and T or Z which prevents the "charged gas" leaving the vat to be
emptied. E is a branch from main E leading to a ring M aud to the interior
of the head of the first vat in the series. It has controlling cocks E' and S'
through which "gas" can be turned into the said vat when desired. We make no
claim to the use of compressed air for filtering purposes, although it is obvious that
there may be a filter at the base of each vat A to enable the charge to be leached
in the same vessels.
Each of the pipes J is connected by a pipe 9 having cock 10 to the return
main W, so as to allow any one or more of the vats to be shut off temporarily from
the circulatory process. This allows emptying, recharging, and other operations,
without interrupting the continuity of the aforesaid circulation through the
retaining vats. This is a matter of considerable practicable importance, especially
when there are a large number of vats in series, and conduces to economy of power,
time and material. As pipes 9 enable any other or additional vats than the last
one in the series to be connected direct to the receiver X, there may be if desired
more than one circuit going on at the same time.
It will be observed that in describing the medium which passes from one vat to
the next by pipos J the term "charged gas" is used. By this is meant a compound
consisting of such gaseous elements as rise through the charge to the top of the

page_text: vats. The constitution of the compound depends upon reactions within the vats
after the entry of the "gas" from the receiver D. The "charged gas" contains
sometimes a considerable amount of hydrocyanic acid gae, which being of value in
the dissolving of gold is intentionally saved by our invention instead of being
permitted to escape into the atmosphere as it does where open vats, either with or
without any kind of stirrers are used. At the same time in the course of the
process there is much less carbonic acid gas brought into contact with the cyanogen
than occurs with open vats, an amount of objectionable decomposition of cyanide
being thus avoided.
The amount of power consumed in working our invention will vary with the
ore, being much less when the charges are easily permeable requiring a minimum
of solution and of agitation. To economise power the pressure at gauges is
kept as low as is consistent with the maintenance of sufficient agitation to reduce
ore and solution to a homogenous pulp and to allow the cyanide to attack
the gold.
. After the extraction of the gold by the solution and before removing the
covers B the "charged gas" may be pumped into the receiver Y and there stored
under pressure until required to be utilized. A quantity of liquor will often
condense and accumulate at the bottom of said receiver whence it should be drawn
from time to time, and when gold is therein it should be recovered. The strength
of solution can be easily varied from time to time. For example it may first be
of 1 per cent. of potassic cyanide, then be increased to 1 per cent. by adding much
stronger solution; and lastly by adding water decreased to one tenth of one per cent.,
the strength of the solution being readily ascertained by drawing off a sample from
cock V and testing the same.
Having now particularly described and ascertained the nature of our said inven-
tion and in what mauner the same is to be performed, we declare that what we
claim is
1. In the extraction of precious metals from slimes and other auriferous and
argentiferous material subjecting said material, when contained in closed vats
together with solvent solution of the kind described, to the action of "gas"
" and
"charged gas" introduced and put in circulation substantially as and for the
purposes set forth.
2. In the extraction of precious metals from slimes and other auriferous and
argentiferous material, charging said material into a series of vats containing solvent
solution of the kind described, closing said vats and causing "gas" and "charged
gas" to be introduced aud made to circulate repeatedly into, through and out of the
various vats in said series successively by the agency of a compressor or pump
outside said vats, and jets within the said vats substantially as and for the purposes
set forth.
3. In the extraction of precious metals from slimes and other auriferous and
argentiferous material, conveying the "charged gas" from the head of closed
vate, containing said material and also solvent solution of the kind described, into
and through a receiver as X substantially as and for the purposes set forth.
4. The general combination and arrangement of parts constituting an apparatus
for the extraction of precious metal from slimes and other auriferous and
argentiferous material substantially as set forth and as illustrated in the drawings.
5. In apparatus for the extraction of precious metals from slimes and other
auriferous and argentiferous material a pear shaped or conical vat having a cover,
discharge door, inlet and outlet pipes, jets, gauges and gratings all in combination
substantially as set forth and illustrated in the drawings.
Dated this 18th day of November 1896.
WHEATLEY & MACKENZIE,
40 Chancery Lane, London, W.C., Agents.