Improvements in Treating Slimes from Ores of the Precious Metals.
Year: 1895

page_text: Date of Application, 13th July, 1895
Complete Specification Left, 13th Apr., 1896-Accepted, 16th May, 1896
PROVISIONAL SPECIFICATION.
Improvements in Treating Slimes from Ores of the Precious
Metals.
I, MIDDLETON CRAWFORD, of Colorado Springs, in the State of Colorado,
U.S.A., Mining Engineer, now residing at the Inns of Court Hotel, High
Holborn, London, (a communication to me from Rudolf Keck, of Colorado
Springs, in the State of Colorado, U.S.A.), do hereby declare the nature of this
invention to be as follows:-
This invention has for its object improvements in treating slimes from ores of
the precious metals. At the present time there is great difficulty in treating
such slimes; the difficulty does not lie in bringing the precious metal into solution
for this can readily be done by treatment with a weak potassium cyanide solvent
or other such like solvent but there is extreme difficulty in afterwards separating the
solvent from the slime. According to this invention the difficulty is overcome by
the addition of chloride of sodium; this without injury to the solvent causes the
solid matter in suspension to readily deposit or precipitate in such a state that it
can be readily removed by filtration, and then by known means the precious metal
can be precipitated from the clear liquor.
Dated this 19th day of July 1805
Improvements in Treating Slimes from Ores of the Precious
Metals.
I, MIDDLETON CRAWFORD, of Colorado Springs, in the State of Colorado,
U.S.A. Mining Engineer, now residing at the Inns of Court Hotel, High
Holborn London (a communication to me from Rudolf Keck, of Colorado Springs,
in the State of Colorado, U.S.A.) 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 :-
My invention relates more specifically to a novel means of overcoming a
difficulty which has always been recognized in all solution processes for the
treatment of gold. This difficulty is the presence in the solution, after it has been
mixed with the ore, of what are commonly known as "slimes." Technically, this
word is applied to all particles of earthy matter of such fineness that they sink in
water with which they are mixed with a speed less than one hundred millimeters
per second. It therefore includes all clayey mud which accompanies, in greater
or less proportions, the gangue as it comes from the stamp mill, or the tailings
which result from an amalgamation or separation process.
In any of the known solution processes, as soon as the material which contains
the gold has been mingled and agitated with the solvent liquid, the liquid becomes
clouded by the presence of these slimes. As soon as the solution has taken up
all of the gold which it is capable of dissolving, the next step in any solution
ונ6...

page_text: process is to run the solvent liquid off, along with the dissolved metal, and
precipitate the gold from it.
The presence of the slimes in the liquid is very injurious to all of the known
precipitation processes, and it is therefore necessary to allow the solvent liquid
to stand long enough for the slimes to sink and the liquid to become clarified
before the precipitation can be proceeded with. Under ordinary circumstances
this requires large settling tanks and occasions great waste of time.
By my process I am able to effect the precipitation of the entire body of slimes
in a very few minutes, thereby accelerating the entire solution process to this
extent.
To carry out my invention, I add from one quarter to six per cent. of common
sait to the solvent liquid; that is to say, the liquid which contains in solution all
of the chemicals which are necessary and desirable for the purpose of effecting the
subsequent solution of the gold.
I have experimented with this process more particularly in connection with
what is commonly known as the cyanide process, that is to say, the process where
the solvent liquid consists of a solution of cyanide of potassium, with or without
other chemical agents, but my process is applicable to other solution processes,
and I therefore claim it without reference to the particular character of the
solution used.
In carrying out my process in the preferred manner, I add this salt either to
the water in which the ore has been crushed, and to which the solvent liquid is
about to be added, or else to the solution itself, and this either before or after the
addition of the ore. As a result of this addition, as soon as the agitation ceases
and the mass is turned into the settling tank, the slimes settle rapidly, the entire
body of slimes going to the bottom in a very few minutes, leaving the solution as
free from impurities as spring water, so that the precipitation or other subsequent
process may be proceeded with almost immediately.
The salt which is used need not be chemically pure chloride of sodium, rock
salt, for instance, which contains a considerable quantity of chloride of magnesia,
may be used, or any other cheap form of common salt.
Although I do not consider that an increase of the quantity of salt above
three per cent. (3%) is desirable, I do not wish to be understood as limiting myself
to such small percentage, as there is no reason to believe that a larger quantity
would do any harm, although it might not do any good.
After precipitation the slimes are filtered out, and a further advantage which results
from my process is that it imparts to them a granular character which renders
filtration easy. After being thus subjected, they may themselves be treated in
any known manner for the reclamation of such gold as they may contain.
In solution processes, and particularly in cyanide processes, where the chemicals
which are added to the water for the purpose of rendering gold soluble therein,
are more or less expensive, it is highly desirable that the process shall be
continuous; that is to say, that the liquid subsequent to the precipitation step
shall be restored to something of the same character that it had prior to the
dissolution of the gold. In certain cyanide processes this is the case.
Under
such circumstances it is obviously of vital importance that the substance which is
to be added to the solvent liquid for the purpose of precipitating the slimes shall
not be one which, by virtue of chemical combination with the substances already
present in the solution, shall endanger its gold dissolving properties.
It is one of the advantages of the substance which I use, to wit common salt,
that when added to a cyanide solution it does not in any way interfere with the
gold dissolving properties of the liquid, but, on the contrary, rather appears to
render the solution more permanent and to increase its capacity for being used
over and over again in a continuous process.
It must be understood that as far as the solution process is concerned, the salt
which I add has no chemical relation thereto, but carries itself entirely neutral

page_text: and performs its function, as far as I have been able to ascertain in entirely a
mechanical way.
Having now particularly described and ascertained the nature of the said
invention and in what manner the same is to be performed I declare that what
1 claim is :-
The improvement in solution processes for the extraction of gold from its ores,
which consists in combining with the ore and a solvent liquid a small percentage of
salt, substantially as specified.
Dated this 11
11000
M. CRAWFORD.