An Improved Process of Extracting Gold from Refractory Auriferous Ores.
Year: 1895

page_text: Date of Application, 28th Nov.,
1895
Complete Specification Left, 23th Aug., 1896-Accepted, 17th Oct., 1896
PROVISIONAL SPECIFICATION.
An Improved Process of Extracting Gold from Refractory Auriferous
Ores.
I, HIRAM STEVENS MAXIM, of 18 Queen's Gate Place, in the County of Middlesex,
Mechanical Engineer, do hereby declare the nature of this invention to be as
follows:-
This invention relates to an improved process of extracting gold from refractory
auriferous ores.
1
In certain parts of America and Australia there exist very large deposits of
auriferous earths containing high percentages of gold, but owing to the refractory
nature of these earths it has hitherto been found impracticable to work them, the
chemicals they contain neutralizing to a large extent all the solvents generally used:
in the extraction of gold from its ores. The earths in which these chemicals do not
exist, such as those found in South Africa, are easily reduced, but such earths do not :
contain so high a percentage of gold.
According to my invention I take advantage of the well known affinity existing :
between lead and gold when both are at a high temperature. I am aware that
others have attempted to extract gold from auriferous earths by the use of metallic
lead but by reason of the oxidation of the lead that takes place in the process such
attempts have heretofore been found impracticable when made on an extensive scale.
I am also aware that metallic mercury has been used, but the employment of this
metal is attended with obvious disadvantages. For instance metallic mercury is much
more expensive than metallic lead, having to be transported in expensive bottles;
moreover the affinity of mercury for gold at low temperatures is very much less than
the affinity of lead for gold at high temperatures.
In order to create the proper affinity between lead and gold it is necessary that the
lead should be very hot, and, as is well known, lead at a high temperature is very
rapidly oxidized and the oxide bas little or no effect on the gold contained in the
earths. If however molten lead be preserved with a bright metallic surface and this
surface while at a high temperature be brought in contact with the gold, it is well
known that the lead will be very active in taking up and holding the gold. In practice
however it has heretofore been found that the surface of the molten lead rapidly
oxidizes and that therefore it is very difficult to bring the metallic lead into intimate
contact with the metallic gold.
Now 1 have found that if lead be heated to a high temperature (say to about the
melting point of copper) in the presence of carburetted hydrogen, or by a reducing
flame in which carbon or hydrogen is in excess of the oxygen, the surface of the
molten lead remains perfectly bright. In fact when the lead is at a bright red beat
the brightness of its surface surpasses that of the brightest mirror. I also find that
the presence of the carburetted hydrogen also prevents other chemical changes which
would be detrimental in the reduction of auriferous earths.
In carrying out my process I prefer to employ a strong rotary cylinder of cast iron
or mild steel whose capacity should be such as to hold about five tons of auriferous
earths when approximately a quarter full, the said earths being placed in the cylinder
in a pulverized, granular or broken condition. If the earths be in a sufficiently fine
condition, pieces of iron, preferably in the form of balls may also be placed in the
cylinder and the whole be revolved and heated at the same time, the object of the balls
•
:
+
'

page_text: being to grind the earths into a still finer condition. The rotary cylinder is heated
until the lead melts and at the same time a current of carburetted hydrogen such as
coal gas, or still better petroleum vapour is allowed to pass through the rotary cylinder,
the said gas or vapour expelling the atmospheric oxygen and also taking up any
oxygen that may be set free in the process. During the revolution of the cylinder,
the lead, under the action of the beat and the pounding of the balls, is finely divided
and distributed throughout the mass within the cylinder and is therefore constantly
brought into intimate contact with the gold contained in the earths. The process may
be continued until all or nearly all of the gold has been taken up by the lead. The
rotation of the cylinder is then arrested, the heat diminished, and the contents of the
cylinder discharged into water or otherwise cooled. The lead is then separated from
the lighter earths by washing, winnowing or other suitable means and is then subjected
to a high temperature in a suitable furnace and in the presence of atmospheric oxygen
until it becomes wholly oxidized, when a "button" containing gold and sulphur will
be found in the cupel of the furnace.
By my process the molten lead is always preserved in a bright metallic condition
the presence of the carburetted hydrogen completely preventing the oxidation of the
surface of the lead and keeping it untarnished at a high temperature.
In some cases finely divided animal and vegetable charcoal or other carbonaceous
materials may be mixed with the earths before or during their treatment with the
molten lead.
The aforesaid cylinder may be placed at an inclination with one end partially open,
and then revolved, a hot reducing flame of gas being directed into the open end of
the cylinder. The contents of the cylinder will thus be heated to a higher temperature
than the cylinder itself and in the presence of a reducing flame.
Dated this 28th day of November 1895.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.
An Improved Process of Extracting Gold from Refractory Auriferous
Ores.
I, HIRAM STEVENS MAXIM, of 18 Queen's Gate Place, in the County of Middlesex,
Mechanical Engineer, 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 process of extracting gold from refractory
auriferous ores.
In certain parts of America and Australia there exist very large deposits of
auriferous earths containing high percentages of gold, but owing to the refractory
nature of these earths it has hitherto been found impracticable to work them, the
chemicals they contain neutralizing to a large extent all the solvents generally used
in the extraction of the gold. The earths in which these chemicals do not exist, such
as those found in South Africa, are easily reduced, but such earths do not contain so
high a percentage of gold.
According to my invention I take advantage of the well known affinity existing
between lead and gold when both are at a high temperature.
I am aware that
others have attempted to extract gold from auriferous earths by the use of metallic
lead but by reason of the oxidation of the lead that takes place in the process such
attempts have heretofore been found impracticable when made on an extensive scale.
I am also aware that metallic mercury has been used, but the employment of this
metal is attended with obvious disadvantages. For instance metallic mercury is much

page_text: more expensive than metallic lead, having to be transported in expensive bottles,.j
and moreover the affinity of mercury for gold at low temperatures is very much less
than the affinity of lead for gold at high temperatures.
In order to create the proper affinity between lead and gold it is necessary that the
lead should be very hot, and, as is well known, lead at a high temperature is very
rapidly oxidized and the oxide has little or no effect on the gold contained in the
earths. If however molten lead be preserved with a bright metallic surface and this.
surface while at a high temperature be brought in contact with the gold, it is well
known that the lead will be very active in taking up and holding the gold. In practice
however it has heretofore been found that the surface of the molten lead rapidly
oxidizes and that therefore it is very difficult to bring the metallic lead into intimate
contact with the metallic gold.
Now I have found that if lead be heated to a high temperature (say to about the
melting point of copper) in the presence of carburetted hydrogen, or by a reducing
flame in which carbon or hydrogen is in excess of the oxygen, the surface of the
molten lead remains perfectly bright. In fact when the lead is at a bright red heat
the brightness of its surface surpasses that of a mirror. I also find that the presence
of the carburetted hydrogen also prevents chemical changes that would be detrimental
in the reduction of auriferous carths.
In order that my said invention may be clearly understood and readily carried into
effect I will proceed to describe the same more fully with reference to the accompanying
drawing which illustrates a longitudinal vertical section of the apparatus for use in
my process.
A is a strong rotary cylinder or retort of cast iron or mild steel whose capacity
should be such as to hold a charge of about five tons of the auriferous earths to
be acted upon. This rotary cylinder or retort is located in an inclined position within
a furnace B and is provided with a cylindrical extension A¹ which extends through the
back wall of the furnace and is carried in bearings supported in strong pedestals A² A³.
The end of the said extension is furnished with a toothed wheel A which gears with
a pinion A mounted on a driving shaft A. This shaft is revolved through belt or
other gearing from any appropriate motor. In order to counterbalance the weight of
the aforesaid retort A and its charge. the cylindrical extension A' may be formed with
a considerable mass of metal near its outer end as shewn in the drawing; or other
suitable means may be employed for the purpose. C is a cover with which the mouth
of the retort is provided, the said cover being advantageously hinged to the retort
and held in its closed position by one or more swivel bolts c. The earths to be acted
upon are placed in the retort in a pulverized, granular or broken condition together
with the lead. I prefer to place within the retort, together with the earths and lead,
a number of loose pieces of iron D D which may be in the form of balls, the inner
surface of the said retort being provided with longitudinal ribs, webs or flanges a a
so that when the retort is revolved the said balls will be raised by the ribs and allowed
to fall again onto the mass at the bottom of the retort, thereby grinding the earths to
a still finer condition and at the same time causing the molten lead to come into very
intimate contact with the gold contained in the earths. During the process a current
of carburetted bydrogen such as coal gas, or still better petroleum vapour is allowed
to pass into the retort through the pipe E, the said gas or vapour expelling the
atmospheric oxygen and also taking up any oxygen that may be set free. Any suitable
substance may be employed with the gas for the purpose of neutralizing the refractory
substances the earths contain. As the retort slowly revolves, the molten lead, under the
action of the heat and the pounding of the balls, is finely divided and distributed through-
out the mass within the retort without becoming oxidized and is therefore constantly
brought into intimate contact with the gold contained in the earths. The process may
be continued until all or nearly all of the gold has been taken up by the lead. The
rotation of the retort is then arrested, the heat diminished, and the contents of the
retort are discharged by any suitable means into water, or are otherwise cooled.
The lead is then separated from the lighter earths by washing, winnowing or other
suitable means and is then subjected to a high temperature in a suitable furnace and
I
:

page_text: in the presence of atmospheric oxygen until it becomes wholly oxidized, when a
"button" containing the gold will be found in the cupel of the furnace.
By my process the molten lead is always preserved in a bright metallic condition
the presence of the carburetted hydrogen completely preventing the oxidation of the
surface of the lead and keeping it untarnished at a high temperature.
In some cases finely divided animal or vegetable charcoal or other carbonaceous
materials may be mixed with the earths before or during their treatment with the
molten lead.
If desired the mouth of the retort may be partially open and a hot reducing flame
of gas be directed into the retort; the contents will thus be heated to a higher
temperature than the retort itself and in the presence of a reducing flame.
In order to effect a more expeditious discharge of the contents of the retort 1
may so arrange the latter that it is capable of being tipped or tilted into such a
position that the whole of the contents will be discharged from the mouth of the retort
at one operation.
The same lead may be used for treating successive charges of the earths in the
retort, that is to say it may be used over and over again until it has absorbed a desired
quantity of gold from the earths.
It will be obvious that my process is also applicable to the extraction of silver from
argentiferous earths.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. The process of extracting gold from refractory auriferous earths, consisting in
subjecting the earths to the action of molten lead in the presence of a reducing gas or
atmosphere substantially as described and for the purpose specified.
2. In the aforesaid process subjecting the auriferous earths and the molten lead,
whilst in the presence of a reducing gas or atmosphere, a pounding operation as
the mass is being slowly rotated or stirred, for the purpose specified.
3. The apparatus for use in my process of extracting gold from refractory auriferous
earths, substantially as described with reference to the accompanying drawing.
Dated this 28th day of August 1896.
HASELTINE, LAKE & Co.,
45 Southampton Buildings, London, W.C., Agents for the Applicant.