Improvements in Leaching Ores and in Apparatus therefor.
Year: 1891

page_text: Date of Application, 10th Nov., 1891
Complete Specification Left, 9th Aug., 1892-Accepted, 17th Sept., 1892
PROVISIONAL SPECIFICATION.
Improvements in Leaching Ores and in Apparatus therefor.
We, SAMUEL HENRY JOHNSON and CHRISTOPHER CLARKE HUTCHINSON,
both of The Engineering Works, Stratford, Essex, Mechanical Engineers, do
hereby declare the nature of this invention to be as follows:-
This invention has for its object the removal of soluble metallic salts from finely
ground minerals after they have been chemically treated so as to render the metal
which it is desired to extract soluble (gold by chlorination or cyanide treatment,
for instance) or when such ores occur mixed with clay, ochre, or gangue, of such
a character as will not readily subside when mixed with water known as
"slimes" etc.
In carrying out this our invention we employ what we call a leaching press,
which is a kind of filter press with arrangements for washing through the cakes
and preferably constructed with the bossed or pyramid type of drainage surface,
as described in our Specification No. 8544 A.D. 1890, and in which by means of
distance frames the chambers are made so as form cakes much thicker than are
usual in ordinary filter presses. The proper depth of chamber to employ depends
on the character of the ore to be treated; the finer it is and the, more slimy its
character, the shallower will be the chambers required, but for efficient working it
may be taken, generally speaking, that when ore is ground fine enough to pass
entirely through a sieve of 60 holes mesh per lineal inch, a depth of 3 inches in
some cases, or less in others, may be used. The proper guide as to this will be
that when the chambers are being filled with the slimes or ground ore in the form
of a thin mud, the presses being supplied by means of a proper arrangement, as
hereinafter described, the chambers should take not less than 3 minutes to fill, and
during the period of filling a gradually rising pressure should be indicated on the
pressure gauge from the beginning, finishing finally with about 50 or 60 lbs. to the
square inch. If, with the depth of chamber employed, the time required to fill
them should be less than 3 minutes, then either the distance frames should be used.
deeper or finer material be worked with the slimes, the object being to increase
the resistance of the material in process of formation on the surface of the filter
cloths so that the pressure shall rise in the apparatus considerably before the
chambers are filled, thus forming the cakes under pressure, rendering them compact
and uniform, and so that they can be more advantageously lixiviated subsequently..
Care should be taken that too long a time be not employed in filling the chambers,
especially where there is considerable mixture of coarser sand with the fine
material and which then would have a tendency to subside in the chambers, making
the bottom parts of the cakes more permeable than the top, thus increasing the
quantity of wash water necessary to thoroughly cleanse the cakes. When material
of this kind is used the chambers should be filled as fast as possible, and they
should be shallower than in cases where there was not much tendency to subside,
the object being to produce a cake of homogeneous character, so that in the
subsequent washing the liquid held in the cakes may be pushed out by the wash
water and displaced from the cakes with as little admixture as possible with the
wash water, and so as to avoid what may be described as short circuiting of the
wash water by passing through the more porous parts of the cakes in the machine.
We have given above generally the mode of working which should be the guide
to obtain the best results in the operation of leaching in this class of machine.
In forming the cakes preliminary to the subsequent process of washing and in
conjunction therewith it will be readily understood that the mode of feeding the
apparatus will have an important bearing on the character of the resulting cake.

page_text: In all cases, the material should be fed into the filters so rapidly that very shortly
after the commencement of the operation the resistance of the material on the
cloths shall be such as to cause the pressure to rise. From this it will be obvious
where such free filtering materials are being forced into the machine that the
ordinary system of pumping applied to filter presses will not be adequate to the
requirements of the case, as in the beginning of the process of filling a pump
would throw far too little, er if not at the end far too much. We therefore for
this purpose and for the reasons indicated, feed the machine with a compressed
air forcing arrangement, by means of which a large volume of the material can be
thrown into the machine at once and the supply maintained at a greater rate than
the liquid can filter through the deposit on the cloths, in consequence of which,
pressure rises in the machine and the cakes become firmly compacted and uniformly
built up into a homogeneous porous cake in which the coarse and fine particles are
evenly distributed and in the best condition for washing. The arrangement of
pneumatic forcing receiver we employ consists of a vessel of suitable material and
strength capable of holding rather more than a full charge of the mud to be
forced into the leaching machine; it is provided with a dished or sloping bottom
which converges towards the outlet, through which, by means of compressed air
in the upper part of the vessel, the mud is forced through a pipe which leads to
the leaching machine. The compressed air from a storage reservoir at about 50
to 60 lbs. pressure is introduced by means of a pipe which descends almost to the
bottom of receiver, so that on being forced into the receiver it blows up through
its contents, keeping it in a state of agitation and uniformly mixed whilst it is
being forced into the leaching press. Instead of the pneumatic agitator_a
mechanical agitator could be employed to carry out our invention, but we prefer
the pneumatic arrangement on account of the greater simplicity secured. When
these arrangements are properly carried out the internal pressure in the machine
gradually rises until the chambers are full, which is indicated by the complete
cessation of the filtration. The cakes in the machine are then ready for washing,
care being taken to get rid of the air; this is accomplished by allowing water to
enter at the back of the cloths on the drainage surface of every alternate plate of
the machine (the air plug being opened first) so that the water has to pass through
the cakes of material before arriving at the outlet; for this purpose a moderate
pressure will generally he found sufficient, say from 10 to 30 lbs. per square inch.
The wash water may be fed in from a tank placed at a sufficient height to afford
the desired pressure. By these means we effect a more perfect separation of the
soluble metallic salts than has hitherto been practicable in the old methods of
leaching and produce a more concentrated solution. We also effect a large
economy in the consumption of water and considerably reduce the time required
and cost of the leaching process as hitherto carried out.
Dated this 7th day of November 1891
SAML. H. JOHNSON.
C. C. HUTCHINSON.
COMPLETE SPECIFICATION.
Improvements in Leaching Ores and in Apparatus therefor.
We SAMUEL HENRY JOHNSON and CHRISTOPHER CLARKE HUTCHINSON of
The Engineering Works Stratford in the County of Essex Mechanical Engineers
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 has for its object the removal of soluble metallic salts from
finely ground minerals after they have been chemically treated so as to render the
metal which it is desired to extract soluble (gold by chlorination or cyanide
treatment for instance) or when such ores occur mixed with clay, ochre, or gangue,

page_text: of such a character as will not readily subside when mixed with water known as
❝ slimes " etc.
In carrying out this our invention we employ what we call a leaching press,
which is a kind of filter press with arrangements for washing through the cakes
and preferably constructed with the bossed or pyramid type of drainage surface,
as described in our Specification No. 8544 A.D. 1890, and in which by means of
distance frames the chambers are made so as to form cakes much thicker than
are usual in ordinary filter presses. The proper depth of chamber to employ
depends on the character of the ore to be treated; the finer it is and the more
slimy its character, the shallower will be the chambers required, but for efficient
working it may be taken, generally speaking, that when ore is ground fine enough
to pass entirely through a sieve of 60 holes mesh per lineal inch, a depth of
3 inches in some cases, or less in others, may be used. The proper guide as to
this will be that when the chambers are being filled with the slimes or ground ore
in the form of a thin mud, the presses being supplied by means of a proper
arrangement, as hereinafter described, the chambers should take not less than
3 minutes to fill, and during the period of filling a gradually rising pressure
should be indicated on the pressure gauge from the beginning, finishing finally
with about 50 or 60 lbs. to the square inch. If, with the depth of chamber
employed, the time required to fill them should be less than 3 minutes, then either
the distance frames should be used deeper or finer material be worked with the
slimes, the object being to increase the resistance of the material in process of
formation on the surface of the filter cloths so that the pressure shall rise in the
apparatus considerably before the chambers are filled, thus forming the cakes
under pressure, rendering them compact and uniform, and so that they can be
more advantageously lixiviated subsequently. Care should be taken that too long
a timė be not employed in filling the chambers, especially where there is considerable
mixture of coarser sand with the fine material and which then would have a.
tendency to subside in the chambers, making the bottom parts of the cakes more
permeable than the top, thus increasing the quantity of wash water necessary to
thoroughly cleanse the cakes. When material of this kind is used the chambers
should be filled as fast as possible, and they should be shallower than in cases
where there was not much tendency to subside, the object being to produce a cake
of homogeneous character, so that in the subsequent washing the liquid held in
the cakes may be pushed out by the wash water and displaced from the cakes
with as little admixture as possible with the wash water, and so as to avoid what
may be described as short circuiting of the wash water by passing through the
more porous parts of the cakes in the machine. We have given above generally
the mode of working which should be the guide to obtain the best results in the
operation of leaching in this class of machine. In forming the cakes preliminary
to the subsequent process of washing and in conjunction therewith it will be
readily understood that the mode of feeding the apparatus will have an important
bearing on the character of the resulting cake. In all cases, the material should
be fed into the filters so rapidly that very shortly after the commencement of the
operation the resistance of the material on the cloths shall be such as to cause
the pressure to rise. From this it will be obvious where such free filtering
materials are being forced into the machine that the ordinary system of pumping
applied to filter presses will not be adequate to the requirements of the case, as in
the beginning of the process of filling a pump would throw far too little, or if not,
at the end far too much. We therefore for this purpose and for the reasons
indicated, feed the machine with a compressed air forcing arrangement, by means
of which a large volume of the material can be thrown into the machine at once
and the supply maintained at a greater rate than the liquid can filter through the
deposit on the cloths, in consequence of which, pressure rises in the machine and
the cakes become firmly compacted and uniforinly built up into a homogeneous
porous cake in which the coarse and fine particles are evenly distributed and in
the best condition for washing. The arrangement of pneumatic forcing receiver

page_text: press, only that in this case the material would have to be agitated for a longer
time and it would be necessary to have several forcing receivers and they might
conveniently be arranged to work into a common forcing main from which a series
of presses could be supplied.
R. and R' are two leaching presses provided with distance frames between the
plates so as to make the cakes of suitable depth to suit the ore under operation.
F and F are the feed inlets, W. and W' the wash water inlets which communicate
by internal passages formed by the juxtaposition of the frames and plates and
having ports into the alternate filtering diaphragms of the leaching apparatus.
The plates with the outlet cocks jjj are those into which the wash water ports
come from the wash water passage. The alternate plates with plain outlets left
always open have no ports to the wash water passage, so that when the cocks jjj
are shut and the wash water valves opened the only outlet for the wash water is by
passing through the cakes on both sides of the plates jjj to run away by the
outlets o o o.
T is a truck into which the contents of the leaching presses may be discharged
and V is a shoot by which the slimes may be fed into the forcing receiver, which
should be provided with a cover capable of being quickly opened and closed on a
rubber or other suitable packing joint.
Having particularly described and ascertained the nature of our said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
1. The leaching of ores by the employment of a filterpress having arrangements
for washing through the cakes with chambers of depth graduated according to the
permeability of the ore under treatment, worked in conjunction with a pneumatic
forcing receiver with agitator for the purpose of working fine ores
substantially as described.
or slimes
2. The mode of forming homogeneous and uniformly permeable cakes of ore or
slimes for the purposes of leaching substantially as described.
3. The apparatus consisting of a filter press having arrangements for washing
through the cakes with chambers of depth graduated to suit the permeability of
the ore under treatment in combination with a pneumatic forcing receiver with
agitator substantially as and for the purpose described.
Dated this 9th day of August 1892.
SAML. H. JOHNSON.
C. C. HUTCHINSON.