Bisbee daily review., 1917-12-02

ing iron IN the subsequent preclplJd'
ton. 1t does more than this; the
rapid corrosion of iron in the preci.
pitation tanks when ferric salts are
abundant would add to the amount of
corroded iron-scale, which becomes
ct ach ed and accumulates in
the cement-copper. 1t also provides
acid which maintain sweet" condi-
ton of liquor in the precipitating tanks
and prevents settling of basic iron
salts, thereby improving The recovery.
An indication of the influence of the
pyrite filter in accomplishing the re-
duction of the ferric salts is shown
by the fact that after introducing the
filter the grade of the precipitate re-
covered was raised from less than
400 to an average of 500 copper.
Economies follow from such a change
in assay-value, not only in the hand
ling. drying, sacking and shipment,
but in the subsequent melting at the
refinery.
Each filtration vat is provided with
a large door on the level of the filter
bed. through which the accumulated
sediment may be flushed at intervals;
it is also used for discharging the spent
filter. The mud is washed out once a
month. If allowed to collect for too
long a time the particles of pyrite be-
come coated with slime and the chem
ical action of the filter ceases. II is
also desirable at intervals to turn the
material that constitutes the filter bed
in order to expose fresh surfaces to
the action of the solutions. Mr.. Irving
is now preparing to modify the ar
rangement of the ore-filter by raising
the tank, using a 3-ft. filter bed of
screened pyritic ore and filtering down
ward. This will permit percolation
of 500 gallons per minute. The fit
cred solution will flow by a siphon
from the lower part of the vat to the
top of precipitating vat set two feet
lower. The sediment caught in the
filter will be flushed from time to
time without removing the ore bed.
The promptness OF the reaction is
the interesting feature of Mr.. Irving's
application of the pyrite filter. Nishi-
hara has shown that many common
minerals yield a relatively prompt re-
duction of tenth-normal ferric sulphate.
For example. he obtained sharper
and more immediate effect with kaoli-
mite than with pyrite, although after
more prolonged contact the larger re-
ducing effect was obtained with an
equal weight of pyrite. Pyrrhotite was
far more active, the reduction, ex-
pressed in terms of cubic centimetres
of KMnO4, used in titration, being four
times greater than for pyrite. The va
rious common ferro-magnesian sill
Gates found in the gangue of many
ores also exert a not inconsiderabie
reducing power. CAalcopyrite likewise
displays a reducing action and. as
might be expected, marcasite is more
pronounced in its effect than pyrite.
Moreover, the reaction in all cases
becomes more energetic when copper
sulphate is present in the solution and
this is the case in the solutions de-
rived from copper mines and from
the heap-leaching of copper ores. II
should be considered, also, that the py-
rite ores from different mines and
perhaps from different parts of the
same mine. would be expected to show
important variations in reducing pow
er. since refined analysis proves that
pyrite rarely, if ever, corresponds TO
the formula FeS2: il is a somewhat
indeterminate solid solution of FEES in
FeS2. The effect of this on the ability OF
rite to reduce ferric sulphate in wa
ers coming in contact with it, is TO
be taken into account, and upon this
nrnha hlx- HnnnraIu tho continued
ton of the filter, which must repre-
sent a penetration and breaking down
of the pyrite particles rather than a
mere superficial reaction.
Another feature in the economic use
of pyrite as a reducing filter in the
preparation OF copper-bearing solutions
for precipitation is the fact that the
filter itself gradually becomes depict
ed of its copper. Ferric sulphate re-
acts with either cupric or cuprous sui
phides, reducing the iron salt to the
ly, copper sulphate and copper sui.
plate plus cupric sulphide. The mine
water at the Copper Queen gives an
extraction OF 500 OF the copper in the
filter in five months. lowered from
the original assay of 1920 10 0.6q,
in the discarded filter bed, and at the
end of a year the filter has become
too inactive to yield economic results.
The whitewater varies materially in
its load of metallic salts at different
times of the year. depending on the
rainfall. A tpyical analysis shows
about p grains of copper per gallon,
equivalent to 0.04ft. about the same
quantity of ferrous iron. and approx
imately l6 grains of ferric iron. or
0.03E. The amount of copper in the
dry season often increases to double
the above quantity.
Precipitation. The clarified and re
duced liquors after filtration are con
Quoted to the precipitation watts, OF
which four are now in service. These
are of the same size as the two watts
that contain the pyrite filters. name
ly. 20 feet diameter by 10 feet deep,
They are similarly fitted with false
bottoms to support the scrap-iron en-
ployed for precipitation. By the pres
ent arrangement only the mine-water
passes through the filters. since the