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Page 34
* * * * *
THE NEWBERY-VAUTIN CHLORINATION PROCESS.
The process of extracting gold from ores by absorption of the precious
metal in chlorine gas, from which it is reduced to a metallic state,
is not a very new discovery. It was first introduced by Plattner many
years ago, and at that time promised to revolutionize the processes
for gold extraction. By degrees it was found that only a very clever
chemist could work this process with practically perfect results, for
many reasons. Lime and magnesia might be contained in the quartz, and
would be attacked by the chlorine. These consume the reagents without
producing any results, earthy particles would settle and surround the
small gold and prevent chlorination, then lead and zinc or other
metals in combination with the gold would also be absorbed by the
chlorine; or, again, from some locally chemical peculiarity in the
water or the ore, gold held in solution by the water might be again
precipitated in the tailings before filtration was complete, and thus
be lost. Henderson, Clark, De Lacy, Mears, and Deacon, all introduced
improvements, or what were claimed to be improvements, on Plattner,
but these chiefly failed because they did not cover every particular
variety of case which gold extraction presented. Therefore, where
delicate chemical operations were necessary for success, practice
generally failed from want of knowledge on the part of the operator,
and many times extensive plants have been pronounced useless from this
cause alone. Hence it is not to be wondered that processes requiring
such care and uncommon knowledge are not greatly in favor.
Mr. Claude Vautin, a gentleman possessed of much practical experience
of gold mining and extraction in Queensland, together with Mr. J.
Cosmo Newbery, analytical chemist to the government of Victoria, have
developed a process which they claim to combine all the advantages of
the foregoing methods, and by the addition of certain improvements in
the machinery and mode of treatment to overcome the difficulties which
have hitherto prevented the general adoption of the chlorination
process.
By reference to the illustrations of the plant below, the system by
which the ore is treated can be readily understood. The materials for
treatment--crushed and roasted ore, or tailings, as the case may
be--are put into the hopper above the revolving barrel, or
chlorinator. This latter is made of iron, lined with wood and lead,
and sufficiently strong to bear a pressure of 100 lb. to the square
inch, its capacity being about 30 cwt of ore. The charge falls from
the hopper into the chlorinator. Water and chlorine-producing
chemicals are added--generally sulphuric acid and chloride of
lime--the manhole cover is replaced and screwed down so as to be gas
tight. On the opposite side of the barrel there is a valve connected
with an air pump, through which air to about the pressure of four
atmospheres is pumped in, to liquefy the chlorine gas that is
generated, after which the valve is screwed down. The barrel is then
set revolving at about ten revolutions a minute, the power being
transmitted by a friction wheel. According to the nature of the ore,
or the size of the grains of gold, this movement is continued from one
to four hours, during which time the gold, from combination with the
chlorine gas, has formed a soluble gold chloride, which has all been
taken up by the water in the barrel. The chlorinator is then stopped,
and the gas and compressed air allowed to escape from the valve
through a rubber hose into a vat of lime water. This is to prevent the
inhalation of any chlorine gas by the workmen. The manhole cover is
now removed and the barrel again set revolving, by which means the
contents are thrown automatically into the filter below. This filter
is an iron vat lined with lead. It has a false bottom, to which is
connected a pipe from a vacuum pump working intermittently. As soon as
all the ore has fallen from the chlorinator into the filter, the pump
is set going, a partial vacuum is produced in the chamber below the
false bottom in the filter, and very rapid filtration results. By this
means all the gold chlorides contained in the wet ore may be washed
out, a continual stream being passed through it while filtration is
going on. The solution running from the filter is continually tested,
and when found free from gold, the stream of water is stopped, as is
also the vacuum pump. The filter is then tipped up into a truck below,
and the tailings run out to the waste heap. The process of washing and
filtration occupies about an hour, during which time another charge
may be in process of treatment in the chlorinator above. The discharge
from the filter and the washings are run into a vat, and from this
they are allowed to pass slowly through a tap into a charcoal filter.
During the passage of the liquid through the charcoal filter, the
chloride of gold is decomposed and the gold is deposited on the
charcoal, which, when fully charged, is burnt, the ashes are fused
with borax in a crucible, and the gold is obtained.
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