_Azurite_, 2CuCO_{3}. Cu(OH)_{2}, and _Atacamite_, CuCl_{3}.
3Cu(OH)_{2}, from Chili.
In modern work, the chief ore smelted is impure chalcopyrite. Carbonate
and oxidised ores, when they can be obtained, are mixed with it,
increasing the concentration and shortening the process; except under
certain special circumstances.
=Preliminary Treatment of Ores.=—The treatment of ores preparatory
to smelting includes the processes of sampling, wet concentration,
agglomeration of fines, and roasting.
=Sampling.=—Since sampling is not a part of the extraction process
proper, in copper smelting, it will be convenient to deal with the
subject separately here.
It is important that ores and all other products entering or leaving
the works, as well as many of the intermediate products of the various
operations, should be properly sampled and assayed. Great attention
is paid to this point at the best organised smelters, since only by
this means can the work of the plant and of its several departments be
properly checked and controlled. Each works has its own special method
of taking samples from the stocks, the Anaconda practice, for example,
being to pass the whole of the first-class ore, amounting in quantity
to 25,000 tons per month, through the sampling mill, whilst of the
poorer, second-class, ore for concentrating, every fifth car-load is
sampled.
There are many different types of sampling plant, and the methods
employed vary also, but the principle is much the same in each
case—namely, to use some automatic device which cuts out and deflects
a certain proportion of the stream of ore on its course through the
mill;—the deflected portion being crushed finer, and a part of it again
cut out and deflected; repeating the operation in this way three or
four times.
The sampling process and plant at Anaconda is so representative of the
best practice, that it may be reviewed in brief, as an example.
[Illustration: Fig. 9.—Outline of Sampling Scheme, Anaconda.]
[Illustration: Fig. 10.—Section through Sampling Mill.]
The _Anaconda Sampling Plant_ is entirely automatic in its action.
The mill is built in two sections, each of which treats 1,800 tons
daily. Each section consists of a set of four sampling machines with
intermediate crushers. The ore goes from the bin to a Blake crusher,
breaking to 3-inch to 4-inch size; the crushed ore is elevated and fed
down a chute to the first sample cutter, which takes out one-fifth (400
lbs. per ton) as a sample, and deflects the rest down another chute.
The sample is crushed further in a Blake crusher, and passes a second
sample cutter (rather smaller in size), which again takes out one-fifth
(80 lbs. for every original ton of ore), and rejects the rest down the
“rejects-chute.” The sample is now crushed in rolls, a third cut of
one-fifth (16 lbs. of the ton) taken as before, the rest rejected. The
sample passes to a final set of crushing rolls, and the last cut of
one-fifth is taken. Hence each ton of ore is represented eventually by
3·2 lbs. of sample.
The sample cutter employed is of the Brunton form. It consists
essentially of a curved boat of 120° arc, which rotates to and fro on
a central spindle. The top is open; one side has one hole cut in, the
other has two, the area of the latter being together four times that
of the single one, so that the falling stream is cut continually, and
one-fifth is deflected to one side, falling down a chute to the next
crusher, whilst the other four-fifths fall from the other side to the
rejects-chute.
[Illustration: Fig. 11.—Brunton Sampler.]
The above description is quite general, several details for certain
classes of ore having been omitted, but it gives a fair idea of the
general principles underlying such work.
The final sample, say 3,200 lbs. per 1,000 tons of ore, is mixed on an
iron plate on the floor, quartered several times by a Brunton shovel,
and the chosen sample then ground in an Englehardt mill (small Gates’
crusher with two discharges). The material is passed through a 1-foot
riddle of 100 mesh wire cloth, the very small quantity of coarser stuff
remaining, is bucked down and added, and the whole is then thoroughly
mixed in a canister of 1 foot side gripped at opposite corners, and
rotated mechanically.
References.
_Constitution of Copper Mattes._
Keller. _Mineral Industry_, vol. ix., 1900, p. 240.
“Elimination of Impurities from Copper Mattes.”
Röntgen. _Metallurgie_, vol. iii., 1906, p. 479.
Hofman, Caypless, and Harrington.
_Trans. Amer. Inst. Min. Eng._, vol. xxxviii., 1908,
pp. 142–153.
Gibb and Philp. _Trans. Amer. Inst. Min. Eng._,
vol. xxxvi., 1906, p. 665.
Heyn and Bauer. _Metallurgie_, vol. iii., 1906, p. 84.
Fulton and Goodner. _Trans. Amer. Inst. Min. Eng._,
vol. xxxix., 1908, pp. 584–620.
_Refining of Copper._
H. O. Hofman, R. Hayden, and H. B. Hallowell,
“A Study in the Refining and Overpoling of Electrolytic Copper.”
_Trans. Inst. Amer. Min. Eng._
Hofman, Green, and Yerxa,
“A Laboratory Study of the Stages in Refining Copper.”
_Trans. Amer. Inst. Min. Eng._, 1904, vol. xxxiv.,
pp. 671–95.
Stahl, “Ueber Raffination, Analyse and Eigenschaften des
Kupfers.” _Berg. and Hüttenmännische Zeitung_,
1889, vol. xlviii., pp. 323–4; 1890, vol. xlix., p. 399;
1893, vol. lii., p. 19; 1901, vol. lx., pp. 77–79.
Keller. _Mineral Industry_, vol. vii., p. 245, _et seq._
_Sampling._
D. W. Brunton, “Modern Practice in Ore Sampling.”
_Mining and Scient. Press_, Oct. 30, 1909.
“Theory and Practice of Ore Sampling.”
_Trans. Amer. Inst. Min. Eng._, vol. xxv., p. 826.