Charles George Warnford Lock.

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U17 percentage of sulphur, and to fusion or sintering ; for chloridising,
salt can be added at any point ; and the furnace can be used for drying
or for cooling. The proportion of flue dust is much reduced. Capacity
varies from 10 to 20 tons per 24 hours. Very inferior fuel can be
used* As operated on copper pyrites at the Boston and Colorado


PxARCB "Turret" Furnace.

Smelting Co.'s works at Denver, it appeared to the author in 1894 to

be doing excellent work at a cost of about 60 c. (2«. 6<i.) a ton. It is

made exclusively by the Steams-Roger Manufacturing Co., Denver.*

Fig. 119 is firom a photograph of a battery of these furnaces at the

• See al»o •* Fumaoefl for Boasting Gold-bearing Ores," by C. G. Wamford Lock,
in Jour. Soc Arts, March 1, 1895, No. 2206, xliiL 364.

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Argo works, Denyer, and shows the overhead tramway a by which
ore and fuel are brought, ore feed hopper \ and discharge opening
whence the ore is drawn and shovelled into wheelbarrows.

Smelting to matte is performed in a variety of fnmaoeB, according
to special circumstances.

Perhaps the simplest and crudest is a native Mexican form of
shaft furnace, shown in Fig. 120, used at Jalisco.* It consist
essentially of a pair of air-channels or long tuyers a, constructed in
the top of a mass of crude masonry &, with a bellows c at one end,

FiQ. 119.— Peaboe "Tubhet" Furnaob.

and what answers for a crucible d, at the other. These stone channel!
are about 7 ft. long, slightly conical, and sufficiently raised at tU
back to allow free motion for the bellows. The fire ends are
nated by clay nozzles e, about 18 in. long and 2 in. diam. at tl
outlet ; their ends come nearly to the edge of a circular basin d, a'
1 8 in. diam. and 3 in. deep at the centre, simply a depression in
earthem floor, lined with the ashes of the enctna, a species of
rammed in moist, and formed by a man stamping quickly aroui
with leather sandals on his feet ; it is repaired in the same mann
For each tuyer, a round bellows c, about 3 ,ft. diam. is attach(

* W. B. Deyereiiz, Trans. Amer. Inst. Min. Engs., 18S2.

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directly against the stonework ; the back of the bellows is fastened to
an npright frame, which is hinged at ^, and is provided with a cross-
piece at the top for a handle ; it is worked by a man standing on a
raised platform /, taking a single step backward and forward at each
blast. The blasts are given nearly alternately, and the two cnrrents
are directed by the nozzles toward the centre of the basin. When
smelting is to commence, a green pine pole about 10 in. diam. is laid
across the basin in front of the nozzles, the fire end supported by a
roller, so that it can be moved up easily. Pine charcoal is piled upon
both sides of this over the basin, and plates of foul slag are laid
across from the nozzles to the charcoal, securing greater concentration
of heat. When the fire is well lighted, ore is placed on that part of
tiie charcoal outside of the log, and coal and ore are afterward added
iniffioieutly fast to maintain the compact character of the pile ; thus
jflie blast is prevented from breaking through with force and blowing
the ore away, for it is quite powerful, and the flames are constantly
iiiiged with green. The encina makes a stronger ooal than pine, and

FiQ. 120. — Mbxicak Shaft Furnace.

bettenc for shaft furnaces, but it snaps too much for this process. By
the time the ore has worked down to the bottom of the log, it seems
o have agglutinated, and the melting copper and slag commence to
Irop at once. The whole of the smelting seems to take place before
t settles into the basin, as after that the surface is almost constantly
covered with charcoal. The log seems to be an essential both for
ontrolling the force of the blast and for supporting the charge so
hat it is acted upon gradually, but with increasing power. When
he basin is nearly full of slag the blast is stopped, and the ooal is
craped away. The slag is then removed in plates as it cools, the
nly implement being a round pole, which is slipped under the edge
.nd then carefully lifted up with the cake balanced upon it. If the
ake of copper is not large enough, smelting is resumed: when
ufficient has accumulated, the slag is removed as before, the dust is
>lown off with a bamboo tube, and the copper is allowed to cool in the
lasin. It is said that 300 lb. of ore can be smelted with one furnace
ci 4 hours, which seems doubtful. The quartz gangue separated in
uncentration is used for flux. The slags are very basic, biit well

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fused, and seem to oontain little metallic oopper. The oopper cakes
(40-60 lb.) produced are soft, and seem quite pure. They are melted
in a similar furnace once more, however, being treated precisely ss
the ore was treated, except that no slag is used ; scrap and r^ioe
copper are added at the same time. There is no poling or stirring of
the copper, the action of the heated charcoal being apparently all that
is necessary to produce the proper pitch. This would indioate Uiat
oxide is formed daring the melting down. No tests are made, bat
the uniformity of the product is remarkable.

Bio Tinto employs a number of low brick furnaces lined with soft
but compact day-slate, for smelting the calcined ore, kernels, vA
precipitates, producing a matte with about 36 per cent, copper.
oome of these furnaces are now replaced by water-ja^et cupolas, witb
economy. . Peters * states the cost of matte smelting in a Herreaholl
furnace at 7«. Gd. a ton, with cheap fuel and a fusible ore; and
instances a cost as low as 39. 4<2. with large quantities of ore, coke
costing 10«. a ton, in a rectangular brick furnace measuring inside
12 ft by 3 ft. 6 in., and having tuyers on all sides.

At the Tilt Cove mines, Newfoundland, the Austin pyriti<
smelting process has been adopted, with the object of producing s
matte of one-third the weight of the raw ore.

At the Willows Syndicate works, Transvaal, W. Bettel has intro-
duced some important innovations to suit the peculiar conditions, viz.
(a) very bad coal containing 18-40 per cent, ash, and (6) an on
carrying chiefly hydrous oxide and antimoniate of iron, with 40 oe,
silver per ton, and 4 per cent, copper (blue and green carbonates), wiUi
scarcely any sulphur. After investigating the causes of previous non-
success, he deciaed to adopt the following arrangements : (a) to con-
struct vaults as a foundation ; over these a number of bric^ channeli
(suitably aiTanged along the whole width of the furnace), oovere<3
with bncks (rubbed joints and grouted), communicating with a steaoh
blast arrangement at one comer of the flue end of the fomaoe U
ashpit at outlets, and, after cooling bridge, to blowpipe jets in bridge
and roof; (6^ to work the furnace iinder pressure with closed ashpit
using an ejector arrangement similar to, but simpler than, tb<
Koerting. Thus he could (a) reduce the heat in the grate, making
the ash loose and friable, and (&) transfer such heat (as well as \xx»S
from furnace bottom abstracted by passage of air and steam through
the brick tubes) in the form of hydrogen and carbonic oxide, to ^
laboratory (hearth) of the furnace where these gases are burned wit!
the hot-blast from roof and bridge, producing an intense temperature
similar to that obtained in a Siemens regenerative gas fiimaoe
Having reduced the usual depth between skimming plate and bottom
ho smelted the bottom in three thin layers, the first two with sifted
sand with which 1^ per cent, lime was intimately mixed, and on thii
a seasoning charge of sharp slags smelted. The upper layer consisted
of sifted river sand only, which, after smelting, was seasoned as before
To smelt the refractory untimonial oxide and carbonate ores (70 p«i
cent, in pieces 2]^-3 in. cube) without sulphides (except in traces) ani!
still produce clean slag, collecting at least 90 per cent, of the copper and

♦ E. D. Peters, • Modern American Methods of Copper Smelting *

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silver at one operation in a matte, at a profit, coal being 50«. per ton
of 2000 lb., stores generally about 600 per cent, over English prices,
and white labour 27/. per month (furnacemen), he used as flux a
silioious carbonate of iron, b'me, and magnesia, containing 5 per cent,
and upward of anthracitic carbon. The matte produced is a copjjer
antimonide, thus : antimony oxides fluxed with lime (and magnesia)
will dissolve in a bath of basic ferrous silicate, and be reduoBd by
carbon conjointly with <x)pper and silver, forming a fusible and brittle
argentiferous antimonide of copper (formula Sb^Cus), provided that
the slag does not contain more than 5 per cent, magnetic oxide of iron ;
otherwise the slag is rich, copper and antimony are lost, and some
silver is volatilised. Excess of carbon is .avoided, as tending to throw
down metallic iron, making the matte coarse and difficult to break.
With ores carrying 85 oz. silver, 16J tons ore (or 21\ tons charge) are
concentrated into 1 ton matte; 91*3 per cent, silver is recovered
(7^-8 per cent, going into slag and
remainder volatilising), and the
matte contains 52 per cent, copper,
38 antimony, 3^ iron, 2 arsenic,
2 sulphur, \ lead, and 1 • 69 silver
(520 oz. per ton\ Further oxidis-
ing treatment m a special, hot-
blast, blow - pipe reverberatory
gives crude copper (93 '55 per
cent.) containing 3*26 per cent,
silver (1064*9 oz. a ton), 1*31 anti-
mony, and '6 arsenic. Steam
(which may be raised by waste
beat) at 20 lb. pressure, introduced
through two -i^-in. jets, has a
marked influence in preventing
formation of all except " rotten "
clinker, and causes even such poor
coal as here used to bum to a clean

Water-jacket furnaces are, how-
ever, growing in favour, and
assume many forms. Fig. 121
illustrates Stewart's " rapid "
smelter, a being the crucible ; &,
water jacket ; c, water supply
pipes ; S, air chamber ; e, tuyers ;
ft charging door ; ^, tapping spout ;
K drop bottom. The cost of a
single furnace plant complete is

about 6000L ; its capacity, 30 tons Fio. 121.— Water Jacket Furnace.
a day ; water consumption, 25,000

gaL per 24 hours ; power required, 30 h.p. ; fuel consumed, 30-40 bush,
csharcoal per ton of charge (ore and flux) or 13 per cent good coke.
Some smelters prefer the rectangular form, as giving a greater output
for the same labour and consuming less fuel. If charcoal is used as

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fuel, it is essential to keep it dry and unbroken. The water leaving
the jacket should be as hot as possible short of being steanu and the
outlet should be in full view of the f umaceman. When the blower is
stopped, all the tuyer holes are at once out off, to prevent snbsequeiit
explosions of inflammable gases. Usually the different matemk
forming the charge are fed in separately from their respective biia,
though some advocate mixing the charge thoroughly before feeding.
The removal of chilled slag and crusts should be repeated at short
intervals, to reduce risk of injury. An approximate estimate of ooi4
for working a '' SO-ton " furnace (36 in. diam. at tuyers, taking 35
short tons), on average ore, is : —

£ t. d.

5 tons limestone or iron flax at 12« 3

Sf'tonscokeatei. S4 5

Labour 16 10

Fuel for boiler, 2 ooida wood at 25t. .. .. 2 10

Assay supplies, Ac. 3

Gleaning and weighing product 10

Bepairs, &o., at 10 per cent. 6 5


or, on 35 tons, \l. 17«. 9<2. per ton of 2000 lb. With an 80-ton fumaoe,
the cost is reduced to 12. IO9. 6d

In smelting the low-grade ores of Torreon, Chihuahua, Mexico,
Collins* introduced some innovations with great suooess. Thus,
instead of using the drop-doors in oases of freezing, he raised the
furnace stack by screw-jacks placed over the 4 short oast-irazi
foundation columns, and removed the chilled ^ bottom " in one piece,
breaking it up outside by dynamite. To help prevent obiUing
when working on poor ores, he walled round the open space
below the bottom plate and between ' the foundation colunmB
with slag bricks laid in clay, so as to shut off circulation of
air beneath the fomace. Costly fire-bricks for lining he replaced by
local soft refractory trachyte, cut to shape and laid in a mixture of
pounded trachyte and clay. With a small low fumaoe (36-in. cir-
cular) no lumps of more than fist-size should be admitted, and a
benent results from breaking all silicious or otherwise refractory
lumps to the size of walnuts ; but 25 per cent, of fine ore in a 36-in.
round fumaoe gives fully as much trouble as 40 per cent, in a fumaoe
36 by 100 in. with a bodi. The pieces of coke snould not be allowed
to exceed 9 sq. in. in sectional area, while pieces smaller than .a walnut
either get burned up before reaching the tuyers, or enveloped in. slag
which protects them frt>m the action of the blast. The slags are mors
free from copper and silver when small charges are employed ; but
the pile of coke corresponding with each charge must be large enough
to spread evenly over the whole area of the furnace, and the b^
results were got by a charge of 90 lb. fuel, corresponding with
450-620 lb. ore. The consumption of fuel is about 2 cords a day
of dry mountain oak, which lasts well and gives a hot flame, proving
itself equal to about 1^ ton ordinary western coal, over which — ^besides

♦ H. F. Collins, •♦ Smelting Processes for Extraction of Silver and Gold,- Prot
Inst. Civ. Engs., Paper No. 2655.

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being somewliat cheaper — it offers the advantage of giving better
results with inferior stokers. The Torreon ores are docUe, and rarely
Deed any flnx ; 2 classes are produced, the general average of the first
class being 13 • 05 per cent, copper and 14 oz. silver per ton of 2000 lb.,
and of the second class, 6 * 3 per cent, copper and 4 oz. silver per ton.

The cost of smelting, with wages at 3«.-6«. a day for workmen,
&nd 15«.-17«. 6{i. a day for foremen and mechanics, inferior coke at
57f. 6d a ton, coal at 44«., and wood at 259. a cord, is : labour, 5«. ;
materials, l9. 3e2. ; boiler fuel, 1«. 6i2. ; coke, 10«. 3e2. ; superintendence,
2i.— total, 20#. jper ton of 2000 lb.

At Siemens copper-smelting works at Eedaberg, in the Trans-
Caucasus, the residues from naphtha distillation have been applied
both in the calcination and fusion of pyritic ores, the furnaces for
both operations being combined into one structure, having a chimney-
itack in common. The smelting furnace has a circular bed 18 ft. diam.,
x»vered by a domed roof, having a maximum height of 1^ ft. in the
5entre. The heating is done by two of Leng*s pulverising burners
placed about 9 ft apart on the same side of the furnace, with the up-
Ake flue between them. The jets are not quite square to the admission
x)rt, 80 that two eddying bores of flame are produced under the roof,
vhich unite and pass out by the flue over tne bed of the calcining
lurface. The latter is 50 ft. long, with a bed 9^ ft. wide, and 3 ft.
leight of roof, which is laid with an upward slope of nearly 1 in 7.
The ore, containing 7 per cent, copper, is first roasted in the ordinary
vay, and then run down to coarse metal, containing 25 per cent,
opper ; but when the roasting is omitted, the regulus contains only
8-20 per cent, copper. With this furnace, in 33 working days,
•38*6 tons of ore were smelted, yielding 368*2 tons of coarse me^,
veraging 25 per cent, copper, with a consumption of 185*6 tons
taphtha residues, or rather more than 50 * 43 per cent, of the weight
f the product.*

Fines are not so easy to deal with, but they may be ** bricked "
•y mixing with slimes or flue-dust, lime, or even cement, and smelted
n a wator-jacket furnace with low burden and very light blast, or in
large section blast furnace using a fan blast. Peters describes such
furnace, costing 700Z.-1000Z. complete, smelting 30,000 tons of a
lixtore containing 50 per cent, green fines, yielding a 10} per cent.
latte, at less than 8«. a ton.

The Swansea method as formerly practised was conducted entirely
Q reverberatory smelting furnaces. A mixture of sulphuretted and
atnrally or arofioially oxidised ore, containing sulphur enough to
onoentrato all the copper into a matte of 20 to 30 per cent., and suffi-
ient silica to combine with all the iron that did not enter the matte,
nd with all other bases, so as to make a clean fusible slag, was run
oinm in a reverberatory furnace. The resulting matte was re-charged,
cvasted, and smelted again at a low heat, whereby some of the sulphur
ras oxidised and passed off as sulphurous acid, and the oxidised iron
ombined with the silica of the fimiace lining, unless silicious ore or
tag was added. This operation was repeated till all the iron was

^ G. Sehnabel, '* Liquid Fuel in Copper Smelting," Zeit d. Yer. D. Ing., 1891,

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eliminated, and a pure sulphide of oopper, known as ** white m^al,
was obtained. These repeated roastings and fdsions produced a goa
oopper, bat required an inordinate quantity of fuel and labour. I
the modified Swansea method now employed, the ores and slags &qi
subsequent operations are mixed so as to produce a matte of 30 to 3
per cent. ; this grade being preferred, because if it be lower in cx>ppc
an extra fusion would be required, if higher the cost of siubsequMi
operations would not be materially reduced, while the slags would \
enriched by the higher tenor of the shots of matte which are nnavoil
ably drawn out of the furnace when skimming. If the ore is fosild
4 charges of 8000 lb. each can be smelted in a large fdmace i
24 hours. When the fusion is complete, the slags are skimmed ofi^ an
the matte, if sufficient in quantity, is tapped. But the English poM
tioe of limiting the tenor of the first matte to 33 per cent, is n
followed everywhere. In the Guayaquil smelting works. Chili, ti
mixture is made up to 15 per cent, copper, from sulphuretted an
naturally oxidised ores, and a matte of 50 to 55 per cent, is made i
the first smelting. At the Butte works, Montana, where a roaste
concentrate of about 20 per cent, is matted in' reyerberatoriee, tl
product runs from 60 to 65 per cent. Sometimes the 30 to 85 per oen
matte is tapped into water and thus granulated ; but most works crui
it between rolls previous to calcining it in some suitable fdmace. I
England, where the law is stringent against polluting the atmoepha
wi& noxious gases, the most highly sulphuretted ores and mattes ai
calcined in furnaces which yield a gas of sufficient density for ad
making ; thus, by the use of the Oerstenhdfer kiln, 47 per oent« of a
the sulphur is utilised to make sulphuric acid. The matte is roasts
so as to leave in the roast about 12 per cent, of the 23 per cent. <:
sulphur which it contained before roasting, but a still higher pn
portion of the iron is oxidised. When this roasted matte is agai
fused, either with a silicious desulphuretted ore or a silioious sU^
there is produced what is technically known as white metal, oon
taining 72 to 75 per cent, oopper, about 20 to 18 per cent, salphm
and the balance iron. The product of the last operation, if it h
properly performed and has yielded a regulus of over 70 per oent^ i
now reauced to the metallic state in the blister furnace. It is melte
down very slowly, so as to oxidise as much as possible of the sulphui
The slag formed is skimmed off^ and air is blown upon the melre
mass, the result being the formation of copper oxide and sulphiiit»i
acid — the copper oxide coming into contact with unreduced snlphid
yields metallic copper and sulphurouM acid, which latter being evolve)
in the body of the mass causes it to swell to much above its norma

2 CuO + CuS = 3Cu + SOa;

CuO + SOa = Cu + 80s.

From the extreme density of the fumes evolved they would »^
carry some sulphuric acid, which may be derived from the sulphuzoia
acid, when rising through the mass, reducing an equivalent of ooppai
to the metallic state. The chilled charge when again fused should be
^ady to tap as " blister " of 98 per cent, oopper.

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Comparing reyerberatory with water-jacket fumaoeB, it may be said
it elimination of arsenic, &c., is more effective in the former, anci
lere wood is very cheap while coke and charcoal are dear or infe-
T, the reverberatory may hold its own ; but generally the water-
iket is mnch preferable on the score of economy. Wnen ores are
lie enough to form their own slag, they may be smelted into bars
over 94 per cent, in circular water-jacketed furnaces 36 in. diam.
the tnyers at a rate of 40 tons per day, at a cost not exceeding
1. 6d. per ton of ore, if coke can be got at about 12. per ton ; and
^r iiumaces can be used to still better advantage.
** Bessemerising " is now largely applied to copper mattes. It
isists in utilising the sulphur in the ore as fu6l for bringing the
ftal a stage forward in purity. Its first form was the Hollway pro-
IB (English), followed by the Hanh^ (French), to which several
edifications have more recently been added in America. By it,
rites containing only 2\ per cent, copper can be concentrated into a
-25 per cent, matte with a minimum consumption of fuel.
As used at Leghorn in treating the Tuscan copper ores, crude 10
r cent, ore is mixed with a smsul quantity of roasted lump ore, as
Domes from the mines, is run down into a 30-35 per cent, copper
itte, and tapped direct from the well of the furnaces into a trough-
iped Bessemer converter. Air is blown through this for 20-30
nntes, the effect of which is to oxidise a little of the sulphur and
! the iron, which is converted into a slag at the expense of the
kdous lining of the converter. The slag is so fluid that on tilting
I converter most of it flows off. What remains is skimmed into a
^ ^^gg7> leaving in the converter an almost pure copper sulphide,
te converter is then returned to position and the blast is turned on.
about \ hour the sulphur is eliminated as sulphurous acid and the
pper is reduced to 97 per cent, metal. The whole operation occu-
ss a little over an hour. With patching, the lining lasts for 7
irges. While one converter is in blast, another is being relined,
d the lining of a third is being dried. The converters in use there
oduoe at each blow about \ ton 97 per cent, copper, and therefore
B 80 light that they can be tilted by hand. The capacity of the
ttU pkuQt is 5 tons of copper a day.

At Butte, Montana, the matte produced in the blast furnaces is
Qghly iron monosulphide mixed with copper subsulphide, and runs
^5 per cent, copper, 22 iron, 26 sulphur. A percentage of iron is
ten replaced by small quantities of zinc, lead, antimony, and arsenic,
bich elements are partly volatilised in the converter and partly
iter the slag. When the matte has become cold enough to handle,
18 broken up by sledges to about the size of a n^an's fist, and ele-
cted in cars to a high track leading above the mouth of the remelting
tmace (Fig. 122), which consists of a simple cupola shaft a, the
ain body supported upon 4 hollow cast-iron pillars 6, terminating
ilow in a detachable well c, made of boiler iron, lined deeply with
mixture of crushed quartz and fire-clay, pounded hard in the well
a thickness of about 12 in., and somewhat deeper in the bottom,
he ciipola shaft is also lined with the same material, but decreasing
I thickness above, and running out entirely near the feed-door. The

2 G

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well is placed on wheels for conyenience in running it ont on
iron floor, when it is necessary (every few weeks) to reline it. ""
enter the shaft just above the well, and have peep-holes <2,
which the workmen can observe the level of the molten matte,
junction between the cupola shaft and the well is made by a
wall of the lining material, and this is often broken ihroagh by
fire, as the iron of the melting matte is very prone to eat it
When this occurs the man in charge patches it from outside
lumps of composition kept in readiness. The well has a heavy
iron lip e, by which skimming is performed. The whole famacei

arranged that the tap ki
A, at l^ttom of well, shall]
about 2 ft. higher than \
mouths of the con^
when horizontaL At / <
matte is fed in with
and coke; charges are
weighed, but uie ooke

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 50 of 76)