Charles George Warnford Lock.

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separating from the magnetic stratum by the lifting and wedging
action of the upward current of air following along between the
periphery of the drum and the upper portion of the partition d. The
magnetic stratum follows the path of the belt around the periphery
of the drum, by reason of the attraction to the maraet e, and its
wave-like- motion is continued, constantly gathering the more highly
magnetic particles closer to the poles, and consequently to the belt.
During its passage around the periphery of the drum, a scouring action
is kept up upon the surface of the mass by the opposing current of

Fio. 145.— Magnetic Sefabatob: Hoffman's.

dr and by the agitation of the mass, which effectually brings all the
Articles into contact with the air current. After passing the par-
it ion /*, the less magnetic material continues first to fall from the belt,
v^hile the more magnetic is still carried forward, and finally leaves the
«lt after the latter has carried it beyond the holding force of the
ast pole of the magnet. The power required is \ h.p. mechanically
nd 2 h.p. electrically.

At the Friedrichseger (Oberlahnstein) argentiferous lead mine,
rhere much mixed blende and spathic iron ore are produced, mag-
netic separation has long been successfully applied.* The initial step
s roasting, to render the ore magnetic, by converting the ferrous
arbonate into magnetic oxide. The larger lumps are roasted in kilns,
barged alternately with coke screenings in the usual way. Owing
the large amount of sulphur in the ore, the consumption of fuel is
ery smaU, being only 1 cwt. per 8 tons daily put through the kiln,

♦ O. Heberle, Berg. u. Hut. Zeit, xliii. 509.

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which is served by two men. The ooet of kiln roasting is about 9U.
per ton. The roasted ore is rednoed by breakers and rolls to partkM
of 5 mm. maximum sise* which are fed mechanically to the magnetk
machines. Fine-grained products are calcined in long flat-bedded
reverberatory furnaces for about Ij^ hour. The cost both for f^et
and labour is much higher than in the kilns, and is conoiputed at
2f. M. per ton. The roasted ore is spread out on a floor to oooLi
separated from sintered lumps, and passed through a sLnug drum w
remove particles above 4 mm., which are returned to the cmsherj
while the finer siftings pass to the magnetic machines. Thua rough
stuff carrying 12-15 per cent, zinc and 20-22 iron is made to affi»d
sine ore of 33 per cent. ; and iron ore of 36-38 per oent. iron and
10 per cent, manganese.

in order to prepare the ^* clay-band " ironstone, which is the ore
roost largely raised in this country, for being smelted, it is neeeeeary
to calcine it ; and this calcination is usuallv, although not alwaysi,
done in the locality of the mine, even when tne ore has not to be used
there. The reason of this is that the bulk of material is leasened and
its transportation is thus facilitated. Clay-band ironstone consists ia
great part of iron carbonate, the other largest constituents beiii|^
silica and alumina, but it also contains small quantities of lime and
magnesia, with a little phosphoric acid and sulphur. What is termed
the ** black band " is black in colour from containing ooaly matter
mixed up in it. The object of the calcination is to drive off' carbonic
acid, to raise the iron protoxide with which it was united to the state
of peroxide, and by altering the physical condition of the ore, to
render it more easy of reduction in the furnace. Two modes of calci-
nation are practised, namely, in <* clamps " and in kilns.

In clamp calcining ordinary grey clay ironstone, it is customaiy
first to sprc^ a layer of coal in lumps upon the ground, and on this to
raise the heap of ironstone, interspersing coal occasionally, and then
to cover the surface of the heap with slack. In calcining ^ black
band " it is not necessary to use any coal, there being sufficient car-
bonaoeous or coaly matter in the stone itself, and often also adhering
to the surface of the lumps, to furnish the necessary oombustibie
material. The heaps thus formed are built about 6-8 ft. high, some-
times much higher ; they are made of variable extent, up to so large
as to cover h acre of land, and the calcined stone may be removed
from one ena while the heap is being freshly made at the other. The
heap is ienited, and bums through in a smouldering way, emitting a
good deal of smoke, a little flame breaking through the surfiEkce id«o
in places. An ordinary sized clamp takes about 3 weeks to become
thoroughlv calcined, and at the end of this time its bulk is found to
be reduced to about half.

For calcining in kilns an ordinary open kiln, like a common ^g-
shaped lime-kiln, is sometimes used ; but for the most part iron cap-
shaped kilns, made of iron plates lined with firebrick, are used. Thej
are about 24 ft. high, and are so arranged that while the ore and fii«J
can be fed in continuously above, the calcined ore is discharged at
the bottom either upon a raised platform or directly into the wagoia
that are to cany it away. The kiln being once ignited, all that h
necessary is from time to time to throw in a layer of coal on the top

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of a charge of stone ; each calcining kiln is constructed to hold about
250 tons of stone, and the quantity of coal used is about 7 per cent, of
the weight of stone calcined.

The calcining of ironstone in clamps is often a very great nuisance,
from the large quantities of sulphurous smoke emitted during burn-
ing. Of course smoke of the same suffocating character issues from
the open tops of calcining kilns, but it is very much less in amount,
ind 18 delivered into the atmosphere at a higher level ; not more than
>De-tenth of the quantity of coal is used ^at is used in clamp cal-
cining. Whenever the nature of the stone permits of kiln calcining,
;his method ought to be pursued ; but there is a limit to the use of
he kiln. It is applicable to the ordinary grey ironstone with which
x)al has to be used for calcination, since, if the quantity of coal be
lot exoeesive, that is to say, if it be not used in greater quantity
han IB necessary to effect the calcination, the calcined stone falls out
rom the kiln in separate pieces ; but it is not applicable to the black-
»and ironstcme or the *' red shag " of North Staffordshire, inasmuch as
hese stones become partially fused during calcination, and run to-
;ether into large blocks and masses which require a pick-axe to break
bem down, and would not run out from the kiln.

For desulphurising iron ores, heap roasting, after the manner de-
cribed under copper, was first adopted, to be followed by several
arieties of kiln. The rules * which govern the roasting of pyritic
nes are mainly that : (a) heat alone, without access of air, can remove,
t best, only one-half tiie sulphur present ; (6) atmospheric oxygen is
bsolutel^ necessary ; (c) even at a low heat, ore is properly desul-
hurised if air can gain access freely to the FeS, in it ; (d) iron sul-
hato can be decomposed by heat equally well with or without air ;
\) if the residuum of sulphur in roasted ores is to consist, so far as
Dssible, of sulphates, the roasting must be done under free access of
J- ; (/) fusion or sintering of ore is likely to prevent any further
»ulplinrisation ; {g) sintering does not allow much of the remain-
tg sulphur to be in the form of sulphate ; {It) fusion should never
;cur in roasting except after continued heating in air at a lower tem-
^ratore ; (t) ores cannot be properly desulphurised in the upper part
r the blast furnace ; (&) an efficient roaster must allow easy control
' heat, abundant access of air to the hot ore, and rapid removal of
le products of combustion.

The Davis-Colby gas-fired kiln is perhaps the most popular. It
insists in general, Fig. 146, of two concentric shafts a of brick-work,
iclosing between them an annular space 6 18-24 in. in section, to
mtain the ore. The inner shaft is continued above the top of the
aster to form the draft stack, or it may be covered, the products of
mboBtion being carried downward and out through the flue c to a
parate chimney, allowing utilisation of the fumes. A cone-covered
p d permits of more convenient charging, as ore dropped from car-
uppers upon it gets an even distribution. In tlie outer wall are
utea «, &:e-arches /, gas flues ^, and poking holes and air flues A.
MXiings t in the inner wall admit the fumes and products of com-
utum to the draft-stack or to the flue c, and are placed higher or
•rer, according to the ^ecessities of the ore under treatment. With
• a G. Vttleotine.

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dense hard magnetiteB, the height of the kiln is increased for tbi
pnrpoee of giving the ore a longer exposure to heat ; and the fini
arches are put at a greater vertical distance apart, so that the ore mft)
partially cool after its first heating, snd 6
cracked or fissured, therehy exposing the i»
maining sulphur more thoroughly to the actiai
at the second fire-arches. Generally the ga
used is surplus gas from the blast furnace M
producer gas is much preferable. When pru^
perly charged, as much as 30-40 per cent c^
fine ore can be used; but fine and ooani
should be thorougUy mixed in filling, as i
solid mass of fine ore before a fire^arch ehokej
off the gas and prevents the heat and air b^
penetrating the ore. Their capacity is 75-10^
tons of a reasonably porous ore in 24 homl
Of course, a hard dense ore reouires a longd
exposure and the output of sudi ore is scsm
what less. The roaster at the Eatahdin fni
nace, 20 ft. high and 15 ft dianu, rotffa
about 40 tons a day ; those at the Golebrool
and Cornwall furnaces, 75-90. Clinkers caoai
little difficulty in working; they seldom ex-
tend beyond the bounds of one or two fire
arches, and as the annular space is narrow
and widens downward, they aire readih
reached and broken up while hot; wid|
proper attention, there is no reason why thej
Fio. 146.— DEauLPHTE- should form at all. The upper fireircbel
isiNO Kiln. should generally be kept at a somewhat low^

temperature than the second set, gradaall]
raising the heat, so that if clinkering does take place it is only aftei
long heating at a lower temperature, and after atmospheric oxjgei
has had full play on the reasonably hot ore. The cost per ton c^
roasting varies with circumstances, and is greatly afiected by th<
method of breaking and filling the ore, and by the use of fumaoe-t oi
producer-gas. New kilns witb a capacity of 75-100 tons a day t«
built by contract, for 600Z,, including royalty ; but the system can \i
adapted to any ordinary Ojers kiln, the expense varying with tb
size and shape of the originsd roaster.

Smelting, — ^The impure metal in the shape of ores is brought bsc)
tp a relatively pure state by the process of smelting in fumaoee sup
plied with fuel and oontinuous blasts of heated air. The furnaces an
fed with ore and coal, in the proportion of about 3 parts fuel to 1 o!
ore, and with a certain proportion of limestone as a purifier or fita
for the removal of the earthy matter of the ore. The metal, being
the heaviest, drains to the bottom when fused, and is run off intt
moulds, when it becomes ** pig-iron," and is ready for use in foundries
but it has taken up too much carbon from the fuel to be available at
once for the manufacture of " wrought " iron, and must, therefore, K
subjected to various further purifying processes. Until coal canw
into general use, these further processes wore not separated from tliv

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aneltmg, and ** malleable " iron was produced direct from the ore
^ith charcoal fuel by continuous working. The iron was not actually
-endered molten, but was separated out and made to coalesce into a
olid lump whilst in a pasty condition, and was taken out sufficiently
Vee from carbon to be at once malleable — ^the Catalan process, fol-
owed by many native races all over the world. The furnace maj)r be
lescribed as a rectangular cavity or hearth, of various dimensions,
vithin a building. Three sides were formed mainly of iron and clay,
nd the fourth of stones luted with clay, while the bottom consisted
f a flat or slightly hollowed refractoiy stone, such as granite. On one
\^<ib the tuyer passes through a small arched opening about 18-19 in.
rom the bottom. There was no chimney, but a hole was left in
bo roof. A Catalan forge employed 10 men in France. The ore is
Tst crushed under a hammer and sifted. The furnace is heated with
harcoal, which is packed almost as high as the bottom of the tuyer,
rhen alternate layers of ore siftings and charcoal are piled up so as
> form a ridge, one slope of which is covered with moistened charcoal
reeze, beaten well down with a spade. The blast is turned on, and
16 level is kept up by additions of ore and charcoal. At the end of
bout 6 hours the iron has coalesced into a solid lump at the bottom,
hich is lifted over the edge of the furnace by levers, and is ready
»r hammering.

The blast nimace is only a magnified Catalan, increased in size to
ike larger charges, with forced draft to bum inferior fuel, and in-
kpable of producing a malleable iron owing to the percentage of
krbon combined with the metal. It has gone through many changes,
id will probably continue to be modified. In its earlier forms it
as capable of making either malleable or cast iron at wiU. The
mal mmensions in Britain for furnaces working on Cnmberland,
leveland, Scotch, or Spanish ores are 70-75 ft. high and 18-20 ft.
am. at the boshes, using good coke, anthracite, or' splint coal,
merican practice offers important contrasts.*

The conversion of pig iron into malleable iron is effected by
idation in a " puddling ** furnace, the oxygen bein^ derived from
[>n peroxide provided m the "bull-dog" or "fettlmg** used for
ling the furnace. To produce steel, the decarburising is not
lowed to proceed so far. Malleable iron is converted into steel by
Ating with charcoal in a " cementation " furnace. The introdaction
^ r^enerative " heating made it possible to produce steel from pig
>n in the " open hearth " or reverberatory furnace, either using pig-
>n and ore (Siemens process) or pig and scrap iron (Siemens-
artin); and from pig-iron aJone m a "converter" (Bessemer);
[lile the phosphorus is eliminated by using a basic instead of a
icioxis lining in the converter (Thomas-Gilchrist), and a valuable
rtilising material containing 25 per cent, phosphoric acid is obtained
a l)ye-product Owing to the multiplicity of forms which these
vera! furnaces have taken, and the number of modifications of
>rking introduced in consequence of the variety of ores, fuels, and
txee dealt with, no one example can be considered representative or
lily instructive, and available space quite prohibits a proper de-
-iption of the various examples necessary to do justice to the
• W. Colquhoun, at S. Wales Inst. Min. Enga., Nov. 1891.

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Bubjeot It is therefore deemed better to refer the reader at oooe V
the reoognised works on the metallurgy of iron. Moreover, a soul
installation of iron smelting plant is an indnstrial impoesibilitj, txk
a large one is only to be undertaken with abundant capital and thi
services of experts, so that a synopsis such as could be ^yen besi
would fulfil no useful purpose.

Om<* — An important element in the cost of producing iron la ^
transportation of the raw materials, and in this respect the Unitei
Kingdom is well situated. Several of our iron-producing districts an
also seats of large ooal industries, and the works are situated on Ui
coalfield itself. In the district of Cleveland, the ooal is only separatei
from the ironstone by about 30 miles ; whilst Lancashire ai^ Cnmber
land possess deposits of ore and limestone in the vicinity of thei
fiiinaces, the coke for which is, however, obtained from Dnrham
about 80 miles away. These facilities, although not entirely abees
in the United States, are not of so frequent occurrence. The depoei
at Cornwall, in Pennsylvania, is within 40 miles of anthracite coal
and accessible to coke at rates which leave nothing to be desired
When we pass to the south, we find in Alabama that the ooal and or
are usually within 25 miles of each other, and sometimes to be foun
lying one over the other upon the same property. In conneotzoi
with the Lake Superior ore mines, however, a large proportion of th
produce of which is transported to Pittsburgh, the ore in oariied fa
790 miles, and this appears to be a feature which characterises tb^
northern states in contradistinction to the southern.

The geological formations of the seams containing the ore is, ii
addition to geographical situation, a controlling fiustor in the snppli
of iron ore, and one which influences the miner more directly thai
does the former. In the United Kingdom the general conditions o
iron-mining are concomitant with a large output, although there an
some districts — as South Staffordshire and some parts of CumberlazK
and Lancashire— where, through natural causes, the workings are r«
stricted. In Lincolnshire the ore is very accettsible, as it also is ii
Northamptonshire and in places in North Staffordshire, deposit
occurring in the Carboniferous formations. In Scotland, the mine?
on an average cuts about 1^ tons, whilst in South Staffordshire sod
a great quantitv of shale has to be excavated that the miner onl^
attains about l| tons a day. Judging from the statistics which an
available in respect to the United States on this subject, the lai^esl
individual output noticed is that of Alabama, where the ore is of i
soft nature, and where an individual production was made of 509 *6£
tons in 1889. The lowest outputs per employ^ registered weie is
Ohio (157-95 tons), Virginia and West Virginia (209-87 tons). These
statistics, taken in connection with other information, prove that tb«
ore in the above-mentioned states is difficult of attainment. It ii
noticeable, too, that in Pennsylvania over 1000 employ^ are at worlq
above the number engaged in Alabama, although in the latt^* cas^
the production exceeds that of the former by over 10,000 tons. It id
notable that in districts whore the highest-valued ore is won, tb^
average profits per ton have also been largest, although the averagel
output per man has been amongst the smallest. These are the dis-
•icts also in which the highest remuneration has obtained, but whert

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the outputs of ore have been of small extent. In these states, there-
R>re, the ores have been easily worked, and mining maohinery has
[irobaUy extensively been in use. Cleveland, Scotland, Cumberland
lod Lancashire are the districts of the United Kingdom where the
bigh-value ores are found, and here, it would seem, the miners are
the best paid. In all these districts, too, unlike those of the United
States, the outputs are the largest in the kingdom. The highest-
ralued ores, and the production thereof, are given under : —

United Kingdom,


Value of Ore
per too.
Tons. 9. d.

Gnmberland 1,594,461 .. 11 llf

Lancaghire 1,021,990- .. 8 8}

Yorkshire (N.) 5,728,314 .. 10 9

Scotland 1,061,734 .. 9 SJ

UniUd 8tate$.

Idaho and Montana 24,072 .. 27 6

Colorado .. 109,136 .. 18 7

NewJereey 415,510 .. 13 5

New York 1,247,537 .. 12

The value of the red hematite ore worked in Michigan is pretty well
Ml a par with that of our own derived from Cumberland. In the
former, the value is lis, 3d. per ton, whikt in the latter it is price<l
it 11«. lljd. per ton. In both places the ore in generally worked
without very much diflSculty.

The average oust of grey forge iron in Great Britain is given at
32«. a ton, as compared with 36«. on the Continent, 43». in the
Southern States, and 56«. in the Northern States, the chief difference
between the Northern and Southern States Ijing in the cost of ore.
The average cost of Bessemer iron is given as 4l8. in Great Britain,
47 8. on the Continent, and 61«. in the Northern States, none being
produced in the South; and the figures for spiegeleisen are 44«. in
Great Britain and 608. on the Continent. These figures refer to the
period 1887-90, and are given only for comparison between the great
producing centres.

The detailed cost of producing a ton of pig-iron in a Sequachee
Valley furnace in 1888, using its own local ore and coal and buying
soft ore, are thus given :* —

$. d.

Hard ore at SO per cent, 2750 lb. at H«. 4

Soft ore at 50 per cent, 2325 lb. at 9« 10 6

Add 10 per cent for waste, moistore, &c, 16

Ore per ton (2000 lb.) iron.


Coke, 2750 lb. at 8«., pins waste 12

Labour, on a daily make of 85 tons 7

Htore8,&o. 10

Freight on coke 10

Depreciation 10

Interest 9

£1 18 9

Or, on the English ton £2 3 6

» W. M. Bowron.

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The annexed figures* refer to Birmingham, Alabama, when
conditions are exceptionally fayourable.

(1) Furnace, 75 x 17 ft; brick Btovee; 8 tnyers 6 in. each,
blowing 21,000 cub. ft. air per minute; making 160 tons a d^j,
80 per cent, foundry ; burden : —

Coke (86-27 carbon, 11*22 ash, 2-51 yolatile matter, 1 -55 snlphiir) 9G00
Hard red ore (89*47 iron, 8i2 lime carbouate, 8*17 dlica, 3 '47

alumiDa) 8600

Soft ore (51*57 iron, 1*02 lime carbonate, 16*62 silica, 5*05 ala-

mina) 5000

Limonite (51 iron, 8 silica, 4 alnroina) . . ..- 2500

Bilidous red ore (34*7 iron, 1*79 lime carbonate, 42*84 nlioa,

403 alumina) 1200

Limestone (86*26 lime carbonate, 7*50 magnesia carbonate, 3*78

(diicn, *75 ainmina) 2070

Dolomite (55 lime carbonate, 42*9 magnesia carbonate, 1 silica,

1 alumina) 2070

(2) Furnace, 76 x 18 ft.; brick stovee; 8 tuyers 7 in. eadi
12 ft hearth; 22,000 cub. ft. air a minute; averaging 193 tons \
day of high silicon iron, over 80 per cent, foundry; burden : —

Coke (89*15 carbon, 10*33 asb, 1 *27 sulphur. *52 volatile matter) .. 5000
Hard red ore (37 irou, 28 lime carbonate, 10 silica, 2 alumina) . . 6800

Soft ore, as in (1) 2650

Limestone, as in (1) 620

Blag : 42 per cent lime, 38 silica, 14 alumina.

(3) Furnace, 76 x 20 ft. ; brick stoves ; tuyers and blast as ii
(2); 11 ft. hearth ; averaging 200 tons a day, 86 per cent, foundiy
burden : —


Coke, as in (2) 5600

Hard ore, as in (2) 6800

Soft ore, as in (1) 2740

Limonite, as in (1) 2740

Limestone, as in (1) 1320

Slag : 45 per cent, lime, 36 silica, 14 alumina.

The cost of the coke at the different furnaces varies from 1%, to 9*
a ton ; limestone, 3«. 9d. ; hard ore, crushed, f. o. b. mines, 2«. 6<i. ;
freight, 7d.-l«. ; soft ore, f. o. b. mines, 1«. 6d. ; freight, 9d ; Irondale
soft ore (61 per cent, iron) at furnace, 4«. 6d. ; limonite (50 per cent
iron) at furnace, 4«. 9d. On a month's production of 12,000 tons from
two furnaces, the figures of cost of 1 ton (2000 lb.) pig-iron are:—
CJoke, 9«. 3i. ; ores, 8«. 7d. ; limestone, 8cJ. ; labour, 3«. 4<i ; in©-
dentals, 3«. lid. : total, 26«. 9(f.

Production, — The approximate yearly production of pig-iron and
steel in the principal countries is : —

♦ E. C. Pechin, En. and Min. Jl., July 14, 1894.

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Pig Iron.


nited Kingdom






issia .. .. ••

nited States

Iter ooimtries
























Bye-products. — Taking the weight of the slag produced at 1 j tone
)r ton of pig iron, we may assume that the vast heaps of this com-
fcratively refuse bye-product are increasing in this country alone at
le rate of upwards of 18 million tons annually. Not only do these
^ps cover many thousands of acres of land, rendering the same barren
id unprofitable, but in some cases, where sufficient vacant ground
omot be obtained near the works, manufacturers are compelled to rid
lemsel ves of the slag by conveying it away to considerable distances,
r by casting it into the sea, at a very heavy annual expenditure. Slags

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 57 of 76)