Charles George Warnford Lock.

Economic mining: a practical handbook for the miner, the metallurgist and ... online

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fore, with less consumption of sulphur as fuel.

When the wall that closes the front opening / begins to heat, anj
the kiln is ready for running, a small hole is made with a pointed iti
strument,so as to allow the melted sulphur to flow off iuto woodei
moulds. The horizontal flue or condensing chamber 7i should have \
sloping floor, and when the temperature in it reaches the meltinj
point of sulphur, the flowers that have been deposited on the sid^^
are liquefied and run off. Towards the end of the operation it wi|
be found prudent to close all the dampers as well as the bole m, t|
prevent the over-heating of the kiln, in which case the sulphur wouw
become thick and difficult to run off, and the yield would conseqnentlj
be lessened.

The first cost of the structure is slight, as the materials neoesear^
are usually at hand. The yield, too, is much increased; bat on iH
other hand the extra cost in charging, discharging, and attendance
as compared with the ordinary calcarone^ make a large hole in thi
increased returns.

Doppione. — It will require little reflection to see that only a smal
quantity of the finely pulverised mineral, necessarily produced in tb<
operations of mining and breaking down the ore, could be dealt wit^
in the calcarone ; consequently for a long time the bulk of this portit^
of the ore was simply thrown away, though it often assayed 70 pe^
cent, sulphur. The doppione was one of the earliest succofisful stru<^
tures designed to remedy this state of things. As shown in Fig. IGi
it consists of a set (generally 6) of cast-iron pots, holding about 30 U
40 gal. each, arranged in a gallery furnace e, so as to be completely en*
velo^ed by the heated vapours from a fire beneath. Each pot a oomi
municates by a long arm b with a cooling condenser e for the di8till6<
sulphur, placed outside the furnace. The apparatus is generally em
ployed on rich material, or on that obtained from the eoicoroiii, but it i^
also applicable to ores which are too poor to bum in the caieartmi^
though the profit in that case must be smsJL l^he heat generated in ihi
doppione is Hkely to encourage chemical action between the snlj^u
and any lime carbonate that may chance to be present in the mineni



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NON-METALLIFEROUS MINERALS. 381

reating a farther loss of sulphur. The pots are charged and dis-
harged by openiDg the lids, which are kept luted during the distilla-
Lon. The volatilised sulphur is conducted by the cast-iron tube 6,
Qto the receptacle c, over which a small current of cold water con-
tanily flo¥rs, reducing the sulphur to a fluid condition; it then



Fig. 102.— Doppione.

ncapes into the dish d beneath, whence it can be ladled into the
inoalds. The pots last for about 300 working days, and the furnace
•ervee about the same time with a couple of repairings. The work-
man is expected to turn out 100 lb. clean sulphur from every 109 lb.
taloarone sulphur.

Calcium chloride. — The principle underlying the use of calcium
chloride is that, while raising the boiliug point of water to about
239® F., the melting point of sulphur, it is cheap, and is inert in the
presence of sulphur. The wafer to be used in the melting process is
charged with 66 per cent, of the calcium chloride, and heated to boil-
ing, in which state it is run into the vessel containing the sulphur to
he melted. No doubt the sulphur is efiBciently melted, but the very
■light difference in specific gravity between the sulphur and the as-
sociated impurities from which it had been, melted out practically
precludes any real separation taking place. Consequently the process
18 virtually a failure, as I am assured by those who have worked it.

Steam. — At the Babbit Hole mines, Humboldt county, Nevada,
advantage is taken of the liquidity of sulphur at 232° F. to use steam
at 60 to 70 lb. pressure for melting the sulphur out of the gangue.
The apparatus employed consists of a cylindrical iron vessel, about
lOJ ft. high, divided into an upper and a lower compartment, by
means of a horizontal sheet iron diaphragm perforated with ^-in.
holes. As soon as the upper compartment is charged with ore (about
2 tons)^ steam is introduced for about ^ hour, and the sulphur, liquefied
by the heat, flows down through tbe diaphragm into the lower com-
partment, kept at the proper heat by injection of steam, and escapes
by an outlet, opened at intervals into a receptacle placed outside.
When water commences to flow out with the sulphur, steam is injected



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382



ECONOMIC MINING.



at full pressure for a few minutes, to clear out as much as will
and the solid residue is afterwards removed through a door abore 1
diaphragm. Each charge requires ahout 3 hours for its treatment.
Carbon bisulphide. — Whilst hot water and steam haye no sc^ti
action upon sulphur, but merely change it from a solid to a liqi
state by the action of their heat, carbon bisulphide actually dissol
the sulphur and re-deposits it by evaporation. The plant n<



1'


— i


w




r>s^




^%


<1ni


III


^."n




FlO. 108. — SULPHUR-DISSOLTINQ PlANT.

for carrying out this process is shown in Fig. 103. It is designed o!
dimensions suitable for dealing with 20 tons raw sulphur mineralpet
diem, yielding 60 per cent pure sulphur. The 4 extracting pans a *
c d have each a capacity of 5 tons, and are made of ^in. wrought-iron
plate ; they measure 6 ft. long, 4 ft wide, and 4 ft. deen internally ;
and are fitted with a perforated bottom diaphragm, with connecting
pipes w leading to the underground solution tank /, with another set



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NON-METALLIFEROUS MINERALS. 383

>f pipes k for admittiog steam from the boiler t\ and with a third set
>f pipes I communicating with the store tank g. The still e is a
»team-jacketed *' wrought jacket " pan, 6 ft. long, 4 ft. wide, and 4 ft.
leep, with cast iron (" loam casting ") oval-shaped bottom and ends,
[ in. thick, and provided with a domenshaped lid, having an inlet
)ipe n and outlet pipe ; its capacity is 3 tons. The store tank g
neasures 10 ft. diam. by 7 ft. deep, has a capacity of 10 tons, and is
;onstracted of ^in. wrought-iron plates. The worm A is a coil of 2 in.
»ipe. The boiler t is of 20 h.p. nominal, and must be placed where it
nil be impossible for bisulphide vapours to find their way to the fire-
lole- Force pumps are required to pump the bisulphide from the
tore tank into tne extracting vats previously charged with the
alphnr mineral. When the sulphur has been completely dissolved,
he solution is run into the tank/, and thence pumped into the still e,
rhere by the application of steam in the jacket, the bisulphide is
vaporated, and passes into the store tank g for future use, while tbe
alphnr forms a deposit in the still, and is collected therefrom. When
tie extracting pans have been emptied of solution, steam is let in so
» to force any remaining bisulphide vapours into the worm for oon-
ensation and recovery, thus avoiding waste of bisulphide and con-
iquent risk of fire and explosion by ignition of its dangerous vapours,
'he bistilphide is allowed to remain all night in contact wi^ the
large. The diaphragm at the bottom of each extracting vat may
ivantageously be covered with bagging cloth to filter flocculent
atten from the bisulphide.



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384



ECONOMIC MINING.



TALC.

Under the oommon name of soapstone or talo are inclnded the wU
range of minerals chemically defined as hydrons bi-silicates of ma
nesia. In this sense talc \& a common mineral ; bat it is gene:
impregnated with other minerals, such as magnetite, dolomite,
pontine, or epidote, rendering it valueless for technical purp
Fure talc is recognised by its great softness and greasy feeling. It
highly refractory, and generedly of a somewhat flexible, tenado
character, which makes it very diflScult to crush. The different td
minerals occur in such a variety of form and approach each otharl
closely, that it is difficult to classify or define them comprehensi
Steatite, or soapstone, is the most common form. When pure it
massive, amorphous mineral, generally white, light green, or g
but sometimes blue or ro^e-coloured. Schistose modifications
common, and gradually approach rensselaerite, or typical foliated
which is comnosed of thin scales of an almost mica-like, pearly lui
toughness and tenacity. The colour is generally a silvery vrhite
gray. Agalite, or fibrous talc, is found only in a few localities. ~
following analyses give the composition of the three typical Yarii
described above : —



Loss by ignition
Silica .. ..
Alumina
Ferrous oxide
Ifagneaia




61**M
26*58



Intimately mixed with the talc are often found nodules, veins, &i
horses of anhydrous silicates, such as hornblende, bexagonite, actiD
lite, tremolite, and others. The manner in which these minerals lu
varyingly appear has given rise to the theory that the talc ws
deposited originally as hornblende, which gradually has becou
hydrated.

Steatite has for ages been used for hearthstones, cooking-pots, an
other household utensils, for which its softness and refractory natm
make it especially adapted. As French chalk it is a familiar artid
in every workshop. In the United States it was, in the early dajs <
the iron industry, largely used for refractory furnace linings, fc
bridges in puddling furnaces, <&c., instead of expensive imported fire
brick ; and up to tiiis day cupola and converter linings in Easter
steel works are frequently built of soapstone. Slabs of the sair
material are also employed to a limited extent in the building trad



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NON-METALLIFEROUS MINERALS. 385

[n powdered form, talo finds a far more extenBive employment, enter-
Dg largely into the oomposition of mineral paints as a filler, and also
18 a principal component in fire-retarding paints. In paper mann-
actare, talc is largely snpplanting the more expensive ohina clay as a
reightener and filler. The fibrous and foliated varieties have proved
specially valuable for this purpose, as of the talc added to the pulp

5 to 90 per cent, is retained in the paper, as against 30 to 35 per
ent of the china clay similarly employed. The fibrous texture of
he mineral also tends to strengthen the paper, and to do away with
be brittleness characteristic of paper weighted with clay. The name
mineral pulp," under which this talc is known to the trade, testifies
trongly to the value of this feature. For toilet powders, in soap, and
B an adulterant for many white, powdery substances, talc is also
tihsed extensively.

The fibrous variety of talc is mined in the vicinity of Qouvemeur,
few YorL The first mines were opened there about 15 years ago,
ad have reached a depth of more than 400 ft. The mineral recovered
> principally agalite, discoloured near the surface, but turning beauti-
tUy white when a depth of 30 or 40 ft is reached. It occurs in
sins, sometimeB as much as 20 ft. wide, embedded in strata of granite
id gneiss. About 51,000 tons, as nearly as can be learned, were
ined in this district in 1892, all of which was reduced to an im-
ilpable powder before leaving Gouvemeur. After being broken in
ro saccessive crushers, the rock is either run through two sets of
ihr stones, a 6ri£Bn mill, or a cyclone pulveriser, and is at last
lifihed in Alsing cylinders. For the American market it is shipped
1 60-lb. paper bags, while for export it is put up in 100-lb. canvas
cks. liie requirements are fibrous nature, freedom from grit, abso-
to fineness and uniformity of grinding, and opaque whiteness of
lonr. GouTemeur talc is sold, free on boiard in 5lew York, for about
\ to 55t. per ton of 2000 lb.

Fibrous talc is also mined and prepared near Wiehle, Fairfax
)imty, Virginia, where the mineral recovered is fully as fibrous as
e best varieties of the Gouvemeur article, but is slightly discoloured.
be deposit worked is of considerable extent, and it is expected that
e colour will improve as a greater depth is reached. Fibrous talc
nnot be sized by screening, as the particles mat and close the screen
enings. This fact explains the elaborate and expensive processes
iployed to effect a uniform reduction. The supply of this most
Jnable mineral is very limited.

The principal American centres for the soapstone industry are in

6 neignbournood of Easton and Philadelphia. On the Bushkill,
ar the former place, a number of veins are being worked. The
ineral, i«hich is of good quality, is reduced by means of crushers and
tbr stones. At Lafayette, a few miles north-west of Philadelphia,
apstone quarries of considerable importance have also long been
crated. The stone is trimmed into large slabs for various purposes,
bile the offal is disposed of to be powdered by buhr stones. The
ticle mined and prepared at Einsey, North Carolina, is noticeable
r purity and colour, and is sold almost exclusively to the drug trade,
le entire product of the various grades of talc marketed during 1892

2

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386 ECONOMIC MINING.

is estimated at about 70,000 tons, of which 61,000 tons were fihom
talc and 19,000 tons were soapstone.*

Soapstone quarries in the Behlaipahari range of Central India
have been worked by the natives for over a century- Shafts 4 ft
diam. and 40 to 60 ft. deep are sunk, and from the bottom of them
galleries are cut out in different directions following the strata of the
stone. Descending these shafts is not an easy matter, and one has to
be barefooted to do it. In some, primitive ladders made of woodes
poles, the rungs of which are lashed on with the bark of a jungk
plant, are used as a means of descent ; in others, portions of the rods
are left projecting, the ledges affording places for foothold. Soap-
stone being lubricant, the descent has to be made with the greats
care. The galleries are barely high enough in places for standing
room, and in parts one has to crawl along on all fours. Work at tbe
quarries is in full swin^ during the cold season, and has to be donebv
candle-light. In the hot weather lights will not burn satisfactoriiy
inside the quarries, and in the rains work has to be stopped to a
great extent owing to the pits getting flooded, so that in the o(^
weather work goes on night and day.

There are three different sets of workmen employed, and all an
paid by piece-work. One set works down in the pit and galleriee,
and they cut out slabs of the stone about 18 in. diam. and more or lea
circular in shape, and send them up by women and children to tbti
mouth of the shaft. Then another set of workmen with small mat*
tocks chip and cut the slabs into rough plates, the work being doD<
with astonishing rapidity and accuracy ; as soon as a number of the«6
rough- hewn plates are ready, they are sent down to the village bj
another lot of coolies. At the village a third set of artizans turn tbe
plates on lathes ; they soon assume a perfectly smooth surface, and an
then ready for the market. A very large number of plates are tomec
out daily, and are sent to Burdwan and other Bengal districts^ when
they sell for as much as a rupee apiece. The lessees of the quarnei
make very large profits by this industry. The cost of a plate, in^
eluding wages of workmen, carriers, and freight, is about 3 annas
and even looedly they sell for 4 to 5 annas each.

In China large quantities of soapstone are produced and i
chiefly in paint for both wood and stone.

* A, SaUin, < Mineial Industry,' i. 485.



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387



METALLIFEROUS MINERALS.



ALUMINIUM.

Phe distribtitioii of aluminitim in nature is very wide, rivalling that
)f iron, yet there are few minerals which serve as sources of the metal.
These are: Bauxite (Al^O^HA a limonite in which most of the iron
replaced by aluminium ; soft and granular, with 50 to 70 per cent.
dumina. Corundum (Al^Og), crystalline and very hard, sp. gr. 4,
jienerally quite pure, but too valuable for abrasive purposes to be used
is an ore. Diaspore (H^^^^), bard and crystalline, sp. gr. 8*4,
^th 64 to 85 per cent, alumina, and ordinarily quite pure. Oibbsite
TliAl^O,), stalactitic, sp. er. 2 • 4, containing, when pure, 65 per cent,
ilnmina. Aluminite or alunogen (Al^SOc + OHjCV), sp. gr. 1*66, a
inlphate of aluminium, found in large beds, chieny along the Gila
iiver in New Mexico, containing about 30 per cent, alumina, and
Mily soluble in water. Cryolite (Al^Fe., 6NaF), sp. gr. 2*9, easily
nsible— and when fused its sp. gr. is about 2— containing 40 per cent,
luminium fluoride and 60 per cent, sodium fluoride. All clays con-
un a large percentage of aluminium, but always in the state of
ilicate ; and the difficulty of removing this silica has so fjEU* prevented
be employment of clay as an ore of aluminium.

Of the ores above named the most important is bauxite, of which
here are vast deposits at Baux near Aries, in S. France ; in Ireland ;
nd in Alabama, Arkansas, the Carolinas, Georgia, Tennessee, and
Virginia. Following are average analyses of bauxite : —





AI2O,


810,


FeaO,


H,0


no.


GaOOs


liite ftom Bans, France .. ..
Rnmiah-red from BeTett, Fmnoe
(ditio from AllBBoh, Fianoe

^frtND Georgia

eddidk-lvown from Georgia


58*10
57*60
55*40
58*50
58*70


21*70
2*80
4*80
5*20
4*80


3*00
25*30
24*80

2*30
20*50


1400
10*80
11*60
30*10
13*20


3*20
3*10
3*20
3*25
2*10


tiaoe
0*40
0*20
0*30
0-45



Other analyses of bauxite from Baux, quoted as typical, differ
idely from the above and from each other, Uius : —

AlmniDa 64-24 57*4

SiUca 6-29 2*8

Iron oxide 2*40 25*5

Lime oarbonate *55 *4

Magneda "38

80& JiO

PotMh '46

Tituiiimi oxide 3*1

Water 26-74 10*8

100*26 10000

2 C 2

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388 ECONOMIC MINING.

The mineral from the mines of the Irish Hill Co., in Irekn^
carries 44-64 per cent, alnmina and 1*16 per cent. iron. About 10,00
tons yearly of banxite are mined in the United Kingdom (chiefl
Ireland), valued at about 6«. a ton.
. The Arkansas deposits are said to cover a large area, and to
a thickness of 40 ft., forming an interbedded mass in fei
Tertiary sandstone.

The Alabama deposits are better known, and all oocnr in
lower part of the Lower Silurian formation; the district has 1
badly broken up by sharp folds and great thrust faults; and
mineral occurs as pockets in close association with brown iron
(limonite) and clay. In Cherokee County the deposits appear to
along two parallel lines of outcrop, that run in a general north'
and south-west direction, and are 150 to 200 yd. apart, following th
crest of two sharp anticlinal folds. In places the bauxite oveniee
white or yellow sandstone, for the most part iriable, but sometuxi
hard and cherty, and underlies an unctuous clay in the upper part
which the brown ore occurs. At one end the bauxite eJiowb as
irregular seam 60 ft. thick. An excavation about 75 ft deep has
made. To the south-east of Dike's bank, the mineral occurs in
irregular seams, separated in places by a band of unctuous day 15
thick, but cutting out to a mere selvage. The upper seam is afc
30 ft. thick, the lower 20 ft. To the north-east of Dike's bank
deposit has been tested to a depth of 20 ft, and is still good. Half
mile farther toward the north-east is the Warwhoop deposit, tei
for 20 ft. and still good. There is no reasonable doubt of the exi
of the bauxite deposits in this district ; they have been tested c
two miles, and have not been found less than 15 ft. thick, and
places 20 to 80 ft. The average composition of the Cherokee Coa
bauxite, as per car-load sample, is as follows : alumina, 56 to 60
cent; oxide of iron, 2*75 per cent; insoluble silicious matter, 7
cent. ; titanic acid, 2 to 3 per cent ; water, 25 to 30 per cent

Bauxite for the manufacture of alumina is worth about 2J. a td
It* has to undergo purification for the purposes of the aluminiui
manufacturer. Several methods are used : —

(1) It is chosen as free from iron as possible, and is roasted at
low red heat, and afterwards treated with sulphuric add, which coi
bines with the alumina present, forming sulphate of alumina,
is readily dissolved by water, leaving the great bulk of silica and
behind. The solution of sulphate of alumina is allowed to settle,
supernatant liquid is siphoned off into an evaporating tank
evaporated to dryness. The dry sulphate of alumina is calcined at
red heat, driving off the sulphuric acid, leaving as a residue anhydnn
alumina.

(2) It is treated, either by fusing it with carbonate of soda as
dissolving in w^ter, or by boiling it with a strong solution of canstj
soda. In either case a solution of sodium aluminate is obtainc]
which is filtered from the residue of silica and ferric oxide,
decomposed into aluminium hydrate and carbonate of soda by pnm
carbonic acid gas through it. After a thorough washing, the h; '
is calcined at a high heat and the resulting alumina is finely



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METALLIFEROUS MINERALS. 389

THe ore next in importance, and which long ranked as the fore-
most, is cryolite, of which there is practically only one prodnctive
mine, that at Ivigtnt, South Greenland. The mine is worked as a
quarry, and has been opened 450 ft. long, 150 ft. wide, and 100 ft.
deep, while diamond drills have proved the permanence of the ore for
a farther depth of 150 ft. The stone broken in the mine is loaded on
cars of 5 tons capacity, which are drawn np an incline by means of
an endless chain. At the surface the mineral is sorted and piled in
heaps between the mine and the shore. In preparing the mineral for
shipment, the large masses of impurities^ which amount in all to
aboQt 20 per cent, of the rock broken, are thrown away, and also the
6ne particles of the mineral, as only the large pieces are shipped.
The contract requires that 90 per cent, of the material shipped shall
he cryolite, and in bringing it to this state of purity about 2000 tons
are lost annually. The vein appears to widen with depth, but the
quality of the mineral becomes inferior. In order to support the
wulls, pillars of cryolite 8 ft. diam. are allowed to stand at intervals
>f 30 ft. When the mine is closed for the winter, salt water is run
n from the Arsuk Fiord until the pit is filled to about one-third its
iepth, so that it is necessary to un water it at the beginning of opera-
tions every spring. About 10,000 tons annually are shipped to the
[Jnited States, valued at about 11. 10«. a ton.

While the older processes of aluminium manufacture dependent on
he reduction of the double chloride of aluminium and sodium, must
iways have an academic interest, they have been beaten out of the
ield of commercial industry by the newer electrolytic methods, which
&tter therefore alone demand description here. There are four
varieties of the electrolytic process. In England and America,
k»wlee' and Hall's patents are followed ; on the Continent, Heroult's
nd Minet's. They are all virtually modifications of the original
)eville-Bunsen process, maintaining fusion by the heat of the electric
orrent.

The experience gained at the Lockport, New York, works with
he Cowles process led to some innovations in the more recent English
rorks at iklilton, Staffordshire, notably in increasing the dynamo to a
apacity of 5000 to 6000 amperes with an E.M.F. of 50 to 60 volts,
od in enlarging the furnaces At Milton, the current from the
ynamo is led by the copper bars to an enormous cut-out calculated to
3fie at 8000 amperes, and consisting of a framework carrying 12 lead
latea, each 8^ in. by -^^ in. thick. From this it passes into the
imace rooms. A current indicator is inserted in the circuit, consist-
ag of a solenoid of nine turns. (This was cut out of a cylinder of
\bX copper by means of a parting tool in a screw-cutting lathe.) In
ie solenoid is an iron core suspended by a spring. The movement of
lis is communicated to two pointers, one dial being placed in the
Qgine room and the other in the furnace room. The range of the
idicator is such that the entire circle of 360^=8000 amperes.

There are two furnace rooms, each containing 6 famaces. The
rst room contains the bronze furnaces, in which is carried on the
lannfacture of aluminium copper and silicon copper. The second is
eYoted to the production of ferro-aluminium. The furnaces are



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390 ECONOMIC MINING.

rectangular in form, built of fire-brick, the internal dimensionfl being
60 in. by 20 in. by 86 in. Into each end is built a cast-iron tabe,
through i^hioh the carbon electrodes enter the furnace.



Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 43 of 76)