Charles George Warnford Lock.

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

. (page 56 of 76)
Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 56 of 76)
Font size
QR-code for this ebook

(400,000 to 500,000 tons yearly) ; Chateaugay and HammondviUe an
nextt Similar lenticular beds occur in the Archsoan gneiss ad
crystalline limestone in New York, New Jersey, and Pennsylvasia
and are more regularly distributed. The Tilly Foster mine is typical
and important. The Chaffee county, Colorado, lenses are in syenite
(Silurian age") ; the ores average 57 per cent, iron, • 1-2 sulphur, an^
only -009 pnosphorus. Immense beds of soft magnetite occnr a<
Cornwall, Pennsylvania, associated with green slates, Cambrian lime-
♦ H. V. Winchell. f J. F. Kemp, • Ore Deposita.'

Digitized by



itones, and Triassio sandstones, pierced by dykes of Triassio diabase.
The ore is mined in enormons quantities by open cuts. In Iron
ionnty, Utah, are beds of magnetite and hematite bearing evidence
^f being metamorphosed limonite, in limestones of questionable
iilarian age, and associated with eruptive rocks described as trachyte.
Che limestones have been much upturned, metamorphosed, and pierced
»y dykes and eruptive masses. The ore forms great projecting ridges
nd prominent outcrops, locally called "blow-outs," of the usual
^Dtioular shape. Magnetite sands are concentrated on many sea-
eaches, but uie proportion of titanic acid generally present is a bar

3 their use on account of its destructive action on the furnace linings.

Limonites, in their simplest form as bog iron, are not often prac^
ically available, on account of low percentage in iron Tdue to sand
ad silt washed in) and frequent large amounts of sulphur (pyrite)
ad phosphoros (Vivianite). Sometimes much chromium is present,
rben the ore has oeen formed by leaching serpentine. Beds resulting
rem basalt occur in Ireland and Hesse. An oolite or limonite sand
)rm8 in some Swedish lakes at the rate of about 1 ft. in 20 years,
blorado limonites are found in cavities in Silurian limestone, and are
sed as flux in lead smelting, while a similar use is made of limonites
jcountered in Carboniferous limestones in Utah. Sometimes (in
[assaohusetts, <&c.) limonite forms geodes, or ** pots," pipes, stalactitio
lasses, cellular aggregates, and smaller lumps, from which the barren
ays and ochres can be removed by washing. The ore is but a
action of the material mined, occurring in irregular streaks through
le clays, &c., and is mostly obtained by stripping and open cuts,
imonites are commonly formed by the weathering of ferruginous
nestones. They are not generally Bessemer ores.

Siderite or spathic iron ore often contains more or less calcium,
agnedum, and manganese. When concretionary, embedded in
tales, and containing much clay, the ore is called *' clay ironstone ;"
hen the concretions enlarge and coalesce, so as to form beds of
[nited extent, generally containing much bituminous matter, they
e called " black-band," and are chiefly developed in connection with
cal seams ; when in beds, it is sometimes called '* flagstone " ore %
hen broken into rectangular masses by joints, " block " ore. The
-called ** ferriferous " limestone of Pennsylvania aflbrds beds of car-
mate known as *' buhrstone" ore, which is largely altered to limonite
a common feature with siderites. They are especially found in the
urboniferous, sometimes in Jura-Trias, and rarely in Cretaceoua

The Ouban iron ore deposits, found in the Sierra Maestra range, are
le of the most important groups of Bessemer iron mines in the world,
id are operated by Philadelphia smelters. The oto can be mined
ith great facility by open cuts. Analyses show 67^ per cent, iron,

4 silica, *026 sulphur, and '014 phosphorus, on delivered cargoes.
Pyrite beds are not valuable for their iron in a crude state, as the

Iphur must flrst be removed. This is usually done in sulphuric
id works, by which the sulphur is utilised. The " cinders " are
terwards available for iron-making or for mineral paints.
Of importance in connection with iron ore deposits are the recent

2 K

Digitized by VjOOQIC


fitndies * of the distribution of phosplionis along certain (^ isoebeauc"
lines in the beds, by a knowledge of which it is possible to ka^ iboi
valuable Bessemer ore distinct Irom less yaluable.

CcfneenkraHim. — The enrichment of iron ores is aocxnnpliahed \
washing, screening, and jig^g, to remove clay, sand, and simili
impurities ; roasting, to eliminate water, sulphur, and carbonic acid
and magnetic concentration.

Dry screening to remove an excess of earthy matter and aaad Im
given fair results in cases where the ore has simply been mixed wit
these constituents ; but it causes a waste of the very fine ore, and i
material useful for pain^making, while it leaves both stones an
scoria behind, and unless the ore averages 45-47 per cent, metolii
iron in the first instance, there is much difficulty in getting it up \
the necessary 50.

Another system has been adopted for removing the aand fira
somewhat adhesive furnace ores, though it causes the loss of a
under 2*75 mm. in size, and any greasy metaL The apparatus coi
sists of a cylinder of boiler plate 12-16 ft. long, having an xntenu
angle iron screw to carry the ore forward as it is scoured. At the «
of the barrel a hood is fixed, the circumferential edge of whidi i
composed of perforated steel plate, through which the finer portioi
of the mass escape, and the large parts, which consist of comparative

Sure ore, is lifted by buckets and pitched on to a tron^ whic
clivers it into wagons. Water and crude ore are put into the bac
end of the barrel, which works on friction rollers, the barrel revohio
at about 100 ft per minute. Some 10-12 tons of crude ore per hoi
can be dressed in this manner, but the waste is great, and is general]
composed of that portion of the ore which is richest in metallic iroi
EeaUy this hooded cylinder is only fitted for the removal of Bilk
when it is in the form of sand, and of such matters as will be broke
up and removed by the water. Stones, scoria and other wa«te t<:
large to pass through the perforated hood, and which cannot be see
by the pickers in the wagons, will of necessity remain, and whei
gravel and pebbles are anyway abundant, the sample of dressed oi
will be poor.

Aluminous ores can be treated by the wet process, and vnll gii
two products, one of which is very rich in metallic iron for blai
furnace or annealing (puddling) purposes ; the other, which consist
of aluminous earth and a proportion of iron ore, being fit for pain
making. Magnetite can also be treated by the wet prooees, but whei
ores are already magnetic, or can be made magnetic by roastini
magnetic concentration is a cheaper and better way of handling thei
In the Green and Kennedy arrangement, the cmae ore is passed inl
a revolving barrel or cylinder placed at an angle, and having an angl
iron screw or worm along its length to propel the ore forward. Aboi
3 ft. of the upper end has perforations \ in. diam. through whidi A
finer parts escape, and are carried to the revolving sizing screens vm
'water classifiers, which deliver the fine ore to jigs and buddies whei
it is separated and cleaned. The large ore from the barrel is tak^i o
to a talile which swings to and fro with a jerking motion, and whil

♦ D. H. Browne.

Digitized by



m thiB table it is hand-pioked to temove all waste and rubbish as far
18 pofldble. The whole of the concentrated ore is then delivered into
vasons or hoppers. Clay is sent to a disintegrator. The cost of
lealiDg with the ore is high, and even with a free sandy ore too many
lands are needed to secure the greatest economy. However, these
>Iant8 have raised crude ore from 35 per cent, to 51 per cent, metallio
ron with a corresponding loss in silicious insolubles. With an
Terage analysis of 36*90 per cent, metallic iron, 39-03 silicious
DBoliU)les, and 7*94 moisture, in the crude ores, an average result in
he concentrate when treating over 11,350 tons of crude ore, was 51 * 11
letallic iron, 20*31 insolubles, and 3*65 moisture. The highest
oesible result to be had with the ore treated would be 54* 10 per cent,
letallic iron, 19*24 insolubles, and 1 *30 moisture, this 1)eing obtained
rom especially selected hand-picked samples. The loss in bulk of
rode ore was practically 43*32 per cent. The average amount of
re treated was 360 tons per week of 48 hours, and the cost of treat-
lent was just over 8J. per ton.*

At the Champion mine, Marquette, hand sorting is so e£fectually
arformed that 4 grades are obtained, giving respectively 66 j^
er cent, and upwards, 63J«66i, 60-63J^, and 57-60. With wages
ding at 7«. a day, and a man's average capability being 7 tons crude,
le cost for labour is Is. 7d. a ton on the 5 tons selected.

In all systems of concentration, the comminution and sizing of the
aterial to be treated are of primary importance ; the degree of fin^
S8 to which an ore will be crushed for separation, and the special
achinerv employed, is affected by (a) the size of the grains or
ystals in the crude ore; (6) the foreign matter which is to be
iminated, and its physical condition ; (c) the purpose for which the
ncentrate is to be used ; (di) the condition of the ore and the method
aployed for separation. If the ore to be treated is a magnetite with
rge crystals, or if the object of separation is to remove silicious
aterial only, a coarser sizing can be employed than in other cases ;
r practically, complete elimination of silica is not at present essen-
kl, and in some ores a e^ystem of mechanical sorting or cobbing,
toting pieces from fist to walnut size, may be practicable. If, hew-
er, the ore is dense, and the crystallisation or granulation fine, or if
atite is to be removed, the reduction, of size must be carried further,
as to separate, as far as practicable, each particle of magnetite from
e other materials. In dephosphorisation by mechanical means a
w hundredths of 1 per cent, phosphorus will determine whether the
3 will be in or outside the Bessemer limit, and hence influence its
mmercial value. The extent to which an ore is to be crushed will
o be influenced by the demand for certain sizes or by the objection
others. The condition of the crude ore will materially influence
9 machinery to be employed, a dry or a thoroughly wet ore beinff
der to manage than one which is damp or partially saturated with
dstnre. The problem, therefore, is to be determined specially for
di ore to be treated.f

At the mines of the Ghateaugay Co., New York, the ore, a mag-
tite containing 30-40 per cent, iron, mixed with fragments of
* W. J. May. t See Mpynard and Kunhardt, in School Bfinea Qly^ is. 2.

2 K 2^

Digitized by VjOOQIC


quartz, felspar, hornblende, mioa and trap is oonoentrated in a modified
Conkling jig. It is first crushed to 2 m. or less by two large Blake
crushers. The material from these crushers passes by a shute lined
with screens, having holes f in. diam., to a seoond set of 4 crashers,
set so ns to close to 1 in. The product from this set of cnishen,
together with that which passes through the screens in the shute, is
then taken by an elerator to the top of the mill, and passed throui^ a
revolving screen perforated with 4-in. holes. The ore which pt»ei
through the screen goes to the jig-hoppers ; that which passes ors
goes to a third set of 6 crushers, set *to jT in. These are of the Blake
multiple-jaw pattern, having 8 jaws. The product from these third
crushers is again screened through a double revolving screen haTing
holes \ in. diam. That which passes through goes to hoppers ; what
passes over goes to a fourth set of crushers. These are of the Blake
multiple-jaw pattern, having 6 jaws, set so as to dose to ^ in. The
product from these last crushers is again screened, and the grains
which are still too large pass again through the final crashers. All
the material which passes through the ^-in. holes goes to the jip
without further sizing. The ore is crushed dry, and goes to the ji^
in that state. The jig has a capacity of treating 5 tons of ore per
hour, requiring 135 geJ. water per minute, or 1620 gal. per ton treated.
One man or boy is sufficient to attend- to two jiss, his duty beiog to
see that the jig is properly supplied with material to secure a unifom
depth on the screen ; that the wa
(a depth of ^-f in, over the oolla
oentrates are free from gangue.
product, the attendant lete out a 1
to the lever-beam, to make the i
tailings amounts to 23 per cent.,
ore or '^slimes," and small parti
pieces of gangue. The causes c
follows •—-(<») the fine ore, almost
on the surface of the water ; (6) t
than the gangue ; hence, without
ence in the falling-time between
produce a good separation, and i
into the teilings ; (c) the materia
the ore from the gangue,*

The various inventions for sep
be grouped under two general he
nent magnete ; (6) those which h
of electricity passed through mag
may again be classified into such
which pass under or over, or whi
which consist of magnetic rolls <
their surface or revolving over tl
influence draw the magnetic porti
trajectory so as to separate it frc
bo further subdivided into those
which immerse the material for c

• F. 8

Digitized by VjOOQIC


While in some oi'es satisfactory and economical concentration is
possible, in others the ph^^sical structure and the magnetic properties
>f some of the impurities may interfere so as to reduce or even out-
i^eigh the advantages.

Ferriferous sands have been concentrated by passing the material
between rolls, the adjacent portions of iwhich were in a magnetic
Seld, while the opposite parts were without this field. The iron rolls
'eyolved on journals carried on insulated standards wound with
»pper wire. By connecting these wires with a battery (latterly with
Ijnamos) the standards became electro-magnetic, of opposite polarity,
iDd the rolls were charged thereby, making a magnetic field between
ihe rolls. The ore being fed on the rolls, whidb revolved towards
sach other, was carried around the magnetic portion, adhering until
t passed beyond the magnetic influence, while the non-magnetic
articles fell between the rolls. The Buchanan machine, Fig. 142,

Flo. 142.— Maonetio Skpabatob : Fio. 143.— Magnetic SbpaKator r

Buchanan's. Wenstb^m's.

^as of this type : a, feed hopper ; 6, rolls ; c, magnet ; d, concentrates ;

tailings. It has been used in America and New Zealand for beach
mds; and at the Croton mines. New York, it treated magnetite
ushed to 16-mesh, bringing the iron from 31-38 to 62^64^ per
•nt-, and leaving 4-^-13 per cent, in the tailings, as against plunger
gs which lost 14-22 per cent.

The WenstrTim machine, Fig. 143, has a stationary field magnet
id. an armature barrel consisting of a number of soft iron bars,
'parated from one another by a non-magnetic material—in this case
ripe of wood. The whole is bound together by non-magnetic end
ngs. The bars are cut away alternately on the inside to make one
&r project only towards the north poles of the magnet and the next
ilyto the south poles. This gives each succeeding bar opposite
ametism. On each of the 4 sections of the magnet are wound
> lb. of copper wire. An Edison dynamo furnishes a current of
) amperes and 33 volts. The ore is fed to the barrel by means of

hopper, the cylinder turning in the direction of the arrow. The

Digitized by




magnetite adheres to the bars of the barrel and is carried paat tli
first delivery shoot a, where the tailings fall, until, on passiiig beynn
the influence of the magnet c it drops off at h. In Sweden, thee
separators are used at the iron mines for extracting from old and nei
dumps of waste material the good ore which has been missed in hand
picking, or was too fine to be picked out in that way. They are als
applied to the ore now being mined, which in former timaa wi
selected by hand. The larger of the two sizes made treats 6—7 t<ni
of matenal per hour, and the magnetism is strong enough to snppoc
pieces of ore up to 7 lb. in weight, and separate them from the ro^
The smaller size treats 2-3 tons per hour of finer material, bekn

Lib. in weight of single pieces. The cost of hand-pickiiig a
innemora, previous to the introduction of this machine, was 1& i^
per ton. It now costs hd.. per ton, and 30 per cent, more ore i
obtained from the same material ; the separated ore averages 59 pe
cent, iron for the coarse, and 45 per cent, for the fine. Besult
obtained in America are : —


Beach Glenn
Port Henry

Crude Ore.









15- 10



The principles of the Conkling separator are shown in Fig. 144
The ore is fed from a hopper a on a belt and carried along under i
series of belts, running at right angles to the first. These oroes belt
pass between the magnets h and the ore lying on the distributing belt
and may be placed at varying distances from the latter. As the ore
reduced to the proper size, passes along on the distributing belt» thi

M jgi B

Fio. 144.— Maqmbtio Separator: GoNKLraG^s.

magnetic Ijelts, which may be influenced by magnets of differeiit
powers, pick up and carry to one side the magnetic particles of th«
ore, while the non-magnetic portion of the gangue is carried off at &
It is used on the waste dump material at the Tilly Foster mine*
New York, where the metal is so widely and finely disseminalsd
through the ore that it has been necessary to resort to fine crodbing.

Digitized by VjOOQIC


riiiB (water being used in the separation) increases the proportion of
(limes, which carry off mechanically small particles of mineral.
•*mally, Uie lean character of the ore calls for the handling and
onveying from the mill of a large bulk of tailings. The process
nclndes crushing tiie ore by a Blake rook-breaker on the dump;
emoving it in train*loads to uie bins in the mill ; passing it under two
tall stamps, provided with screens of iV^^* mesh ; elevating it to the
/onkling electrical sepfirating belts ; and delivering the concentrates
» the cars and the tuUngs to 4he settling reservoirs. The following
asults were obtained in 1890 : * —

Ore used per month • .. .. 8009 tons

CoDoentrates made 1039 „

1 ton of concentrate firom 2*89 „

Cost of labour per ton ooncentmteft 5«.

Total cost per ton concentrates 9«.

Iron in crude ore 27*39 per .Cent.

Iron in concentrates 49*14 „

Iron In tailings 10*21 „

Unless under exceptional conditions it will not pay to treat waste
imp material carrying lees than 25 per cent. iron.

The Edison unipolar non-oontact separator differs from the forms
iscribed in that all parts of the apparatus are fixed. It consists simply
a hopper, a magnet, and a partition to separate the concentrates and
i lings into different receptacles. The ore, properly crushed and
ced, is placed in hoppers, from which its discharge is controlled by
irs closing slots which extend the length of the hopper. These slots
d made adjustable to suit the size of the ore. The magnet is a mass
iron 6 feet long by 30 in. wide and 10 in. thick, weighing 3400 lb.,
d wound with 450 lb. of copper wire, the coil being connected with
lynamo consuming 2^ h.p. and requiring a current of electricity of

amperes and an electromotive force of 116*5 volts. I'he material
ling from the hopper passes the face of the magnet, but does not
sch it. . The distance of the magnet from the vertical plane of the
ling material is so chosen that its attraction causes the magnetic

separate from the non-magnetic particles sufficiently to alter
dr direction. By reason of the force of gravity, this deflection of
5 trajectory, while sufficient to draw the magnetic particles away
m the non-magnetic, does not draw them against the magnet, but
mid any ore accumulate on the magnet it can be instantly dropped
breaking the current. The exact distance, however, is maintained
that none can stick to the magnet. Owing to the altered trajectory^
) magnetic ore falls upon one side of the partition, while the gangue
terial drops upon the opposite side. An intermediate grade called
iu|pirump " (mixed concentrates and tailings) may be returned to
t hoppers or passed before a second magnet. A series of magnets may
arranged so that the concentrates, mugwumps, or tails are each
jjected to repeated magnetic influence. With a hopper 6 ft. wide,
1 arranging the slot to pass readily ore crushed to pass a 10-mesh
Mil* each side of the magnet will separate conveniently about
\ tons of material daily, making the capacity of the two-face machine
\ Vamm a day.

» F. H. McDowell.

Digitized by



Magnetic oonoentration has attained a high state of efficieiiCT * «
the Groton mines. New York, where the presence of 2 per cent, sn^ba
demands economic roasting. This is acMeved in the Davis-Colbj fn
nace, using 3*6 gal. oil fuel per ton of raw ore, at a cost of 1||^. p«
gal., labour costing Ij^. The average roasting tempemtnTB i
1250^ F. The roasted ore is ground to 12 mesh in Sturtevant miDi
entering them at about 350^ F., having been cooled by a water bat
during conveyance.

Under these conditions liie ore is quite friable, and there is n
difficulty in grinding 22 tons per hour with the 20-in. mill, and 16 ton
in the same time witJi the 15-in. milL One set of Sturtev&nt mi
bushings will grind 4000 to 6000 tons of ore, according to the dept
of the chill in &e bushing, the cost of each set being 32. The screei
blocks for this amount of ore cost 2Z. This is less than one-half tli
cost of renewal on any other machine formerly used. At 22 tcms p<
hour the 20-in. mill required 94 h.p. to drive it ; but the product j
finished. The 15-in. mill requires 70 h.p. The ground ore is elevate
from the discharging nozzles of liie Sturtevant mills to the seven
screens, covered with slotted steel plates ; slots are ^ by j^ in. in son
plates, and -j^^ by f in others. The slotted plates are easily remove<
and when the requirements are exacting as to phosphorus, ^ mesh i
used on two of five screens. Two sizes of screen plateSy mree eej
coarse and two sets fine, will prepare ore containing * 426 phoephon
for a separation having *036, with two passes on the noagneti
separators. Ordinarily, the phosphorus in the Croton ore runs froa
* 1 to * 3 ; when higher than * 6, three sizes of screen platee should \
used, delivering to three receiving bins, and each size snould be treata
separately on the magnetic separators. Using 18-mesh acreens, an
with ore prepared for this grade, will produce continuously, with tv^
passes, concentrates showing 70' 6 metallic iron, *018 phosphorus, aii
*22 sulphur. The latest Hoffman separator, using 12-meBh hcrcei
and making two passes, produces concentrates showiuK 70*93nietallj
iron, '017 phosphorus, and *231 sulphur; 18-meui screens giv
71 per cent, concentrates with one pass on this machine, whic^ j
illustrated in Fie. 145. In operation the material fed upon the b^
is carried along by the latter to the field of the magnet a, where tli
particles, subject to magnetic influence, are attracted toward th
nearest pole and at the same time are carried along by the belt pti
the succession of opposite poles. As the particles pass the sucoeesit

rles of the magnet they do not follow the line parallel with the be!
, but assume positions, under the influence of the magnetic lines o
force, which are in the forms of curves from the end of one pole to ^
end of the nearest pole of opposite polarity. By following these curve
and at the same time being moved along by the belt, the material t^
be separated assumes a rising and falling or wave-like motion, whic)
causes an expulsion of the slightly magnetic or non-magnetic matem
and that of lea^t specific gravity toward the top of the mass on tb(
belt, and results finally in a stratification of the substance to V
separated, the most magnetic and heaviest portions being broogbl
closest to the belt, and the lighter and non-magnetic or slightij

• W. H. Hoffman.

Digitized by



magnetic particles farthest from the belt^ The particles forming the
upper stratum will, under the horizontal motion imparted to them by
the belt, leave the magnetic stratum in a trajectory as the belt begins
to follow around the' periphery of the drum c, and will be assisted in

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 56 of 76)