Charles George Warnford Lock.

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

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easing operations, when the water used for driving machinery is
placed by steam.

Under ground the ore is separated from absolutely barren gangue
id wall rock. Arrived on the surface, it begins its course of treat-
ent in the second storey of the breaker house, where it is dumped

bar grates, which separate it into two classes, above and below

mm. The fine stuff drops through the grates into a revolving

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522 ECONOMIC MINING.

Boreen, where it is screened wet. The coarser particles remainipg en
the grates are pnshed down an incline into the feeder of a ^ab
crusher, and broken to the required size of 64 mm. and under, aa
fall into a revolving screen to be screened dry. These screens ^yn^
the ore into two sizes— above and below 32 mm. All the larger m
is taken to the picking houBes. The ore from the breaker screens i
kept separate ft-om that from the grate screens throughout tiiet
operations. The products of the first picking are : — (a) crushing or
containing coarse particles of galena; (6) stamping ore oontainiiij
finelj-disseminated grains of galena; (c) copper pyrites; (J^ ira
pyrites ; (c) zincblende ; (/) marcasite ; {g) barren gangue and w«I
rock. Of those, the pyrites and marcasite aie turned over to coppe
and iron smeltine establishments, also belonging to the G(ovemmeo<
while the zincblende is disposed of in open market.

The now partly purified ore, of 32 mm. and under, deeoenda to tli
coarse separating house on the fourth level, where it is parted in th
wet way into 8 sizes; the largest, over 17*78 mm., is once moP
picked over in the second picking house on the same floor, when tk
same products are obtained as in the first picking. The other sin
resulting from the coarse drums are: — 17 -78 mm., over 13*44 mm
and under 17*78 mm., over 10*00 mm. and under 13*44 mm., ove
7*60 mm. and under 10*00 mm., over 6*62 mm. and under 7 '60 mm.
over 4-22 mm. and under 5*62 mm. These 6 sizes are nexttietta
on coarse jiggers. The particles less than 4*22 mm. go throaghtbi
holes of the last screen of each set, and are caught in a funnel Tb^
turbid water, carrying with it particles of ore under 1 mm. in siia
flows ofl" to a settling box, from where the fine sands are taken to th^
auxiliary washing house, while the coarser sizes up to 4*22 mm. aij
drawn ofl' from the funnels to a series of fine sizing drums, whid
produce the following 7 classes: — 4*22 mm., over 3*16 mm. and imd«
4*22 mm., over 2*37 mm. and under 3*16 mm., over 1*78 mm. anj
under 2*37 mm., over 1*33 mm. and under 1*78 mm., over 1*00 mm
and under 1 * 33 mm., and material of 1 mm. and smaller, which i
caught in a funnel below the last screen of each series. The samj
sizes are also obtained in the middle and fine crushing house, wher
the products of coarse ji^ng are crushed and sized. The sizes fron
4*22 to 1 mm. are next treated on fine jiggers. The intermedia^
products from these and the stamp ore resulting from the difieresi
pickings are taken to the stamp mill for further treatment Tb
slime produced by the stamp battery is conducted through a clasiS
cation apparatus, consisting of a number of boxes of increasbg sid
in which the particles are deposited according to gravity. Tb
water flows from the last box through a settler, where it deponts it
fine slimes. The sand is drawn off from the boxes, jigged, if neoesstfj
rejigged, and huddled. The turbid water from eawon set of ji^i^
runs through an adjoining labyrinth, having a circulation of 2d-4o ■
where the slimes carried by it in suspension are deposited into clei
ing tanks outside. The slimes in the settlers are conveyed by met
of a rising stream of water to the upper one of two overU
buddies, on which piire slime and enriched sand is obtained,
latter is passed on to the lower huddle. The remaining intermedil

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METALLIFEROUS MINERALS. 523

trodncts of the sand jiggers are treated on tables, and the slimes are
rom time to time removed from the pits and labyrinths, and bnddled.
rhe slimes from the settlers attached to the coarse separating and
rushing honses are dressed in a similar manner and on similar appa-
atTis in the auxiliary washing house. It is one of the characteristics
f the method adopted in these works that the jigging and sizing are
arried out to the extreme limit, and that all puritied ore is obtained
">°^ jigg^rs^ buddies, and tables, and none by hand picking.

The machinery in use is in no way peculiar. The coarse crushing
oils are set 18 mm. apart, and make 24 rev. a minute, having a
apocity of 5-7^ tons per hour and pair. The middle and fine crush-
t)g roUa are set to 6 and 2 mm., respectively, have a capacity of
i-3 tons per hour and pair, and 60 rev. a minute. The sizing
pparatus consists of revolving screen drums of perforated sheet iron ;
hose having holes of 1 mm. are of sheet copper. Those used for
rashing and sizing grate smalls are conical in shape, with horizontal
xes, about 9 ft. long and 2 ft. 8 in. to 3 ft. 6 in. diam., and have
2 mm. perforations. Their capacity is 2^3^ tons an hour, and they
lake 12 rev. a minute. Those used for breaker smalls correspond,
iccpt in length, which is 6 ft. The screens, with perforations from
7 '78 to 4*22 mm., have the same length, but vary in diameter; the
irger being 3 ft. and smaller 2 ft. These drums make 12 rev. a
linute, and have a capacity of 3^5^ tons per set of 3. The drums
)rfine sizing, that is, those having holes 3*16-1 mm., respectively,
re arranged in sets of 5, having about the same capacity as the last,
hey make the same number of revolutions, and are 6 ft. long by
-2 J ft diam. The jiggers are continuously working, have stationary
eves, and receive their jigging action itoxa the upward impulse,
iven by a succession of strong jets of water, to the ore placed on
lem, produced by pistons, one for each jigger, placed in a compart-
lent behind the one in which the sieve is fixed, separated on top, but
)Dnecting below. The buddies are arranged in sets of 3 ; 2 are fitted on
le shaft, and the third on a separate one. The uppermost is concave,
id about 9 ft. 10 in. diam. ; the next, convex, and 12 ft diam ; the
west, on a separate shaft, is also convex and about 14 ft. 9 in. diam.

The Laurenberg works,* on the Lahn, Nassau, treat a very mixed
■e — galena, blende (the black variety predominates over all other
•es), spathic iron ore, grey copper, copper pyrites and a small amount
' iron pyrites. Culling is done dry and on the ground, three classes
jing selected : blendiferous, ealeniferous and spathic ores (i.e. those
intaining a large amount of siderite), and each kind is subsequently
eated separately in the concentrator. The ore selected is run down
I cars by gravity to top of concentrator building. The wash dirt is
slivered to a screen with holes, 35 mm., 16 mm., and 8 mm., and the
Arsest is delivered to and picked on a round culling table, while the
> mm. and 8 mm. go to the 3- or 4-oompartment jigs. They are
iven by eccentrics, and discharge through vents on one side of the
TL (the newest style have no vents). Fine sand jigs of the usual
rm are used, and rotary and Rittinger tables. The latter do not
ve satisfEiction, while the rotary tables, with the modifications made
♦ J. W. Meier, En. and Min. Jl.



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524 ECONOMIC MINING.

by Sohranz, the mill saperintendent, are doing welL One of diese
modificatioDB is to run the pulp on to the table at two points, and to
finish washing when the ore has travelled half-way round. The table
thus does double the amount of work. Another modification is to
have sprinklers delivering water in a very thin sheet. To a Itfge
sprinkler pipe is attached a sheet-iron skid, against which the water
is thrown from numerous nozzles, and runs down from it on to tk
surface of the table in a thin sheet. The rotaries have a covering of hard
cement 2 in. thick, held around the periphery by a wrought-ironband.
The floor on which this cement is laid has iron beams to sapport it
These tables furnish clean lead and clean blende. Salzburg tables are
used very extensively. They produce clean galena, and blende witi
only 2-3 per cent. lead. For crushing wash dirt and middlings the
mill has a modification of the Blake crusher invented by Schrau,
rolls, and Schranz mills. The total output of the works per month L«
606 tons (2000 lb.), blende with 38 per cent, zinc, and 165 tons galeni
with 66-75 per cent, lead, and containing on an average 32 os. silver
per ton. Tailings of this mill at present carry '3- '4 per cent le»d
and 7 per cent, blende ; the work may therefore be called very good
At the Werlau mill* in the same district, the ores are argentiferoos
galena, blende, copper pyrites, iron pyrites and siderite, but no grey
copper ; the gangue is quartzose and slaty. The coarse ore is delivered
to a Blake crusher. The screen has large square holes in the bottom;
a sprinkling pipe supplies water, and the ore falls through on to a
culling table, where tbe crushed ore is also delivered. Culling is dosi?
by 2 boys, who throw the waste into a central opening, and pnt dean
blende and galena into boxes ; a scraper deflects all the re m aining ore
into a large screen, with holes of several sizes (3, 8, and 14 mm.),atti
the rejections over 14 mm. diam. pass to a second culling table, attwideJ
by 6 or more boys, at 9cJ. a day. A scraper clears this revolving taUe,
and passes the ore to rolls, whence it goes to a long screen wiih 8, 4,
5, and 6 mm. holes. Eejections pass to other rolls, until evoythii^
traverses 3 mm., when it goes to pyramidal boxes. All the jigs dit-
charge through the bed (punched boiler plates or sheet iron, witii
square holes 2 mm. larger than the ore being jigged), by wbidiiti*
said the beds never foul, and more rapid and clear discharge is aecorai
There has always been difficulty in getting clean blende fitom thf
slimes. The most recent apparatus employed consists of Lnhii|
vanners and Salzburg tables. The blende from the Ltihrig is ncrtfre?
from galena and pyrite, nor are tbe tailings clean. The blende firoo
the firbt Ltihrig passes to a novel feeder, consisting of a wooden cooicil
basin, which receives a slow revolving motion from bevel wheels vA
pulley placed below it ; a box hangs suspended over the cone, ai^
receives the pulp, while water is added from a pipe. The reTolvitC
cone carries with it the required amount of pulp, which passes throBgi
an opening to the distiibuting apron of a second Ltihrig. The taihop
from this go to Salzburg tables, of which there are 4 in the ©ii^
Each of these has a wooden or iron hopper, into which pi^P ®
shovelled ; sufficient water is added from a pipe, and the pnlp ii "^
by a screw conveyor. The Salzburg tables work in two paiis: tb
* J. W. Meier, En. and Min. JL



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METALLIFEROUS MINERALS. 525

irst treats certain sands carrying lead — ^they are first washed for a
^hile on one of the tables, then the table is shovelled off and the upper
x>rtion is worked a second time on Salzburgs, while the lower portion
^oee to stamps and thence to sandjigs. The other pair of Salzbnrgs
8 nsed for the washing of middlings from the second Ltlhrig. There
8 one difficulty which may interfere with successful treatment — i. e.
he middlings running off the lower edge of the first vanner are very
iqnid, and if the sprioklers on the second vanner add much more
v^ater, there will be an excess, the cloth will be washed clean, and no
oncentrates will remain. This new concentrator saves largely in
abour and faeL The old Werlau concentrator in 24 hours cleaned
^0,000 kilos of wash dirt, employing 90 labourers and burning
i8,000 kilos of coal. The present cleans 40,000 kilos in 10 hours,
nrith 45 labourers and 1600 kilos of coal. The tailings are lean;
x>arser sizes carry at most 2 per cent, zinc and a fraction of 1 per cent.
ead oxide. The assays of tailings from slimes could not be obtained,
rhe wash dirt carried 9*26 per cent, galena and 18*96 per cent.
>lende. Concentrates have 64-^5 per cent, lead oxide, 41-42 per cent,
dnc, and 11 oz. silver.

The dressing miU at the Arranyes mine, near Linares, Spain, has
ately been completely equipped by the Humboldt Engineering
i¥orks, at Ealk, near Cologne, to treat 500 tons galena, containing
M) per cent, lead, per day of 10 hours. The proper utilisation of the
latural situation, the efficient and thorough dressing of the medium
products, and the careful treatment of the slimes, have contributed
materially to make this an exemplary ore-dressing mill. The plant
is arranged stepwise in 4 departments. In the first department,
irhich consists of the picking shed and first washery, all the crude
3re, that is 50 tons per hour, is tipped into 4 masonry bins, whence
rt dides on to grids with 80 mm. square holes, one to each bin, which
lerve at the same time as picking tables. On the 4 picking tables,
the crude ore is separated into pure lead ore, steriles (gangue), and
ODedium products. The small ore, under 80 mm., which falls through
the picking tables, descends into the lower part of department 1, and
b classified in 2 systems of trommels, consisting each of 4 trommels,
and, except the fine grains below 4 mm., is then enriched in 16 jiggers.
The medium products or middlings from the picking tables and from
the jiggers are forwarded to department 2 to be dressed, the former
being lowered by means of brake platforms to the lower level. The
wash water of the jiggers in department 1 is allowed to settle in pits
on the same floor, and then forced back by a centrifugal pump. This
department is driven by a separate condensing engine. In depart-
ment 2 the following machinery is erected: — 2 stone breakers,
2 classifying trommels, 2 roller crushers, 2 revolving picking tables.
The middlings from department 1 are first broken in the stone
breakers, the product then passes the classifying trommels, the large
pieced are sorted on the picking tables, from which the poor passes
to the roller crushers. The reduced product passes on to depart-
ment 8, where it is classified in two sets of 4 trommels each, and then
enriched in the 16 fine jiggers. Together with the reduced product,
the grains below 4 mm. from the trommels in department 1 are passed

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526 ECONOMIC MINING,

through these trommels in department 3. The water fW»m the 15
jiggers is olaiified in settling pits on the same level, and pnmpeil
back. The middlings fr«>m the fine jiggers are pasned on to finerolkr
crushers, and the reduced product, after passing the guarantee troni-
mels (one to each crusher), reaches department 4, the slime wasbery,
to which the finest grains from the trommels of departm^:it 8 aba
slide. Department 4 contains :— 1 classifying apparatus, 1 pyiamidil
box, 4 slime jiggers, and 4 Linkenbach tables or rotary buddies, 6 sad
7 m. diam. respectively. The coarse grains from the classifier an
conveyed to the slime jiggers, and the thickened slimes from tiia
pyramidal boxes run on to the buddies. The three lower departuMnti
are driven by a horizontal compound condensing engine, and steam
for the whole mill is supplied by 3 Lancashire boilers on the k^
of de(>art;ment 2. The pumps for elevating the clarified wash water
in the various departments are centrifugal pumps or piston pompi,
according to the height to which the water has to be lified.

The extensive dressing works at Neuhof, near Beuthen, Germaoyi
are also constructed by the Humboldt Company.

A detailed and illustrated description of the galena and blende
dressing works at Sentein, in the Pyrenees, fitted by George Ore^i,
Aberystwith, will be found in the author's ' Mining Machinery/
p. 884.

In Missouri and Kansas,* the ore is found in many different fanu
and with a number of gangues, such as chert, limestone, calcite, iroo
pyrites, and mud sediment. Here a 5-sieve jig is used to advantage
when the gangue is heavy, such as black chert or baryta.

The dressing works of the St. Joseph Lead Co., at Bonne Terr&,t
Missouri, have a capacity of 500 tons a day. The mineral yields cm
an average about 7 per cent, non-argentiferous galena, and 1 per cent
or more of cobalt and nickel-bearinc^ pyrites ; the gangue is magnesian
limestone. The ore is crushed by jaw-crushers and rolls, and screened
dry through a 6 mm. screen. The sands passing through the screeo
are thoroughly mixed with water, elevated by centrifugal pumps to
distributors, and divided among Parsons jigs, without any previons
sizing or classification. The tails (" chats ") after passing over the two
sieves of these jigs receive no further treatment, and are conveyed by
launders to the '^ chat-tanks." Coarse galena and raggings aie
skimmed by hand from the jigs at intervals, leaving always a svdfficiait
bed to ensure good hutchwork. The hutch work which comes throagii
the sieves of the Parsons jigs passes through a series of pyramid
boxes. The heavy galena, mixed with some sand and slime, settles
in the first box of the series, from which it is fed to a tmnking'
machine. The pure galena from this machine falls into nulroad can
and goes to the smelting-works. The tails from the trunking-madiine,
together with the sands settling in the second box, are elevated liy
centrifugal pumps and divided between Harz 8Hsieved jigs. The
tails of the Harz jigs receive no further treatment, going directly ^
the chat-tanks. Galena and pyrites are skimmed from the sieves of
these jigs ; a bed of galena is, hoi^ver, maintained on all, so as to

♦ G. T. Cooley, En. and Min. Jl.

t H. S. Monroe, Trans. Amer. Inst Bfin. Engs., 1888, p. 659.



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METALLIFEROUS MINERALS. 527

ensure a rich hutchwork. The hutchwork of these finishing-jigs is
nearlj pnre galena, and goes to galena-boxes on the lower floor, which
are emptied from time to time, and the galena is loaded on cars to go
to the smelting-works. Tho fine slimes settling in the third and
fourth boxes are nnited and raised by centrifugal pumps to the dis-
tributors feeding the first row of Parsons-Rittinger tables. The
middlings fk>m these tables are treated on the second row of tables.
The tails from all the tables flow into the chat-tanks, and the heads
run into galena-boxes on the lower floor from which they are loaded
into cars. The raggings, containing 12-20 per cent, lead, which are
ddmmed from the Parsons jigs, are recrushed by fine rolls, and elevated
without screening to a line of Harz 3Hsieved jigs. These raggings
contain considerable pyrites.

The mill is a two-storey structure. On the main floor are the ore-
bins, roughing-jigs, finislung-jigs, and tables. There is nothing to
intercept the light fedling on tiie jigs and tables, and the roof is a
mere umbrella of corrugated iron, with light iron trusses, and sup-
ported on slender columns. The arrangement in two floors is unusual,
but permissible under the conditions, as, after passing over the
roughing-jigs, 600 tons of waste sand go at once to the chat-tanks.
Of the remaining 200 tons, 74 tons are mineral and raggings, and
20 tons escape with the overflow of the boxes, leaving only 106 tons
to be elevated again. The average lift is less than 30 ft. If the mill
had been arranged in steps, it would have been necessary to deliver
the ore at a level 40 ft. higher, involving a much more expensive
building, and increased cost of hoisting the whole 800 tons, to save
tibe elevating of 106 tons a second time ; moreover, both the wash-
water and feed-water for the different machines would have to be
laised about 20 ft. higher, and as 29 tons of water are required to
treat 1 ton of ore, this additional lift would be a serious matter. In
round numbers, the saving amounts to over 20 h.p. Of the ore coming
from the mine, nearly 40 per cent, is as fine as if it had passed through
the jaw-crushers, 15*5 per cent, is as fine as though it had passed
through the rollis, and 8 per cent, is fine enough for the jigs. This
latter portion is very rich, carrying over 20 per cent. lead. The dis-
tribution of sands or slimes is performed by a feeder divided by
partitions into a number of radial boxes, ensuring uniformitv. Sands
end sUmes are treated together on the same jigs, and though the loss
of galena in the very finest slimes is large, yet the method has
advantages, notably in allowing very much finer material (^ mm. and
less) to be treated sucoessfuUy, and in the large proportion of sands
finally disposed of by the roughing jigs alone. Thus, out of 800 tons
h day, only 136 tons require further treatment — ^viz. 30 tons raggings,
cm^ed and treated on the 3-sieve jigs ; 66 tons fine sand, also treated
on 3-«ieve jigs ; and 40 tons slimes, treated on side-bump tables. The
disadvantage lies in the difficulty of forcing all the very finest slimes
to go through the jig-sieves. The material treated on the finishing-
jigs is very rich, containing about 25 per cent, lead, and the losses are
;nite lai^; it is also very fine, over 90 per cent, being less than
mm. ; the losses are confined to the stuff below ^ mm. For the
year ending May 1, 1887, the yield of the ore treal^ was 5-65 per



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528 ECONOMIC MINING.

cent; tbe loss in tailings, about 2*13 per cent., or 27*4 per cent of
the total in the ore ; and the cost, 1«. 6^. a ton, abont \ being for
labonr and \ for fuel

Smeliing. — While the metallurgy of lead may be said to consist
simply in reducing the metal from its ores, the reactions which take
place in the operation are most complex, and probably not yet com-
pletely understood. Besides the usual text-books the student will do
well to consult a recent paper by J. B. Hannay.* PracticaUy all
methods hitherto successful rely on roasting or calcining (to remore
sulphur) and smelting. The ores arrive at the smelter more or less
*' dressed," and the proportion of lead in the ore varies from a vexv
low figure in some richly argentiferous ores (smelted more for tbsis
silver than their lead) to 80 per cent, or more. The foreign substasov
present in different proportions are chiefly antimony, arsenic, coppib
gold, iron, silver, sulphur, and zinc. The characters (chemical aai
physical) of the ore, and cost and kind of fuel and fluxes, prindpally
determine the method followed.

Beverberatory furnace practice may be conveniently dealt with
first.

In England, the so-called Flintshire method, adopted in Wales,
Yorkshire, Shropshire, and Derbyshire, employs a furnace such «
shown in Fig. 147. On each side are 3 openings, capable of being
closed by iron doors ; those on one side a are used by the workman
for manipulating the charge. The central opening o on the other
side has an iron pot c outside it, into which the lead ia tapped off
when the operation is completed. The remaining two openings d are
used fer removing slag. The charge is introduced by a hopper in
the crown. Under the whole length of the furnace runs an ardied
brick vault, open to the air at .both ends, and supporting the working
bed proper. This is formed of " grey slag " from a previous operation,
broken small, and fed into the furnace when the latter is at rod heat;
it melts and forms a pasty mass, which is spread in a layer &-18 in.
thick, hollowed in the middle towards the tap-hole 6, and allowed to
solidify, about 5 tons of slae being required. The fireplace e is at one
end, and has an ash-pit which contains water ; the flue openings / at
the opposite end communicate with the shaft g. The charge of ore»
usually 21 cwt, is introduced by the hopper and spread over the
floor, care being taken, however, that none of it shall lie on the most
depressed part near the tap hole. The process of the smelting maj
be described as having two stages, the first being calcination of the
ore, and the second the melting down and reduction of the metaL
During the first stage, which lasts about 1^ hours, the doors are left
open, or are only partially closed, so as to allow of access of a sufficiency
of air, and the heat is regulated by keeping down the damper con-
siderably. During the whole process of calcination a workman
repeatedly rabbles or turns over the charge so as to expose all parts of
it to the action of the air and heat. The doors fturthest from the
furnace are then closed, and the fire is urged so as to bring about the
commencement of the second stage of -the operation, when rednetiai
begins to take place, and lead to trickle dovm into the welL At the
• *• MetaUnrgy of Lead," Tiana, Inet Min. and Met, m. 17L

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Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 59 of 76)