Charles George Warnford Lock.

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» be 56 per minute. The feed can be regulated by opening or shutting
be hopper door c. Coarser stuff requires slower feed. The apron d is
dvanced when magnetite is abundant, and pulled back when there is
ass. The proportion of blende to magnetite and middlings varies with
be ore, but usually 50 per cent, of marketable (97 per cent.) blend^ is
btained, assaying 48*6 per cent, metallic zinc, and containing 2 per
mt. magnetic matter, and 1 per cent, pyrites and gangue, at a cost,
deluding coal and repairs, of about 5«. per ton of crude ore. If no
middlings " are made, it is impossible to get Uie blende above 40 per
ent metallic zinc, without great losses, and smelters do not care to
iiy below 45 per cent. The middlings are a non-marketable article
i present prices, though they carry 25-27 per cent. zinc.

Certain Spanish ores,* consisting mainly of ferruginous calamine,
nd earthy or calcareous brown hematite, which it is impossible to

* A. I3. Colliiu.

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separate by hand picking ordresung-, are crushed and roasted in
reverberatory furnaces with an admixture of coal, by which means
tbe hematite is reduced to magnetic oxide of iron. On suhseqiient
treatment by magnetic separators, it is found that this artifici&l
magnetite is easily separated, and saleable zinc ore is left behind.
The expense of roasting must be considerable, but as the calamine
ore is always roasted in any case before export, to lower the freight
charges, it is not so great as it seems.

Iq Wisconsin, Blake dresses a mixture of blende and pyrites
parrying 20 per cent, blende, and gets a 60 per cent, product, 1^ Terr
careful oxidation of the pyrites without altering the character of the
blende and galena, which he achieves by calcination in presence of
abundant unbumed hot air, using Siemens regenerators.

At the Bertha works, Virginia,* the dumping or storage bins for
receiving the calamine as it comes from the mines are provided witk
a water-carriage system. The bins consist of timbered trestles buii:
out from a hillside and provided with V-shaped floors, down the centre
of which passes the water-trough. The ore, having been dumped, i*
fed regularly into the water-trough, and is carried by a current 0:
water down to the dressing-house 1300 ft. below. The trougb cf
" flumes " are 12 in. wide and 6 in. deep, made of cast iron. Tk
water required is pumped up from the river by heavy Worthingtfs
pumps, through a 6-in. column pipe, to a large tank on the hilltop,
whence it runs into the flumes. The zinc ore brought down theflnBK
falls upon a "grizzly" (through which the large lumps are broketi
and passes into a single, revolving log- washer, which gives it a gentk
primary sluicing, and where the adhering clay and "buckfefars
separated and djjBSolved. The lumps are then crushed by a BUfe
breaker and a pair of Cornish rolls, after which the ore is sized byi
conical, perforated revolving screen ; the large pieces drop npra »
steel-plate conveyor, where they are hand-picked, while the smalk:
pass down to 4 sets of Parsons jigs, on which they are thoroogiLy
concentrated. The tailings from the above treatment pass throng 1
spitzkasten or classifier, and thence to 2 Harz jigs. The slimes ftf
discharged into a slime pond, whence the muddy water is drained of
into the river. The capacity of the dressing-house is 80 tons oon«o-
trated zinc ore per day of 10 hours. The yield is approximately ow
third of the crude ore treated, and the product erives the foUowiic
average analysis when drii
cent; zinc oxide (ZnO\ A
cent. ; oxides of iron and al
combined water, 8 • 23 per o
cent.; magnesium carbonai
For drying the concentrate
dressing-house, containing a
revolving roaster 30 ft. lon(
the smelting works.

Calcination of calamine
flat^bedded reverberatories,
p. 157) have replaced the
» E.

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tout,' The ore pa^es through in abbut 4 hours, and loses some 28 per
cent, by weight, each furnace yielding about 12 tons calcined ore per
24 hours. The 8 Oxlands, costing 9752., turn out 36 tons daily, as
against 5 reverberatories, costing 10002., 32-33 tons, and the difference
in working cost per ton of output is: (a) Reverberatory— wages,
1«. 9|d.; fuel, 3«. lid.; tools and sundries, 4(i. ; repairs and general
charges, SJd. ; total, 6«. 9id. ; (6) Oxland— wages, 8<l. ; fuel, 3#. 2|(l. ;
tools and sundries, 2|{2. ; repairs and general charges, 8d.; total,
4«. 9jd, The fuel used is a mixture of c^ and lignite. The Oxland
consumes 15*11 per cent, less fuel than the reverberatory, but this is
reduced to 12*41 per cent, by that required for generating motive

At Monteponi, Sardinia, the Ferraris furnace is used. This is a
gravitating calciner, similar in principle to that of Moser, used for
calcining small spathic ore at Eisenerz, in Styria. It has a bed about
38J ft. long and 6^ ft. broad, indined upwards from the fireplace to
the flue at a slope of about 1 in 3^. The furnace is heated by a gas-
producer burning lignite on a, step-grate, and having an a{r-heating
flue round the fireplace. Two similar beds are imited in one block,
and have a gas-producer and stack in common, the heat being regu-
lated by dampers in the flues, which direct the flame from one bed to
the othet as required. The ore, fed into the furnace through a hopper
into a short vertical shaft at the upper end of the bed, forms a conical
talus, which is gradually driven down the slope as fresh material is
added above, and falls over the slope at the bottom into a receiving-
chamber, whence it is drawn at intervals of about 4 hours. The ore
remains in the furnace 25-30 hours ; the yield is 20-21 tons in 24
hours, with a loss in calcination of about 25 per cent. Using lignite
carrying 12 J per cent, ash, costing 15«. lOd. a ton, the working
expenses are — wages, 1«. 9i<J.; fuel, 2«. 9^^.; repairs, 2^4.; total,
4«. 9W.

The fume from blende roasting contains sulphates of zinc and
iron. At the works on the Ehine it is usually leached in water and
the solution treated with lime, precipitating the zinc as hydroxide ;
but the precipitation is only partial, and the lime is very destructive
to the furnaces. Another method, invented by Dr. G. Krause-Cothen,*
consists in precipitating by sodium carbonate, producing an artificial
calamine carrying 45-50 per cent. zinc. Leaching is done hot, and
sodium carbonate is added in excess ; the mixture is filtered, and the
filtrate contains, besides the zinc and iron carbonates, some glauber-
salt, which is recovered by treatment with sulphuric acid and evapo-
ration. Operations on 1000 kilo, fame, containing 11 per cent, zinq
and 2 per cent, iron (both as sulphates) gave 200-250 Hlo. calamine,
carrying 45-50 per cent, zinc, and 260 kilo, anhydrous glauber-salt,
which covers the cost of the 190-200 kilo, sodium carbonate used.

The dissociation of the zinc from its ores is effected by distillation

in fireclay vessels in presence of carbon, followed by condensation out

of the reach of oxidising agents. The dimensions of ^he distilling

' vessels are restricted within very narrow limits by the pature of

^ refractory materials and the thickness of the charge through which

♦ Berg. u. Hiitt 55tU., 1801, p. 2IG.

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the neoeesary heat to effect redaction can be economically tnuiCTiittad;
the operations to which the ore and products must be sobmitted are
numerons, and the repeated handling of them cannot be aTotded.
The recent improvements in practice have not been the malts of
changes in the form of the furnaces so much as the applicalkm of
regenerative gas heating instead of direct firing, leading to a saviag
of fnel, an economy of labour, a prolonged life for the retorts, and an
augmented yield of metal.

The zinc ores smelted at Freiberg are black blendes, eontaiiiiiig
an average of 35 per cent, zinc, 30 per cent, sulphur, and 4-5 per
cent. lead. They are arsenical, and very fermgiDOUs. They are foii
calcined in kilns, to utilise the sulphur, and again roasted in rever-
beratory furnaces with double stages until they contain no more than
1 per cent, sulphur. Thev are then distilled by the Silesian prooees
in furnaces, each of which contains 32 muffles, heated by gas on the
Siemens regenerative principle. The charge of each muffle is 100 Ih.
CHlcined blende ; the distillation of this quantity lasts 24 hours, and
produces 32 lb. zinc ; 50 lb. coal and 5-6 cub. ft. wood are conimmed
as fuel to each muffle. The muffles last about 6 weeks. The product
is ultimately refined by fusion in a reverberatory furnace.

The Boetius zinc famace * has 2 gas generators, the gases travers-
ing half the length of the furnace, then passing down a channel, uid
thence into the flues between the muffles. The air necessary to com-
bustion is obtained partly directly into the gas shaft, and in part
through passages in the walls of the furnace. Thus the gases are
partly burned in the upper portion of the generator, but mainly m
the furnace itself, by means of air channels which are fitted at UMir
iulet with regulatins screws, so that the furnace temperature may be
under perfect control. The heat is thus evenly distributed, and ^
muffles are therefore not destroyed so frequently. To carry off the
fumes, which are so annoying to the workmen, a flue passes along the
top of the furnace connected with the hood of each pair of muffles. At
the Lipine works, Silesia, a movable iron hood connected with an iron
flue passing Just through the roof serves the same purpoeOk but is
useless when the wind is high and causes a down draugnt. Glased
muffles have been used at some works, but the ordinary fonn is
generally adopted. These cost 4«.-5«. apiece, with an average life of
32 days. Dagner*s condenser | has been tried at several works in
Silesia, but the yield of metal does not appear to have been finally
increased, though more oxide is obtained. The originally increased
yield gradually became less as the condensers became older and
cracked, until at last it was but little greater than by the previous
method. One advantage of this system lies in the £EM)t tnat tke
nozzles need not be removed in order to ladle the zina Cylindrical
upright nozzles, as at the Hohenlohe works, collect a larger portioii of
the dust and oxide than those generally used, and when employed in
conjunction with Dagner's condenser, no zinc flame appears at the
orifice, and the gases pass out through a conical nozzle on the sidto
nearest to the furnace, and thus are far removed from the workmuL

♦ K. F. Fobr, Berg. u. Hutt. Zeit., 1883-4.
t Ding. Polyt. Jl., 236, 486.

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A flap-TalT6 at the bottom of the nozzle allows ihe zino-dast to be

The Bertha smelting works, yirginia, oonsist of 10 lar^ Welsh-
Belgian fomaoesy having 140 retorts or pots each. Eacm furnace
oQ&sistB of a large skeleton combustion chamber with iron pi^eon-
lide front) into which are set the retorts. The latter are 4 ft. lon^,
and have an inside measurement of 8 by 10 in., being elliptioal in
■eotion. They are luted into the furnace with ordinary day. The
retorts are made of selected fireclay, capable of making a tenacious
paste, which can be formed into the desired shapes without pulling
apart and cracking. It must also be absolutely fireproof, so that the
retorts will not weaken or break when resting upon their extreme
ends in the furnace at a white heat. The following is an analysis of
two days, Na 1 being found slightly the better because more elastic,
and be«rase it will bend slightly before breaking, at a very high
degree of heat: —

No. 1. Na a.

8illfla(oombined) £*^0 40*56

Alumina 81*53 35*90

Combined rndsture 11*30 12*80

Titanic acid (TiO,) .. 1*50 1*30

Free riliea (quartz) 12*70 6*40

Pota8ti(K^O) -40 '28

Soda(Na,0> none *16

Ifon aeaqniozide (Fe,0,) 1*92 1*10

HygroBOopio moifltnre 2*50 1*50

The cost of one retort, dried and ready for use, is in the neigh-
bourhood of 4#.

The calcined ore, mixed with the proper proportion of anthracite
soal, is chained into these retorts, and a short clay condenser is set
in the mouth of each and luted with clay. Then tne furnace is fired
from below, the flames circulating around and between the pots,
saofiing the reduction of the zinc ore by the combination of the
sa rbon of the coal with the oxygen of the ore. At first, a bright blue
F^iine bums at the mouth of each condenser ; but when the furnace
diarge reaches a bright red heat, say 1900^ F., metallic zinc is
wlatilised, and bums at the mouth of the condenser with a brilliant
;reenish-white flame. Conical iron pipes are then placed over the
condensers, in order to assist the condensation of the metal, which
lepoeits inside the pipe in the form of metallic zinc. At stated
ntervals the pipes are removed, and the molten metal is scraped out
if the condensers into ladles, firom which it is poured into moulds,
brming slabs of commercial spelter. This is continued until the
ximace has been worked off and all the metal is extracted from the
»re, which takes 24 hours, when the pipes and condensers are removed,
be residue is scraped out of the retorts, and the furnace is recharged
vith ore. Of the metallic contents of the ore 80 per cent, is usually
obtained, the remaining 20 per cent being lost by volatilisation,
^bwnrption b^ the retorts, or left in the residue. The ordinary charge
y&t furnace is 8500 lb. ore and 6000 lb. coal per day of 24 hours, and
he average yield of metal is 1950-2000 lb. ; thus the output of the
)lant is 300-^15 tons per month. The fuel used to fire the furnaces

Digitized by LjOOQIC


is Pocahontas ooal, whioh gives a very long flame, necessary to retch
the higher rows of retorts in the ^maoe, and has the following
analysis: Fixed oarbon, 74-27 per cent.; volatile matter, 10-52 per
cent. ; ash, 6*94 per cent. For mixture with the ore in the fomaoe,
another coal is used, semi-anthracite in character, and having the
following composition : Fixed carbon, 62 -72 percent.; volatile matter,
10*62 per cent.; sulphur, 1'43 per cent.; ash, 25*33 per cent
Although so high in ash, the ooal serves its purpose aamirablj.
Both white and coloured labour is used in the smelting works, the
latter being found quite advantageous ; 5 men are required to each
furnace, and they work 24-hour sUfts. The cost of smelting a ton of
ore is, approximately : Furnace labour, 140. ; yard labpur, 7cl. ; retorts,
3«. 6(2.; Pocahontas coal, 9«. 3J.; mixing coal, 3i. 8d.; all other
expenses, 1%. 4i2. ; total, 38«. 4d. ner ton. As metallic zinc has a
strong affinity for iron, no iron tool or vessel is allowed to oome inl
contact with the zinc in its molten condition.

Becent experiments* on direct production of zinc in the bUitJ
furnace by separating the metallic zinc from the fumaoe gases by
means of a centrifugal machine, would indicate that the ordinal^
prooefe .of zinc-smelting might be modified as follows : — (a) Caref
roasting of the ore, whether calamine or blende, to convert it
nearly as possible into oxide ; (6) mixing the zinc oxide with 3 tii
its weight of bituminous coal and .5 per cent, of lime, and coking
giving a material with 22 • 7 per cent, srinc, partly in metallic form
(c) burning the zinc coke by hot blast in a dosed top furnace, having
a flue at the top connected with a centrifugal machine ; the volatilise^
zinc carried off by the gases is collected in the flues and in the ~
of the centrifugal; the cleaned gases are utilised as fuel; (d) sul
jecting the zinc dust to a pressure of about 1500 lb. per sq. in., whi<
reduces it to about 10 per cent, of its original bulk, making it per]
fecily compact ; {e) distilling the compressed zinc dust in retoi
without addition of carbon, when about 66 per cent, metallic anc
great purity is obtained. Lead and silver, if present, remain in t
fixed residue. This operation requires much less fuel for heati
than the ordinary method of reducmg, as the material in the retoi
being practically metallic zinc, is a good conductor of heat as ooz
pared with the mixture of zinc oxide and carbon. Probably moi
complete reduction might be obtained electrolytically, as low<
tension current would be required, the material being kurgely in th^
metallic state.

GomuMTce, — The world's annual production of zinc is about 300,000-
350,000 tons. Of this quantity, Belgium affords 130,000-140,000 tons
Silesia, 80,000-90,000 ; United States, 50,000-60,000 ; Great Britain
20,000-30,000 ; France and Spain, 15,000-20,000 ; Austria, 4000-7000
Poland, 3000-4000. The output of zinc ores mined in the Unites
Kingdom is about 25,000 tons yearly. Germany's total production o
zinc ores in 1891 was 793,442 tons, all but about 1000 tons of whid
was raised in Prussia ; Upper Silesia in 1890 had 35 mines working
which yielded 635,538 tons, in the proportions of about 59 per cem
calamine and 41 per cent, blende. The total zinc ore afifcurded b;
* W. Hcmpel, Berg. u. Hutt Zoit, 1894.

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Spanish rnmes was 55,817 tons in 1891 and 50,100 tons in 1892 ; one
enterprise, the Beal Compania Asturiana, turned out over 27,000 tons
calcined calamine in 1891, and oyer 24,000 tons in 1892, from the
rich mines of Beooin and TTdias. About ^ of all the spelter produced
in Belgium is made by the Yieille Montaene Co.

The market value of spelter (pig zinc) is liable to fluctuation, and
may be said to range between 17/. and 25/. a ton. Brands such as
the Bertha, containing 99 * 98 per cent, pure zinc, are worth something
more than current prices. Almost aJl zinc ores carry some lead,
perhaps -01 per cent., which is a drawback, and in any appreciable
quantity will render a zinc ore unsaleable. Further, antimony,
arsenic, cadmium, copper, and iron hinder the roasting of the blende,
cause loss in the subsequent distillation of the oxide, and, together
with sulphur, lower the value of the metal produced, rendering it
unfit for some of its most extended applications, e. g. fine brass and
lithographic plates. Comparison of the two ores blende and calamine
gives the latter a preference for the smelter because it is less costly
to work and more readily gives up its metal, besides assisting to
liberate the metal from blende when mixed with it in the charge ;
but as it carries less metal per ton, it reduces the output of the fur-*
nace, and its low specific gravity makes it more difficult to dress
clean, besides which it cannot beu: so much cost for transportation.
The smelter in buying blende or calamine, bases his estimate of the
value to him in the following manner. From the market price of
spelter, say 22/. a ton, he deducts 6/. a ton as the cost of smelting,
reducing the value to 161. Then, from the zinc contents of the ore by
»88ay, say 45 per cent., he deducts 15 per cent, for blende or 10 per
cent, for calamine, as being the probable loss in slag, fume, &C., so
that he has 80 per cent, or 35 per cent, metal which he can reckon on
recovering. Finally, the market value of the zinc product of the
ore is arrived at by a rule-of-three sum, e. g. —

^ ^^T. ^ worth 16/. a ton, then ^^^^ is worth 4/. 16«., or
lUOp.c. ' oOp.c.

60 p. o.

The smelter therefore offers as much less than the 96*. or 112ir. a
ton as will give him the profit he desires. A very impure ore will
suffer a greater loss than 15 per cent, in slags, <&c., and is therefore
not in demand ; anything less than 45 per cent, is undesirable, and
under 40 per cent, may bo unmarketable at any price.

Digitized by


Digitized by



Acids deoompodng rooks, 2
Adits, 81

Adobe silver Airnaoe, 611
Aetial ropeways, 118, 575

- tramways, 491

Air ooirents, resiiCaiioe to, 60

^ in mines, 59


^ supply nnder pressure, 62

Airways, conditions, 61

Akron cement fot buddies, 610

Aibertite, 167

Alkali mnd cement 184

Alkaline waten, 352

Allen fnmaoe, 440

Allnvial diamonds, 238

Almaden, 563

Alum, 153

-rock, 153

- shale, 153

- stone, 153
%liiminite, 387
ilnmininm, 387

- aUoys, 397

- by deotiolysis, 389

- from alumina, 894

- from bauxite, 389
~ from cryolite, 392

- fomaoee, 389, 392

- in lead purifying, 548

- mannfitoture, 3^3

- properties, 396

. nmelting, 38^ 392
Jonogen, 387
jnalgamaiion, lime in, 608

- manganese in, 608

- flilver, 601
mber, 155
nelesite, 515
nhydrite, 819
ntimonite, 899
Dtimon^, 899

• American, 401

Antimony, auriferous, 399
^- extraction, 401

— flux, 404

— ftmie, 405

— furnaces, 402-406

— geology, 399, 400

— in igneous rooks, 2

— industry, 407

— ingots, packing, 406

— lodes, 400

— ores, 399
dressing, 401

— Portuguese, 399

— refining, 404

— smelting. 402-406

— starring, 402

— yield, 405
Apatite, 305
Aigentite, 590
Aigillaceous iron ore, 487
Arkansas stones, 371
Arrastres, 482, 604
Arsenic, 156

— calcining, 157

— commerce, 161

— condensing, 158

— in igneous rocks, 2

— in pyrites, 323

— kettle, 160

— refining, 160

Arsenical copper refining, 460
Asbestos, 163

— AiHcan, 165

— American, 165

— Oanadian,' 163

— commerce^ 166

— composition, 166

— dressing, 164

— grading, 164

— Italian, 164

— mining, 163

— Russian, 165
Asbolane, 411
Asphalt, 167

— American, 171

— Cuban, 178

— Mexican, 173

Digitized by




Asphalt, purifying, 173
Astrakamte, 819
Atmospherio pressure, 61
ADuabergite, 572
AugUBtine process, 613
Aoriferons samples, testing, 7
Austin pyritio smelting, 444
Azurite, 415

Bailit'b pomps, 76

Balbaoh nimace, 547

Baling tanks, 72

Ball mUls, 131

Banddoom, 239

Banket, 476



Barrel amalgamation, silver, 603

— quartz, 474

Base ores, sampling, 8
Bauxite, 326, 388

— American, 887

— French, 387

— geology, 388

— Irish, 888

— purification, 388

— value, 388

Bertha dressing works, 646

— zinc, 641
Bessemer iron, 509
Beasermerising copper, 449

— nickel matte, 578
Betters smelting process, 444
Bilharz concentration, 149
Biotite, 265

Bischofite, 319
Bismuth, 408

— geology, 408

— sources, 408

— treatment, 408
Bismutite, 408
Bits, drUl, 84
Bitumeu, 167

— with mercury, 564
Black band, 487

— brush ore. 487
Blackjack, 639
Blaoklead, 249

Blake breaker, 121, 122

— multiple crushers, 500
Blanc fixe, 309

Blast furnace, Castilian, 536
zinc, 650

— furnaces, 508
Blasting, 43, 361

— disasters, 46, 47

— explosives, 43

— firing, 47

— ineflScient, 47

— leverage, 46

— tamping, 46

— wetigc* replacing, 50

Bleichert ropeways, 118, 491
Blende, 639

— separating firom iron, 505
Blister, smelting to, 447
Block ore. 497

Blomers, 59, 63
Blue billy, 462

— peaoh,632

BoStius zinc ftimaoe, 648


Boiler reefs, 469

Boiling soda nitrate, 347

Bole, 310

Boliohe, 533

B<nraoio aoid, 174, 177


Borax, 174

— American, 175

— refining, 174, 175

— Thibet, 174
Bordeaux s, 616

— zinc frune, 647
Lead, 515

— American, 517

— Australian, 519

— Balbaoh furnace, 547

— Bonne Terre, 517

— British, 515

— Broken Hill, 519

— carrying silver, 521

— Gastiliaa blast fiimaoe, 536

— Oolorado, 518

— Oorduri^s desUverising process, 547

— Oomish frimaoe, 529

— crystallising, 544

— oupelUng, 542

— desilvering, 542

— electrolysis, 548

— Flach*s dedlverising process, 547

— Flintshire furnace, 528

— flue dust, 550

— fluxes, calculating, 540

— French, 515

— fume, 550

— furnace l^e-produotB, 549

— geology, 515

— German, 516

— Idaho, 519

— in ifrneous rocks, 2

— Indian, 517

— jumbo furnace, 552

— Laveissi^re paocees, 544

— Lewis- Bartlett process, 552

— liquating, 542

— Marseilles process, 544

— matte, 550

— Missouri, 517, 518

— ore, 515

dressing at Arranyes, 525

at fionne Terre, 526

^ at Olausthal, 521

at Laurenberg, 523

at Sentein, 526

Digitized by




Lead ore dressing at Werlan, 524

mill^ two story, 527

hearth. 533, 407

impurities, 521

simple washing, 521

Talueing, 541

— oxidisinff, 542

— Parkes dedWeridng prooess, 546

Online LibraryCharles George Warnford LockEconomic mining: a practical handbook for the miner, the metallurgist and ... → online text (page 74 of 76)