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1 2 3
32 X
1
2
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4
5
6
ON THE EXTRACTION OF COPPER J^ROM ITS ORES
IN THE HUMID WAY.
Hy Thomas Macfaiilane.
From the Canadian Nut ura'Ul for June 1865.
In the last Report of the Geological Survey of Canada refer-
ence wa.s made to the poor pyritous copper ores of the Eastern
Townships ; and with regard to the best method of utilizin- them
It was remarked as follows : " It is much to be desired that some
of the various methods which have been proposed for removing
the copper in a soluble form, could be applied to these or'>s "*
The importance of this question has by no means diminished
since the publication of the report alluded to. The recent discov-
ery, in the neighborhood of Lennoxvillo, of several very promising
beds of pyritiferous copper ore, the difficulty of coLcatratiD-
those by any of the usual mechanicui processes of ore-dressino"
and the obstacles to the establishment of smelting-houses near to
the mines for the production of ingot copper, all combine to ron- "
der this subject one of somewhat mo.e than ordinary interest
The processes which have been from time to time proposed and
put into practical operation, for the humid treatment of copper
ores are so numerous and diverse, tha. I shall not attempt to de-
«cnbe them minutely. I shall merely refer to some of the more
important among them, and especially to those which bear some
resemblance in principle to the method pursued in certain experi
ments which I have performed on a small scale, with various
Canadian ores, in order to the extraction of the copper contained
in them. The results of these experiments having been very
satisfactory, I shall proceed to describe them, and, in conclusion
refer to the manner in which the method of extraction founded
on them might be most advanta-cously carried oufon a large scale
1. One of the oldest modes of producing copper in the wet way
IS the precipitating it, by means of metallic iron, from the water
of mines, or that resulting from lixiviating old waste-heaps in
their neighborhood. These waters contain the copper in the form
of sulphates, derived doubtless from the oxidation of sulphuret
^'^'xT , f f*""^'" '' °' ''"' °°' ^°°S "S*^ °^'""«d «n at SohmoUnitz
and Neusohl in Hungary, at Moldava in Croatia, in Anglesea. and
at ivauimciBDerg in the Lower Hartz.
• Geology of Canada, page 130.
2
the, Ihiviatal. °"'- ^ ''")"« '•""Stol in l,oap,,.„d
ml wee a .l,e, are lixi.iaW i„ .he „,„„, Z:iT '"' "'•
..i-.w.« cue .heC- or:,i SI""" °"»'°"""^ "-" «>'
beratory furnaces ,U ...- J*'"''™^** ^^ calcining m rever-
««a appear ,„ be a. all co„S"' tl^^.tln: """■
isremovej in the soluble form l„t f„nr * '""^''f"'
'e.id„e ,«. . subjeee -o Sbi" i2:;r,i:r:.' '- "°
Tbe peroxide „f rron eo„W dl, L'","' T^ '«"» "'''■"«'•
versie,. into .ulplmrie a" Mof » « • °'''™'<','"« '""'«» «.o <»»-
luLt?""!!? r''^"'' P'"?"' ^"^ ^'*'^ «°™"'«" «^J^ and then
I
■1
eopper m the form of a sub-
I
3
chloride. The latter in conJenHecl and treate.I furtlior TIuh
process labors under the huu.o disadvantage as Longn.aid's wi
regard to copper in the residues.
Atnonj. the various processes just enumerated, those which are
,nost advantageous .n econonueal respects, and which are b
suited to the local c.rcun.stances of Canada, are evidently tho. t
wh.ch few or no extraneous substances are required to r nder t
copper soluble, and in which the acid necessary to torn, t ^u
ble salt ot copper is derived from the oxidation of elcme ts n "'
sent .n the ore itself. At first sight the sin.plest a d ^f^v
mos eftcent means of rendering the copper .soU.ble wouuEe^'r
o be t at of merely calcining the sulphuret ores and lixiS,
theproduct. Almostallsuchorcs,whethercontainingcopper hne
purple copper, or copper pyrites, certainly yield by such t' e. '
.nent u.ore or less of their copper in a soluble sLe ; but an unt'
the metal so yielded in proportion to the ,uan ity co a Td Tn
the ore, ,s .nvanably very small indeed. Even wJth ore Ihi
contain a very considerable excess of s.ilr nr ♦! . .
be very carof^U, co„d„otea7 Ze «'. :, ' ^^T" "'°f
g.yen off, .„ the second ,„lph„,c of i,o„ « f„„„cd 7ur "1h.
tangdeoompMod. It U thereforo extrcmol. d£L T'
thiaproocs,, and tho d«dva„.a^,of Tbein p Lt^t t'"
low a temperature consist not only in the o„r!^.T u • . ""
feet, b„. also i„ tic deposition of lltl^^r wS° ,,'"''"'■
per u being preeipitaled. In this wav tho U„ I ^^
ta^inated tbat ».an, specimens X'proj'lr"'" " """
do not ,ieH , ^,, „,„ ,„ ccnTof ■: : ;;' IT"'"'""
These disadvantages are to a verv -r^nf .J V
u.ofo„„n.„„sa„/B, its .cL:!": ^7: [rrt J^ "!
H decomposed at a low teniner»t„r. .Ja ,,"»" "'st formed
cbloride of iron produced S la 11 fT "' "^ »""
posed, and i„ cb,ori„c UansfLed rnaT,', ^ ™"^ ''"'°"-
Oa treatin, tbe calcined predrwit:r."^r„ ilr".
which IS very nure offpn «««♦ • • . »oiuuon is obtained
t,' T. - ^ ' " containins merelv a tncc- of •
which cas. the deposition of basic iron 8ali8''hl °"' '"
Butaltbongbcommon s.t ma, r..:,; t.^^^ZZ^Z^l
4
it cinnot i„,,ke up for « Hnfi •
^"00 grains of slim.N f.v
;^/0 per 00,.. or co,:; i^'I^^L^T '''"-' -"tain.V
^00 gra.„.s of ore from K,s ot ^ . ' "'''"''''^-
copper «Mdnn a.lmixtur. of ir" ' '""*'^"""/.' 10.4 per cent of
per- Con«ec,uentl^ 7G.0 per ce^t of 1 1 .7 '" "^'"''^ «^ oop-
. In reflecting? on the necessitv ni- 1""'"' ^'^^ '•«"'ovcd
'* occurred to n.c that a ny ^ '" -"f ^-t supply of sulphur
version of the «ulph»r into si.' ^^-^ '''''^'^ ^''"'''^"te the con
-ape as sulphuric acid ^^^rof'd ' '"'''''' «^«"-in^ i to
ealc.n.ng operations „.s those h re reJ: r'''" '''^'''"^ '" «"^^^^
expenments -^ demonstrated thathf .'.•'"• ^^"^'"" '" ^^-rner
-creased the amount of .. phur d"f '"T-^^ ^--''^c o^ i-n
t occurred to me that it nlrb? ' n™'^ '" '"^'^ calcinations
ta'n.ng no more sulphur, i„ plo ,r t ' ."''" ^'^'^ '^^ ^^e con
Pyntes, to convert so n,uch of t nl" 1 ^ ^'^^P^''' ^^«" copper
he presence of common salt dc^oCri' "" ""'' «« ^^^^^ in
.the whole of the copper soluble J 1"^?* '^'^'''^' *« render
-g materials together : accordingly calcined the follow'
200 grains copper pyrites. '•
400 grains f.rric oxide.
200 graitid salt.
TJio n • ^^^ grains in all
«" grain,, .„, „„ „„^;:^- J^k^J^'duo afteroalcl„.«„. ^h"^;
Insoluble iron oxide..
Insoluble cupric oxide ^^^
Sulphate of soda 2.2 = i.g copper.
Chloride of copper. ^^'^
Chloride of sodiumCb/d^ffeVencV.).*.; 'sA^ '■' *'°i'J'"-
___________ 100.0
' Canadian Natura^t7;rv;~^
^'^'W be treato.1 with thj
I'cst proportion of 8ui.
■ ^^PennientN ,„ay he
'c Mines, containinrv
copper pj-ritcs, but
fy^hh m g,ai„«
'•^•7 grains of copper
extracted.
fe' 10.4 per cent, of
■e calcined with 100
-f -iO grains of cop-
' was removed.
supply of sulphur,
' facilitate the con-
adofaJlowingitto
o'fappliedinsuch
Having in former
f peroxide of iron
such calcinations,
with an ore con-
PPer, than copper
»c»d, as would in
lioride to render
cined the follow.
'ained 23.5 per
nation weighed
•8 copper.
8 copper.
Frouj this it appeared that in the residue there were present of
c(ipj)er —
In an insoluble state. ... l l.8;i grs. = 25.15 per cent.
In a soluble state 10.51 " =22.30 •'
22.33 gis.
Amount of copper lo^^i .. 24.67 " =52.49 "
47.00 gi3.
The only way in which this extraordinary loss of 52.49 jwr cent,
can be accounted for, is by supposing it to have been volatilized ;
and other eireunistances confirm this view. The calcined sub-
stances contained UO.IJa grains of Sulphate of soda. Consequently
53.11 grains of common salt must have been decomposed, and
.'{2.08 grains of chlorine liberated from it. Uf thi.M, 11. 82 grains
are found in combination with the copper in a soluble state. ' The
remaining 20.20 grains were more than sufiiciont to form sub-chlo-
ride with the 24.(17 grains of copper volatilized. The whole of the
.32.08 grams of chlorine were not however sufficient to convert the
forty-seven grains of copper contained in Ihe ore into soluble proto-
ehloride.
From this experiment it became evident, 1st, tha. even with
the use of a large (,uantity of peroxide of iron, it is difficult to treat
copper pyrites so as to produce enough of sulphuric acid to render
all the cpper soluble; and 2nd, the calcination must be per-
formed at as low a temperature as possible, in order to prevent the
volatilization of the cop, er. The experiment was theiviore per-
formed a second time, care being taken to keep the temperature
low. Ihe same materials, in the same proportions, were ised and
the product this time fr.mi the 800 grains weiglied 7J»2 -rains
and contained — ° '
Iron oxide and other insoluble lUHtter.. G6.00
Sulphate of sodii. ., i-jqq
Chloride of copper q « . _ , r -
-,,, ., . " »-o4 = 4..');) copper.
tlilondeot sodium (by diflcnence).... o.7(j
100.00
Thirty-six grains of copper out of the original forty-seven were
this time removed in a soluble form ; equalling seventy-six per cent
mstead of the twenty-two per cent, of the former experinJnt F r!
ther, ^t appears that 139 grains of .«lphat. of sod." were formed ■
and
consequently 111 of chloride of sodium decomposed, and
sixty
««'von of chlorine liberated TJ.n . .
„ '""' "'""•" <">t extracted Si„„ .. * ""ff" M'tcnt, 47
'"■»« o.,»ri«„t „:!;•"" »'■'- »' «» vela.,-,,- J;; ,;: ;^;»
2»»er.l„,c„pp.,p „„
°»0 er„„, i„„ „,|j^
^00 grains gnji.
Sulplmteofsoda 1.87 ~ir
«"»'*ofc„;;;;::; .«'-'■"""■""•
• • • • J U,Uo
I* is evident from this n.nf ^'^^ °"
<^««faincd in theonVin «^'^«"tj^-three per eent of th.
-- per oent::r;^ rtrr^t^^^^^'-''^^'-^^^^^^^^
L: ? °^-»>-Woride or o.ideTd"; ""'"''^' '"^ -'-«-«•"„
culate from the amount nf ^ , "^ "*'* ««ccrtain If „/ ,
ted that ,n order to a perfect cxt.n.r *^^-P«r"»ont a]«o
"'* ^« P'-os.n(ed to the co^pen '""' ^'" ^'^^^^^ ^^ el.lorine j
i
»"« y was ,uffi,i,„j j^
'■^'''oride. It becomoa
««PPer contents, 47
eruture was kept very
POHsibly have affected
^' "^ <lie caJoination
'nt <Iocomposition of
^pper.
'«ccount<.d for i„ the
« volatilized, tlio fol-
icr.
"' *'>'*' -2 grains
wnperature until
chlori
"0 ceased,
i7.33
2.6
'•14=3.8
).oe
copper.
1.00
It of the copper
^d that twentj-
but whether in
'"• Ifwecal-
iii this experi-
ilorine was de-
the copper as
pose that the
of oxide, and
e- The result
' Was decisive,
♦lie product ;
wiment also
^s of chlorine
It will bo recollected that (he experiincntH juHt described wore
made with an ore joor in sulphur; containing no more of
that clement in pro|M>rtion to the copper than is contained
in copper pyrites. The rvjsults not proving satisfactory, I pro-
ceeded to ixperiniont ujion ores tontainlng more sulphur, taking
care always to keep (ho t( mpcrature very h.w, and to interruj)t the
calcination bo soon as the developeinent of sulphurous acid had
ceased, and while that of chlorine and other ga.se.s was going on.
The following are some of these cxiHirimonts, with their results:
500 grains ore from Escott, containing 10-4 per cent copper
(and both iron pyrites and cop{K)r pyrites), were calcined with 500
grains of iron oxide and 200 grains of salt. The product weighed
1184 grains, and gave with water a solution from which iron pre-
cipitated 40G grains of copper. Since fifty-two grains were pi-eseut
in the ore operated on, it is evident that 94 2 percent of the
copper was removed in a soluble form.
500 grains ore from Escott, containing 45 per cent of copper,
and a considerable amount of iron pyrites, were calcined with 100
grains of iron oxide and 100 graitis of salt. The result weighed
618 grains, and when heated with water yielded a solution contain-
ing 22-2 grains copper. 22-5 grains were present in the original ore;
hence 97- 7 per cent of the copper was dissolved.
300 grains of the same EfcM ore, with 45 per cent of
copper, 300 grains of ore from Bruce ftlines containing 8 7 per
cent of copper (and no iron pyrites), 300 grains of iron oxide, and
300 grain.s of salt, were calcined until chlorine was strongly de-
veloped. The result treated with water i .5 a green solution con-
taining thirty-six grains of copper. .Since the ore used in this
experiment contained 39-0 grains copper. 909 percent of the metal
was removed in a soluble state.
300 grains of Bruce Mine ore of 8-7 per cent, 200 grains of
iron pyrites from Brockville, 300 grains of iron oxide, and 200
grains of salt were calcined in the manner above mentioned. The
product gave with water a solution containing 27-1 grains copper.
The ore contained only 26-1 grains, and the excess may have been "
derived from the iron pyrites. In this case, therefore, the whole
of the copper of the ore was dissolved.
The same u»ixture as the preceding, calcined for a longer time,
yielded only 145 grains of copper in a soluble state.
400 grains of Bruce Mine slimes of 5-1 per cent, 400 grains of
iron oxide, 100 grains of pyrites from Brockville, and 100 grains
8
u UrauH ol hm>U coppor pyrites of o-k,.
calcuod t.,gothor. Tk- product wl "< -'"Ogn,i„„ of s„lt wero
.In ord,,. ,. p,,^^. ,,,^^^ ^ » t e or wen, rendorod soluble.
th.« favorable .......If, the last 7x1 . ' ''''^"^'"' *« Producing
-i''« boin, exei..ded'no.n Z : ^:'"; '^"^ -P-'^^- the irou
•%'. only :j;{.4 .r«in.s of enp,„./; ^'" " V" «'''^"""f,'«nd li.iviat-
---iyin«te.dor„i„.;j;;;;::^;-'vod;t,..^
pared by e.Ieini,., iron p'rij ,",. '^ '7 «-J« -od was pre^
d/Jing. Tl,o following rial, w " ""'' ""^" ''-^'^'^ting and
^-1^ -re to the n.ettdt ,:;,:;:':; '" " T"'' "PP-'"-
««'-ry.n,. out the proce.H on a l!^' 1'"'""'^ ^' "^«P*«J in
"-ely «tin-ed on an iron p, t Z T * '"'^' •"•^'" '- --e
wood in a conunon «tove. And f "^, '''•" '"" '^'"''^^ »>"'«*« of
o-do of iron neceasary in tl ' ^ I' " T" ''^ «-» "'«* the
-:;pcnnu„ted on. Thi. ore wa frrrr^*;''"^'^ ''•^'•" ''»« ^^e
v'"«. and had the followin.. 2lZ ^^^ ''''"•'^"*^«'' ^-«"«ox.
Copper " ''"*'""^"' <*0'npn.sition :
^•"^^ .!'.*.'.".".! 860
«"ll'l>ur(bjr difference).. 30-31
Wilicft and argillaceous nmt'ter ^^'^^
26-75
Those figures corre.spo„d to tho f.ii •
ni
Copper pjTites . .
Iron pjri teg
Quartz, Ac
10000
ineralogical compa.
.. 24-72
.. 4!) -79
•• 26-75
101.26
of ob..,„i„g tl,e neoe^ry C : r° P""-P»"Kor .hep„rp«
'ned.
wliieli water di»-
|ncd 204 grain.;
^^•ent,lOOgrninfl
^T'liHH of salt wero
'•"'■"^ rroin wliicl,
>»f'y ninoty-eight
ciiilorcd soluble.
'""I to producing
Pfofed, the iron
'"K and lixiviat-
•t i«, He verity per
'"ti><ofiire-cIay
lo used was pre-
lixiviating and
'cr npproxinia-
fw adopted in
"lixhires were
ited billets of
»wn that the
from the ore
"car Lonnox-
8-60
30-31
3434
26-75
10000
[ical compo.
24-72
lf)-79
J6-75
1-26
ted of one
irth rock.
>e purpose
' quantity
I
10,000 grains of the ore were first calcined with 2,000 grains of
wit, and without oxide of iron. The result weighed 1 0,8(50 grainn
Water oxtracte<l from it 0-S per cent of copper, and diluted
sulphuric acid dissolved further a quantity of floeculent matter con-
taining 1-8 per cent. Of the 8G0 grainn copper contained in the
crigiual ore there were therefore,
DiMolved by water 86-88 grainn = lo por cent.
DlMolved by dilute acid 195-48 " " 2i '<
Left in the residue 577-64 " " qh "
860-00
The product of the foregoing experiment after lixiviation and
drying assayed (V i per cent, copper. A .second calcination was
perlormed with it and other substances having copper content.s as
follows : '
400 grains lixiviated product of aoove experl
ment containinE 6-4 ner cent or\,< _>„•_
.... B " •• !'«:« tens — ijb grains copper.
2000 grains Iresh ore ofl3-6 percent = 172 "
l-'OO grains salt
7200 grains mixture with 478 grains ropper.
After being calcined in tlic usual manner the whole weighed
7850 grains, and contained four per cent of copper soluble in water
Blightly acidulated with sulphuric acid, and Ml per cent of
copper insoluble therein. Of the 428 grains there were therefore,
Dissolved , , .
, . . , 314 grain?.
Left insoluble ^.^ „
Unaccounted for 27 "
428 grains.
Thus 73-3 per cent of the original copper content.s were obtained
in a soluble form.
The product of the foregoing experiment was, as in the first case
hxiviated and dried. It then contained ^ per cent of copper
and was calcined a third time, with fresh ore and salt in the foU
lowing proportions :
4800 grains residue with IJ per cent. . . .= 64-0 grains copper.
2400 grains fresh ore of 8-6 per cent = 204-5
1440 grains common salt
8640 grains, containing 2"w7 grains copper.
iCi
I ii:
. 10
5'iiifl mixture was trant a •
weighed 8900 erain. T '° ^^^ "s«al manner Tk
^"" grams, and contained '""'"•er. The product
Soluble
Insoluble. . .". ' 2 ■ '^7 per cent. = 24R o.«-
l^naccounfed foV.V.V.V.:. . .''' " 22.2 ' T 'T''
13 « „
Thus 91-4 per , „ 270.4
J«' outage, »„, t' XT; '"""' ~«» ™« .ha„ t'
2000 grains residue of aa ■
1000 " f..„i, •■** per cent = 8-fin...o-
3600
The product weighed 3710 grains and . V- ^'"'"' '"''''■
^-« oxide and insoluble Jtter ' ''"''^ '« ^'^"«^« -•
Cupnc oxide insoluble in t. '2-13
^ ^"te sulphuric acid '""'''• '^"ddi-
Cupnc^oxide soluble i„ diiui: "J ui^ V "^^ = 0.22 copper.
Sulphate of soda..' 13 = 0li "
Chloride of copper.:;;::; '^'^a = 433 sulphur
^erch oride of iron V. ' " ^ = 2-22 copper '
^'^'o-deofsodiu..b,differ;;;;:;;:;:-;;//
Of the 94-8 o-min. ^<^O.oo
DiSSoliredby ivftfpr
Dissolved by dili.fl "• V ' ^^ -36 grains - sr . 00
I^eftinre&e '"'"^- ^'OS " = ^3 P^-C^nt.
t^iaccounted for 8-16 "
-20
= 8-6
= -22
It
94-80
•»«'•• The product
246 grains copper.
2.2 <t „
1-3 «( „
1.4 '< u
'the ore originally
2d, after thorough
'.* copper. Now
"1 iess than this
ore in dressing,
having produced
8« the above, it
copper contents
liowever, almost
the ore, and by
csh ore to pro.
lent extraction
ts usefulness in
the following
ms copper.
ns copper,
as follows ;
•22 copper.
II II
■33 8ulpiiur_
22 copper.
ore, there
sent.
11
If however we neglect the 8C grains copper contained in the
residue used, which it is perfectly reasonable to do, then 95-7 per
cent, of the copper in the ore is dissolved in water alone and
the whole of It on the additional use of a slight quantity of dilute
sulphuric acid. One of the most striking facts deduciblefrom the
results of this experiment is that 4(v64 per cent of the sulphur con-
tained in the original ore was converted into sulphuric acid and
then into sulphate of soda. The amount of chlorine liberated by the
formation of such a large quantity of this salt, must have been
greatly in excess of what was necessary to render the copper soluble
On account of this latter circumstance I attempted to reduce
the quantity of salt used, and made four calcinations in the propor-
tions of two parts of residue, one part of fresh -re, and one fourth
of a part of salt, The ingredients, used with . .ir copper contents,
were as follows.
OR8. ' o„s "■ 3 & 4.
J^'f ^ 2000 with 8-8 Cu 1500 with 66 Cu 200o"wUh 20 Cu
Fre8hore......l000 '< 86-0 " 750 "64-5 -' lOOO '< 86 ''
Salt 250 " 175 u 25^ „
3250 with 94-8 Cu 2425 with Yl -1 Cu 3"25o'withTo6 Cu
The products of these four experiments contained of copper
respectively : ^^
1- 2. 3. 4.
Soluble in water sg^i'l An\ -^TL ' "^''-
wc.„„Mf.r...::::::^^«S ,6« llll \lt
9*"8 71-1 106-00 106*00
These results were by no means encouraging, yet the quantity
of salt was quite sufficient for chloridizing the copper. One fact
must however be mentioned with regard to these trials ; they
were very diligently stirred during the calcination
No other resource was left but to return to experimenting with
a larger quantity of salt. Accordingly the following ingredients
were mixed and calcined :
2950 grains residue of 1-0 per cent, = 29-5 grains copper.
1500 fresh ore of 86 " =129-0 '<
750 " salt
5200 grains containinir TTo~I
e vuniuiuiug 158-5 grains copper.
12
Th
cotitainiiicr
^-y^ave a product vvoMun. 5970 •
^•33 per cent r , " ^''"'""^ «"^
^^^^^pe. cent Cu soluble hMvatcr==,22-,o
0-33 .. • , '" ^''"f« acM = ,,.59
' naccoiinted for ~ '^'1<5
■Neither wis tliia 158.50
In order to ascerf^m „ . .^ " ^ operation. ""^^
2000 grains residue on. 1
500 " salt =8«
3500 grains containing..
■i ne operation was n....^- , '°^ ^''"^'"s coi)per
4-J8
It will be seen that th?« » ) • • ^*'^"*-*
«»iallerqn,nntity of sail which n,T ° «lcin,itio„ mthth-
>S left almost wholly™; 'h/r°"''^ "^"^ *« mi* 1
>"»«dio„h were ' ""*=""l»ci during ft^ operation. Th°
3250 grains witli,.
They gave „„ „a,„j„„y^„- - ^ — • _• • • jor gr.l„, ,„p,„
- " per eent, equal to Sis, IT "' i'™''"'. eontaiuio,'
~ are duri, .,,„,„"„-' tr^tt '''
Thp f • X- ' ta me ex-
««-r:&rvrr::[r:^ri™»-
^wn sati
sfactory^
""tl contain
79
Uior
y- This
"I'xture
ised any injurious
he following mix-
"I'ns copper.
i.?
the following mixture containin^r only one fifth part of salt was
calcined :
2000 grains residue of 11 per cent = 22 grains copper.
1000 " fiesh ore of 8-C " =86 "
200 " salt
3200 grains containing 108 grains copper.
This oxperiniont was uriile with the sama care as the others
and with as little stirring as possible. The result weighed 3250
grains, and contained
2-33 per cent, soluble in water = 7tJ-7 grains copper.
•44 " " in dilute acid = 14-3 "
Unaccounted for = i7-o '<
lins copper,
•■"'g as possible.
L,3
copper.
tJy successful,
^as extracted,
'as injurious,
t'on with the
the mixture
ation. • The
$
108-0
Since therefore only 71 per cent of the copper was extracted, it
follows that one fourth of salt i.s the minimum quantity which can
be used, and at the same time a complete extraction accomplished.
I here clo.sed this series of experiments, having obtained all the
definite results sought for. It appears certain that 95 per cent of
the copper contained in an ore such as that produced by the Cape!
mine can be extracted iu the humid way by calcining it with
twice its weight of impure iron oxide (perhaps less would be suffi-
cient), and one fourth of its weight of salt ; provided always that the
operation is performed at a very low temperature, that it is not
continued beyond a certain point, and that while it is going on the
materials are stirred as little as possible. Whether equally good
results can bo obtained in practically applying this process, is a
matter which can only be decided by experience ; but there ap-
pears to be no reason for doubting that it would be completely
successful on the large scale.
opper.
containing
n water; a
Curbed the
is the ex-
•urth part
■isfactory,