Note: Descriptions are shown in the official language in which they were submitted.
~7~
~il687~
1 The present inv~ntlon relates to a process for
extractlng me~al from its ore, and more particularly to
a process for the extractlon of zinc from it~ ore.
Several o~ the ores ~rom which it 1~ commerclally
viable to extract zlnc are sulphidic ln nature, and are
currently processed pyrometallurglcally. Such processes
require considerable heat energy, so that in con~equence
there is an increaslng lncentive to locate proce~ses which
can be effective at moderate temperatureQ.
~ccordlng to the present inventlon thare is provided
a proce~ for the extraction of zinc rom a zinc sulphide-
containing ore, compri~ing the step of agltating the ore
ln ground form with an aqueous ~ulphuric acid leach
ll~uor containing a~ the primary oxldising agent one or
both of hydrogen peroxide and monoperoxosulphurlc acid
at an elevated temperature up to the boillng point of the
le~ching llquor.
The term'prlmary oxidislng agent" is used herein to
lndicate the oxidi~ing agent which provides the ma~or
proportion of oxidation. Thus, e.g. oxygen or air may
be sparged through the vessel containing the mixture of
leach liquor and ore, if desired, but it is the hydrogen
peroxide and/or perox0monosulphuric acid, hereinafter
referred to as PMS, which oxidises the ma~or proportion
o zinc sulphide, thereby enabling the zlnc to go into solution.
The proce~ of the pre~ent invention is particularly
applicable to those ores in whlch the zlnc sulphide is
- 2 -
'
GC78
~ i87Z
1 present as sphalerite (zinc blende). Although, preferably,
the zlnc sulphlde represents the major proportlon of the
ore, the process according to the pre~ent invention can
also be employed to extract zinc from ores in which the
zinc sulphide represents only a minor proportion of the
ore, for example le88 than 204 w/w. Other components of
the ore aan lnclude chalcopyrlte and arsenopyrlte. It
i~ partlcularly dlfficult to extract zlnc from sphalerlte
ores using only sulphurlc acid leachlng liquor~ containing
only oxygen as the oxidant at atmospheric pressure, ln that
no more than approximately a third of the available zinc can
be leached out in any reasonable ~ngth o time. By the u8e
of a process according to the present invention, however,
under comparable conditions, not only can a higher
proportion of zinc be extracted, but the rate of leaching i9
also faster.
It ls highly preferable for the temperature o~ the
leaching liquor to be maintalned during the leaching at
a temperature of at least 70C, preerably at least 80C.
Although the upper limit of the temperature rang~ is the
bolling polnt of the leaching llquor under the conditions
employed, i.e. pressure and concentration of solvents in
the sulphuric acid solution, a temperature ln excess of
100C ls normally not employed. In practice, the
temperature of the leaching llquor is often malntained
ln the range of 90 to 100C.
Another important parameter, which is independent of
the temperature of the leach liquor, is the particle size
of the ore. As the particle size of the ore decreases,
-- 3
GC78
i87~
l so the efficlently of utilisatlon of ths primary oxldising
agent lncreases. Thus, although the present invention
process can be employed ln respect of partlcles retained
on a standa~d BSS 50 mesh, it ls preferable to use particles
which pass through BSS 50 mesh, and more preferably
partlcles which pa~s through a ~SS lO0 mesh. In hlghly
preferred embodlments, the ore i~ ground to about BSS 200
mesh or smaller beore being leached. The lower limit of
the particle slze ls, in practice, determined by the
apparatu~ to be employed ~or separating the leach liquor
from the spent ore. Generally, at least the ma~or
proportion of the particles are retained by a standard
BSS 250 meRh.
An lmportant varlable ln the process of the present
lnventlon i~ the acidlty of the leaah llquor. Thi5
~; par~meter i~ independent of both the particle ~lze of
the ore and the temperature of the leach llquor. ~eslrably,
the leach liquor i8 maintained at a pH of below 1.5.
Durlng the cour~e of the zinc extractlon ln solutlon, there
1~ a tendency for the pH of the llquor to rise. Allowance
can be made for thls tendency by ensurlng that enough
acld ls present lnltlally, or by addlng further amounts of
acid durlng the course of the reactlon, or by employlng
a comblnation of the two technlque~. In preferredj
~mbodlment~, the acidlty o the leach liquor 1~ malntalned
... .
at a ph of up to or below 1.0, because u~e of such an acldlty
enables a hlgher proportlon of the zinG to be extracted
in ~olution at a faster rate than if a less acid solutlon
: `
_ 4
GC78
37~
1 is used. Such a~ acidity often can be achieved by employing
an initial sulphurlc acid concentration of at leaet 150 gpl,
desirably in the range of 170 to 250 gpl, but it will be
recognised that the actual pH obtained will vary with the pulp
density. It will be recognised, that in the case of the use
of PMS as primary oxidising agent, PMS is normally employed
in solution in sulphuric acid, and allowance for thls
sulphuric acid must be made in calculating the amount Of
sulphuric acid present in the liquor. Moreover, where PMS
is added during or throughout the extraction process, its
introduction, coupled with that of sulphuric acid, means that
less acid need to present initially. However, the presence
of exces~ acid is not in itself inherently disadvantageous
to the process, except to the extent that useof unnecessary
amounts of any Inaterial renders any process less attractive
commercially. Instead of treating the zinc sulphide mineral in
a single stage, the process can also be effected in two or
more stages, in successive stages increasingly depleted zinc
sulphide mineral being contacted either with fresh sulphuric
acid solution containing or to which is added the primary
oxidising agent or with solution that increasingly approaches
fresh ~olution. It will be recognised that whilst the fresh
solution desirably has a pH as indicated above, when the
solution passes to successive stages in the process it eontacts
less depleted zinc sulphide mineral and a progressively rising
pH may be tolerated.
The hydrogen peroxide or PMS can be introduced into
the leach llquor in various methods. In the first method,
all the hydrogen peroxide or PMS to be used ls present
GC78
1116~7Z
`: `
l lnitially in the leach llquor. Thi~ method is les~
preferred, because it normally results in greater losses
of hydrogen peroxlde or PMS through decomposition than do
the other methods descrlbed hereln, and also could
introduce an undeslrable con~traint upon the pulp density
that could be employed. In other methods, a part of the
hydrogen peroxide or PMS is introduced durlng the
extraction perlod. Such methods are preferred, in that
they tend to result ln a more efficient utilisation of
the primary oxidant. The introduation of the prlmary
oxidant can be either at prearranged lntervals or at
a pre-arranged rate throughout the leaching perlod. In
such methods, the total amount o primary oxldising agent
requlred can be pre-determlned by, for example, carrying
out prellminary tests on a sample of the ore under the
other conditions that would be employed, i.e. partlcle
slze, temperature and acldity of the leach l1quor and
duration of the leaching period. In other and more
preferred methods, the hydrogen peroxide or PMS i8
added during or throughout the leaching period ln amount~
and/or at a rate determlned by the ore itself. Although
lt will be recognlsed, that some varlations can be easily
achieved without departlng from the splrlt of this method,
lt ls hlghly convenient to employ the output from a
standard electrode pair monitorlng the electrochemical
potentlal ~emf) to regulate the lntroduction of the
hydrogen peroxide or PMS. Such regulation can be
achleved by establishing a palr of limits about the
- 6
.~ :
.
GC78
37~:
l desired emf, herein measured with respect to a ~tandard
calomel electrode which iq normally at least 450 ~V, and o~ten
from 450 to 650 mV, ~o arranging that when the lower llmlt
1~ reached, introduction of hydrogen peroxide or PMS into
the leach liquor is triggered, and that when the emf is
at or above the upper limit, the flow of hydrogen peroxide
or PMS is cut of. If desired, the flow of ths prlmary
oxidislng agent into the leachlng liquor can be aut in
and cut of~ sharply at the re~pective limits, or
alternatively, by using a proportloning pump whlch pumps
the primary oxldising agent solution at a rate ln lnverse
relation~hip with the emf, a smoother and a closer control
of the emf can be achieved. Use o~ methods in which a part
of the prlmary oxldising agent i~ added durlng or throughout
the leachlng period, and ln partlcular in tho~e method~ in
which the lntroduction is controlled so as to maintain a
substantially constant emf, enables more eficient use to
be made of the primary oxldlslng agent~ By employing
approprlate control of the lntroduction of the prlmary
oxidlslng agent, ln comblnation with the grlndlng of the
ore to an appropriate partlcle slze and by uslng a leach
l$quor of the appropriate acldity, relatlvely efflcient
u~e of the primary oxidising agent can be made. Thus,
ln a proce~s ln whlch the emf ls malntained at 450 mV or
higher, the partlcle size is below 100 mesh ~BSS) and
preferably below 200 mesh ~BSS) and ~he acidity 1~ at or
below pH 1.2, the utilisation of the primary oxldlsing
agent normally will be wlthin the range of about lOOX to about
GC78
7~
1 200X of the theoretical amount re~uired to extract lOOX of
the zinc from the ore into solution, in the c~se of hydrogen
peroxlde and about 8~% to lOOX in the case o PMS.
.~, . . .
~he further that th~ process strays away from ~uch a
comblnatlon of parameters, the greater the tendency to
; waste prlmary oxldl~lng agent. Thu~, e.g., use
of an ore containing a high proportlon of par~iclas in
the range of above lOO mesh ~BSS) can require over 500
by weight of the theoretlcal ~mount. Slmllarly, where
the lntroductlon of the primary oxidl~lng agent ls not
controlled properly, the rate of extractlon of ~lnc lnto
... . .....
~olutlon can suffer, and utillsation of the prlmary oxldl~lng
agent can ~lso suffer.
- ~ Often, slnce zinc sulphlde ore can contain i9 an
lmpurlty iron compounds, such As pyrite, the leaching
~ liquor can contaln undeslrably high level~ of iron compounds.
; ~ The level of ~uch lron aompounds, however, can be
drastlcally reduced by reduclng the acidity of ths leaching
llquor to wlthln the range of pH 2.5 to 4.0, preferably
about pH 3.0, and maintalnlng the pH of the llquor at
uch a value untll ferrlc salts have preclpltated out,
often a period of up to an hour. ~he pH ad~u~tment can
be effected by any sultable alkallne hydroxlde, such as
~odlum hydroxlde or ammon ~ hydroxlde. Alternhtively,
the pH can be adju~ted to a pH of approximately 1.5 by the
additlon of ammonlum hydroxlde, and the lron 1~ preclp$tated
out of solutlon a~ a ~arrosite salt.
- 8
,
GC78
1~1687~
1 The concentratlon o hydrogen peroxide solutlon whlch
is lntroduced into the leachlng liquor can be any commercially
available concentration up to 65~ w/w. Concentratlons
o~ten employed are in the region o 6% w/w, 10~ w/w, 20% w/w,
and 30-35% w/w. Preferably the solutlons contain stabill~ers
In hlghly desirable embodiments, the princlpal
oxidi~lng agent is PMS, because it tends to be more stable
under the process condltions than does hydrogen peroxlde.
In consequence, ore that has been ground to some extent
le~ finely can be employed than lf hydrogen peroxide were
to be used. The concentratlon of PMS wlll normally fall
within the range of 5 to 75~ b~ weight, the concentration
of from 10 to 65~ by weight often belng used. In one
convenient method for lts productlon, PMS ~olutlon 1B
made by reacting agueou~ hydrogen peroxlde wlth oleum
or concentrated sulphuric acid. Consequently, solutlons
containing PMS often contain in addltion a small percentage
of hydrogen peroxide.
Sultable condltions for the production of PMS are
described in Brlti~h Patent Specificatlons Nos 738407 and
844096. Broadly 6peaking, it is particularly deslrahle to
employ concentrated hydrogen peroxide solution, e.g. in the
range of 60 to 85~ w/w hydrogen peroxlde together with oleum
since ~uch a combinatlon enables conversion of the sulphate
specie~ to peroxymono6ulphurlc acid to occur to a greater
extent than when more dllute solutlons are employed.
Provided that precautions normal in respect of exothermlc
reactions, such as cooling, are carried out, PMS can ~e
GC78
87~
1 generated aa~ly and ef~iclently by the method outllned
above~ Alternatlvely, lf desired~ PMS can be obtained
by hydrolysis o~ a peroxydlsulph~te, especlally peroxydi-
~ulphurie acld produced, e~g. by electrolysis, or the ~odlum
po~a~sium or ammonium salts thereof/ hydrolysi~ to PMS
rather than continuing to h~drogen peroxld~, occurring mo~t
rapldly at temperature~ ln the range o 50 to 70C. ~ecau~e
PMS ~olutions tend to lose thelr av~ilable oxygen aontent upon
~torage, even at amblent temperatuxes, lt 1~ praferable to use
~re~hly prepared PMS, for exampl~ mada and u~ed on the sam~
day. It 19 convenlent, ln som~ ~mbodiments of the pr~sent
~nvention, to produce PMS at the rate at whlch it i5 ¢ongumed,
such as by controlling the rate at which hydrogen peroxide and
sulphuric acld are ~ed into a reaction chamber by the rate at
whlch the PMS ~olutlon ls lntroduced into the leachlng llquo~.
Su¢h control can be effected lndependently from or in con-
~unctlon wlth the method of controlling the rate at which
PMS i~ introduced lnto the leaahing liquor. It will be
r~aogni~ed that apparatus for controlling the rate of flow
of fluld~, 3uch a~ valves and proportioning pump6 are well
known, a~ are mechanlcal and electrical system~ ~or transmittlng
the control &lgnal ~rom a detector to these control means.
The pulp denaity of the mixture o ore and leach
liquor can be any density up to the maxlmum at which the
mixture can be aglt~ted. Dn praatlce, the pulp den~ity
i~ o~ten around 40 to 50~ beaau~e at ~uch pulp dan~lt~e~
the equlpment ls belng u~ed relatively ~f~iciently and
the flnal concentration ~f zinc in the l~aching liquor
-- 10 --
GC78
~ ~16 ~7 ~
1 ls relatlvely high, ~ereby expedltlng its subseguent
removal from the leach liquor and purlficatlon.
Lower pulp denslties, e.g. in the range of lO to 20%
can be used/ if deslred, and ar~ partlcularly sultable
for demonstrating afectivene~s o hydrogen peroxide and
P~S on the small 3cal0.
Reference hereln ha~ been made to the treatment of
ore, but lt will be recogni~ed that th~ pr~ent invention
i~ eapecially useful in re~pec~ of dre~ed ores, such a~
ore sub~ected to a differentlal ~otatlon to separate the
zlnc concentrate rom, e.g.,galena.
zinc whlch ha~ been extracted into solutlon in the
l~aah liquor can th~reafter be removed ~nd purifled by
.
.... . . , ., . . _ ,.. _ , , _ . .,
methods conventionally employed when sulphated aalcine
has been leached with ~ulphurlc acid. Consegu~ntly, ~h~
proaes~ can lnclude neutrallaation with zina oxld~ to
precipltate iron, arsenic, and antimony, clarlflc3tion
of the pulp in thickeners, and displacement of cadmlum
by addltion of zinc dust. One ~enefit of the pre3ent
lnventlon 1~ that the proportion o arsenl~ extraçted
into solution from arsenopyrlte, the arsenia-containing
mlneral mostcommonly associated wlth sphalenite is compara-
tlvely low, thereby reducing the problems of di3posing of
; extracted arsenic. One additional feature ari~lng from the
use of hydrogen peroxlde and PMS in the present invention
is that, whilst on the one hand, the amount of polsonous
hydrogen sulphide ga~ involved i8 exceedingly small, to the
point of being frequently undetectable, a very substantial
GC78
~ 7 ~
l proportion of the sulphur is produced in elemental form
rather than being oxidised through to gaseous sulphur dioxide.
This is a feature that becomes increasingly advantageous as
restrictlons upon the admission of sulphur-contalning gases
into the atmosphere are tightened. Moreover, transportation
and sale of a solid like ~ulphur i8 much ea~ier than a gas
.. ..
llke sulphur dioxlde which would requlre either additional
processing stages or to be liquified before it could be
transported readily- In view o the fact that PMS has
gsnerally greater stablllty to decomposition tha~ doe~
hydrogen peroxide, PM~ be used as a secondary oxidislng
ag~nt over a wide range of conditlons from ambient up to
the boiling point of the leachlng liquor. When the
~econdary oxidation agent 1~ added under the condltions
described it is hlghly desirable for lt to be present
durlng a substantlal proportlon of the time, preferably
added incrementally or continuously during the leaching perlod.
_, . . _ ... . .. .. _ .......... . . .___
Various zinc sulphide ores contain additionally ~~ ~ -
copper sulphlde as chalcopyrite. The prlmary oxldislng
agents described herein can be employed to leach out the
zinc at a faster rate than the copper, thus effecting a
partial separatlon. A suitable method for preferantially
extracting zlnc from an ore containing sphalerite and
chalcopyrlte comprlses the ~tep of agltatlng the sph~erlte and
chalcopyrite-containing ore at a temperature of from 65
to 75C with aqueous sulphuric acld at a pH of below 1.5
and containing sufficient hydrogen peroxide to maintain
the oxidatlon potential at above 450 mV, preferable between
- 12 -
GC78
7~
1 450 mV and ?00 mV, and separatlng the ore from the leach
llquor after a pre-determined proportion o~ the zinc has
been axtracted in solution. In practlce, the pre-determlned
proportlon of zinc would generally fall wlthin the region
of 80 to 95~, typically appro~ately gO% by welght. Such
a process would ~roduce a leach llquor containing a
comparatively small proportlon of copper, and therefore
reduce the C08t of produation of substantlally pure zlnc
matal. If desirea, thereafter, the ore whlch has been
; 10 separated rom the zlnc containing leach llquor could be
contac~ed with fresh sulphuric acld leach llquor
contalning hydrogsn peroxide or PMS at a tempera~ure of
between 75 and 100C, and a pH of below 1.5 to extract th~
remalnder of the zlnc and copper into solutlon, thuq
- produclng a leach liquor that i~ comparatively rich in
- copper.
~~~ ~~ ~~ In an alternatlve method for preferentlally extractlng
zlnc from a sphalerite and ohalcopyrite-contalning ore, the
ore can be agltated with a PMS and ~ulphuric acid contalnlng
leach llquor at a temperature o~ above 70C untll a pre-
determined proportlon of zlnc has been extracted lnto solutlon,
preferably from 75 to 90%, typlcally 80%, and thereafter
the partlally spent ore and leach liquor are separated. The
partlally spent ore can be contacted with freJh leach ll~uor
as described in the immedlately precedlng paragraph.
Havlng descrlbed the inventlon generally, speclflc
embodlments will now be described more fully by way of
- 13
GC78
~ 8 7 ~
l example. De~criptions of alternative proees3eQ, ~hown by
the preflx ' C ' are pre~ent by way o~ compari~on only.
....
In Example3 El to E8 and compari~ons Cl and C2, the
ore was an Australlan concentrate, typlcal oS material
currently processed pyrometallurgically, contalning a~
the major constituent sphalerite, and al~o ~ont~inlng
pyrlte, with trace~ o~ chal¢opyrite and metallic iron.
Its compositlon was 52.0~ Zn, 3~.2~ 8, 10.0~ FeO, 1.0% Pb,
1.4 SiO2, 0.44 Al203, 0.24S CaO, 0.034 MgO, percentages
b~lng by weight. The sl~a distributlon of the concentrate
us~d ln Example~ El and E2 ~as as follows
~ABLE 1
,. ........... . . . . .
BSS Mesh % ~y weight Welght %
+ 52 7 0 7.0
- 52 +100 25.4 32.4
100 1200 21.0 53.4
-200 46.4 100.~
In the remaining Examples E3 to E~ and eomparlsons Cl and C2
the concentrates had been ground to pass through ~SS mesh 200.
In Examples E9 to El2, the ore was an ar~enical mixed
sulphlae concentrate produaed a~ a by-product o~ tin operations,
and currently processed pyrometallurgically. The ma~or phase
ln the concentrate was pyrlte, and minor phases were sphalerite
and arsenopyrite and chalcopyrite, the latter belng associated
to some extent with the pyrite. Its composltion was 11.S% Zn,
2.5% Cu, 4.0~ As, 31.0% Fe, 0.8~ Sn, 37.0% S, percentages
being ~y welght. The concentrate had been ground to pa~s
through the BSS me~h 200.
_ 14
GC78
li~687~
1 The compo31tlon~ of hydrogen poroxide employed are ~hown
in Table 2 with other conditlons and reeult~, and the compo~ltion
of the PMS 301ution was peroxomono~ulphurlc aald lO~, ~ulphurlc
aeid 24~, hydrogen peroxide 1.2%, and water 64 . 84, percenta~e6
being by waight. The PM~ solution W~8 ob~ained by reactlng
70~ w/v a~ueou~ hydrogen peroxide and 9~ w/v sulphuric aala
- wlth oontlnuou~ stlrring and aoollng behlnd a safety ~ereen,
and thereafter diluted to a ~oncentratlon of 10~ w~v PMS ~y
addition of dlstllled wat~r.
~he apparatu~ u~ed ln eaah Example and ~ompari~on
comprl~ed a 250 ml reaction ve~el itted with a ~lve necked
lid, and heating elem~nt, a thermostat accurate to ~2C, a
thermometer, a propaller stirrer operating at 4~0~ lO0 rpm,
water cooled condenser, a parl~taltic pump for pumping the
~olutlon, and a standard platinum/calomel electrode to mèa~ure
the potentlal. In additlon, in the Examples, the àpparatu~
lnaluded a f ine bore glas~ tube, whlch was so shaped and
positloned as to introduce the ~olut~on of oxldi~lng agent
lm~edlately beneath the ~tirrer.
In each Example or compari~onl a 31urry ~10~ w/v
lSg/150ml) of ore ln a sulphurla acid 301utlon oS a given
concentration wa~ lntroduced lnto the reaction vo~el,
~tirred continuou~ly and heated to the temperature
indlaated ln Table 2. Throughout tha reaction perlod
the agueou~ solutlon of the ~elected prlmary oxldi~lng
agent was lntroduced into the slurry lntermlttently ~o
as to malntaln an oxidatlve environment, normally wlthin
the range o 450 to 7~0 m~, although ~ome varlatlon
~:78
17~
1 outside that range i~ tolerable. Ater l, 2, 4 and 6
hour ~amples of the leachlng ll~uor were taken and
analysised for zlnc content and expressed as a percentage
o~ the total amount of zinc known to be present ln the
ore initlally. After 6 hours, the electxo chemiaal potentlal
(Eh, expres~ed in mV with respect to the calomel electrode),
the pH, an~ the lron concentratlon in the le~ch llquor
wer~ measured.
In one minor v~riation, the entlre amou~t o~ oxldising
agent in Example E8 wa~ added during the first three hour~.
In comparlsons Cl and C2 no solution of oxidislng agent
were pumped into the leach liquor, but lnstead re~pectlvely
oxygen and argon were ~parged into the reaction ves3el3
continuously durlng the extractlon period.
The reaction conditions and extraction results are
summarised ln Table 2 herein below. In Table 2, the
~; heading % TA is the amount o~ oxidant employed expressed as
~ .
a percentage of the theoretical amount of primary oxidlslng
agent re~uired to enable all the zinc to be extracted lnto
solution in Examples El to E8 or all the copper and zlnc in
Exatnples E9 to E12, assuming in El to E6 and E9 and E10
oxidation solely by hydrogen peroxide, and E7, E8, Ell and
E12 oxidation solely by PMS, and baslng the %TA upon measured
total zinc content of the solutlon and residue. The heaaing
Vol Added is the volume of either H202 or PMS ~olution added,
and the heading Fe Conc~ is a measure of iron in solution,
whether in a ferrous, or principally, ferric state.
- 16
GC78
iB7~
A~L~ 2
Example/ Vol. ~22 H2S04
Comparl~on TecP' Addedstrength ~ TA Conc.
Number ml % w/v gl~ 1
~1 7~ 60 30 444 128
E2 90 80 30 593 128
E3 90 140 6 207 128
E4 90 91 6 134 171
~5 90 112 6 165 213
E6 90 16 30 118 213
E7 90 108 79 128
E8 90 112 8 2 12 8
~9 90 104 6 574 3
~lO 70 g8 6 63 9 3~
Ell go 130 353 32
El2 100 100 272 2
Cl 90 Sp~rg~d Oxygen 213
A,rq ~
~4C2 90 Sparged O~ty~- 213
GC~8
~16;~7;~
~E~L
% Zina Reoov~.
Example/
ComparlYon Eh ~H Fe Conc
Number lh 2h 4h 6h mV
El N.D.~ N.D.* N.D.* 33.0 ~75 0.8 2.0
E2 14.7 33.9 N.D.* 84.3 645 1.1 5.2
E3 13.3 31.2 77.5 79.g 585 1.2 6.1
E4 33.7 60.0 88.4 99.0 550 0.8 4.1
E5 41.6 70.1 98.2 99.3 565 0.6 4.0
E6 41.8 6~.6 85.9 93.6 480 O.S 5.0
E7 46.5 88.1 98.3 98.8 610 0.1 4.3
~8 67.3 95.1 96.5 98.1 595 0.6 4.7
E9 48.3 61.0 91.0 99.0 450 0.4 1.7
E10 47.4 55.2 92.6 98.2 510 0.4 5.4
Ell 72.5 81.4 92.0 99.6 465 0.1 6.8
E12 48.0 86.0 94.S 99.0 575 0.6 4.3
Cl N.D.* 32.8 N.D.* 33.3 288 0.35 N.D.*
C2 N.D.* N.D.* N.D.* 30.5 0 0.3 N.D.*
. __ , , . _ . .. , _ ,
N.D.* not determlned
From Table 2 lt can be seen that the effe~t of rai6ing
the temperature ~rom 70C to ~0C slgnific~ntly ~peed~ up
the rate of extractlon o~ zinc in ~olution from le3~ ~lnely
~round ore. The effect of grinding the ore to bslow BSS
18
GC78
~16~
1 mesh 200 ls to ~ignlflcantly improve the efficiency of
utlllsation of hydrogen peroxlde. An increase in the
concentration of sulphurlc acld tends to resul~ in an
increase ln the proportlon of zinc that can be extracted
withln a given perlod, rom the ore, but that above a
certaln aoncentration, substantially all the zinc i3
extracted. Moreover/ it wlll be seen that when PMS i8
used, the initial concentration o~ sulphuric acld can
be ~ubstantially lower than if hydrogen peroxide were
to be employed. Finally, lt can be seen that there was
no significance in extractlon of zinc into solution gained
from sparging oxygen instead of a chemically inert gas,
, ~ argon, and that both of the~e methods were commerclally
unacceptable even at 90C and ernploying ore milled to pass
through ~SS mesh 200. By comparison, however,, employing
the same tempqrature condltions and milled ore, and the
same or in some cases even longer sulphuric ac~d concen-
tratlon, both hydrogen peroxide and PMS achieved substantially
.
oomplete sxtraction of zinc from the ore during the samq
time period.
In Example~ l9 to El2, the rate of extractlon of
copper into solutlon was also measuxed after l, 2, 4,
and 6 hours. The results are summarised in Table 3
herein below.
- 19
GC78
1~6i~'7~
TABLE 3
Example ~
No. lh 2h 4h 6h
.. . . .
9 12.7 82.1 96.0 98.0
6. 8 17. 3 24.0 92 .0
11 21.7 33.Z 44.3 46.4
12 14.5 38.5 72.5 73.6
From a comparison of Table 2 and Table 3, lt wlll be
observed that whereas a very high propoxtion of the zlnc
had been extracted aftar 4 hours employing hydrogen peroxide
and a temperature o~ 70C, only a very small proportion of
the copper had been extracted.
