Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~3321 10
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The present invention relates to a process for leaching
gold and silver from noble metal containing materials
selected from ores, ore concentrates or wastes of precious
metals, in particular from oxide and sulfide ores or ore
¦ 5 concentrates, also from waste materials of earlier incomplete
¦ leaching, using an aqueous cyanide leaching solution with a
pH value of 8 to 13 while adding hydrogen peroxide to the ore
slurry of an agitated leach or to the barren solution of heap
leach and while maintaining an oxygen concentration of 2 to
20 mg/liter in the leaching solution. By adding
decomposition catalysts for hydrogen peroxide and where ;~
called for separating the formed gold- and silver-cyano~
complexes from the leach solution during leaching, the demand
for chemicals can be lowered and higher yield of precious
metals may be achieved in less leaching time. The process of
the invention has made it possible to substantially increase
the economy of leaching while using hydrogen peroxide as the ;;~-
oxidant. -~i
:
It is known to convert gold and silver by means of a ;
cyanide aqueous solution in the presence of atmospheric
oxygen into soluble cyano-complexes. This is the principle
used to leach these precious metals from ores or ore
concentrates or from wastes of precious metals, for instance
~; electronics scrap. In so-called agitation leaching, the
finely ground ore is dispersed in a water slurry and
following the pH adjustment and addition of an aqueous
cyanide solution with air gassing in cascaded, cylindrical
agitation vessels or Pachuca tanks, it will then be agitated
up to 48 hours and leached during the procedure. Hereafter
the aqueous phase of the ore slurry shall be called the leach
solution. In industry, besides the agitation leach solution,
use is also made of so-called heap leaching, whereby a leach
solution as a rule adjusted between a pH of 9 and 12 and
containing cyanide is made to drip onto heaps of ore, :-
atmospheric oxygen being the oxidant. ~
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:,`
Both in heap leaching and in agitation leaching, an
oxygen deficiency may arise in the ore slurry, resulting in
limited gold yield and lowered rate of leaching. Attempts
already have been undertaken to leach precious metal ores in
the presence of oxidants other than atmospheric air. Among
these approaches is the use of hydrogen peroxide.
Illustratively U.S. Patent No. 732,605 discloses a
procedure for leaching ores, wherein the ore is mixed with a
metal oxide and this mixture is treated in a cyanide solution
containing the hydrogen peroxide that reduces the metal
oxide. The quantity of metal oxide that can be reduced, such
as Fe2O3, MnO2, Ag2O and HgO, should be at least equivalent
to the quantity of hydrogen peroxide. The more of the;metal
oxide is present, the more advantageous the procedure in
relation to forming nascent oxygen. Prior to leaching, the
ore must be so carefully mixed with such a quantity of metal
oxide that there is a content of at least 0.05%, i.e., 500
ppm. This procedure has been known since 1903 and manifestly
applies only to heap leaching. It is not used today in
industry because of failing to meet the requirements of
commercial practice. Adding a metal oxide in the above
proportions not only is uneconomical because of costs and of
the time of required mixing, but also increased consumption
of cyanide must be expected because the metals involved in
- 25 part themselves will form cyano-complexes. Because of the ~;
presence of the admixed metal oxides in the required amounts,
leaching malfunctions, for instance by passivation, can
occur. Also final waste treatments to detoxify the liquids
from cyanides are inevitable.
The leaching procedure known from the U.S. Patent No.
3,826,723 using a cyanide leaching solution and hydrogen
peroxide in addition to the presence of an alkali cyanide and -~
a stabilized hydrogen peroxide solution furthermore requires ~;
a lignin sulfonate. The large quantities of chemical ~`
admixtures, especially of a NACN and H2O2, sta~ted in this ~
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~33~ 10
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document, render an economical procedure not feasible.
The procedure of the Canadian Patent 1,221,842 is for
leaching for instance gold and silver from pyrite
concentrates, the leaching solution containing an alkali
cyanide, an alkali carbonate and hydrogen peroxide. In the ~:
preferred mode of implementation, the leaching solution , -~
contains at least 2% by weight of sodium cyanide and at least
2% by weight of sodium carbonate and 0.6% by weight hydrogen ;
peroxide. At these high concentrations, sodium cyanide is ~;
oxidized to a substantial extent by hydrogen peroxide
according to the known cyanide detoxification using hydrogen
peroxide thereby entailing additional consumption of these
chemicals. In order to be able to feed back the cyaniqe
leaching solution following the separation of the precious
metal cyano-complexes into the leaching cycle, expensive
purification is needed. In view alone of the high demand for
chemicals, this procedure is uneconomical.
As shown by the German Patent 3,637,082, the leaching ~;
procedure employing cyanide and hydrogen peroxide may be more
economical by so controlling the addition of the aqueous H202 ;
solution by means of the oxygen concentration in the leaching
solution that this leaching solution contains between 2 and
20 mg, preferably 7 to 13 mg of 02/liter. Accordingly, in ~
this known procedure, the hydrogen peroxide is added to the -
leaching solution or ore slurry not in one batch, but
continuously or periodically in measured amounts. The lowest
rates of consumption of hydrogen peroxide apply when this
hydrogen peroxide is supplied as a very dilute aqueous ~-~
solution, preferably with a content of 0.5 to 5, in
particularly 1 to 2% by weight. ;
However, where the procedure of the German Patent
3,637,082 has been applied in practice in gold mines, it was
found that the need for sodium cyanide and hydrogen peroxide
does not always meet expectations in spite of carefully
1~321 10
4;
metering the H202 and using a diluted H202 solution. In some
i cases, for instance when leaching pyritic ore concentrates
and/or waste materials from earlier, incomplete leachings,
the demand for chemicals was unsatisfactorily high.
Manifestly this increased demand is related to the physical
and chemical properties of the ores being leached.
The present invention so improves the procedure of the
German Patent 3,637/082 that the demand for hydrogen peroxide
and where possible also that for sodium cyanide is lowered.
It is furthermore desired that the demand for chemicals be
made more independent of the compositions and natural ~
variations of the ores to be leached. In addition it is ~ -
highly significant to the mining industry to recover the~;
maximum amount of precious metal which can be leached with
cyanide in a shorter time than heretofore. -
More particularly, there is provided a process for
leachinq gold and silver from noble metal containing -~
materials such as ores, ore concentrates or wastes of
precious metals, in particular of oxidic and sulfide ores or ;~
ore concentrates as well as waste materials from prior -~
incomplete leachings, by employing an aqueous, cyanide
leaching solution with a pH value of 8 to 13 while adding an
aqueous hydrogen peroxide solution to the ore slurry of an -
agitation leach, or to the barren solution of a heap leach,
while maintaining an oxygen concentration in the leaching
solution of 2 to 20 mg/l. The process is characterized in
tha$ before or during the controlled supply of hydrogen
peroxide, the ore slurry of an agitation leach is fed with a
decomposition catalyst for the hydrogen peroxide. In one
embodiment, di- to hepta-valent manganese compounds are used
as the catalyst in amounts of 1-50 mg computed as manganese
per kg of leaching solution. Organic or inorganic polymers
can also be used as catalysts in amounts of 0.1 to 20 g per ~ ~-
kg of leaching solution. Still further, powdery or
granulated carbon can be used as the catalyst in amounts of -
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0.1-50 g per kg of leaching solution. In heap leaching, the
so called barren solution of a heap leach is fed with di- to
hepta-valent manganese compounds in amounts of 0.01-1.0 mg
computed as manganese per kg of barren solution to act as
decomposition catalyst for the hydrogen peroxide.
A further feature of the invention resides in that the
decomposition catalyst is supplied in controlled manner and
is in the form of aqueous manganese-II-salts, preferably
manganese sulfate, or in the form of a powdery manganese ;
oxide from the group of MnO, MnO2, Mn2O3 and Mn3O4,
preferably MnO2.
More particularly, a di- to hepta-valent manganese
compound can be added in a proportion of 1 to 10 mg. computed
as manganese, per kg of leach solution, to the ore slurry.
Preferably a manganese-II-salt solution in a proportion of
0.05 to 0.5 mg manganese per kg of leach solution is added to
the barren solution for heap leaching.
.:
In further detail, the decomposition catalyst is an
activated charcoal or an activated charcoal laden with a
decomposition catalyst for hydrogen peroxide such as heavy
metals or compounds of heavy metals. Typically, 1 to 20 g,
perferably 5 to 20 g of an activated charcoal suited for the
carbon-in-leach procedure is used per kg of leaching
solution. ~-
During the agitation leach the formed gold- and silver-
cyano-complexers are separated continuously or stepwise from -~
the leaching solution.
It has been found to be advantageous that the separation
of the Au- and Ag-cyano-complexes be performed by adsorption
on powdery or granular carbon. A carbon can be used which
simultaneously decomposes the hydrogen peroxide and
adsorptively binds the formed Au- and Ag-cyano-complexes.
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1 3321 1 0
The separation of the Au- Ag-cyano-complexes can also be
performed by adsorption on an anion-exchanger or polymer-
bound chelating agent. Also, the separation of the Au- and
Ag-cyano-complexes is performed by evacuating the leaching
solution continuously or stepwise and by replenishing it with
fresh leaching solution.
It is preferred that hydrogen peroxide is supplied by
controlled manner in the form of an up to 30% by weight
aqueous solution.
The separation of the formed Au- and Ag-cyano-complexes
during leaching is especially advantageous.
The feeding of the di- to hepta-valent manganese
compounds or of the special inorganic or organic polymers or
of the powdery or granulated carbon entails a decomposition
of the hydrogen peroxide into oxygen and water matching the
~ material to be leached and controlled in relation to it.
; Both the selection of the decomposition catalyst and thereby
its activity as well as its quantity must match the system in
order to achieve the lowest consumption of hydrogen peroxide
and sodium cyanide with the highest yield in gold and the
lowest contents of residual gold. A person skilled in the
art can readily ascertain the optimal conditions by
preliminary trial. The decomposition catalysts are added to
the ore slurry in the so-called agitation leach, but as
regards the so-called heap leaching, wherein only manganese
compounds are used in very low concentrations, the catalyst
is added to the so-called barren solution; that is, to the
essentially ore-free leaching solution which is then caused
to drip onto the heap.
The conventional agitation leach requires an !`
industrially complex gassing of the ore slurry which
frequently entails problems. To increase the oxygen content
in the ore slurry and to improve leaching, suggestions
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already have been advanced to gas by means of molecular
oxygen instead of air and/or to leach under presure.
However, the procedure is made more expensive thereby.
Whereas all gassing methods require the frequently inhibited
oxygen phase transition from the gaseous to the dissolved
form, the oxygen produced in the decomposition of hydrogen
peroxide is directly available for leaching. By selecting
the kind and amount of decomposition catalysts for hydrogen
peroxide, the oxygen concentration and the hydrogen peroxide
concentration in the leaching solution can be matched to the
particular requirements.
Different mechanisms apply when gold is dissolved in the
presence of cyanide and hydrogen peroxide. To achieve
optimal leaching, that is, high gold yield, low residual gold
contents, high leaching rates at minimal chemical consumption
with simple and reliable process control, it is necessary
that the reagents, among which in this case are hydrogen
peroxide and the oxygen arising from its dissociation, shall
be present in matched quantities. This is made possible by
the addition of the invention of a substance dissociating the
hydrogen peroxide. Whereas leaching is accelerated when the
hydrogen peroxide concentration is low, passivation will
apply in the case of higher concentration.
In the course of leaching some ores, for instance oxide
gold ores and waste dump materials from earlier, incomplete
leaching, it was found that the leaching solution known from
the procedure of the German Patent 3,637,082 does in fact
exhibit the desired preferred oxygen concentration of 7 to 13
mg of 02/liter but that simultaneously the hydrogen peroxide
concentration is so high that cyanide is oxidized thereby.
In such instances the consumption of cyanide and hydrogen
peroxide becomes uneconomical. By employing the process of
the invention, it is possible to lower such consumption.
It was found furthermore that in the invention, the
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consumption of cyanide and hydrogen peroxide also can be
reduced when leaching sulfide ores, for instance pyritic and
arseno-pyritic gold ores and that this reduction in amounts
is substantial. This finding becomes clear from comparing
the Examples of using decomposition catalysts of the
invention, and those Examples which do not. To explain this
effect, it is assumed that in the case of higher hydrogen
peroxide concentration in the leaching solution, the sulfide -
will be oxidized. Some of the sulfur compounds formed
thereby can react exceedingly rapidly with the cyanide and `~
thereby contribute to the higher cyanide consumption. ~
;' ,.;
In one embodiment of the invention, namely the addition
of a di- to hepta-valent manganese compound, in the case of
agitation leaching it is to be added in a proportion of 1-50
mg, preferably 1-10 mg. In the case of heap leaching the
proportion should be 0.01-1.0 mg, preferably 0.05-0.5 mg,
each time computed as manganese, in relation to 1 kg of
leaching solution. This is not to be inferred from the
previously known U.S. Patent No. 732,605 as being obvious: -`
whereas in the present invention only catalytic amounts of
manganese compounds are used, the previously known procedure
requires that the metal oxide reducible by the hydrogen
peroxide be present in at least a stoichiometric quantity ;
relative to hydrogen peroxide. Whereas the previously known
procedure requires that only metal oxides reducible by H202 -~
be carefully admixed in a proportion of at least 500 ppm to
the ore prior to leaching, on the other hand the manganese
compounds of the invention are added to the leaching solution
or to the ore slurry before or during hydrogen peroxide
addition. It is furthermore possible to use not only powdery - `
manganese oxides from the group of MnO, Mn203, Mn304 and
MnO2, where MnO2 is preferred, but also other, di- to hepta-
valent manganese compounds such as sulfates, hydroxides, -~
carbonates or manganates. The manganese compounds may be
added, besides the powder form, as metered suspensions or -~
;~ preferably aqueous solutions. An aqueous manganese II
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sulfate solution is preferred, in particular in a
concentration of 1 to 10 g of Mn2+/liter, to adjust the
I manganese concentration in the leaching solution. Using a
¦ Mn-(II) salt solution is especially advantageous in heap
leaching because careful dosing of Mn at the required, very
low concentration is then easily possible.
"Barren solution" denotes that leaching solution which
i8 sprayed onto the ore heap. The so-called barren solution
is widely free of precious metals; however, before spraying,
the pH value and the sodium cyanide concentration will be
adjusted. In addition, the composition catalyst and H202 are
added thereto in the quantities of the invention.
The use of manganese compounds of the invention is
furthermore characterized relative to the other compounds
cited in the U.S. Patent No. 732,605 in that no cyano-
complexes consuming cyanide are formed in leaching conditions
and that no adsorption of heavy-metal ions added in
substantial amounts resulting in degrading the leaching rate,
can take place.
In the leaching solution of the invention, the manganese b~
compounds furthermore may be replaced by organic and
; inorganic polymers decomposing the hydrogen peroxide and ;
present in amounts of 0.1 to 20 g, preferably 1 to 10 g per
kg of leaching solution; typically the polymer shall be
insoluble in the leaching solution and is added to the ore
slurry before or during H202 addition.
The inorganic polymers illustratively can be such ~nown
silicate polymers as zeolites, and the organic polymers
illustratively may be known cation exchangers. To reinforce
or to achieve the required property, namely to decompose H202
into water and oxygen, the polymeric substances may contain
chemically or physically bound heavy metals or heavy metal
compounds, preferably compounds of manganese or copper
_ 9 _
13321 10
compounds. The kind of formation of decomposition catalysts
bound to polymers is significant when their dissociating
effect is to be excluded during cyanide detoxification.
In a preferred embodiment of the process of the
invention, powdery or granular carbon can be used in amounts
of 1 to 50 g, preferably 1 to 20 g per kg of leaching
solution. Activated charcoal, especially in granular form
and of the quality used in the known carbon-in-leach (CIL) or
carbon-in-pulp (CIP) methods, is especially preferred. As a
rule an addition of 1 to 10 g of activated charcoal per kg of
leaching solution is adequate. The use of the invention of ~- -
activated charcoal is especially advantageous when hydrogen
peroxide is used as the oxidant in the CIL method and the
formed cyano-complexes of gold and silver are adsorptively
bound to the same activated charcoal.
It was found it is possible to carry out agitation
leaching especially economically if during leaching the gold
and silver cyano-complexes formed thereby are continuously or
stepwisé separated from the leaching solution. Thereby the
cyano-¢omplex concentration is kept low during leaching. The
leaching duration can be shortened by the above step. This
is especially interesting since heretofore progressive
leaching ~lowed down and a high yield in gold could only be ;
achieved after a long time or not at all. It is essential in -~
~; 25 this respect that after 4 to 8 hours of leaching, practically ~`
all of the cyanide-leachable quantity of precious metal can
be recovered. The term "cyanide-leachable quantity of
precious metal" means that quantity which heretofore even
under the most favorable conditions of leaching, including
the use of hydr~gen peroxide in the presence of dissolved
decomposition catalysts, as a rule could only be extracted
from the ore or ore concentrate after leaching for 24 to 48
hours, and which could not be increased by extending leaching
time.
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i 13321 10
The separation of the precious metal cyano-complexes can
be carried out in a variety of ways: continuous or step-wise
removal of part of the leaching solution during leaching and
replacing the removed amount with fresh solution; i.e., with
a leaching solution free or low in precious metals, thereby
leading to accelerating the leaching.
An alternative to separating the Au- and Ag-cyano-
complexes by removal of the mother liquor resides in
adsorptively binding the complexes to anion exchangers, to
polymerically bound chelating agents or to powdery or
granular carbon. Adsorption to carbon is preferred. This
embodiment is especially advantageous because conventional
carbons act in dissociating manner on hydrogen peroxide and
also exhibit high adsorption relative to Au- and Ag-cyano-
complexes. Accordingly the leaching using hydrogen peroxideis carried out in the sense of the CIL technique. In this
mode, and in manner known per se, leaching may take place in
conventional manner in one, or in several cascaded leaching
tank(s), and in the latter event the activated carbon may be
made to move in counterflow. The application of the
implementation mode of the invention is advantageous not only
relative to ores with a high "head grade" of precious metals,
but also for ores with low gold contents which can be leached
with hydrogen peroxide as the oxidant and with carbon as the
H202 di~sociation catalyst and adsorbent for the Au- and Ag-
cyano-complexes often more effectively and more economically
than when using previously known methods.
It is in fact known to carry out the carbon-in-leach
method with pure oxygen instead of air. As a rule leaching
~; 30 acceleration is achieved and in part also an increase in gold
yield. This so-called CIL0 method (Publication by Kamyr
Inc., Mineral Processing, Glen Falls, N.Y.) is carried out at
an oxygen concentration in the range of 20 to 35 ppm in the
ore slurry. Following leaching for five hours, the CIL0
3~ method achieves a gold yield which upon extending the
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~ 13321 10
~ .
leaching to 24 hours results in a yield increase of 3 to 5%.
Thus leaching is not complete after five hours; but precisely
where ores with high gold contents are concerned, such as 3
to 5~ will not be foregone and therefore the leaching will be
carried out longer than five hours.
.
In the process of the invention, on the other hand,
using carbon and hydrogen peroxide, surprisingly it was
possible to extract the maximum cyanide-leachable amount of
gold from ores in four to eight hours. In a further stage of
the leaching beyond four to eight hours, practically no
increase in gold yield takes place. It was unforeseeable
that in spite of the low 2 concentration, a higher yield of
gold could be achieved in the invention after four to eight
hours than in the CIL0 method. The above described
lS embodiment of the invention is suitable to leach very viscous
and therefore oxygen-repellent ore slurry. The separation of
carbon laden with cyano-complexes from the ore slurry takes
place conventionally, for instance by sifting.
The concentration of solids in the ore slurry of
agitation leaches depends on the ore properties. As a rule
the conaentrations of solids are in the range of about 20-60%
by weight.
I ~' ' ' ~.
In the invention, aqueous hydrogen peroxide is used in
concentrations up to 70~ by weight. Preferably solutions
with a content up to 30% by weight are used. In the
I l previously known procedure of the German Patent 3,637,082,
hydrogen peroxide most of the time must be fed in controlled ~
manner as a very dilute aqueous solution, in particular from ~ -
l to 2% by weight, requiring high dilution. The present ~-
invention enables direct use of highly concentrated, or
moderately dilute hydrogen peroxide.
: ~:
Another advantage of the invention is that the 2 andJ, '
H202 concentrations most advantageous for leaching are ; -~
- 12 -
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1332110
adjusted in the leaching solutions much more rapidly than
when using hydrogen peroxide without the decomposition
catalysts of the invention; as a result the time of leaching
is shortened.
: .
S Leaching takes place at pH value of 8 to 13, preferably
9 to 12. To adjust the pH, preferably alkali or earth alkali
hydroxides or oxides are used, in the same manner as in
conventional leaching. The cyanides used are alkali or
earth-alkali- cyanides. Typically the cyanide concentration
in the leaching solution is 0.01 to 0.1% by weight, however
lower and higher concentrations also may be used.
¦ The hydrogen peroxide is added to the ore slurry or to the leaohing solution continuously or periodically in such a
way that an oxygen concentration of 2 to 20 mg of 02/liter,
preferably 7 to 13 mg of 02/liter, shall be set and
maintained during leaching. The oxygen concentration is
measured for instance by an oxygen electrode and the ~`
deviation of the 02 value from the refer2nce value is used as
an error signal in controlling the hydrogen peroxide.
~ 20 The Examples below show how the process of the invention
¦~ lower the consumption of chemicals compared with the
procedure of the German Patent 3,637,082 and how
simultaneously the maximum gold yield is achieved in less
time.
- .
I Detailed Description of the Invention
EXAMPLE 1
Waste material containing gold and from an earlier,
incomplete leaching was leached continuously in three
cascaded agitation vessels each of 1 m3 capacity. In the
first vessel, the ore suspension with a solids content of
about 55% by weight was adjusted for a pH of 10.5 by adding
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:
milk of lime. The additions of "black cyanide" and the
hydrogen peroxide, which was used as a 1.33% by weight
aqueous solution, took place in a way that the oxygen
concentration during the 9-hour dwell time in the second
vessel remained constant. Each time a cyanide concentration
corresponding to 0.04~ by weight of NaCN was set in the leach
solution. The second vessel also was supplied with the
manganese compounds of the invention in the form of aqueous
MnS04 solutions or as powdery MnO2. The dwell time in the
third vessel also was nine hours and leaching was completed
therein.
Table l shows the leaching results from three samples of
different compositions but from the same mine. It shows the
gold content of the sample used (head grade), the yield in %
and the consumptions of sodium cyanide and hydrogen peroxide
referred to 1 ton of the waste material being used. Leaching ;
took place at an 2 concentration of 8 and 12 mg/liter, each
~ time with and without the addition of the invention of the
- manganese~ or manganese-IV-compound tthe Mn concentration
stated in mg/kg always refers to the leaching solution~. In ;~
every case it was possible to lower the consumption of NaCN
~ and H202 by means of the process of the invention. ; ~
:. , . -' ',,:'
-~ EXAMPLES 2 T0 4 '~
~: :;,:
-~; Pretreated pyrite concentrations are leached using black
cyanide and hydrogen peroxide while keeping constant an
oxygen concentration of 12 mg/1 in accordance with the German
Patent 3,637,082. In Example 2 no Mn compound of the
~ inv~ntion was added, whereas in Example 3 manganese~
- ~ sulface and in Example 4 manganese dioxide were added. A
; 30 cyanide concentration corresponding to 1.5% by weight NaCN
~; was set in each case in the leaching solution. The solid
contents each time were about 25% by weight, the manganese-
(II)-or-(IV~-concentrations in Examples 3 and 4,
respectively, were each 10 mg/kg referred to the ore slurry.
,~. . . ~
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The gold yield and the consumptions of sodium cyanide and
hydrogen peroxide, added as S~ aqueous solution, are shown in
Tabl- 2 a~ a functi~n of 1eaching time.
TABLE I
Mn~ ~d H22
M~rV- Au ~nt~l C~u~d~ Couumption
5umple o~Conc~t~tion Cc~ on ~o~gnde) ~uL~ch~g Co~umption ~gH202)
# (~g~g) (m~d ~ A~1) Yicld ~gNaCN/t) ~0~.~%)/t)
1 8 - Q~3 6S.3 0.~8 0.3~8
a 7ppm ~ Mn~l) 0.798 6~.0 0.164 Q191
2 12 - 0.4~ 3S.6 o.a63 ~.639
12 ~3ppm ~ Mn~l) 0.~1 50.1 0.15S Q~25
1 12 - 0.333 37 0.159 0.513
12 7ppm ~ Mn~ 0~9 37 QIS3 Q4
;
_ TABLE 2 - :
~: 10 E~mp1e 2 E~mplc 3 E~amplc ~
- DO Mn ~dition Mn~ ~dido~ M~n~ ~dition
G~ o~ ~ A~t) :14~0 1~.8 1~1.1.
t~(%~
.e~Y 1~ lcllillR
.g 69.3 62.8
.~ 4 ~.7 86.4 ~.4
,~- 9 89.9 ~.6 8~.S
`~ 2~ ~0 93~ 930
H20~ mption
'.: (IC~ N20~7096 by wdgbt
. :~ pes tor o~py~ite concentratc
ftcl so n~nY h of Ic~chin~
; ~ 1 4A2 2.91 ~.78
~ S.03 ~16 2.70
: ~ - 9 8.52 S.SI J"7~
:~: 2~ 11.80 8.92 8.~5
`i N~C~N--Co~sumption
~ NaCN (10090)/ton of
:~ pyritc ooncentradon
ftcr so ~ny houn of luchin~
4.95 3.58 ~.16
7.63 ~.89 S.82 -
9 8.13 S.7S ~.6S
~; 24 _ 966 ~.82 9.48
~:
.
~:
- 15 ~
~1
3 3 ~
~,
,
Surprisingly the consumption of hydrogen peroxide in the
presence of added manganese dioxide was lower, especially in
the first nine hours, than when adding manganese-II-sulfate.
On the other hand, manganese-II-sulfate caused a lower
consumption of sodium cyanide than manganese dioxide.
;~
The pretreated pyrite concentrate was a concentrate
biologically preoxidized using Thiobacillus ferrooxidans.
¦ EXAMPLE 5
¦ 10 A substantially oxidized gold ore was subjected to heap `-
leaching. The leach solution (barren solution) fed to the
heap contained 0.03% by weight sodium cyanide and its pH `
value was 10.5. ~,~
It was possible to increase the 2 concentration in the
barren solution only by about 2 ppm when adding hydrogen ~
;~ peroxide to it in an amount corresponding to 0.05% by weight ~;
when in the absence of a manganese compound of the invention.
The solution leaving the heap (pregnant solution) however
howed 2 values that had hardly changed (about 5 ppm).
~ 20 Other conditions remaining the same, when 0.1 mg
`~ Mn(II)/kg of Ieach solution was added to the barren solution
as manganese solution, the 2 concentration in the incoming ¦
leach solution could be raised from 6 mg/l to 20 mg/l and in
~` l theloutgoing solution from 5 to 8-12 mg/1. Accordingly,
hydrogen peroxide is decomposed as needed. If now 2.5 mg of
Mn(II)/kg of leach solution are added, then the hydrogen
peroxide decomposes practically entirely in the upper layer
of the heap, degassing taking place and an oxygen deficit, or
a hydrogen-peroxide deficit remains in mo~t of the heap.
:,
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1 332 1 1 0
EXAMPLES 6 AND 7
Pyrite concentrates pretreated by bio-oxidation in the
manner of Examples 2 through 4 were leached using sodium
cyanide and hydrogen peroxide while maintaining constant an
oxygen concentration of 12 mg/1 in the manner of the German
Patent 3,637,802, Example 6 lacked a decomposition catalyst
whereas palladium-laden activated charcoal was added to
Example 7. In each leaching solution the cyanide~ :
concentration was set at 0.33% by weight of NaCN. The solid
contents were 25%. Seven g of activated-charcoal/kg of ore ~
suspension, with the activated charcoal being laden with 5% -
palladium, were added to Example 7. The consumption of :::
sodium cyanide and hydrogen peroxide, in the form of a 1% by
weight aqueous solution is shown in Table 3 as a function of ~
the leaching time. Surprisingly, the consumption both of :
hydrogen peroxide and of sodium cyanide was substantially
less in the presence of the decomposition catalyst.
EXAMPLE 8 - ~.
A gravity concentrate from a South African mine of which
the head-grade contained 871.2 g of Au per ton of ore was
~ leached. The ore slurry contained 16.7% by weight solids;
. the pH was adjusted to 11 and the initial NaCN concentration
was set at 10 gll. Leaching took place in an agitation
. 25 vessel with addition of a 5~ by weight H202 solution and ;:~
while maintaining an 2 level of 18 ppm. Table 4 shows~the
-~ gold yields as a function of leaching time, Test (a) taking
place without exchanging the leachin~ solution whereas in
Test (b), the supernatant leaching solution following the ore
sedimentation was totally exchanged after 1, 2, 4 and 8
.~ hours.
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~33~0
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T~BLE 3
: -
E~ple ~
Ex~mplc 6wilh Pd-l-dcn -.
~o do40~po ition . ~cdv-t~
; . . .
, . .~ .. . _ . . .. . . ..
~p~;on
(~CS Hp~ (70% by ~ ht)/ton
5 of ate ~r ~o o~y ~ of
0.65 0.48
2 I.01 0.?6 . - .4 1.~6 ~ 3
6 2.~0 1.
N~ ~wnption
(K~ NaCN (10096)/ton of ore
o ~nv houF~ of tachin~
2.40 2.3
2 185 2.91
4 ~ 3 75
6 4.'~S 3.
o TABLE 4
, . ~
% ao!d ~%tr~cdon wlth !~ ~3
J, 8 24
0 Cxch~Dse ~.5 50.3 ~6.1 65.7 9g.2
O with e~ e 52.4 74.2 gS.I 99.1 g9. ~ :
, :
Ii 15 I Example 8, carried out in the absence of a decompdsition
catalyst, shows the effectiveness of each exchange.
i: ~.; ;: .
~: EXAMPLE 9
The ore of Example g was leached under the same
~;: conditions except for omission of the leach exchange but in
~0 the presence of 50 g granulated activated charcoal acting as
decomposition catalyst and adsorber for the gold complex. :-
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- 18 ~
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,
Table 5 shows the time-dependent gold yields, the consumption
of H2O2 and of cyanide, leaching taking place in (a) with an
2 concentration of 18 ppm and in (b) of 12 ppm.
TABLE S
2 ~ 3 2
.. .. ._ . .~ . ~ . . . .. . .
~ p~mok 9~.4 9t.7 ~.2 ~.5 ~.6
O 12p~Ck 92.7 9~.1 ~.6 ~.6 ~.6
Com ~ with ~.5 ~.3 56.1 65.7 ~.2
E~ ~(~)
~C~eon~um~i~ (2 ~ton Or ore) .
()1~ppmo~ ~.5 ~1.1 13.2 25.6 42.~
O 12ppmo~ 6.5 7.3 9.9 1~.7 ~.7
P~oL~o~ on~%/lo~ofore)
ppm 2 7.1 11.9 IJ.O ~,S.O 95.~
~)12ppnok 3.2 ~.9 ~.~ 14.1 3~.0
EXAMPLE lO
'
A South African gold ore was leached once conventionally
by the carbon-in-leach technique (a) and once in the manner
of the invention (b) using the same carbon as in (a). The
15 so1id content was 50%, the pH was set at ll using Cao; th
~:~ NaCN concentration was 0.05~ by weight, and the head grade~; .
~:~ was 2.1 g Au per ton of ore; 20 g of activated charcoal were
added per liter of slurry.
In (a) the 2 value in the slurry slowly rises from 1-2:~
ppm to 8 ppm. In (b), an 2 concentration of 12 ppm was set
: by adding 1% H202 solution. Table 6 shows the time-dependent
gold yield~
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TABLE 6
.~ ~ion O
! (~) C~L 56 ~ ~8 97 ~
. :
EXAMPLE 11
This test compares leaching using H2O2 without activated : ~
charcoal, namely (a), with leaching including activated ~.
char~oal, namely (b~.
South African waste material is used, with a head-grade
~:~ 10 of 1.33 g per ton of ore; the NaCN concentration is 0.05% by
weight, the solid contents is 50% by weight and the pH is 11.
An 2 level of 12 ppm was set in (a) and in (b) using 1% by
weight aqueous H2O2 solution, and this level was maintained. : :
: In test 11 (b), 20 g of carbon per liter of slurry were used.
` ~ 15 : ;~
: TABLE 7
o~yHlCk~ 72 ~l 88 S9
u~ 3 92 93 93
~ . .
After about four hours and using the process of the :~
~: 20 invention, (b), the gold yield is 92-93~ and therefore about ~:
~ 4~more gold is extracted than is achieved in 24 h using H2O2
;; but without carbon under otherwise equal conditions. ~;
Shortening the leaching time entails a lowering in the
consumption of chemicals.
Further variations and modifications of the foregoing
- 20 -
1 3321 1 Q
will be apparent to those skilled in the art and are intended
to be encompassed by the claims appended hereto.
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: - 21 -
