Note: Descriptions are shown in the official language in which they were submitted.
CA 02334511 2000-12-06
WO 99/66085 PCT/CA99I00536
~ TREATMENT OF ROASTED METAL SULPHIDE ORES AND FERRITES BY
LEACHING WITH PEROXYSULPHURIC ACID
The present invention relates to a process for the
treatment of roasted metal sulphide ores, and especially
to a process for the treatment of roasted ores containing
copper and zinc sulphides for the separation of copper,
zinc and other metal values therefrom. The present
invention also relates to a process for the treatment of
ferrites (as defined herein) in roasted metal sulphide
ores and from other sources for separation of metals
(metal values) therefrom.
The current industrial methods for separation of
base metals and precious metals from metal sulphides
generally employ smelting. However, metal sulphide
smelters are a major source of industrial pollution, and
of serious environmental concern. Such concerns have led
to the shutting down of base metal development projects
that rely on smelting techniques for the recovery of base
metals and precious metals.
Extraction and refining of base metals from sulphide
ores may be carried out by smelting, a pyrometallurgical
process, which i,s usually followed by metal
electrowinning a~.nd metal refining. Base metal sulphides
are generally ca~.lcined i.e. roasted in air, to produce
a
metal oxide that. is smelted to produce crude metal, for
example blister nickel. The crude metal is subsequently
re-melted, and east into anodes which are used as feed
material for metal electrowinning processes. Precious and
rare metals, e.c~. selenium and tellurium, do not dissolve
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in the electrolyte that is used and fall to the bottom of
the electrolyte cell as anode slimes.
The slimes may be digested with sulphuric acid to
remove the residual base metals. The liquor obtained is ,
then added to a stage for recovery of secondary base
metals. Arsenic usually remains in the electrolyte and
causes environmental problems in the aqueous state.
Residual slimes .are smelted to produce a precious metal
(dore) bar which may contain a residue of base metals
plus antimony, bismuth, tellurium and some rare earth
metals. The dore bar usually contains between 10-50
percent by weight of gold, and is usually shipped to the '
mint for gold exitraction and refining. The refining of
such dore bars ins usuall.y expensive, using for example
the chloride and cyanidation processes that are used in
many precious mei..al refineries fox the separation of
metals from gold. Both processes tend to be very
hazardous environmentally because of the waste that is
emitted.
In other processes, zinc may be recovered by
roasting, leaching and electrowinning. Lead, which is
frequently associated with zinc, is processed. by
oxidation of lead sulphide to oxide, which ~is..thew .
reduced to metallic lead. The resultant material. is
heated and impure copper in the form of copper dross is
skimmed off from the top of the heated material.
Addition of zinc produces insoluble intermetallic silver
Silver, gold and other precious metals are usually
recovered by Bore: liquation i.e. addition of borax or
..
chloride as flux~_ng materials followed by vacuum
distillation and cupel (oxygen) treatment to obtain
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dores. Such a pz-ocess may be referred to as a
pyrometallurgica7, and cupellation process.
In lead refining, addition of calcium or magnesium
(alkaline earth metals) usually results in the formation
of an intermetal7.ic compound with bismuth and oxidation
stags containing arsenic or antimony. Such a process
also involves pynometallurgic procedures.
A process for the recovery of, in particular, copper
and zinc from metal sulphide ores that does not involve
the smelting of t:he ores would be useful, especially to
eliminate the re:~ulting environmental hazards associated
with smelting and other processes.
Many ores contain significant amounts of iron. In
processes involv~lng application of heat, especially under
oxidizing conditions, complex multiple oxides of ferric
oxide are formed" which may be referred to as ferrites
and ferrates; as used herein, all such complex multiple
oxides of ferric oxide are referred to as ferrites, with
further complexes or compounds with other metals being
referred tows mEStal ferrites.
In particular, processes involving dead or
sulphation roasting followed by treatment with sulphuric
acid to recover e.g. zinc as soluble sulphates, generally
result in failure to recover metal values'from ferrites
in the absence o:f additional subsequent severe leach
conditions with :high acid concentrations and elevated
temperature. Fo:r instance, typical weak acid leaching to
recover zinc values from zinc oxide formed during
roasting does not recover zinc values from zinc ferrites.
The latter zinc values must be recovered under more
severe leaching conditions, with higher acid
concentration and higher temperatures. However, under
31-05-2000 CA 02334511 2000-12-06 CA 009900536
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the severe leaching conditions, iron values are not ,only
recovered from zinc ferrite but also from other iron
oxides in the roasted ore. Consequently, solutions
containing zinc contain higher concentrations of iron,
which affects subsequent steps to recover zinc and other
dissolved metal values. In addition, the higher acid
concentrations must. be neutralized, thereby requiring use
of greater quantities of lime or other bases, which
affects steps to recover metal values from tails and in
other downstream processes.
Various ferrit:es are used in the ceramics and
electronics indust~_-ies e.g. so-called ceramic ferrites,
and methods of recycling of metals therefrom are
required.
GB 1 594 851 c3iscloses the use of sulphuric acid
containing peroxysi.zlphuric acid in the extraction of un-
roasted zinc sulphide ores. EP 0 039 83'3 discloses the
selective removal ~of iron from a sulphate leach solution
by .addition of.peroxysulphuric acid to the leach solution
to oxidize ferric ions. iJS 4 452 '706 discloses the
oxidation of iron and arsenic in a leach solution to
ferric and arsenic ions using peroxysulphuric acid.
Processes with the potential for recovery of metal
values .from sulphide ores in a more efficient manner,
with less potential environmental impact, and for
recovery of metal values from ferrites and the potential
use of such ferrit.es are required. Such a process has
now been f ound .
Accordingly, one aspect of the present invention
provides a process for the treatment of a ferrite for the
separation of metals therefrom, comprising:
(a) leachin<3 said ferrite with peroxysulphuric
AMENDED SHEET
J-r-05-2000 CA 02334511 2000-12-06 CA 009900536
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acid; and
(b) 'separating a solution containing metals
therefrom.
Another aspect of the present invention provides a
process for the treatment of a roasted metal sulphide
ore, for the separation of metals therefrom, comprising:
(a) leaching ;said roasted ore with peroxysulphuric
acid; and
(b) separatin!~ a solution containing metals
therefrom.
In preferred embodiments of the processes of the
present invention, the ore has been subjected to a dead
roast or to a sulph.ation roast.
In further embodiments, the roasted ore contains
ferrite .
In another embodiment, a'ferrite is added to the
ore, before or afte:r roasting.
In a further e=mbodiment, a solution containing
copper and zinc is obtained.
In another embodiment, the ferrite is being
recovered from ceramic ferrites or from the electronics
industry.
In particularly preferred embodiments of the
processes of the invention, leaching or treatment is
carried out with peroxysulphuric acid (faro's acid) in
the presence of gaseous chlorine.
In one aspect, the present invention relates to a
process for the treatment of metal sulphide ores, and in
particular to a process for the treatment of metal
sulphide ores that: contain substantial proportions of
copper and zinc sulphides. It is understood that the
AMENDED SHEET
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ores will likely also cantain iron sulphides, and may
also contain at :least minor amounts of a large variety of
other metallic compounds especially in the form of
sulphides. For example, the ore could contain aluminum, m
arsenic, bismuth, barium, calcium, cadmium, potassium,
magnesium, manganese, sodium, nickel, phosphorous, lead,
titanium, tellurium and vanadium, as well as other
metals. Many such ores also contain gold.
The leaching process is operable on ore or ore
concentrate formed from an ore, which has previously been
subjected to a roasting process. The roasted ore or
concentrate shou~Ld be in a particulate form, especially
particles of a size suitable for use in a fluidized bed,
rotary kiln or torbed process for treatment of turbulent
masses of material, as is known. Thus, the ore or
concentrate may have been subjected to a grinding
process.
Methods for roasting of ores are known. In one
method, known as dead roasting, the particulate ore is
roasted in the presence of air, with sufficient air being
present for oxidation of the sulphide to the
corresponding oxide and formation of sulphur dioxide.
Good circulation of air through the particulate during
the roasting process is believed to be important,.both to
expedite the roa.~ting of the sulphide to the oxide and to
prevent the formation of local hot spots within the ore
during the roasting process. A fluidized bed or other
techniques may be: used for the roasting of the ore as is
known.
The roasting of the ore is conducted at a
temperature to effect oxidation of the metal sulphide to
the corresponding metal oxide, particularly copper
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WO 99/b6085 PCT/CA99/00536
sulphide and zinc sulphide to the corresponding oxides,
without agglomeration of the particulate. It is known
that oxides are be formed at relatively low roasting
temperatures e.g~. 700C or higher, but that ferrite is
also formed, if iron is present as is normally the case,
at similar temperatures. Thus, ferrites will normally be
present in roasted ore, even in those instances where
steps are taken to try to reduce formation of ferrities.
As an alternative to dead roasting of the ore in the
presence of air, sulphur dioxide may be introduced into
the roasting chamber to cause the formation of metal
sulphates during the roasting process. Metal sulphates
are water soluble and therefore the roasting material
should require less quantity of acid in order to
solubilize metal species i.e. solubilize metal oxides,
during the leaching step. The use of sulphation roasting
will result in a lower operating temperature than
required for an oxidation roasting.
The roasting may be carried out in the presence of
both oxygen and sulphur dioxide, as such a mixture of
gases will result in conversion of metal oxides to the
corresponding sulphate by reaction with sulphur trioxide,
and the conversion of metal sulphides to the
corresponding metal sulphates by reaction with oxygen.
The first reaction tends to be endothermic and the second
reaction exothermic, thereby permitting control of the
temperature in the process.
Both dead roasting and sulphation roasting are known
per se, and not part of the process of the present
invention. The present invention may be applied to
roasted ore from both processes, but in aspects it also
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applies to combinations of roasting and leaching as
described herein.
According to one aspect of the present invention,
roasted ore is subjected to leaching with peroxysulphuric ,
acid. Caro's acid is peroxysulphuric acid, also known as
persulphuric acrd, which has the formula HZSOS or
HOS0200H. Such an acid is both highly acidic and a strong
oxidizing agent.
In embodiments of the present invention, the
leaching is carried out in multiple steps, with the acid
concentration in the first step being relatively dilute
compared to the concentration in a subsequent step.
The process provides a leach solution, which is a
solution of leached. metals. The metals are in a soluble
form, which would normally be in the form of a sulphate
of the metal. The peroxysulphuric acid is converted to
sulphuric acid during the leaching process, and many
metal sulphates Especially those of copper and zinc are
soluble in the solution.
Leach solutions may be diluted, if necessary or
desirable, and then be treated for recovery of metal
values therein. In particular, the leach solutions are
treated for recovery of copper and zinc. Techniques for
the recovery of cropper and zinc from acid solutions,
especially sulphuric acid solutions, are known.
It is to be anticipated that the leach solutions
will contain relatively high concentrations of one or
more metals, and that such metals would normally be the
first to be recovered from the leach solution. The leach
solution subsequently remaining would normally then be
further treated for recovery of other metal values.
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Techniques for the recovery of such other metal values
from such solutions are known.
In the roasting process, the presence of both iron
and zinc in a metal sulphide ore lead to the formation of
zinc iron ferrite compounds which are generally resistant
to weak acid leaching conditions. Other ferrites are
also known. However, ferrites are teachable in the
process of the present invention. Ln particular,
embodiments of the invention, ferrites may be added to
roasted ore or treated separately according to the
invention.
Ferrites are multiple oxides of ferric oxide with
another oxide. A variety of techniques are known for the
formation of ferrites, including heating metal oxides
with ferric oxide. This occurs naturally in roasting of
ores as roasting tends to form metal oxides e.g. metal
sulphides are converted to the corresponding oxides.
Many ores contain significant quantities of iron, which
tends to be converted tv iron oxide, especially ferric
oxide, during roasting. Thus, ferrites tend to be formed
during roasting even under controlled temperature
conditions. As noted above, temperatures used in
roasting are similar tv those for formation of ferrites.
Other sources of ferrites are known. For instance,
ceramic ferrite: are obtained by sintering or firing
mixtures of the oxides. Ferrites are used in rectifiers,
recording tapes, permanent magnets, semiconductors,
insulating matex-ials and dielectrics, e.g. in the
computer, television, radio, radar and other industries,
especially electronics industries.
In the treatment of ferrites with Caro's acid, it is
believed that iron is converted to higher oxidation
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states such as the Fe'6 state, in which it is a strong
oxidizing agent. In particular, it is believed that it
oxidizes ferrites to effect separation of the metal value
from the iron, thereby facilitating recovery of the metal ,
5 value. While formation and use of Fe+6 is believed to be
important in the leaching of ferrites from a variety of
sources, it is believed to be particularly so in leaching
of metal values from roasted sulphide ores.
In preferred embodiments of the invention, leaching
10 or treatment is carried out using both Caro's acid and
gaseous chlorine. As exemplified herein, use of
combinations of Caro's acid and chlorine can provide
further improvements in the degree of extraction.
Arsenic oxides tend to vaporize and be removed from
the roasting chamber. It is believed to be advantageous
to remove arsenic during roasting, and prevent arsenic
from entering the aqueous phase during the leaching step.
There may be difficulty in controlling the presence of
arsenic in aqueous solutions, with the consequent
environmental hazard.
Tails obtained from the leach solution may be
treated for separation of gold and other metals from the
tails. A preferred method for the leaching of gold from
the tails is to aubject the tails to treatment with
Caro's acid, as :is described in WO 97/05294 of Protium
Metals Inc., pub:Lished February 1.3, 1997.
The process of the present invention provides a
method of recovery of a variety of metal values,
including copper and zinc, from roasted sulphide ores
without requirinc3 the smelting of the ore. This has
substantial advantages in reducing environmental hazards
associated with amelting processes. The present
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invention also provides a versatile process for
recovering copper, zinc and other,metals, including
precious metals, from roasted metal sulphide ores and
concentrates. In addition, the present invention
provides for the recovery of metals from ferrites
obtained from a number of sources including roasted ores
and recycled ferrites used in~other industries.
It is believed that the process of the present
invention will lead to less consumption of acid cf. use
of weak acid/strong acid leaching in sequence, less base
to neutralize acid, less slime and/or less material sent
to settling ponds.
The process of the present invention is illustrated
by the following examples.
EXAMPLE ~
A metal sulphide ore concentrate containing copper,
zinc and iron was subjected to a roasting step at a
temperature of about 950°C.
Samples of the calcined ore obtained were subjected
to leaching with aqueous solutions of sulphuric acid or
Caro's acid at.temperatures of 25°C or 90°C. Details of
the calcined ore and leaching conditions are given in
. Table 1. Other leaching conditions, especially leaching
time, were the same for all leaching steps.
The results obtained are given in Table 1.
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Table 1
Weight Cu (%) Zn (%) Fe (%)
Run A: Leach with HZS04 at pH 3.5, 2'5C
Concentrate 100 17.35 18.65 22.9
Residue 63.5 18.9 7.99 36.6
Extraction (%) 49.4 83.7 11.4
Run B: Leach with HZS09 at pH 1.0, 90C
Concentrate 100 17.7 19.1 24.2
Residue 49.3 11.9 7.5 38.1
Extraction (%) 67.3 80.9 23.1
Run C: Leach With Caro's acid, 90 C
Concentrate 100 17.7 19.1 24.2
Residue 27.8 2.9 7.5 34.1
Extraction (%) 96.3 90.2 70.7
Rua D: Leach with Caro's acid plus chlorine, 90C
Concentrate 100 17.7 19.1 24.2
Residue 25:2 1.9 6.7 32.5
Extraction (%) ~ 97.2 93.3 73.5
The results show that leaching with Caro's acid, at
90°C, was substantially more effective in separation of
copper, zinc and iron values from the concentrate than
leaching with strong sulphuric acid at a pH of I.0 at the
same temperature or with weaker acid at 25°C. For
instance, copper extraction increased from 67.3% to 96.3%
with the residue of copper decreasing from 11.9% to 2.9%.
Copper extraction was further increased to 97.2% and the
residue decreased to only 1.9% by using Caro's acid in
the presence of chlorine.
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The result~~ for both copper and iron indicate that
complex iron oxides with copper e.g. copper ferrites are
extracted in the' process and/or that the use of Caro's
. acid is causing formation of Fe+6 or other highly oxidized
states of iron, which act as oxidizing agents and further
increase extraction of copper.
Similar re;~ults were obtained for zinc.
