Note: Descriptions are shown in the official language in which they were submitted.
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TITLE
PROCESS FOR THE TREATMENT OF
ROASTED METAL SULPHIDE ORES AND FERRITES
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 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 is usually followed by metal
electrowinning and metal refining. Base metal sulphides
are generally calcined 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 cast into anodes which are used as feed
material for metal electrowinning processes. Precious and
rare metals, e.g. selenium and tellurium, do not dissolve
in the electrolyte that is used and fall to the bottom of
the electrolyte cell as an 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
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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 extraction and refining. The refining of
such dore bars is usually expensive, using for example
the chloride and cyanidation processes that are used in
many precious metal refineries for 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 then
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 dore liquation i.e. addition of borax or
chloride as fluxing materials followed by vacuum
distillation and cupel (oxygen) treatment to obtain
dores. Such a process may be referred to as a
pyrometallurgical and cupellation process.
In lead refining, addition of calcium or magnesium
(alkaline earth metals) usually results in the formation
of an intermetallic compound with bismuth and oxidation
slags containing arsenic or antimony. Such a process
also involves pyrometallurgic procedures.
A process for the recovery of, in particular, copper
and zinc from metal sulphide ores that does not involve
the smelting of the ores would be useful, especially to
eliminate the resulting environmental hazards associated
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with smelting and other processes.
Many ores contain significant amounts of iron. In
processes involving application of heat, especially under
oxidizing conditions, complex multiple oxides of ferric
oxide are formed, known as 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
ferrites in the absence of additional subsequent severe
leach conditions with high acid concentrations and
elevated temperature. For 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
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 ferrites are used in the ceramics and
electronics industry, and methods of recycling of metals
therefrom are required.
Process 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 ferrites from various sources are required.
Such a process has now been found.
Accordingly, one aspect of the present invention
provides a process for the treatment of a roasted metal
sulphide ore, for the separation of metals therefrom,
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comprising:
(a) leaching said roasted ore with peroxysulphuric
acid;
(b) separating a solution containing metals
therefrom.
Another aspect of the present invention provides a
process for the treatment of a metal sulphide ore, for
the separation of metals therefrom, comprising:
(a) subjecting said metal sulphide ore to a
roasting step;
(b) leaching said roasted ore with peroxysulphuric
acid;
(c) separating 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 sulphation roast.
In further embodiments, the roasted ore contains
ferrite or metal ferrite compounds.
In another embodiment, ferrite or metal ferrite is
added to the ore, before or after roasting.
In a further embodiment, a solution containing
copper and zinc is obtained.
Another aspect of the present invention provides a
process for the treatment of a ferrite compound
comprising:
leaching said ferrite compound with peroxysulphuric
acid.
In an embodiment of the process, the ferrite is
subject to the process for recovery of metals therein.
In another embodiment, the ferrite is being
recovered from ceramic ferrites or from the electronics
industry.
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
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copper and zinc sulphides. It is understood that the
ores will likely also contain iron sulphides, and may
also contain at least minor amounts of a large variety of
other metallic compounds especially in the form of
5 sulphides. For example, the ore could contain aluminum,
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 should 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 roasting 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
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. 700°C, but that ferrite is also formed,
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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
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 acid, which has the formula HZSOS or
HOSOZOOH. 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
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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 copper 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.
Techniques for the recovery of such other metal values
from such solutions are known.
In t-he 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 leachable in the process of
the present invention. In 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.
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Many ores contain significant quantities of iron, which
tends to be converted to 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 to those for formation of ferrites.
Other sources of ferrites are known. For instance,
ceramic ferrites are obtained by sintering or firing
mixtures of the oxides. Ferrites are used in rectifiers,
recording tapes, permanent magnets, semiconductors,
insulating materials 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 a 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 value. While use of Fe+6 is
believed particularly so in leaching of metal values from
roasted sulphide ores.
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 subject the tails to treatment with
Caro's acid, as is described in WO 97/05294 of Protium
Metals Inc., published February 13, 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
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without the requiring the smelting of the ore. This has
substantial advantages in reducing environmental hazards
associated with smelting processes. The present
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
overall extraction of iron, less base to neutralize acid,
less iron to separate during recovery of metals values,
less slime and/or less material sent to settling ponds.
