Note: Descriptions are shown in the official language in which they were submitted.
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
1
METHOD FOR REFINING CONCENTRATE CONTAINING PRECIOUS
METALS
The invention relates to a method for refining precious metal concentrate
defined in the preamble of claim 1. In the method according to the invention,
there is used a supension smelting furnace; the matte created in said, furnace
is
conducted into hydrometallurgical treatment, and the slag is reduced in an
electric furnace. The metallicized matte created in the electric furnace is
either
fed back into the suspension smelting furnace or to hydrometallurgical
treatment together or separately with the matte from the suspension smelting
furnace.
Generally precious metals Au, Ag, Pt, Pd, Rh and Ir are in the wolrld produced
by using various different manufacturing methods. Gold is produced either
directly, by making use of the special features of gold, or as a side product
in
traditional copper production. The majority of world's platinum and a
remarkable
share of palladium is produced by using primary electric furnaces. The
majority
of world's palladium production is mainly based on nickel side production from
ores by means of the suspension technipue, where the obtained intermediate
product is nickel concentrate. An essential step in both processes is the use
of
a converter as part of the process. However, the use of a converter in the
processes is harmful, as sulfur dioxide emissions and intermediate products
caused by the transportation of melts are increased. Mattes obtained in the
above described ways are further treated in hydrometallurgic plants. There are
several different hydrometallurgical processes for the further refining of
matte
obtained from smelting, when precious metals should be recovered as side
products.
The Finnish patent application 890 395 describes a manufacturing method and
arrangement for producing high-grade nickel matte. According to said method,
high-grade nickel matte is directly produced in a suspension smelting furnace.
At least the slag from the suspension smelting furnace is reduced in an
electric
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
2
furnace, where the electric furnace slag and the metallicized matte are
formed,
so that at least part of the metallicized matte is returned as feed to the
suspension smelting furnace.
From the Finnish patent 94,538, there is known a method for manufacturing
high-grade nickel matte and highly oxidized slag in a flash smelting furnace,
and for reducing the slag from the flash smelting furnace and for sulfurizing
the
created matte in an electric furnace. The matte created in the flash smelting
furnace and in the electric furnace are both conducted directly to
hydrometallurgical further processing. A specific object of the invention is
precisely to simplify the manufacturing process of high-grade nickel matte and
to avoid the use of a converter in the process.
The object of the present invention is to bring forth a new type of method for
refining precious metal concentrate, so that the precious metals are
advantageously recovered by making use of the suspension smelting process.
Another object of the invention is to realize a refining process for a
concentrate,
the value of which lies in the precious metals contained therein, and where
the
nickel and/or copper only represent a side product in value.
The invention is characterized by what is set forth in the characterizing part
of
claim 1. Other embodiments of the invention are characterized by what is set
forth in the rest of the claims.
The method according to the invention for refining precious metal concentrate
has several advantages. The invention relates to a method for refining
precious
metal concentrate, and according to said method, at least the treated precious
metal concentrate, the reaction gas, the slag forming agent, i.e. flux, and
the
flue dust are together fed into the reaction shaft of a suspension smelting
furnace, so that in the suspension smelting furnace, there are created
separate
phases, matte and slag. The slag created in the suspension smelting furnace is
conducted to an electric furnace, where metallicized matte and waste slag are
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
3
formed, whereafter the matte from the suspension smelting furnace is
conducted to hydrometallurgical treatment, and the slag conducted into the
electric furnace is processed together with a reducing agent and possibly an
agent that lowers the melting point or improves fluidity, and the created
metallicized matte is conducted either to hydrometallurgical treatment or back
into the suspension smelting furnace. According to the invention, in the
refining
of a precious metal concentrate containing precious metals, particularly
platinum and palladium, there is advantageously used a suspension smelting
furnace, such as a flash smelting furnace.
The method according to the invention for refining precious metal concentrate
can also be utilized so that part of the supplied precious metal concentrate
is
replaced by sulfide concentrate. However, the process according to the
invention essentially differs from said publications (FI patent 890,395 and FI
patent 94538), because the raw material used in the process is precious metal
concentrate and not nickel concentrate, wherefore high-grade nickel matte is
not created.
According to a preferred embodiment of the invention, the matte obtained from
a suspension smelting furnace and the metallicized matte obtained from an
electric furnace are granulated prior to the hydrometallurgical treatment.
According to various different applications of the invention, the matte from a
suspension smelting furnace and the metallicized matte from an electric
furnace are processed either in the same hydrometallurgical process or in
different processes. According to a preferred embodiment of the invention, in
the hydrometallurgical treatment, also the matte from the suspension smelting
furnace is leached at least in one step. Thus the desired components of the
concentrate are recovered. According to an embodiment of to the invention,
also the metallicized matte from the electric furnace is leached at least in
one
step in the hydrometallurgical process. According to a preferred embodiment of
the invention, the leaching of the matte takes place in sulfate atmosphere.
According to another embodiment of the invention, the leaching takes place in
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
4
chloride atmosphere. According to yet another embodiment of the invention,
precious metals are recovered from the leach residue. According to a preferred
embodiment of the invention, the ferrous precipitate created in the
hydrometallurgical treatment of matte and metallicized matte is conducted to a
suspension smelting furnace.
In the process according to the invention, the energy contained by the raw
material, such as the oxidizing heat contained by iron and sulfur, is utilized
more efficiently than if the concentrate were treated in a primary electric
furnace. Because in the process the matte phase is separated from slag in two
steps, both in the suspension smelting furnace and in the electric furnace,
the
recovery of precious metals is remarkably increased when compared to
processing in a primary electric furnace. In the process according to the
invention, the amount of created exhaust gases is remarkably smaller than
when using only a primary electric furnace in the treatment of the
concentrate.
Along with the method according to the invention, also dust losses are
reduced.
A relatively smaller quantity of gas facilitates the recovery and
manufacturing of
sulfur dioxide either into pure sulfur dioxide or into sulfuric acid. Now the
necessary investments related to the gas and sulfur dioxide are smaller than
in
a process based on a corresponding primary electric furnace fulfilling the
ecological requirements. The elimination of the use of converters results in
the
same advantages described above as the fact that primary electric furnaces are
not used anymore.
The invention is described in more detail below with reference to the appended
drawing.
Figure 1 Description of the process according to the invention.
Figure 1 illustrates a suspension smelting furnace 1 to be used in the method
according to the invention, such as a flash smelting furnace. In the top part
of
the furnace reaction shaft 3 there is fed precious metal concentrate 9,
oxidizing
reaction gas 10, slag-forming agent, i.e. flux 11 and flue dust 12 obtained
from
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
the cooling of exhaust gases from the waste heat boiler 6. Into the suspension
smelting furnace 1, there can also be fed iron precipitate created in the
hydrometallurgic units 15 and 16 in the treatment of the matte. The
ingredients
fed into the reaction shaft 3 react with each other, and on the bottom of the
5 settler 4, there is formed a matte layer 8 and on top of it a slag layer 7.
The
gases created in the suspension smelting furnace are removed through the
uptake shaft 5 into a waste heat boiler 6, wherefrom the created flue dusts 12
are recirculated back into the suspension smelting furnace, and the exhaust
gases 18 are conducted for further processing. A remarkable share of the
concentrate 9 are precious metals that are accumulated in the settler, mainly
in
the matte phase 8. The matte 8 is subjected to granulation 17, and it is
conducted into hydrometallurgical further processing 15, where the matte is
leached, in which case the precious metals are leached last.
The slag 7 created in the suspension smelting furnace is conducted into an
electric furnace 2, in which, apart from oxidized slag and reducing agent,
there
also is fed, if necessary, a sulfurous or other material for lowering the
melting
point or for improving the fluidity in order to adjust the melting point of
the matte
to be created. In the electric furnace, as a result from the reduction
process,
there is created metallicized matte 14 and slag 13. Without a sulfur addition,
the sulfur content of the metallicized matte may remain very low, and
respectively the melting point and viscosity may remain high. In the electric
furnace, the precious metals are mainly transferred into a matte phase 14,
which is further conducted, according to the invention, either to
hydrometallurgical treatment 16, together with the matte from the suspension
smelting furnace or separately. Another alternative is to recirculate the
metallicized matte 14 or part thereof back into the suspension smelting
furnace
1. Prior to the hydrometallurgical treatment 16 of the metallicized matte 14,
the
matte is subjected to granulation 19. The slag 13 created in the electric
furnace
2 is waste slag, i.e. it is discarded. The precious metals are recovered in a
hydrometallurgical process.
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
6
Both in a suspension smelting furnace and in an electric furnace, precious
metals are mainly trasferred to the matte phase, from which they are recovered
in a hydrometallurgical process. Both. the matte 8 from the suspension
smelting
furnace and the metallicized matte 14 from the electric furnace are leached
either in the same leaching line or separately. The leaching steps are
dependent on the contents of the precious metal concentrate to be treated.
According to a preferred embodiment of the invention, the leaching is carried
out in a sulfate atmosphere, i.e. the solution at some stage contains sulfate.
Now the cobalt and nickel possibly contained in the concentrate are leached in
the first selective pressure leaching step as sulfate. In the same step there
also
is leached iron that can at the same time be precipitated as iron hydroxide.
Nickel is recovered as salt, or it is turned into metal in the electrolysis.
In the
second leaching step, copper is leached as copper sulfate, which can be
separated as such or turned into metallic copper in the electrolysis. Copper
sulfate can also be crystallized and fed back into the suspension smelting
furnace after drying. By adjusting the degree of oxidation in the leaching
process and the oxidation in the pyrometallurgical process, the sulfate
balance
of the solution can be affected. The precious metals are left in the leach
residue. The precious metal content of the leach residue is increased for
instance by means of a strong sulfuric acid and sulfur dioxide treatment. The
created concentrated precipitate is a good raw material for various precious
metal refineries. According to an embodiment of the ,present invention, the
leaching is carried out in a chloride atmosphere, in which case there is used
chloride gas in the leaching, and in the solution, there are created cobalt,
nickel, copper and iron chlorides.
The invention is illustrated with reference to an example below.
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
7
Example
The method according to the invention was applied for the precious metal
concentrate mentioned above, so that part of said concentrate was replaced by
nickel concentrate. The iron precipitate created in the hydrometallurgic unit
was
recirculated back into the suspension smelting furnace. The abbreviation PGM
means precious metals.
The analyses and the material flow into the suspension smelting furnace:
Precious metal concentrate Nickel concentrate Fe precipitate
Share % 75 22 3
Analysis
Ni % 2 9
Cu % 10 3
Fe % 23 39 58
S % 20 27
Si02 % 28 14
AI203 % 4 1
Mg0 % 8 6
PGM ppm 75 3
When applying oxygen enrichment in the feed gas and a suitable degree of
oxidation, as well as when taking into account the exhaust air, the oil demand
for the heat balance, the recirculating dust quantities, the required fluxes
and,
as regards the electric furnace, the need for coke and a small amount of
concentrate for the sulfurizing the matte, the following products were
obtained
from the suspension smelting furnace and from the electric furnace.
CA 02484416 2004-10-27
WO 03/093516 PCT/FI03/00343
8
Material flows of the feed mixture quantity and analyses:
Suspension smelting furnace Electric furnace
Matte Slag Matte Slag
Material flow
of feed 12 71 4 67
Analyses
Ni % 20 1,3 24 0,1
Cu % 54 2,4 31 0.7
S % 21 0,2 8,0 0.3
Fe % 3, 36 34 37
0
Si0% 0,0 32 0,0 35
Mg0 % 0,0 9,7 10 3,5
PGM ppm 440 2,2 32 0,4
The gas created in a suspension smelting furnace contains more than 10%
sulfur dioxide, and is thus suitable for the production of sulfuric acid. The
exhaust gases from the electric furnace are nearly free of sulfur dioxide, and
consequently do not strain the environment. The method described above also
functions without nickel and even so that a large part of the copper is
replaced
by iron, if the source material does not contain a sufficient amount of
copper.
For a man skilled in the art, it is obvious that the different embodiments of
the
invention are not restricted to the examples given above, but may vary within
the scope of the appended claims.
