U.S. patent application number 11/579092 was filed with the patent office on 2007-10-25 for method for recovering gold.
This patent application is currently assigned to Outokumpu Technology Oyj. Invention is credited to Matti Hamalainen, Olli Hyvarinen.
Application Number | 20070245856 11/579092 |
Document ID | / |
Family ID | 35185129 |
Filed Date | 2007-10-25 |
United States Patent
Application |
20070245856 |
Kind Code |
A1 |
Hamalainen; Matti ; et
al. |
October 25, 2007 |
Method for Recovering Gold
Abstract
The invention relates to a method for recovering gold from an
intermediate product or residue containing sulphur and iron
generated in the leaching of a sulphidic raw material. The recovery
of gold and the other valuable metals in the raw material takes
place in a chloride environment. The gold contained in the
intermediate product or residue is leached with divalent copper and
chlorine in a copper (II) chloride--sodium chloride solution in
conditions where the oxidation-reduction potential is in the range
of 650-750 mV and the pH between 1 and 1.6. The acid generated
during the feed of chlorine is neutralized with a suitable alkali.
Neutralization avoids the costs of dissolving the iron.
Inventors: |
Hamalainen; Matti; (Pori,
FI) ; Hyvarinen; Olli; (Pori, FI) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
Outokumpu Technology Oyj
Espoo
FI
FI-02200
|
Family ID: |
35185129 |
Appl. No.: |
11/579092 |
Filed: |
April 25, 2005 |
PCT Filed: |
April 25, 2005 |
PCT NO: |
PCT/FI05/00194 |
371 Date: |
October 30, 2006 |
Current U.S.
Class: |
75/744 |
Current CPC
Class: |
C22B 11/044 20130101;
C22B 11/06 20130101; Y02P 10/214 20151101; Y02P 10/20 20151101 |
Class at
Publication: |
075/744 |
International
Class: |
C22B 9/00 20060101
C22B009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 30, 2004 |
FI |
20040621 |
Claims
1. A method for recovering gold from an intermediate product or
leach residue containing sulphur and iron generated in the leaching
of a sulphidic raw material in atmospheric chloride leaching,
characterised in that the gold is leached from the intermediate
product or residue in an aqueous copper (II) chloride--sodium
chloride solution in atmospheric conditions with chlorine and the
divalent copper contained in the solution, where the
oxidation-reduction potential of the suspension that is formed is
kept in the range of 650-750 mV; the acid generated during the
dissolution of sulphur is neutralized with alkali and thus the pH
is kept at a value between 1-1.6, so that the iron remains mainly
undissolved; the dissolved gold is recovered by some method known
as such.
2. A method according to claim 1, characterised in that the amount
of divalent copper in solution is 20-80 g/l.
3. A method according to claim 2, characterised in that the amount
of sodium chloride in solution is 200-330 g/l.
4. A method according to claim 3, characterised in that the
temperature is maintained in the range between 80.degree. C. and
the boiling point of the suspension.
5. A method according to claim 4, characterised in that the acid
generated during the dissolution of sulphur is neutralized with
basic copper (II) chloride.
6. A method according to claim 4, characterised in that the acid
generated during the dissolution of sulphur is neutralized with an
alkali, which is one of the group NaOH, KOH, CaO, CaCO.sub.3 or
MgO.
7. A method according to claim 6, characterised in that the
dissolved gold is recovered using active carbon.
8. A method according to claim 6, characterised in that the
dissolved gold is recovered by electrolysis.
9. A method according to claim 6, characterised in that the
dissolved gold is recovered by chemical precipitation.
10. A method according to claim 1, characterised in that the amount
of sodium chloride in solution is 200-330 g/l.
11. A method according to claim 1, characterised in that the
temperature is maintained in the range between 80.degree. C. and
the boiling point of the suspension.
12. A method according to claim 1, characterised in that the acid
generated during the dissolution of sulphur is neutralized with
basic copper (II) chloride.
13. A method according to claim 1, characterised in that the acid
generated during the dissolution of sulphur is neutralized with an
alkali, which is one of the group NaOH, KOH, CaO, CaCO.sub.3 or
MgO.
14. A method according to claim 1, characterised in that the
dissolved gold is recovered using active carbon.
15. A method according to claim 1, characterised in that the
dissolved gold is recovered by electrolysis.
16. A method according to claim 1, characterised in that the
dissolved gold is recovered by chemical precipitation.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a method for recovering gold from
an intermediate product or residue containing sulphur and iron
generated in the leaching of a sulphidic raw material. The recovery
of gold and the other valuable metals in the raw material takes
place in a chloride environment. The gold contained in the
intermediate product or residue is leached with divalent copper and
chlorine in a copper (II) chloride--sodium chloride solution in
conditions where the oxidation-reduction potential is in the range
of 650-750 mV and the pH between 1 and 1.6. The acid generated
during the feed of chlorine is neutralized with a suitable alkali.
Neutralization avoids the costs of dissolving the iron.
BACKGROUND OF THE INVENTION
[0002] Several methods are known in the prior art, which are used
to leach gold from material containing sulphur and iron in
connection with a chloride-based copper recovery process.
[0003] U.S. Pat. No. 4,551,213 describes a method in which gold can
be leached from sulphur-containing material, in particular the
residue from hydrometallurgical processes. The preferred starting
material for the method is the residue from the CLEAR process. The
CLEAR process is a hydrometallurgical copper recovery process,
which occurs in a chloride environment and at elevated pressure.
The gold-containing residue is elutriated into water and the
chloride concentration of the resulting suspension is adjusted so
that it is 12-38 weight percent. The oxidation-reduction potential
is adjusted to the range of 650-750 mV and the pH to below 0.
Copper (II) chloride or iron (III) chloride are added to the
suspension to oxidize the gold contained in the raw material, so
that it dissolves.
[0004] EP patent 646185 relates to the recovery of copper from
sulphidic concentrates with chloride leaching in atmospheric
conditions. The gold from the leach residue is dissolved into
electrolyte, which includes two or more halides, such as sodium
chloride and sodium bromide. The purpose is to store oxidising
energy in the bromine complex on the copper electrolysis anode, and
thereby leach the gold from the residue.
[0005] There are certain drawbacks to the above-mentioned methods.
In the method of U.S. Pat. No. 4,551,213 the leaching conditions
are very severe. The patent mentions that sulphur is not dissolved
in the patent conditions, but the mention is not universally
applicable, since the dissolving tendencies of elemental sulphur
and the iron compounds mentioned in the patent depend on the manner
in which the sulphur and the compounds in question are generated.
In the tests we carried out it was found that when leaching
residues formed in atmospheric conditions are treated in conditions
in accordance with the said patent, the dissolution of sulphur and
iron is considerable. Since, according to the publication, the
sulphur and iron do not dissolve, there is no mention either of how
to recover them from the solution. The gold leaching method used in
EP patent 646185 using a bromine complex is not advantageous from
an environmental point of view because harmful bromine emissions
may be generated in the concentrate leaching stage.
[0006] WO patent application 03/091463 describes a method for
leaching gold from leaching residue or intermediate product
containing iron and sulphur, generated in the atmospheric chloride
leaching of copper sulphide concentrate. The publication states
that gold may be leached from an iron- and sulphur-containing
material into an aqueous solution of copper (II) chloride and
sodium chloride with copper and oxygen in conditions where the
oxidation-reduction potential is below 650 mV and the pH value of
the solution in the range 1-3. In these conditions iron does not
dissolve and the sulphur remains undissolved to a large extent.
Thus the costs that arise when iron and sulphur are removed from
the solution are avoided. The recovery of gold from the solution is
made by one of the methods of the prior art such as electrolysis or
active carbon. The method in question is in itself quite good, but
in practice however it is somewhat slow.
PURPOSE OF THE INVENTION
[0007] Now a method has been developed for the recovery of gold
from an intermediate product or residue that contains sulphur and
iron, generated in the leaching of a sulphidic raw material. Raw
material leaching is carried out using a concentrated aqueous
solution of alkali chloride and copper (II) chloride in atmospheric
conditions. When oxygen or oxygen-containing gas is fed into the
sulphidic concentrate leaching stages, iron is oxidised and
precipitated as oxide or hydroxide and the valuable metals, with
the exception of gold, dissolve. The leaching of gold from the
remaining residue is carried out with an alkali chloride--copper
(II) chloride aqueous solution and chlorine in atmospheric
conditions. The oxidation-reduction potential of the leaching stage
is raised to the range of 650-750 mV by means of chlorine. A high
oxidation-reduction potential enables the elemental sulphur in the
residue to dissolve and as a consequence, acid is formed in the
stage, which is neutralised by some suitable alkali. The
simultaneous neutralisation of the acid keeps the pH at a value of
1.0-1.6, whereby the dissolution of iron is prevented. The
dissolved gold is recovered by some method known as such in the
prior art.
[0008] The essential features of the invention will be made
apparent in the attached claims.
SUMMARY OF THE INVENTION
[0009] A gold-bearing intermediate product or residue is leached
into sodium chloride solution containing copper(11) chloride
forming a suspension and the oxidation-reduction potential required
for gold leaching is obtained particularly by means of divalent
copper and chlorine gas. If the feed to gold leaching still
contains undissolved copper- or other sulphide, oxygen-containing
gas can be fed to the start of the leaching stage in order to
dissolve it. The oxidation-reduction potential is measured with Pt-
and Ag/AgCl electrodes and the potential is kept at a value of
650-750 mV. The amount of divalent copper, Cu.sup.2+, in the
solution is preferably 20-80 g/l and the amount of sodium chloride
in the region of 200-330 g/l. Gold dissolves as a chloro complex in
accordance with the following reaction:
Au+3Cu.sup.2++6Cl.sup.-.fwdarw.AuCl.sub.4.sup.-+3Cu.sup.++2Cl.sup.-
(1) Leaching occurs in atmospheric conditions at a temperature,
which is between room temperature and the boiling point of the
suspension, preferably, however, between 80.degree. C. and the
boiling point of the suspension.
[0010] Thus, tests have now revealed that raising the redox
potential of the reacting slurry with chlorine gas accelerates the
dissolution of gold. There is however a drawback to this
acceleration. Raising the redox potential increases the dissolution
of the elemental sulphur (S.degree.) in the material to be leached,
which probably occurs in accordance with the following reaction
(2): S.degree.+3Cl.sub.2+4H.sub.2O.fwdarw.H.sub.2SO.sub.4+6HCl (2)
Reaction (2) shows that a lot of acid is generated (8 mol H+/mol
S.degree.). The acid generated in the solution must however be
neutralised, since at pH values under 1 the iron in the solids
begins to dissolve. The dissolution of iron causes process costs,
as dissolved iron is circulated and consumes reagents. The
preferred pH region to keep iron in the residue is between 1.0 and
1.6.
[0011] Some suitable alkali from the group NaOH, KOH, CaO,
CaCO.sub.3 or MgO is used to neutralise the acid. If the process is
combined with a chloride-based hydrometallurgical method of
producing copper, in which basic copper (II) chloride is generated
in the precipitation of divalent copper from leaching, the use of
the copper (II) chloride is the best option. When basic copper (II)
chloride dissolves, the copper (II) chloride generated can be used
for raw material leaching. The neutralization of hydrochloric acid
and copper (II) oxychloride leaching occur according to the
following reaction:
3Cu(OH).sub.2CuCl.sub.2+6HCl.fwdarw.4CuCl.sub.2+6H.sub.2O (3) The
sulphuric acid generated can be neutralised for example with lime:
H.sub.2SO.sub.4+CaCO.sub.3.fwdarw.CaSO.sub.42H.sub.2O+CO.sub.2 (4)
The recovery of gold from the solution takes place by some method
known as such in the prior art, for instance active carbon,
electrolysis or chemical precipitation.
LIST OF DRAWINGS
[0012] The method of the invention is further described in the flow
chart of FIG. 1, where the recovery of gold is combined with the
hydrometallurgical recovery of copper.
DETAILED DESCRIPTION OF THE DRAWINGS
[0013] According to FIG. 1, a sulphidic raw material such as copper
sulphide concentrate 2 is fed to the first leaching stage 1, and
solution 3 from a later process stage, which is an aqueous solution
of copper (II) chloride and sodium chloride, is also circulated to
this stage. The thicker arrows denote solids and the thinner arrows
the flow of solution. The stage always includes one or more
reactors and thickening. The copper and other valuable metals of
the concentrate mainly dissolve into the process solution and the
resulting solution 4 includes copper chloride, in which about 70
g/l of copper is mainly monovalent. The further treatment of the
copper chloride solution is not presented in more detail here.
[0014] The leaching of the solids 5 from the first leaching stage
is continued in the second leaching stage 6 with solution 7, which
is taken from a later process stage. Air is fed into the reactors
at this stage in order to enhance leaching of the valuable metals
and to precipitate the iron. Thickening is done at the end of this
stage.
[0015] The solution 3 from the second stage is routed to the first
leaching stage 1 to leach the concentrate. The leaching of the
solids 8 from the second leaching stage is continued in the third
stage 9 in order to leach the rest of the copper and the gold. In
the third leaching stage i.e. the gold leaching stage, the residue
is leached with copper (II) chloride--sodium chloride solution 10,
in which the Cu.sup.2+--content is 20-80 g/l and the sodium
chloride content 200-330 g/l. If the residue entering this leaching
stage still contains undissolved sulphide, oxygen, preferably in
the form of air, can also be routed to the first reactor at the
beginning of the stage. Copper and other sulphides should be
leached out of the residue before the gold dissolves. In order to
raise the redox potential to the range of 650-750 mV, chlorine gas
11 is also fed into the reactor. Because of the high potential,
sulphur starts to dissolve and as a result acid is formed in the
stage. So that the pH of the stage does not fall below 1.0, some
alkali 12 is fed into it such as NaOH, KOH, CaO, CaCO.sub.3or MgO.
If the process is combined with a chloride-based hydrometallurgical
method to produce copper, in which basic copper (II) chloride is
generated in the precipitation of divalent copper from leaching,
the basic copper (II) chloride is used.
[0016] The gold-chloro complex solution 13 obtained from the
leaching stage is routed either as it is or filtered to gold
recovery, which in this case occurs in a carbon column 14 by means
of active carbon. The gold product 15 is obtained from the column.
The solution exiting column 14 is a gold-free solution 16, which is
circulated to the second stage of leaching 6 and sodium chloride
solution is routed there as required to achieve a suitable copper
(II) chloride content for leaching. The residue of the gold
recovery stage, after normal after-treatment such as filtration and
washing (not shown in detail in the diagram), becomes the final
leach residue 17, which contains nearly all the sulphur and iron of
the concentrate. The residue filtrate and rinse water are returned
for example to the concentrate leaching process.
[0017] The flow chart in FIG. 1 presents a gold leaching method in
connection with copper-bearing raw material leaching, but the
method of the invention is not limited to the copper-bearing raw
material leaching process shown in the chart. The crux of our
method is that the leaching of gold-bearing material is performed
with divalent copper and chlorine in conditions where the redox
potential of the solution is raised to a value of 650-750 mV, and
the acid formed during the dissolution of sulphur is neutralized so
that the pH is minimum 1, preferably at least 1.0-1.6.
* * * * *