Title of Invention

METHOD FOR DECOMPOSING METAL SULPHATE

Abstract The method of the invention relates to the decomposition in a fluidized bed of metal sulphates generated in the metallurgical industry. The decomposition of metal sulphates is carried out so that the metal oxides generated are recovered in such a pure form that they can be recycled to be reused in the manufacture of metal alloys such as steel. In particular, sulphates containing nickel, iron and chrome are decomposed in oxidising conditions using pyrites or pyrrhotite as the fuel and bed material.
Full Text FIELD OF THE INVENTION
The method of the invention relates to the decomposition in a fluidised bed of
metal sulphates generated in the metallurgical industry. The decomposition
of metal sulphates is carried out so that the metal oxides generated are
recovered in such a pure form that they can be recycled to be used again in
the manufacture of metal alloys such as steel. In particular, sulphates
containing nickel, iron and chrome are decomposed in oxidising conditions
using pyrites or pyrrhotite as the former and fuel of the bed material.
BACKGROUND OF THE INVENTION
Metal sulphates are generated in various metallurgical processes such as for
example during steel pickling or in the electrolytic purification of metal into
anodic sludge. Mixed sulphate waste containing sulphuric acid cannot be
used as such anywhere, and is largely hazardous waste.
US patent 4,824,655 describes a method for producing sulphur dioxide by
the thermal decomposition of sulphur-containing metal sulphates in a
fluidized bed. The metal sulphate is mainly iron sulphate, which includes a
small amount of other metals such as compounds of aluminium, magnesium,
titanium, manganese, chrome and vanadium. The sulphate originates largely
from the manufacture of titanium. The decomposition of metal sulphate
occurs at a temperature of 800 - 1100°C. It is essential that sulphur-
containing material, such as sulphur waste or fine pyrites, be used in
sulphate reduction in order to produce the largest possible amount of sulphur
dioxide. The energy required for sulphate reduction is produced with a
carbon-containing fuel such as coal, coke or heavy fuel oil. The majority of
the fuel is introduced with the bed material, but some is fed separately with
the carrier gas. The key point in the method is the production of sulphur
dioxide, and there is no mention of the use of the metal-containing solids that
are generated, so they go to waste. The amount of waste generated in this

way is considerable. The feed of extra fuel, particularly of extra liquid or
gaseous fuel, makes it difficult to keep the temperature regulated evenly,
since localised feeding to the bed may result in hot spots, which cause the
sintering of the bed. Carbon-containing fuel creates carbon dioxide
emissions, and the aim is to reduce the amount of these emissions.
PURPOSE OF THE INVENTION
The purpose of the method of this invention is to avoid the drawbacks of the
method described above. The aim of the method now developed is to
decompose metal sulphates generated in the metallurgical industry,
particularly mixed sulphates that contain nickel, so that the fuel used in their
decomposition produces bed material on oxidising, whereupon the uniform
distribution of fuel prevents the generation of hot spots. The fuel does not
contain carbon either, so that carbon dioxide emissions are not produced.
SUMMARY OF THE INVENTION
The essential features of the invention will be made apparent in the attached
claims.
The invention relates to a method for the decomposition of a residue
generated in the metallurgical industry, containing at least one metal
sulphate, into oxides. The decomposition of metal sulphide is performed in a
fluidised bed furnace, whereby the energy required for decomposing the
sulphate is obtained from roasting the iron sulphide used as the bed material.
Roasting is performed in oxidising conditions to form an oxide that is
essentially free of sulphur for reuse in the steel industry, and the sulphur
dioxide that is generated is used in the manufacture of sulphur and/or
sulphuric acid.
According to one embodiment of the invention the metal sulphate is a mixed
sulphate, including nickel, chrome and iron sulphate. Mixed sulphate is for
instance the mixed sulphate generated during the pickling of steel.

According to another embodiment of the invention the metal sulphate is
nickel sulphate. Nickel sulphate is formed for instance during the electrolytic
purification of copper.
The iron sulphide used as the fluidised bed material and energy producer is
pyrite and/or pyrrhotite. The decomposition of sulphate is carried out at a
temperature of 800 - 900°C and the residence time in the bed is around 1 -
5 h. The sulphur concentration of the alloy of the oxide or oxides formed is a
maximum of 0.5%.
DETAILED DESCRIPTION OF THE INVENTION
Impure sulphate sediments are generated in the metallurgical industry, such
as in steel manufacture and the electrolytic purification of metals, which
contain sulphates of nickel, chrome and iron etc. Sulphates are soluble
enough that they cannot be removed from the circuit as they are but in
addition their metal content should be recovered in an environment-friendly
way. As described in the prior art, sulphate residues, in particular those
generated during the manufacture of titanium, are treated in a fluidised bed
furnace, but mainly in order to produce sulphur dioxide gas for the
manufacture of sulphuric acid.
Mixed sulphate precipitate is generated in the pickling stage of steel
manufacture, containing in addition to iron sulphates (FeSO4H2O, Fe2(SO4)3)
also nickel and chrome sulphate (NiSO4, Cr2(SO4)3) and sulphuric acid. In
oxidising conditions iron sulphates and chrome sulphate decompose at a far
lower temperature than nickel sulphate. Nickel sulphate may also
decompose at lower temperatures in reducing conditions, but then there is a
danger that in addition to oxides, sulphides will also form. When the purpose
is to produce a product fit for a steelworks for example, its sulphur content
must be quite low i.e. below 0.5 %.

The end product of the pyrometallurgical fabrication of copper is copper
anode, which is further purified electrolyticaily into pure cathode copper. The
anode sludge that is generated contains the impurities of the anode, of which
nickel in the form of nickel sulphate is one of the most significant.
The decomposition of sulphates into oxides is an endothermic reaction. In
the method according to the prior art, the bed of the fluidised bed furnace
was formed so that reducing sulphur-containing material and some of the
carbon-containing fuel were mixed with the sulphates, pelletised and then fed
into the furnace. In addition, part of the fuel was fed separately. In the
method now developed the fuel required for decomposition acts as the bed
material i.e. no separate carbon-containing fuel is required at all. Iron
sulphide such as pyrite or pyrrhotite acts as the fuel and bed material, which
is roasted and, simultaneously, the sulphates fed into the bed are
decomposed into their oxides. The reactions that occur in iron sulphide
roasting are so exothermic that the heat generated is enough for the
endothermic reactions required in sulphate decomposition without the need
for any extra heat.
Sulphate decomposition is carried out at a temperature of 800 - 900°C and
the residence time in the bed is around 1 - 5 h. In particular the
decomposition of nickel sulphate requires the temperature mentioned above,
in order for the decomposition into oxides to take place in a reasonable time.
The invention relates thus to a method for the decomposition of one or more
metal sulphates, where nickel sulphate is preferably one of the sulphates.
Sulphate decomposition is carried out in oxidising conditions, in order to
avoid sulphur remaining in any form among the oxides. Sulphur-free oxides
are fit for reuse e.g. in a steelworks. The sulphur dioxide-containing gases
that are formed are routed to sulphur and/or sulphuric acid manufacture, but
the process is regulated on the basis of producing metal oxides that are as
pure as possible rather than sulphur dioxide production.

It is preferable to keep the sulphur content of the oxide alloy to be fed to the
steelworks as small as possible, since it will reduce the demand for oxygen
used for sulphur removal in conversion.
When all the energy required for sulphate decomposition is brought in the
form of bed material, the drawbacks that can arise from feeding fuel to the
bed separately can be avoided. The use of separate fuel is awkward
because it is difficult to feed it into the bed so evenly that no localised hot
spots are generated where the bed material and sulphates would be
sintered. Hot localised points are also harmful to the equipment. Introducing
a separate fuel to the fluidised bed means carbon-containing material,
generally feeding gas into the bed. The drawback of carbon-containing fuel
is that the fuel produces carbon dioxide emissions and in addition it requires
a post-combustion chamber as additional equipment.
When iron sulphides are used as the energy producer in the fluidised bed
decomposition of sulphates, it is easy to control the shutdown of the bed nor
does a malfunction in the sulphate feed cause problems. When using iron
sulphides the operation is run in oxidising conditions, and there are no
additional sulphides to be burnt in the bed. If the operation is run in reducing
conditions and there is a malfunction, then the sulphides burn and hot spots,
molten phase and sintering occur.
EXAMPLES
Example 1
The decomposition of impure nickel sulphate was carried out in a fluidised
bed furnace using pyrite as bed material and fuel. Air was used as the
fluidising air and fluidising was carried out at a rate of 0.2 m/s in slightly
oxidising conditions. After 1.5 h the sulphur concentration of the nickel oxide
removed from the furnace was 0.34 % and after 3 h It was 0.15 %, so that it
was highly suitable for recycling to the steel industry.

Example 2
The decomposition of mixed sulphate was performed in a fluidised bed
furnace, where the composition of the mixed sulphate was Fe 12.8%, Cr
1.8%, Ni 1.8%, Mo 0.08% and SO4 44.4%. Pyrite was used as fuel and bed
material. Air was used as the fluidising air and fluidising was carried out at a
rate of 0.2 m/s in slightly oxidising conditions. After 1.5 h the sulphur
concentration of the oxide mixture removed from the furnace was 0.32 % and
after 3 h it was 0.17 %, so it was highly suitable for recycling to the steel
industry.

We Claim
1. A method for decomposing a residue generated in metallurgical
industry, said residue containing at least one metal sulphate,e.g. nickel
containing metal sulphate, into oxide, and sulphur dioxide that is used
for the manufacture of sulphur and/or sulphuric acid,
characterised in that the decomposition of the nickel containing metal
sulphate is carried out in a fluidised bed furnace at a temperature of 800
to 900 °C, whereby the energy required for sulphate decomposition is
obtained from roasting of an iron sulphide employed as the furnace bed
material, the decomposition being carried out in oxidising conditions to
form an oxide having a maximum of 0.5% sulphur, for recycling to the
steel industry.
2. A method as claimed in claim 1, wherein the metal
sulphate is a mixed sulphate, which comprises nickel, chrome and iron
sulphates.
3. A method as claimed in claim 1 or 2, wherein the metal
sulphate is the nickel-chrome-iron sulphate generated during
pickling in steel industry.
4. A method as claimed in claim 1, wherein the metal
sulphate is nickel sulphate.
5. A method as claimed in claim 1 or 4, wherein the
metal sulphate is the nickel sulphate generated in an electrolytic
purification of copper.
6. A method as claimed in any of claims 1 to 5, wherein
the iron sulphide is pyrite and/or pyrrhotite.

7. A method as claimed in any of claims 1 to 6, wherein
the decomposition time is 1 to 5 hr.


(54) Title: METHOD FOR DECOMPOSING METAL SULPHATE
(57) Abstract: The method of the invention relates to the decomposition in a fluidized bed of metal sulphates generated in the
metallurgical industry. The decomposition of metal sulphates is carried out so that the metal oxides generated are recovered in such
a pure form that they can be recycled to be reused in the manufacture of metal alloys such as steel. In particular, sulphates containing
nickel, iron and chrome are decomposed in oxidising conditions using pyrites or pyrrhotite as the fuel and bed material.

Documents:

01689-kolnp-2008-abstract.pdf

01689-kolnp-2008-claims.pdf

01689-kolnp-2008-correspondence others.pdf

01689-kolnp-2008-description complete.pdf

01689-kolnp-2008-form 1.pdf

01689-kolnp-2008-form 3.pdf

01689-kolnp-2008-form 5.pdf

01689-kolnp-2008-gpa.pdf

01689-kolnp-2008-international publication.pdf

01689-kolnp-2008-international search report.pdf

01689-kolnp-2008-pct request form.pdf

1689-KOLNP-2008-(11-04-2012)-ABSTRACT.pdf

1689-KOLNP-2008-(11-04-2012)-AMANDED CLAIMS.pdf

1689-KOLNP-2008-(11-04-2012)-AMANDED PAGES OF SPECIFICATION.pdf

1689-KOLNP-2008-(11-04-2012)-DESCRIPTION (COMPLETE).pdf

1689-KOLNP-2008-(11-04-2012)-EXAMINATION REPORT REPLY RECEIVED.pdf

1689-KOLNP-2008-(11-04-2012)-FORM-1.pdf

1689-KOLNP-2008-(11-04-2012)-FORM-2.pdf

1689-KOLNP-2008-(11-04-2012)-FORM-3.pdf

1689-KOLNP-2008-(11-04-2012)-OTHERS.pdf

1689-KOLNP-2008-(11-04-2012)-PETITION UNDER RULE 137.pdf

1689-KOLNP-2008-ASSIGNMENT.pdf

1689-KOLNP-2008-CORRESPONDENCE.pdf

1689-KOLNP-2008-EXAMINATION REPORT.pdf

1689-KOLNP-2008-FORM 18 1.1.pdf

1689-kolnp-2008-form 18.pdf

1689-KOLNP-2008-FORM 3.pdf

1689-KOLNP-2008-FORM 5.pdf

1689-KOLNP-2008-GPA.pdf

1689-KOLNP-2008-GRANTED-ABSTRACT.pdf

1689-KOLNP-2008-GRANTED-CLAIMS.pdf

1689-KOLNP-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

1689-KOLNP-2008-GRANTED-FORM 1.pdf

1689-KOLNP-2008-GRANTED-FORM 2.pdf

1689-KOLNP-2008-GRANTED-SPECIFICATION.pdf

1689-KOLNP-2008-INTERNATIONAL PUBLICATION.pdf

1689-KOLNP-2008-INTERNATIONAL SEARCH REPORT.pdf

1689-KOLNP-2008-OTHERS.pdf

1689-KOLNP-2008-PCT PRIORITY DOCUMENT NOTIFICATION.pdf

1689-KOLNP-2008-PCT REQUEST FORM.pdf

1689-KOLNP-2008-REPLY TO EXAMINATION REPORT.pdf


Patent Number 253624
Indian Patent Application Number 1689/KOLNP/2008
PG Journal Number 32/2012
Publication Date 10-Aug-2012
Grant Date 07-Aug-2012
Date of Filing 28-Apr-2008
Name of Patentee OUTOTEC OYJ
Applicant Address RIIHITONTUNTIE 7, FI-02200 ESPOO
Inventors:
# Inventor's Name Inventor's Address
1 METSARINTA MAIJA-LEENA SAURAMOTIE 7, FI-28450, VANHA-ULVILA
PCT International Classification Number C01B 13/32,C23G 1/36
PCT International Application Number PCT/FI2006/000361
PCT International Filing date 2006-11-10
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 20051180 2005-11-18 Finland