NO20160949A1

NO20160949A1 - A method for converting waste material from sulphide ore based nickel refining into nickel pig iron

Info

Publication number: NO20160949A1
Application number: NO20160949A
Authority: NO
Inventors: Knut Henriksen
Original assignee: Knut Henriksen
Priority date: 2016-06-02
Filing date: 2016-06-02
Publication date: 2017-08-28
Also published as: NO341101B1; WO2017207684A1; NO341101B2

Description

The present invention relates to a method for converting a waste material from sulphide ore based nickel production to a ferroalloy product.

Background

A major nickel source on earth is nickel ores containing pentlandite, an iron-nickel sulphide mineral of chemical formula (Fe, Ni^Sg. Pentlandite containing ores are also known as sulphide nickel ores and is usually being treated by pyrometallurgical techniques to form a nickel matte håving an increased nickel content and reduced iron content (and other impurities) before being utilised as raw material in nickel refining. However, the nickel matte still contains a significant residue of iron, making iron the most significant impurity (in tonnage) in nickel sulphide ore based production of nickel.

At the Glencore Nikkelverk As in Kristiansand, Norway, the iron content of the nickel matte is removed by a chlorine leaching process forming a solid residue containing the iron and other hydrometallurgical residues which are sent to deposition halls excavated in the mountain ground. The chlorine leaching process converts the iron content in the nickel matte to an aqueous solution of ferrous iron chloride. By simultaneous addition of chlorine gas and nickel carbonate to the ferrous iron chloride solution, the iron content may be precipitated as ferric hydroxide, the overall chemical reaction is:

The solid residues form the precipitation step are presently being treated as an environmental hazardous waste material which need to be deposited in deposits equipped with capability of collecting and treating leakage water from the deposit. At the Xstrata Nikkelverk AS the amount of waste material for deposition is in the order of 20 000 tonnes per year - an amount which clearly poses challenges related to costs, environmental issues and safe handling of the waste material and its deposits.

It is thus desirable, both from an environmental and a cost perspective to find a method for recycling the mineral content of the waste material and convert it to a valuable product.

Prior art

From CN 101 463 402, it is known a method for producing nickel chilled pig iron by using nickel ore and stainless by-product, the method includes steps of spraying nickel ore of 20 wt% or less, stainless by-product of 50 wt% or more, reductant of 7-13 wt%, slag making material of 7-12 wt% and recycle slag of 10 wt% or less into a SAF electric stove to melt in the SAF stove.

From WO 2008/140265, it is known a method for retrieving iron and nickel content in a waste fraction from acid washing step during manufacturing of diamonds by manufacturing a Fe/Ni-containing material håving a low content of sulphur (S) from an Fe/Ni/S04-containing liquid waste, a ferronickel mass using the Fe/Ni-containing material, and a method of manufacturing the ferronickel mass. The method of manufacturing an Fe/Ni-containing material from an Fe/Ni-containing liquid waste includes: removing SO4from an Fe/Ni/S04-containing liquid waste by adding an S04neutralizing agent to the liquid waste so that pH of the liquid waste can be maintained to a pH level of 0.5 to 2.5; precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)] by adding NaOH to the S04-free solution; washing the precipitate with water; and manufacturing an Ni/Fe-containing material by filtering and drying the washed Ni/Fe-containing sludge. The method of manufacturing a Fe/Ni-containing material may be useful to suitably apply to the field of recycling of waste acids since a Fe/Ni-containing pellet and a high purity plaster are recovered as the stainless steel material from the waste water at the same time.

From WO 2008/075879 it is known a method for manufacturing a raw material for stainless steel using a sludge containing Fe, Ni and Cl. The method comprises: neutralizing a sludge containing Fe, Ni and Cl by adding calcium hydroxide to the sludge at a molar ratio (moles of added calcium hydroxide/ moles of existing Cl) of 0.5-1.5; filtering, drying and pulverizing the sludge prepared in the neutralization operation; mixing 5-15 parts by weight of a reducing agent with pulverized sludge, based on 100 parts by weight of the dried powder; adding 5-15 parts by weight of a cement binder to 100 parts by weight of the mixture powder and forming the mixture powder into mass; and curing the formed mass. The raw material for stainless steel may be used since raw material may be prepared without completely removing Cl from the sludge, and therefore there is no problem about environmental pollutions caused by the Cl evaporation.

From CN 104 178 624 it is known a method for preparing ferronickel by using red mud and laterite-nickel ore. According to the method, iron-nickel reduction products in the red mud and the laterite-nickel ore are directly utilized and low-cost ferronickel can be provided for stainless steel smelting production, ferroalloy casting and alloy steel production. The laterite-nickel ore also contains a little of chromium, and in the production method disclosed by the invention, chromium enters the iron-nickel alloy, so that beneficial chemical components of the iron-nickel alloy are enriched. The contained iron-nickel alloy produced by the method disclosed by the invention is iron-nickel alloy with low P and S content.

From CN 104 120 209 it is known a method for producing nickel-containing molten iron by smelting and reducing liquid-state nickel slag. The method comprises the following steps: feeding liquid-state nickel slag and a reducing agent into a smelting and reducing furnace according to a predetermined mass ratio; enabling the liquid- state nickel slag and the reducing agent to react in the smelting and reducing furnace, and stirring at the same time; and generating nickel-containing molten iron and smelting slag after the reaction is ended, wherein the nickel-containing molten iron is at the lower layer of the smelting and reducing furnace, and the smelting slag is at the upper layer of the nickel-containing molten iron. The nickel-containing molten iron can be directly used for steelmaking, and the obtained smelting slag can be used for producing building materials. The method for producing the nickel-containing molten iron by smelting and reducing liquid-state nickel slag, which is provided by the invention can realize energy-saving production, comprehensive utilization of resources and good economic benefits.

From CN 101 538 631 it is known a process and a device for smelting ferronickel and nickel-containing molten iron by using lower-nickel materials, which belongs to metallurgical industry steel-making raw material. The process comprises the following steps: mixing ferronickel containing raw materials with reducing agent, solvent and catalyst to prepare ultra fine powder, mixing to make pelletizing materials, sending the pelletizing materials into a reducing furnace, obtaining chromium irons pellets after the reduction reaction, and directly adding reduced pellets into an lining electroslag furnace for being smelted into ferronickel alloy or the nickel-containing molten iron.

From RU 2 539 884 it is known a method for disposal of metal-containing wastes with iron content 15% and over, such as slags of copper and nickel manufacturing processes, sludge of copper ore floatation and similar materials, and may be used during manufacturing of the construction materials and metal extraction. Iron-containing wastes are milled to particles size 1-2 mm, mixed with carbonic deoxidant, subjected to reducing roasting at temperature 0.6-0.8 of melting point of most churlish oxide phase of the material. The final stage of the reducing roasting is performed at temperature at least equal to melting point of the less churlish oxide component. The obtained mixture is cooled by thermal shock with rate at least equal to lesser critical cooling rate for the given component, milled to particles size 1 mm and separated by separation method to metal and oxide components.

KR 100 672 089 discloses a method for manufacturing a Fe-Ni alloy mass with excellent strength and high purity more economically by pelletizing FeNi powder in the middle of reduction heat treatment, thereby utilizing FeNi-containing sludge is provided. A method for manufacturing Fe-Ni alloy mass using FeNi-containing sludge comprises the steps of: neutralizing FeNi-containing sludge with a neutralizer to remove chlorine from the FeNi-containing sludge, and drying the chlorine removed FeNi-containing sludge to a moisture content of 5% or less; deagglomerating the dried sludge into powder with an average particle size of 30 to 700 mum; molding the deagglomerated powder into an molded body with a molding density range of 1.7 to 4.7 g/cc; increasing temperature of the molded body at a temperature increasing rate of 100 °C/min or less to sinter the molded body at 500 to 950 °C; performing heat treatment of the sintered material by primarily reducing the sintered material in a temperature range of 500 to 750 °C under a reductive gas atmosphere for 15 to 60 minutes, and secondly reducing the primarily reduced sintered material in a temperature range of 750 to 1000 °C for 15 to 60 minutes such that sintering reaction is occurred during the reduction; and cooling and extracting the reduced and sintered alloy mass.

JPH 11 50162 discloses a recovering method of a valuable metal which can recover it in the form of Fe-Ni alloy or Fe-V alloy and unnecessitate the reseparation at the time of using as alloy additive for iron or steel in a dry type method. Iron component is added to burnt ash obtd. by oxidized-roasting heavy oil ash and removing carbon component, etc, and melted, separated and recovered as a Fe alloy. The melting-separation is executed in two steps of a Fe-Ni alloy recovering step for melting and separating the Fe-Ni alloy and a Fe-V alloy recovering step for melting and separating the Fe-V alloy by adding the iron component and a reducing agent into slag produced in the Fe-Ni alloy recovering step.

Objective of the invention

The main objective of the invention is to provide a method for extracting and converting the iron content in the waste fraction from the iron-precipitation step in nickel sulphide ore based production of nickel to nickel pig iron.

Description of the invention

The invention may be considered as the reduction to practice of the realisation that there is a useful amount of nickel in the solid waste fraction from the Fe(II)-precipitation step in nickel sulphide ore based production of nickel, such that the iron content may be converted into nickel pig iron.

Thus in a first aspect, the present invention relates to a method for converting waste material from sulphide ore based nickel refining into nickel pig iron, wherein the method comprises the following process steps: - drying the waste material by heating it to a temperature in the range of 100 to 650 °C and maintain this temperature until water and moisture is driven off, - calcining the dried waste material by heating the dried waste material under exposure to an oxygen containing gas to a temperature in the range from 900 to 1400 °C and maintaining this temperature at least until the gassing from the mixture of dried waste material ends,

- forming a smelting mixture by adding:

- from 0.07 to 0.21 kg C per kg Fe-content in the calcined waste material, and

- an amount of slag forming compounds,

- melting the smelting mixture in a graphite free crucible by increasing the temperature to the range of 1400 - 1600 °C to form a molten metal phase and a slag phase, and

- tapping off and solidifying the molten metal fraction of the melt in the graphite free crucible to form the intended nickel pig iron product.

The waste fraction from the Fe(II)-precipitation step in nickel sulphide ore based production of nickel typically contains a substantial amount of water, up to about 50 weight%, such that it needs to be dried before being processed to nickel pig iron. Thus, the term "drying the waste" as used herein means any heat treatment which enables vaporising and driving off any free water (i.e. not bound as crystal water) present in the waste fraction. Any heat treatment enabling driving off water and moisture from the waste may be applied by the present invention. In practice, the heat treatment may advantageously involve heating the waste to a temperature of one of the following intervals; from 100 to 650 °C, from 200 to 650 °C, from 400 to 650 °C, or from 600 to 650 °C. The term "until water and moisture is driven off as used herein means that the waste fraction material is to be heat treated for a sufficiently long period to ensure that practically all free water in the waste material has evaporated and been driven off in the gaseous state, transforming the waste fraction into a dry solid residue. Depending on the amount of waste, with or without use of stirring of the waste material, the actual drying temperature being applied, use of natural or forced convection (i.e. with our without fans blowing air over or through the waste material) to drive off the water vapour etc, the period of time required to dry the waste may vary considerably. Thus, the temperature during the heat treatment for drying the waste fraction may advantageously be maintained at a period ranging from one of; from 1 minute to 10 hours, from 10 minutes to 7 hours, from 30 minutes to 4 hours, or from one to two hours. The drying step may advantageously comprise one or both of the following steps; stirring of the waste fraction, and heating air to the intended drying temperature and then blowing it over and/or through the waste material.

In addition to the water, the waste fraction from the Fe(II)-precipitation step in nickel sulphide ore based production of nickel contains mainly iron present as solid precipitates of ferric hydroxide Fe(OH)3and/or goethite, FeOOH and about 2 weight% NiCl2. In order to enable reducing the iron and nickel content to elemental iron and nickel, the elements should be transformed to oxides, Fe2C>3and NiO, respectively, which may be reduced to elemental iron and nickel by addition of carbon and heated to a temperature above 1400 °C. The conversion of the Fe(OH)3and/or FeOOH and NiCb of the dried waste fraction material to Fe203and NiO, respectively, is according to the invention, obtained by heat treating the dried waste fraction material under exposure to air or another oxygen containing gas to a temperature in one of the following ranges; from 900 to 1400 °C, preferably from 900 to 1200 °C, or more preferably from 900 to 1000 °C, or most preferably from 940 to 960 °C. Thus, the term "calcining the dried waste" as used herein means a heat treatment under exposure to an oxygen containing gas in one of the above temperatures ranges until practically all of the Fe(OH)3and/or FeOOH and NiCb content of the dried waste fraction material is oxidised to Fe203and NiO, respectively. In practice, this is obtained when the visible gassing from the waste fraction material ends. The heat treatment times required to complete the calcination may vary considerably depending on the amount of waste, with or without use of stirring of the dried waste fraction material, the actual calcination temperature being applied, and with or without use of natural or forced convection. Thus, the temperature during the heat treatment for calcining the dried waste fraction material may advantageously be maintained at a period ranging from one of; from 10 minutes to 48 hours, from 20 minutes to 24 hours, from 30 minutes to 12 hours, or from 60 minutes to 6 hours. The calcination step may advantageously further comprise one or both of the following steps; stirring of the dried waste fraction, and heating air to the intended drying temperature and then blowing it over and/or through the dried waste material.

Another factor which advantageously may be tåken into consideration is the content of the impurity compounds containing As, Cl, and/or S which may be present in the waste fraction material. The chlorine content of the dried waste material fraction results mainly from the chlorine addition of the Fe(II)-precipitation step in nickel sulphide ore based production of nickel which produces NiCb and smaller amounts of other chlorine containing compounds. The NiCbCs) in the dried waste fraction material reacts with oxygen during the calcination and forms solid nickel oxide, NiO(s), and the poisonous and chemically aggressive chlorine gas, CbCg). Thus, the calcination step may advantageously additionally comprise a collection of the furnes being gassed off the waste fraction material during the calcination step and passing the collected furnes through a chlorine trap or similar measure for removing the chlorine gas in the furnes before venting them into the atmosphere.

Other compounds which may be present in sufficiently high concentrations in the dried waste fraction material to cause an environmental problem are arsenic and sulphur. Both arsenic (both in elementary form and as oxides) and sulphur have sufficiently high vapour pressures at the temperatures involved in the calcination step to be to more or less driven off with the furnes gassing from the waste fraction material during the calcination step. Thus, the calcination step may advantageously additionally comprise a collection of the furnes being gassed off the waste fraction material during the calcination step and passing the collected furnes through a condenser for condensing the arsenic and/or sulphur content for removing the arsenic and/or sulphur content in the furnes before venting them into the atmosphere.

After the calcining, the iron and nickel content of the waste fraction is mainly present as NiO and Fe203, respectively. Both these oxides may be reduced to elementary nickel and iron respectively by heating them with elementary carbon as reducing agent. Due to the electronegativity of nickel as compared to iron, the carbon will preferentially reduce the nickel oxide before the ferric iron oxide. This provides an advantage by enabling increasing the nickel concentration in the produced nickel pig iron as compared to the nickel content of the waste fraction material, by simply adding the reduction agent (carbon) in under-stoichiometric amounts (as compared to the total iron content of the calcined waste material) such that not all ferric iron oxide of the waste fraction material becomes reduced to elemental iron. The excess ferric oxide of the calcined waste material will be part of the slag phase during the subsequent melting step.

Experiments made by the inventor indicates that adding carbon to the calcined waste material in an amount in the range from 0.07 to 0.21 kg carbon per kg Fe-content in the calcined waste material results in an alloy (after melting and reduction) håving a nickel content qualifying to be a commercial grade nickel pig iron. This amount of added carbon corresponds to a molar ratio C:Fe in the mixture of calcined waste material and carbon of approximately 1:3 to 3:3. Thus, the term "adding from 0.07 to 0.21 kg carbon per kg Fe present in the calcined waste material" as used herein, means that the waste fraction material which is to be melted and refined to nickel pig iron is mixed with a total amount from 0.07 to 0.21 kg of elementary carbon per kg Fe, being present, either as Fe203, Fe304or a mixture thereof, in the entire mass of calcined waste material which is to be treated. For example, if the calcined waste material contains a total of 5 kg ferric oxide, Fe203, which corresponds to about 3.5 kg Fe, the carbon addition for forming the smelting mixture according to the first aspect of the invention is to be in the range from 0.25 to 0.75 kg elementary carbon. Alternatively, the method according to the present invention may apply an addition of carbon per kg Fe present in the calcined waste material in one of the following ranges; from 0.09 to 0.19 kg C per kg Fe, preferably from 0.10 to 0.18 kg C per kg Fe, more preferably from 0.11 to 0.17 kg C per kg Fe, more preferably from 0.12 to 0.16 kg C per kg Fe, more preferably from 0.13 to 0.15 kg C per kg Fe, and most preferably from 0.135 to 0.145 kg C per kg Fe present in the waste fraction material.

The smelting mixture according to the first aspect of the invention should contain an amount of slag forming compounds to enable forming a protective cover of slag on top of the molten smelting mixture to protect the molten elementary iron against excessive oxidation upon exposure to surrounding air or other airborne oxygen sources. The chemical composition of the melt may have an impact on which slag system which should be applied. For instance, if the melt contains acidic minerals it may be advantageous applying an acidic slag composition, and if vice versa, if the melt contains alkaline minerals it may be advantageous applying an alkaline slag composition. However, the calcined waste material according to the first aspect of the invention contains mainly iron oxides, i.e. it is very little of other mineral phases in the melt, such that it may optionally be applied either acidic or basic slag compositions. That is, the invention according to the first aspect of the invention may apply any slag forming compound or mixture of compounds in any amount which forms a suited slag cover for liquid iron melts. Slag protection of liquid iron is well known to the person skilled in the art such that there is no need for a more detailed specification. However, alkaline slag compositions are known to be suited for ferronickel melts in combination with a crucible lining of MgO. Alkaline slag compositions have the advantage of being efficient absorbers of sulphur and chlorine, two contamination elements present in the calcined waste material, and are thus a preferred choice. An alkaline reducing slag typically comprises mainly basic oxides such as CaO, FeO, MgO, MnO, etc. An especially preferred slag composition comprises 70 - 80 weight% FeO, 10-20 weight% CaO and up to 5 weight% Si02.

Also, fly ash from municipal waste incineration and other incineration processes often have relatively high contents of both lime, CaO, and silica, Si02, and may thus advantageously be applied as slag forming addition. This has the advantage of providing the slag forming compounds at very favourable costs and at the same time solving another problematic waste disposal problem. Fly ash often contains dangerous levels of dioxins and furan, C4H4O, making it necessary to deposit the fly ash in specially secured deposits. However, both dioxin and furan are organic compounds which would be completely destroyed when exposed to molten iron.

The use of carbon as reduction agent has another advantage of being a reducing agent also for eventual remains of arsenic oxides after the calcination step, reducing the arsenic oxides to elementary arsenic which is very volatile at the temperatures of molten nickel pig iron. Thus, as an alternative, it may be added an amount of carbon to the dried waste fraction material to enable removing more arsenic at the calcination step by reducing arsenic oxide to elementary arsenic. Thus, in one example embodiment, the calcining step may be performed with the addition of an amount of elementary carbon to enhance the extraction of arsenic by utilising the carbon to reduce arsenic oxide to elementary arsenic which evaporates off the waste material. At the calcining temperatures of the first aspect of the invention, the addition of elementary carbon to the waste material may have the effect of partially reducing the ferric oxide Fe203of the waste material to iron(II, III) oxide, magnetite, Fe304. However, both iron oxides, Fe203and Fe304, will be reduced to elementary Fe during the subsequent melting step of the method according to the first aspect of the invention. The addition of carbon at the calcining step is thus an optional choice falling within the scope of the invention. The amount of arsenic in the waste material is usually sufficiently low to ignore the carbon consumption for reducing the arsenic oxide to arsenic, such that the addition of elementary carbon to make the smelting mixture does not need to take the arsenic content into consideration since it is approx. two orders of magnitude lower than the iron content. However, if the arsenic content is significantly higher, the amount of carbon added to the waste material may advantageously take the arsenic content of the waste fraction material into consideration.

The resulting nickel pig iron from the method according to the invention may have nickel contents up to 5 weight%, and is thus a valuable ferroalloy product for the steel industry. The invention according to the first aspect is thus able to remove the problematic waste disposal from sulphide ore based nickel production, and optionally also the problematic disposal of fly ash from incineration of municipal waste and other solid wastes.

Verification of the invention

The invention will be described in further detail by way of an example embodiment.

In the example embodiment, it is applied waste material from the Fe(II)-precipitation step at Glencore Nikkelverk AS in Kristiansand, Norway. This waste material typically contains about 60 weight% Fe, 1-3 weight% Ni, 1-3 weight% S, 3 - 5 weight% Cl, and about 1 weight% As. The rest is mainly water and other impurities. The waste material has an orange colour, an indication that the iron of the material is mainly present as goethite, FeOOH.

A sample of 15 kg of the waste material was heated in air to a temperature of

110 °C and held at this temperature for 10 hours. A small sample of approx. 100 g of the dried waste material was sent to analysis to establish its composition.

The rest of the dried waste material was calcined in a first step by heating the material to a temperature of 650 °C and held at this temperature for a period of 4 hours. A sample of the material of approximately 100 g was tåken and sent for composition analysis. The result for a selected number of elements is given in the

table below.

The rest of the waste material was added 5 weight% carbon, in the form of petroleum coke, based on the weight of the dried waste material. As seen from the composition analysis summarized in the table below, this corresponds to about 0.1 kg C per kg Fe in the material. Then the material was calcined in a second step by heating it up to a temperature of 950 °C and maintained at this temperature for a period of 4 hours. After cooling, a sample of approximately 100 g of the material was tåken after the second calcination step and sent for composition analysis. The result is given in the table below. The waste material turned black during the second calcination step, an indication that the iron content of the calcined waste material was dominantly present as magnetite, FesCV

Then a smelting mixture was formed by mixing 10 parts of calcined waste material with 3 parts CaO, one half part Si02and a minor amount of petrol coke. This corresponds to a composition of approx. 53 weight% Fe, 22 weight% CaO, 4 weight% Si02, and about 5 weight% C.

13.5 kg of the smelting mixture was added to a graphite crucible håving a lining of MgO and then heated to 1400 °C and held at this temperature for a period of 30 minutes. Then the slag phase, which amounted to 4.5 kg, was tapped off. The metallic melt, which amounted to 4.7 kg, was transferred to a solidification crucible and cooled to room temperature. A sample of the resulting nickel pig iron was sent to composition analysis. As seen from the table below, the example embodiment of the invention resulted in a nickel pig iron of about 85 weight% Fe and 3 weight% Ni.

The MgO lining of the graphite crucible turned out to be incapable of preventing the molten iron melt from dissolving a major part of the graphite crucible wall. Thus, the melting step reduced a larger fraction of the iron oxide of the melt than intended. This is the reason why it was obtained a final composition of the nickel pig iron håving less than 5 weight% Ni. The present verification test is nevertheless a proof of concept since it is obtained a nickel pig iron with a considerably increased Ni-content than in the waste material. Furthermore, with a better control with the reduction of the iron oxides of the melt (which will be obtained when using a graphite free crucible), the verification test indicates that the method according to the present invention is expected to be able to produce nickel pig irons håving up to about 10 weight% Ni.

Also, the digestion of the graphite crucible resulted in significantly increased contents of some of the impurity elements in the nickel pig iron. Thus, the results shown in Table 1 regarding the impurity levels in the nickel pig iron is misleading. It is the results from the calcining process that are most informative of the effect of the present invention. And as seen in the table, arsenic was reduced by 41.8 %, chlorine by 99.6 % and sulphur by 96.7 %. The other impurities problematic for steel manufacturing are present in trace amounts. Thus the test verifies that the method as defined in the claims is able to transform the problematic waste fraction from sulphide ore based nickel production to a valuable ferroalloy product.

Claims

1. A method for converting waste material from sulphide ore based nickel refining into nickel pig iron, wherein the method comprises the following process steps: - drying the waste material by heating it to a temperature in the range of 100 to 650 °C and maintain this temperature until water and moisture is driven off, - calcining the dried waste material by heating the dried waste material under exposure to an oxygen containing gas to a temperature in the range from 900 to 1400 °C and maintaining this temperature at least until the gassing from the mixture of dried waste material ends, - forming a smelting mixture by adding: - from 0.07 to 0.21 kg C per kg Fe-content in the calcined waste material, and - an amount of slag forming compounds, - melting the smelting mixture in a graphite free crucible by increasing the temperature to the range of 1400 - 1600 °C to form a molten metal phase and a slag phase, and - tapping off and solidifying the molten metal fraction of the melt in the graphite free crucible to form the intended nickel pig iron product.

2. A method according to claim 1, wherein the drying is obtained by - heating the waste material to a temperature of one of the following intervals; from 200 to 650 °C, from 400 to 650 °C, or from 600 to 650 °C, and - maintaining this temperature for a time period ranging from one of; from 1 minute to 10 hours, from 10 minutes to 7 hours, from 30 minutes to 4 hours, or from one to two hours.

3. A method according to claim 1 or 2, wherein the method further comprises one or both of the following steps; stirring of the waste fraction, and heating air to the intended drying temperature and then blowing it over and/or through the waste material.

4. A method according to any preceding claim, wherein the calcination of the dried waste material is obtained by: - heat treating the dried waste fraction material under exposure to air or other oxygen containing gas to a temperature in one of the following ranges; from 900 to 1200 °C, or preferably from 900 to 1000 °C, or most preferably from 940 to 960 °C, and - maintaining this temperature for a period ranging from one of; from 10 minutes to 48 hours, preferably from 20 minutes to 24 hours, more preferably from 30 minutes to 12 hours, and most preferably from 60 minutes to 6 hours.

5. A method according to claim 4, wherein the calcination further comprises one or both of the following steps; stirring of the dried waste fraction, and heating air to the intended drying temperature and then blowing it over and/or through the dried waste material.

6. A method according to any preceding claim, wherein the calcination step further comprises collecting the furnes being gassed off the waste fraction material during the calcination step and passing the collected furnes through a chlorine trap or similar measure for removing the chlorine gas in the furnes before venting them into the atmosphere.

7. A method according to any preceding claim, wherein the calcination step further comprises collecting the furnes being gassed off the waste fraction material during the calcination step and passing the collected furnes through a condenser for condensing the arsenic and/or sulphur content for removing the arsenic and/or sulphur content in the furnes before venting them into the atmosphere.

8. A method according to any preceding claim, wherein the calcination step further comprises adding an amount of carbon to the dried waste fraction material.

9. A method according to any preceding claim, wherein the amount of carbon being added to the calcined waste material is one of the following ranges; from 0.09 to 0.19 kg C per kg Fe, preferably from 0.11 to 0.17 kg C per kg Fe, more preferably 0.11 to 0.17 kg C per kg Fe, more preferably from 0.12 to 0.16 kg C per kg Fe, more preferably from 0.13 to 0.15 kg C per kg Fe, and most preferably from 0.135 to 0.145 kg C per kg Fe present in the calcined waste material.

10. A method according to any preceding claim, wherein the slag forming compounds comprises one or more of: CaO, FeO, MgO, and MnO.

11. A method according to any of claims 1-9, wherein the slag forming compounds comprises 70 - 80 weight% FeO, 10-20 weight% CaO and up to 5 weight% Si02, based on the total mass of the slag forming compounds.

12. A method according to claim 10, wherein the slag forming compounds further comprises fly ash from municipal waste incineration.