FI123241B - Process for improving the degree of reduction in melting of a ferro-mixture - Google Patents

Abstract

The invention relates to a method for improving the reduction degree of metal components in a chromite concentrate when smelting ferroalloy suitable for manufacturing of stainless steel. The chromite concentrate is fed together with nickel-containing raw material so that by means the amount of nickel-containing raw material it is achieved a desired reduction degree for the metal components of ferroalloy.

Description

METHOD FOR IMPROVING THE DEGRADATION DEGRADATION OF FERROSE ALLOY

This invention relates to a process for improving the degree of reduction of metal components in a material to be treated by melting a ferro-alloy, such as a ferro-chromium alloy suitable for the production of stainless steel. According to the method, a nickel-containing material is added to the ferro-alloy to be melted.

From WO Patent Publication 2010/092234 is known a process in which a nickel ore and / or nickel concentrate or intermediate precipitated from solutions of nickel ores and / or nickel concentrates is agglomerated in the process of making ferrochrome by making the nickel-containing material together with iron-containing and The drying and calcining of the material containing 15 is preferably carried out in the context of a single step heat treatment, sintering. In the case of heat treatment of pellets, the bodies are reinforced so that, if desired, the heat-treated bodies can be transported substantially whole between different process steps. If necessary, the pellets can be preheated before sintering. The heat-treated pieces 20 can, if desired, be transported substantially whole between different process units. The heat-treated pieces can also be reduced, if desired, as the pieces are transported between different process steps or process units. Sintered and thus reinforced pellets are used as raw materials in the smelting process under reducing conditions, whereby the smelting product is a ferro-chromium nickel containing 25 nickels.

Thus, the aforementioned WO Patent Publication 2010/092234 is directed mainly to the preparation of pellets containing nickel by sintering. In contrast, the melting conditions of the sintered pellets are not described in more detail. However, when describing the energy-30 efficiency of the process, it has been mentioned that nickel in the pellets catalyzes the reduction of chromium in the pellets and thus reduces the specific consumption of a reducing agent, preferably carbon, in ferro-alloy production.

2

It has now surprisingly been found that nickel in pellets not only catalyses the reduction of chromium in chromite pellets, but that nickel in the chromite smelting furnace feed improves the smelting furnace feed of all essential metal components, iron, chromium and nickel, in the smelter. It is an object of the present invention to take advantage of this surprising discovery and provide a more efficient method of improving the reduction rate in the chromite material smelting process, wherein the reduction of chromite metal components in smelting is improved by doping the nickel-containing The essential features of the invention will be apparent from the appended claims.

According to the invention, a fusible feedstock of ferro-alloy production, such as chromite, is alloyed with a nickel-containing material before smelting, whereby the nickel-containing material improves the reduction of the metal components in the feed material while the nickel-containing material itself is reduced to a metallic component. The amount of nickel added to the ferroalloy according to the invention can advantageously control the degree of reduction of the metal components of the ferro-rose alloy and at the same time provide a ferroalloy having the desired nickel content, such as ferro-chromium nickel alloys. Ferro-chromium alloys containing the desired nickel content can be used, for example, in the manufacture of various stainless steels, such as austenitic or duplex stainless steels.

In the process according to the invention, nickel oxide, at least partly nickel ore and / or nickel concentrate or at least partly nickel ore and / or nickel concentrate intermediate by leaching and / or precipitation can be used as nickel-containing raw material. The nickel-containing raw material is fed to the smelting process together with the ferrochrome raw material. Prior to feeding into the smelting furnace, the nickel-containing raw material is either pre-treated to form sintered pellets of the nickel-containing raw material together with the ferrochrome raw material, chromite, or so that the nickel-containing raw material is treated separately to the chromite pellets. It is also possible to pre-treat the nickel-containing raw material by treating part of the nickel-containing raw material fed into the melt furnace together with the chromite pellets and some of the nickel-containing raw material fed into the melt furnace separately from the chromite pellets. Due to various pretreatments, the nickel-containing raw material fed to the smelting furnace and contributing to the reduction of various metal components may be, for example, part of a Nikke-10 lipidic hydroxide intermediate, part of a sulphide or laterite nickel concentrate.

The nickel-containing raw material to be used in the process of the invention is preferably a nickel-containing hydroxide intermediate precipitated from solutions of nickel-rich concentrates of laterite and / or sulphidic ores and / or sulphidic ores. Such a nickel-containing hydroxide intermediate is, for example, nickel-containing intermediate from pressure leaching, atmospheric leaching, or heap leaching of lateral or sulphide ores and nickel concentrates, as well as extraction or separation of nickel-containing materials from leaching or ion exchange processes. Carbonate and sulphate nickel materials may also be used as nickel-containing raw materials in the process of the invention. In addition, a sulphide nickel concentrate per se and a hydrometallurgically precipitated nickel sulphide intermediate are suitable as nickel-containing raw materials for the process.

According to the invention, the amount of nickel-containing material to be fed to the melting furnace is adjusted to between 5 and 25% by weight, preferably 10 to 20% by weight, of the total amount of pre-treatment material to be fed to the furnace. When adjusting the amount of nickel-containing material to be fed to the smelting furnace, consideration is given to obtaining favorable reduction conditions for your energy economy and / or to producing a preferred alloy of ferrous chromium nickel having an advantageous nickel content. By controlling the reduction rate of the material to be melted, a smelting product with a nickel content varying according to the degree of reduction is obtained. With a small addition of nickel raw material, the degree of reduction remains low, whereby a low-nickel ferroalloy is formed, the ferrochrome chelate. Such a low-nickel ferro-alloy is a preferred pre-alloy especially for the production of duplex stainless steel grades. With a higher addition of nickel raw material, the degree of reduction increases and the nickel content in the smelting product is also higher. Such ferric chromium nickel having a higher nickel content is preferably used for the preparation of nickel-rich austenitic stainless steel grades.

In the process of the invention, the composition and microstructure of the nickel raw material is preferably taken into account in the pretreatment of the nickel-containing raw material fed to the furnace. For example, if the nickel-containing raw material is a nickel-containing hydroxide intermediate from mines or other hydrometallurgical processes precipitated from solutions of nickel-containing concentrates which requires, among other things, pretreatment at elevated temperature, the nickel-containing raw material is pretreated with pellet and chromite. Conversely, if the nickel-containing raw material of the process of the invention is a material such as nickel oxide, nickel ore and / or nickel concentrate which does not require any substantial pre-treatment at elevated temperature other than drying, it is possible to feed the nickel-containing raw material . The microstructure and composition of the nickel-containing raw material may also be such that it is advantageous to pretreat the raw material separately from the chromite pelletization and to feed the nickel-containing raw material into the sintering of the chromite pellets prior to feeding into the melting furnace.

30

Preferably, the process of the invention employs a melting furnace with a preheating apparatus installed therein so that the feed to the furnace is led through the preheating apparatus to the furnace. The nickel-containing raw material pretreated in accordance with the invention is also fed to a preheating apparatus in which the nickel-containing raw material is contacted at the latest with other material fed to the melting furnace. In the smelting furnace, the second raw material of nickel silicon-5, together with the chromite pellets, is melted into ferrochrome nickel of the desired composition which can be advantageously used in its composition, for example in the production of austenitic or duplex stainless steel grades.

When the melting of the nickel-containing raw material is preferably carried out in a closed submerged furnace, the carbon monoxide gases produced during the reduction and melting can be used for in different phases.

The process of the invention will be described in more detail below with the aid of the following example.

20

EXAMPLE

A chromium and iron-containing chromite concentrate and a nickel-containing hydroxide intermediate were blended to which 1.2% by weight of bentonite and 3% by weight of slag-forming material, flux, either limestone or wollastonite, was added. Table 1 shows the percentages by weight of chromium, iron, nickel, carbon and sulfur in the mixtures to which 10% by weight (Test 1) and 20% by weight (Test 2) of nickel hydroxide were added. In addition, Table 1 shows as a reference material (REF) an alloy to which nickel hydroxide was not added.

30 6

Cr wt% Fe wt% Ni wt% C wt% S wt% REF 283 Ϊ83 Ö3 0Ϊ2 ÖÖ6

Test 1 263 Ϊ63 53 NIGHT NIGHT3

Test 2 24Ä 15.1 1Ö? I Ö1Ö Ö33

table 1

The blends contained in the binder for each material of Table 1 were pelleted and sintered. Some of the sintered pellets were fed into the melt-5 furnace, respectively, with a slag former and a reducing agent.

The materials of Table 1 were thawed, and Table 2 shows the concentrations of chromium, iron nickel, carbon and silicon in the smelting products, as well as the intake of metal components, chromium, iron and nickel, into the metal melt product. The carbon content is formed by the composition and balance of the alloy. There is so much carbon in the feed charge that there is also some carbon to reduce the silicon in the smelting product. The feed mixture contains silica in the raw and production materials.

Concentrations (% by weight) Yields

Cr% Fe% Ni% C% Si% Cr% Fe% Ni% REF 533 33Ä Ö36 8? L 2Ä 883 9Ö3:

Test 1,493 3Ö? I 7? I 6J 23,863,887 86.0

Test 2 463 263 Ϊ33 6? I 43 913 9ÖJ 88.6 15 Table 2

Some of the sintered pellets were subjected to laboratory-scale thermogravimetric measurements to monitor the degree of reduction of the metal components contained in the pellets, chromium, iron and nickel, under conditions similar to the melting process at a maximum temperature of 1550 ° C. Table 3 shows the results of thermogravimetric measurements for the degree of reduction of chromium (Crmet / Crtot), iron (Femet / Fetot) and nickel (Nimet / Nitot) at temperatures of 1400 ° C and 1550 ° C.

7 (CCmet / Cftot)% (Femet / Fetot)% (Names / Nitot)% REF (1400 ° C) Τ7Ϊ 16 ^ 8 - REF (1550 ° C) 6J 47 \ 2 -

Test 1 (1400 ° C) 2 £ 37 ^ 4 67 ^ 3 "Test 1 (1550 ° C) IM 7Ö6 78 ^ 9" listTÖ4ÖÖ ^ Cj 5 ^ 2 56J 79? I

Test 2 (1550 ° C) 57-94 ^ 3 99J

Table 3

The addition of nickel-containing raw material to pellets significantly increases the degree of reduction of chromium and iron at 1550 ° C, chromium by more than 15% and iron by more than 70%, while the reduction of nickel to almost 100% with the nickel content of Test 2. An increase in the degree of reduction of all the metal components contained in the sintered pellets, chromium, iron and nickel, with the addition of a nickel-containing raw material, at the same time reduces the need for coke used as a reducing agent to achieve the reduction conditions of the melting process.

Claims (16)

Method for improving the reduction of the metal components in the chromite carbonate in the melting of suitable ferro-mixture in the preparation of stainless steel, characterized in that the chromite concentrate is measured together with the nickel-containing filler into the furnace, so that the amount of nickel-containing raw material is measured. provides the desired degree of reduction for the metal components included in the ferro mixture. 10 Method according to claim 1, characterized in that nickel-containing raw material is fed 5-25% by weight, most preferably 10-20% by weight of the total amount of material measured in the furnace. Process according to claim 1 or 2, characterized in that at the melting point, at least 2.6% of the chromium is reduced from the chromite concentrate. Process according to any one of the preceding claims, characterized in that at the melting, at least 37.4% of the iron is reduced from the chromite concentrate. 20 Process according to any of the preceding claims, characterized in that at least part of the nickel-containing fox is measured in the furnace together with the pellets prepared from the chromite concentrate. Method according to any of the preceding claims, characterized in that at least a portion of the nickel-containing filler is pre-treated separately from the chromium concentrate pellets before being measured in the furnace. Process according to any of the preceding claims, characterized in that nickel oxide is fed into the melting furnace as nickel-containing raw material at least in part. 30 Process according to any of the preceding claims, characterized in that nickel ore and / or nickel concentrate is fed into the smelting furnace as nickel-containing raw material at least in part. 5 9. A process according to any preceding claim, characterized in that, in the melting furnace as nickel-containing raw material, at least in part some of the nickel ores and / or nickel concentrates are extracted from the nickel-containing intermediate by leaching and / or precipitation. 10. A process according to claim 9, characterized in that in the melting furnace, at least part is fed from lateritic or sulphidic nickel ores and / or nickel concentrate by nickel-containing intermediate extracted by pressure leaching. 11. A process according to claim 9, characterized in that at least a part of the smelting furnace is fed from lateritic or sulphidic nickel ores and / or nickel concentrate obtained by atmospheric leaching of nickel-containing intermediate. Method according to claim 9, characterized in that in the melting furnace, at least a part is fed from lateritic or sulphidic nickel ores and / or nickel concentrate obtained by high leaching nickel-containing intermediate. Process according to claim 9, characterized in that the nickel-containing precipitating product which is recovered by leaching the nickel-containing materials is fed into the melting furnace at least partially. Process according to Claim 9, characterized in that the nickel-containing precipitating product obtained by separating the distillation solution of the nickel-containing materials is fed at least partially to the melting furnace. 30 15. A process according to claim 9, characterized in that at least a part of the nickel-containing precipitating product obtained by refining the nickel-containing materials is fed into the melting furnace. 5 Method according to claims 1-9, characterized in that in the melting furnace it is fed as nickel-containing raw material, partly nickel concentrate and partly from nickel ores and / or nickel concentrate obtained by solution and / or precipitation nickel-containing intermediate.