Method for producing ferroalloy containing nickel

Abstract

The invention relates to a method for producing a ferroalloy containing nickel. From a fine-grained raw material containing iron and chromium and a fine-grained raw material containing nickel, a mixture is formed with binding agent, the mixture is agglomerated so that first formed objects of desired size are obtained. The objects formed are heat treated in order to strengthen the objects so that the heat treated objects withstand conveyance and loading into a smelter furnace. Further, the objects are smelted under reducing circumstances in order to achieve ferrochromenickel, a ferroalloy of a desired composition containing at least iron, chromium and nickel.

Claims

1. A method for producing a nickel containing ferroalloy, comprising: forming a mixture of a raw material containing iron and chromium, a raw material containing nickel, and a binder material, agglomerating the mixture at atmospheric pressure to form objects having a desired size, heat-treating the objects for removal of water of crystallization bound in the raw material, whereby the raw material containing nickel is calcinated and the objects are strengthened so that the heat-treated objects are conveyable, and smelting the objects under reducing conditions in order to produce ferrochromenickel containing chromium to nickel in a ratio between 2.6 and 3.0, and wherein the raw material containing iron and chromium supplies substantially all the iron and chromium in the ferrochromenickel.

2. A method according to claim 1, wherein agglomeration comprises pelletizing.

3. A method according to claim 1, wherein heat-treating comprises sintering.

4. A method according to claim 1, wherein a proportion of nickel-bearing material in the mixture is 10-25 weight %.

5. A method according to claim 1, comprising heat-treating the objects at a temperature in the range from 10001400 C.

6. A method according to claim 1, characterized in that what is used as the nickel containing raw material, is carbonate nickel materials, sulfate nickel materials, or sulfidic nickel materials.

7. A method according to claim 1, characterized in that the pellet mixture formed of nickel containing material and iron containing chromite concentrate is simultaneously calcined and desulphurized in connection within the sintering process.

8. A method according to claim 1, characterized in that the agglomerated and smelted ferrochromenickel contains 40-45 weight % chromium, 18-24 weight % nickel, 3-5 weight % carbon, the rest iron and inevitable impurities.

9. A method for producing a nickel containing ferroalloy, comprising: forming a mixture of a raw material containing iron and chromium, a raw material containing nickel, and a binder material, agglomerating the mixture to form objects having a desired size, heat-treating the objects for removal of water of crystallization bound in the raw material, whereby the raw material containing nickel is calcinated and the objects are strengthened so that the heat-treated objects are conveyable, and smelting the objects under reducing conditions in order to produce ferrochromenickel containing chromium and nickel in a ratio between 1.5 and 5, and wherein the raw material containing iron and chromium supplies substantially all the iron and chromium in the ferrochromenickel, and further characterized in that what is used as a raw material containing nickel, is nickel-bearing hydroxidic intermediate products precipitated from leach liquors of at least one of hydrometallurgical processes of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

10. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product from pressure leaching of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

11. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product received from atmospheric leaching of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

12. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product received from heap leaching of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

13. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product received from a solvent extraction process of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

14. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product received from an ion exchange process of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

15. A method according to claim 9, characterized in that what is used as a raw material containing nickel, is an intermediate product received from a refining process of at least one of lateritic nickel ores and nickel-bearing concentrates or process precipitates of lateritic nickel ores.

16. A method for producing a nickel containing ferroalloy, comprising: forming a mixture of a raw material containing iron and chromium, a raw material containing nickel, and a binder material, agglomerating the mixture to form objects having a desired size, heat-treating the objects for removal of water of crystallization bound in the raw material, whereby the raw material containing nickel is calcinated and the objects are strengthened so that the heat-treated objects are conveyable, and smelting the objects under reducing conditions in order to produce ferrochromenickel containing chromium and nickel in a ratio between 1.5 and 5, and wherein the raw material containing iron and chromium supplies substantially all the iron and chromium in the ferrochromenickel, and further characterized in that what is used as a raw material containing nickel, is nickel-bearing hydroxidic intermediate products precipitated from leach liquors from at least one of hydrometallurgical processes of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

17. A method according to claim 16, characterized in that what is used as the nickel containing raw material, is intermediate products received from the pressure leaching of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

18. A method according to claim 16, characterized in that what is used as the nickel containing raw material, is intermediate products received from the atmospheric leaching of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

19. A method according to claim 16, characterized in that what is used as the nickel containing raw material, is intermediate products received from the heap leaching of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

20. A method according to claim 16, characterized in that what is used as the nickel containing raw material, is intermediate products received from the solvent extraction process of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

21. A method according to claim 16, characterized in that what is used as the nickel containing raw material, is intermediate products received from the ion exchange process of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

22. A method according to claim 16, characterized in that what is used as the nickel containing raw material is intermediate products received from the refining process of at least one of sulfidic nickel ores and nickel-bearing concentrates or process precipitates of sulfidic ores.

Description

(1) The invention is described in more details in the following referring to the enclosed drawing, where FIG. 1 shows one preferred embodiment of the invention as a schematic flow sheet.

(2) According to FIG. 1 a fine-ground iron containing chromite concentrate 1, a fine-ground nickel hydroxide 2 and a binder 3 for pelletizing is fed into a mixing apparatus 4 so that the proportion of the fine-ground nickel material 2 from the mixture to be received from the mixing apparatus 4 is 18 weight % from the weight of the mixture. The mixture thus generated, containing iron, chromium and nickel is conveyed to a rotating drum 5 for pelletizing. The pellets to be received from the drum 5 are further conveyed to an essentially continuously operated belt sintering 6, for which purpose an essentially uniform material bed of pellets is laid out on the essentially continuously operated sintering belt. In the sintering stage, hot circulation gases are conducted through the material bed and the sintering belt, and by means of these gases and some extra fuel the temperature in the material is made to rise to the range of 1150-1400 C. During the sintering stage, moisture is removed from the pellets, as well as the nickel hydroxide is advantageously calcined, thus providing removal of water from the nickel hydroxide as well as of crystalline hydrate water bound therein. During the sintering stage, sulphur bound in various components is removed from the mixture. The sintered pellets are further conveyed into smelting together with the slag forming agent and the reducing agent in a submerged electric arc furnace 7 either through a preheating 8 or directly without preheating. The molten ferrochromenickel to be received from the smelting furnace 7 is conveyed into a steel smelter 9 for producing stainless steel or the molten ferrochromenickel is granulated for further processing.

EXAMPLE 1

(3) The method according to the invention was applied to a material in which nickel hydroxide intermediate product was present as sulphate nickel hydroxide Ni(OH).sub.x(SO.sub.4).sub.y, received from a leaching process by precipitation, with nickel content in the range of 40-50 weight % and sulphur content below 5 weight %. The chromium content in the chromite concentrate used as a raw material for chromium and iron varied between 30-31 weight % and the chromium/iron ratio in the concentrate between 1.6-1.8.

(4) The sulphate nickel hydroxide was mixed with the chromite concentrate and bentonite used as a binder so that the proportion of the sulphate nickel hydroxide in the mixture was 20 weight % calculated from the final weight of the mixture. The mixture was fed into a rotating drum, where pellets with a diameter between 5-15 mm were formed from the mixture. The pellets received from the drum were further fed onto the sintering belt of the essentially continuously operated belt sintering as essentially evenly spread pellet bed. During sintering hot gases were conducted through the pellet bed as well as also through the holes in the sintering belt and when and if needed, applying other sources of energy so as to calcine sulphate nickel hydroxide and to remove sulphur contained in the sulphate nickel hydroxide into the exhaust gases of sintering, which gases can be treated for the removal of sulphur dioxide by as such known methods. The strength properties of the sintered pellets corresponded to the abrasion resistance of the chromite pellets, tumbler 3-5%, and the compression strength 140-160 kg/cm.sup.2.

(5) Together with coke used as a reducing agent, quartzite used as a slag forming agent and lumpy chromite used as a regulation agent for achieving the desired chromium and iron content in the smelting product, the pellets received from sintering were fed first into a preheating unit of the smelting furnace and therefrom into the smelting furnace itself. The smelting product received, ferrochromenickel, was granulated and contained 40-45 weight % chromium, 18-24 weight % nickel and 3-5 weight % carbon, the rest being iron and inevitable impurities.

EXAMPLE 2

(6) The pelletizing and sintering properties of the same intermediate product material described in the example 1 were tested in accordance with the method of the invention by mixing different amounts of the intermediate product material with a chromite concentrate. The amounts of the intermediate product material were 10 weight %, 15 weight % 20 weight % calculated from the weight of the mixtures. The mixtures also contained bentonite and limestone or wollastonite, a calcium silicate, as binder agents.

(7) The mixtures containing chromite concentrate, nickel hydroxide and the binder agent were fed to the pelletizing drum in order to create pellets having a diameter of 5-15 mm. The pellets were further fed onto a sintering belt where the pellets were sintered in a belt sintering machine. The sintered pellets were tested using the modified Tumbler method and other established industry standard methodologies regarding abrasion resistance, compressive strength, hot loading temperature, porosity, chemical composition and microstructures.

(8) The Tumbler method gave similar values for the sintered pellets with 10 weight % nickel hydroxide as the pure chromite pellets. At the level of 20 weight % nickel hydroxide in the mixture, the abrasion resistance of pellets was degraded, although the compression strength was fairly high and abrasion resistance was improved when wollastonite was used instead of limestone. The Tumbler value for the addition of 20 weight % nickel hydroxide was high, because the porosity of the pellets was high. The porosity with 20 weight % nickel hydroxide was higher than the porosity with 15 weight % nickel hydroxide. However, the compression strength of the pellets with 15 weight % nickel hydroxide was high enough for further processing in the smelting furnace. Thus all the pellets generated from the mixtures having 10 weight %, 15 weight % or 20 weight % nickel hydroxide as a nickel-bearing intermediate product were acceptable for the smelting in a smelting furnace in order to produce ferrochromenickel. The pellets based on the mixtures having originally 10 weight %, 15 weight % or 20 weight % nickel hydroxide were separately smelted for ferrochromenickel and further granulated. The ratios of chromium to nickel in ferrochromenickel based on each mixture were the following: 4.8 for the mixture having originally 10 weight % nickel hydroxide, 3.05 for the mixture having originally 15 weight % nickel hydroxide and 2.1 for the mixture having originally 20 weight % nickel hydroxide.