AU2012363552A1 - Method for recovering ferronickel from nickel ore - Google Patents

Abstract

The present invention relates to a method for recovering ferronickel from nickel ore, comprising: a reduction step consisting of slurrying the reduced powders obtained by reducing nickel ore using a hydrogen-containing reducing gas, in an inert atmosphere, so as to prepare a slurry of reduced powder for leaching; a leaching step consisting of injecting sulfuric acid or hydrochloric acid into the slurry of reduced powder for leaching and dissolving and leaching nickel and iron by ions so as to obtain a solution containing nickel and iron ions; a leach residue removing step consisting of removing leach residue from the solution containing nickel and ferrous ions so as to obtain a leachate containing nickel and iron ions; and a precipitation step consisting of injecting the slurry in which the reduced powder obtained by reducing nickel ore using a hydrogen-containing reducing gas is contained in the leachate by 10 to 40 % by weight with respect to the total weight of the reduced powder for precipitation and the reduced powder for leaching, into the solution containing nickel and iron ions so as to substitute the iron of the reduced powder for precipitation with the nickel in the solution containing nickel and iron ions and precipitate ferronickel.

Description

[DESCRIPTION] [Invention Title] METHOD FOR RECOVERING FERRONICKEL FROM NICKEL ORE [Technical Field] The present disclosure relates to a method for extracting nickel from nickel ore such as low-quality nickel ore, and more particularly, to a method for extracting ferronickel by separating nickel and iron from a raw material containing nickel and iron such as low-quality nickel ore, concentrating nickel in the raw material, and extracting ferronickel from the raw material containing concentrated nickel. [Background Art] Ores such as limonite and saprolite include nickel and iron. Such ores have passivity and high resistance to acids, and are thus relatively slowly dissolved in acids. Therefore, a method for effectively extracting nickel, known as high pressure acid leaching (HPAL), has been proposed. In the method, nickel is extracted from ore by dissolving the ore in a high-temperature, high-pressure autoclave. If a nickel leaching reaction is performed at room temperature, the extraction ratio of nickel does not exceed about 85% even in the case that the nickel leaching Page 1 reaction is performed for several months or longer. However, if HPAL is used, nickel may only be extracted at a extraction ratio of about 90% or above within a 2 hour window, and thus HPAL is widely used for nickel oxide ore hydrometallurgy. Exemplary HPAL methods for extracting nickel are disclosed in Korean Patent Application Laid-open Publication No. 2007-7020915 and Japanese Patent Application Laid-open Publication No. 2010-031341. However, since HPAL is performed under high-temperature, high pressure, and strong-acid conditions, only titanium materials are usually used as materials for autoclaves, and thus high equipment costs and maintenance costs are incurred. In addition, since relatively expensive caustic soda or environmentally harmful hydrogen sulfide (H 2 S) is used as a precipitant, costs for processing the precipitant are high. In Korean Patent Application Laid-open Publication No. 2009-0031321, the inventors have proposed a method of extracting nickel by reducing nickel-containing ore using hydrogen, and leaching nickel therefrom using an acid. The disclosed method is for producing a raw material containing iron and nickel from a residue obtained from a waste catalyst from a petrochemical desulfurization process, the Page 2 disclosed method including: a process of extracting vanadium (V) and molybdenum (Mo) from a waste catalyst used in a petrochemical desulfurization process, and treating the residue of the catalyst with acids to remove alkali elements; a process of drying the residue and heat-treating the residue in a reducing atmosphere within the temperature range of 600 0 C to 13000 C so as to reduce nickel (Ni) oxides and iron (Fe) oxides included in the residue into metals; a process of leaching a reduced material obtained in the previous process by using acids so as to selectively dissolve iron (Fe) and nickel (Ni) ; a process of filtering a solution obtained in the previous process so as to obtain a solution containing leached nickel and iron ions; a process of neutralizing the solution containing nickel and iron ions with an alkali so as to obtain hydrates of nickel (Ni) and iron (Fe) ; and a process of filtering and drying a product obtained in the previous process so as to obtain a raw material containing nickel (Ni) and iron (Fe). If the disclosed method is used to leach nickel from limonite (nickel ore), high-speed leaching is possible. However, since limonite has a high iron content and a low nickel content, when nickel is leached by using an acid, a relatively large amount of iron is leached as compared with the amount of leached nickel, and thus it is very difficult Page 3 to separate iron and nickel from a leachate. [Disclosure] [Technical Problem] An aspect of the present disclosure may provide a method for extracting ferronickel by separating nickel and iron from a raw material containing nickel and iron such as low-quality nickel ore, concentrating nickel in the raw material, and extracting ferronickel from the raw material containing concentrated nickel. [Technical Solution] According to an aspect of the present disclosure, a method for extracting ferronickel may include: preparing a slurry of a reduced leaching ore by reducing a raw material containing nickel and iron with a reducing gas containing hydrogen so as to obtain a reduced ore, and adding a liquid to the reduced ore under an inert atmosphere; leaching nickel and iron ions from the slurry of the reduced leaching ore by adding sulfuric acid or hydrochloric acid to the slurry of the reduced leaching ore to obtain a solution containing nickel and iron ions; removing leaching residues from the slurry from which nickel and iron ions have been leached, so as to obtain a leachate containing nickel and iron ions; and precipitating ferronickel by adding a slurry of reduced precipitation ore, prepared by Page 4 mixing the reduced ore with water, to the leachate so as to substitute iron of the reduced precipitation ore with nickel of a solution containing nickel and iron ions, wherein 10 weight% to 40 weight% of the reduced precipitation ore is added, based on the total weight of the reduced leaching ore and the reduced precipitation ore. The reduced ore may have a specific surface area of 1 m 2/g to 100 m 2 /g. The reducing of the raw material may be performed within a temperature range of 600 0 C to 950 0 C. The reduced leaching ore may have an iron reduction ratio of 50% to 92%. The reduced leaching ore may be prepared by: preliminarily reducing the raw material containing nickel and iron within a temperature range of 450 0 C to 600 0 C using a hydrogen-containing gas so as to obtain preliminarily reduced ore; and mainly reducing the preliminary reduced ore within a temperature range of 600 0 C to 950 C using a hydrogen-containing gas. The reduced precipitation ore may have an iron reduction ratio of 70% to 96%. The reduced precipitation ore may be prepared by: preliminarily reducing the raw material containing nickel and iron within a temperature range of 500 0 C to 700 0 C using Page 5 a hydrogen-containing gas; and mainly reducing the preliminary reduced ore within a temperature range of 700'C to 1050 0 C using a hydrogen-containing gas. The reducing gas may include an amount of hydrogen equal to or greater than twice the amount of nickel and iron of the raw material in moles, and the reducing gas may be hydrogen, a mixture of hydrogen and an inert gas, a coke oven gas (COG), or a reformed liquefied natural gas (LNG). The method may further include: concentrating nickel in the reduced leaching ore by leaching iron as iron ions by adding hydrochloric acid to the slurry of the reduced leaching ore in an amount ranging from 0.5 times to 1.5 times the amount of (Fe+Ni) of the raw material by moles or adding sulfuric acid to the slurry of the reduced leaching ore in an amount ranging from 0.25 times to 0.75 times the amount of (Fe+Ni) of the raw material by moles; and obtaining a nickel-enriched ore by removing a solution containing iron ions by a solid-liquid separating method. The concentrating of the nickel may be performed while maintaining the slurry of the reduced leaching ore within a temperature range of 20 0 C to 80 0 C. The hydrochloric acid may be added in an amount ranging from two to four times the amount of (Fe+Ni) of the slurry of the reduced leaching ore, or the sulfuric acid Page 6 may be added in an amount ranging from one to two times the amount of (Fe+Ni) of the slurry of the reduced leaching ore. The leaching of the nickel and iron ions may be performed while maintaining the slurry of the reduced leaching ore within a temperature range of 20 0 C to 80 0 C. The leaching of the nickel and iron ions may be finished if an oxidation-reduction potential (ORP) of the solution is varied from negative (-) to positive (+). The method may further include: after the leaching of nickel and iron ions, adjusting a pH of the solution containing nickel and iron ions to be within a range of 2.5 to 6 by adding an alkali to the solution; and forming a silicon colloid by agitating the solution to convert silicon ions of the solution into a colloid state and cause leaching residues to adsorb the silicon colloid. The alkali may be Ca(OH) 2 or NaOH. The forming of the silicon colloid may be performed while maintaining the solution containing nickel and iron ions within a temperature range of 40 0 C to 80 0 C. In addition, the forming of the silicon colloid may be performed by agitating the solution for 15 minutes to 5 hours. The raw material containing nickel and iron may be pretreated by: drying an ore containing nickel and iron to Page 7 remove moisture; pulverizing the ore containing nickel and iron to have a particle size of 1 mm or less; and calcining the pulverized ore within a temperature range of 250'C to 850 0 C. The precipitated ferronickel may have a nickel content of 4.5 weight% to 33 weight%. [Advantageous Effects] According to the present disclosure, nickel may be effectively concentrated in a raw material such as nickel ore and extracted from the raw material, and particularly, nickel of low-quality ore may be effectively concentrated and extracted. According to the present disclosure, silicon (Si) included in nickel ore may be removed from a leachate obtained from the nickel ore so as to effectively concentrate nickel. Particularly, nickel of low-quality ore may be effectively concentrated and extracted. According to an aspect of the present disclosure, nickel ore may be reduced through a preliminary reducing process and a main reducing process to save energy used to reduce the nickel ore, and a low-quality, hydrogen containing gas may be used as a reducing gas to use a smaller amount of relatively expensive hydrogen. Furthermore, according to another aspect of the Page 8 present disclosure, in a nickel hydrometallurgy process, reduced ore for a acid leaching reaction, and reduced ore for a substitution and precipitation reaction may be separately prepared so as to increase the extraction ratio of ferronickel. [Description of Drawings] FIG. 1 is a graph illustrating the ORP of reduced nickel ore with respect to time in an example. [Best Model Embodiments of the present disclosure will now be described in detail. The present disclosure relates to a method for extracting enriched nickel from a raw material containing nickel and iron. Particularly, since the method uses acids to dissolve and extract nickel, the method may be usefully used when it is difficult to separate nickel and iron from a leachate which is obtained from a nickel-lean, iron-rich material and thus has a relative high iron content and a relative low nickel content. The method of the present disclosure may be applied to any raw materials containing nickel and iron without any limitations. For example, the method of the present disclosure may be applied to nickel ores such as limonite and saprolite. In the present disclosure, raw materials Page 9 containing nickel and iron will be simply referred to as nickel ores. Although the compositions of nickel ores are varied according to the types thereof, nickel ores usually include 1% to 2.5% of nickel (Ni) and 15% to 55% of iron (Fe) . Limonite, a nickel ore, has a low nickel content in the range of 1% to 1.8% and a high iron content in the range of 30% to 55%. The method of the present disclosure may be usefully used for extracting nickel from an ore having a relatively low nickel content, such as limonite. In some cases, when nickel is extracted from nickel ore, the nickel ore may be treated through pretreatment processes so as to effectively reduce the nickel ore in a later reducing process (to be described later). The pretreatment processes may include drying, pulverizing, and calcining processes. Hereinafter, the pretreatment processes will be described in more detail. Nickel ore which is a raw material for extracting nickel may be pulverized into fine powder for effectively performing a reducing process and a leaching process thereon. That is, nickel ore may be previously pulverized for the following nickel extracting processes. In general, nickel ore may include about 30% to 40% of adhesion water and about 10% of crystal water. However, Page 10 nickel ore having adhesion water may not be efficiently pulverized. In addition, if nickel ore having adhesion water is calcined and then pulverized in a pulverizer, a large load may be applied to the pulverizer due to a large amount of heat. Therefore, nickel ore may be dried in a drying process before a pulverizing process. Process conditions of the drying process are not limited as long as adhesion water of nickel ore is evaporated. For example, nickel ore may be heated to a temperature of 100 0 C to 2000 in the drying process. If nickel ore is dried and then pulverized, the nickel ore may be pulverized to have a particle size of 1 mm or less for improving the efficiency of reducing and leaching processes to be performed later. However, the method of the present disclosure is not limited thereto. As nickel ore is pulverized into particles having smaller sizes, the efficiency of reducing and leaching processes may be increased, and thus the lower limit of the particle size of pulverized nickel ore is not specified. However, a pulverizing process may be performed for a long period of time or a plurality of times to pulverize nickel ore to a particle size smaller than 10 pm. That is, nickel ore may be pulverized to a particle size of 10 pm or above in view of economical efficiency. Page 11 Crystal water included in nickel ore is not removed by the above-described drying process. When nickel ore is reduced in a reducing process, crystal water of the nickel ore is separated from the nickel ore in the form of moisture, which retards a reducing reaction and reduces the efficiency of the reducing process. Therefore, crystal water may be removed from nickel ore before the nickel ore is treated in a reducing process. To this end, nickel ore may be calcined. Limonite discharges crystal water within the temperature range of 250 0 C to 350 0 C, and saprolite discharges crystal water within the temperature range of 650 0 C to 750 0 C. Therefore, nickel ore powder obtained through the above-described pulverizing process may be calcined within the temperature range of 250 0 C to 850 0 C so as to remove crystal water. Saprolite having a high nickel content is usually used as a raw material for pyrometallurgy, and the method of the present disclosure may be used to extract nickel from dust generated from a rotary kiln in a pyrometallurgy process using saprolite. In this case, such dust has a particle size in the range suitable for the method of the present disclosure and is heated to a high temperature in a pyrometallurgy process, pulverizing and calcining processes Page 12 may not performed on the dust. However, for example, if such dust has a particle size outside of the range suitable for the method of the present disclosure because of moisture absorbed from the atmosphere, the dust may be pulverized or calcined. Calcined ore, obtained by calcining nickel ore to remove crystal water therefrom, has sensible heat received in the calcining process. Thus, the calcined core may not be cooled but may be directly treated in a reducing process so as to save energy on heating the calcined ore to a reducing temperature. The method of the present disclosure includes a process of reducing nickel and iron of nickel ore treated through the above-described pretreatment processes. The reducing process may be performed using a reducing gas containing hydrogen as a reductant. A reducing process using carbon as a reducing gas is usually performed at a temperature of 1250 0 C or above to obtain nickel as metal. In this case, however, reduced powder has a low degree of activity, and thus the leaching rate thereof is very low. Particularly, the precipitation efficiency of a precipitation process is very low. In the present disclosure, however, since a hydrogen containing gas is used as a reducing gas in the reducing Page13 process, the reducing process may be performed at a relatively low temperature as compared with a reducing process using carbon as a reducing gas. In addition, nickel metal having a specific surface area of 1 m 2 /g to 100 m 2 /g and a high degree of activity may be produced. Therefore, the nickel metal may be easily dissolved in an acid, and thus the next leaching process may be performed at a high rate. The reducing gas is not limited to a particular gas as long as the reducing gas contains hydrogen. Hydrogen or a mixture of hydrogen and an inert gas may be used as the reducing gas. The reducing gas may remove oxygen other than hydrogen in a reducing furnace during the reducing process. The inert gas is not limited to a particular inert gas as long as the inert gas does not have reactivity. For example, the inert gas may be helium, argon, carbon monoxide, or nitrogen. Other examples of the reducing gas containing hydrogen include: coke oven gas (COG) containing 50% or more of hydrogen which are generated during a iron ore smelting process; and reformed liquefied natural gas (LNG) containing 65% or more of hydrogen, generated in a methane hydrogen reforming reaction. In the reducing process, the ratio of nickel:iron in Page14 a raw material may be varied according to the type of the raw material. If limonite is used as a raw material, the ratio of nickel:iron in the limonite may be 1:30 by weight. That is, for example, limonite includes about 1 weight% to about 1.5 weight% and about 30 weight% to about 45 weight%. When limonite (nickel:iron = 1:29) is reduced by using hydrogen as a reducing gas, reduced ore (reduced nickel ore) is obtained through a reducing reaction as expressed by Theoretical Formula 1 below. (Nio.iFeo.

9 )OFe 2 O3 + 4H 2 = (Nio.iFeo.

9 ) + 2Fe + 4H 2 0 (1) In such a reducing reaction, hydrogen used as a reducing gas reacts with nickel and iron included in nickel ore in oxidized states. As a result, water is produced, and the nickel and iron are reduced. Therefore, the amount of hydrogen in a reducing gas may be greater than that for the stoichiometric equivalent ratio for an efficient reducing reaction. However, since hydrogen is relatively expensive, if an excessive amount of hydrogen is used, manufacturing costs may be increased. Therefore, the amount of hydrogen may be properly determined. For example, the amount of hydrogen may be 1 to 5 times, 2 to 5 times, or 2 to 4 times the stoichiometric amount of hydrogen in moles. The reducing process may be performed within the Page 15 temperature range of 600 0 C to 950 0 C. If the reducing process temperature is lower than 600 0 C, reducing may occur insufficiently. In this case, the extraction ratio of nickel in a later leaching process using an acid may be low, and thus the precipitation yield of nickel may also be low. If the reducing process temperature is increased, both the leaching yield and precipitation yield of nickel may be increased. However, if the reducing process temperature is greater than 950 0 C, even in the case that nickel ore may be efficiently reduced, the extraction ratio of nickel in a leaching process may not be further increased. Reduced ore (reduced nickel ore) obtained as described above may be used in a leaching process to leach nickel ions from the reduced ore by dissolving the reduced ore in an acid. In addition, reduced ore may also be used in a precipitation process to substitute nickel ions of a leachate obtained in a leaching process with iron ions so as to precipitate nickel metal. That is, some of reduced ore may be used in a precipitation process, and the remaining portion of the reduced ore may be used in a precipitation process. Reduced ore for a leaching process will now be referred to as reduced leaching ore, and reduced ore for a precipitation process will now be referred to as reduced precipitation ore. Page16 To this end, nickel ore may be reduced in different conditions according to the use of the nickel ore. For example, nickel ore may be reduced through a preliminary reducing process and a main reducing process. If nickel ore is reduced through a preliminary reducing process and then a main reducing process, energy consumption may be reduced. Particularly, a relatively inexpensive gas mixture including hydrogen may be used in the preliminary reducing process as a reducing gas to reduce costs. First, the preliminary reducing process will be described. Reduced nickel ore obtained as described above is treated with an acid such as hydrochloric acid or sulfuric acid to leach nickel and iron ions from the reduced nickel ore and then extract ferronickel metal by precipitation. That is, reducing of Fe 2 0 3 in the reducing reaction expressed by Formula 1 may be expressed by Formula 2 below. 3Fe 2

O

3 + 6H 2 = 6Fe + 6H 2 0 (2) Formula 2 may be expressed more specifically by Formulas 3 to 5. 3Fe 2 0 3 + H 2 = 2Fe 3

O

4 + H 2 0 (3) 3Fe 3

O

4 + 2H 2 = 6FeO + 2H 2 0 (4) 6FeO + 3H 2 = 6Fe + 3H 2 0 (5) Iron (Fe) metal is finally formed as expressed by Page 17 Formula 5, and hydrogen gas is not formed as expressed by Formulas 3 and 4. That is, since hydrogen is not collected during the preliminary reducing process, a relatively inexpensive reducing gas mixture including hydrogen may be used in the preliminary reducing process so as to reduce the use of a relatively expensive gas including hydrogen. Coke oven gas (COG) containing 50% or more of hydrogen generated during an iron ore smelting process, or gas containing 65% or more of hydrogen generated in a methane hydrogen reforming reaction, may be used as the relatively inexpensive reducing gas mixture including hydrogen. In addition, the preliminary reducing process may be performed at a relatively low temperature as compared with the main reducing process. The preliminary reducing process may be performed to produce reduced leaching ore by supplying a reducing gas to a furnace within the temperature range of 450 0 C to 600 0 C. The preliminary reducing process may be performed to produce reduced precipitation ore by supplying a reducing gas to a furnace within the temperature range of 500 0 C to 700 0 C. In this manner, iron may be reduced at a reduction ratio of about 30% or above. After the preliminary reducing process, the reduced ore (nickel ore) is processed through a main reducing Page 18 process. Hydrogen may be used as a reducing gas in the main reducing process, and nitrogen gas may be used together with the hydrogen as a system purge gas. If hydrogen is used as a reducing gas, since hydrogen is generated in a nickel extracting process (particularly in a nickel leaching process), the generated hydrogen may be extracted to be used as a reducing gas. The main reducing process may be performed to produce reduced leaching ore or reduced precipitation ore. To produce reduced leaching ore, the main reducing process may be performed at 600 0 C to 950 0 C by using a gas including high-purity hydrogen. If the main reducing process is performed at a temperature lower than 600 0 C, it is difficult to obtain an iron reduction ratio equal to or above than 50%. Thermodynamically, nickel is easier to reduce than iron, and the results of many experiments related to the reduction of nickel ore show that if the iron reduction ratio of nickel ore is greater than 50%, nickel within the reduced ore is easily reduced into nickel metal as compared with iron within the reduced ore. Thereafter, in a leaching process, the nickel metal may be dissolved in an acid at a high leaching ratio. Therefore, to produce reduced leaching ore, it may be preferable that the main reducing process be performed at 600 0 C or higher. Page19 If the main reducing process is performed at 950 0 C, an iron reduction ratio of about 92% may be obtained. However, if nickel ore is reduced at a temperature greater than 950 0 C, the activity in reduced ore may be lowered, and the leaching ratio of nickel may not be further increased and may be reduced. Therefore, reduced leaching ore may be produced at a temperature of 950 0 C or below, and in this case, energy efficiency may be improved. As described above, to produce reduced leaching ore, it may be preferable that the main reducing process be performed within the temperature range of 600 0 C to 950 0 C to obtain an iron reducing rate of 50% to 92%. If the reduced ore (reduced nickel ore) is leached with hydrochloric acid, a leachate in which nickel within the reduced ore is dissolved in the form of nickel ions may be obtained at a nickel extraction ratio of 90% or above within 2 hours. In a precipitation process, reduced precipitation ore may be added to the leachate so as to substitute nickel ions of the leachate with iron ions derived from the reduced ore and thus to extract nickel. The reduced precipitation ore may include iron existing in the form of metal, and in this case, nickel ions included in the leachate may be easily substituted with the iron metal and thus may be easily precipitated as metal. This may be Page 2 0 understood by Formula 7 below. As described above, when reduced precipitation ore is produced, if the process temperature of the main reducing process is set to obtain an iron reduction ratio of 70% or above, the extraction ratio of nickel metal by substitution and precipitation may be increased. However, even in the case that the iron reduction ratio is greater than 96%, the extraction ratio of nickel by substitution and precipitation may be slightly increased, and sintering may markedly occur in a heat treatment process for reduction. That is, the efficiency of nickel precipitation may be lowered. Therefore, the iron reduction ratio may be maintained to be 96% or below. To obtain a reduced ore having an iron reduction ratio in the above-described range, the nickel ore processed in the preliminary reducing process may be processed in the main reducing process within the temperature range of 700 0 C to 1050 0 C. After the nickel ore is reduced according to usages to obtain reduced leaching ore or reduced precipitation ore as described above, waste gas is discharged, and the reduced ore is mixed with water to make slurry. The slurry may be formed in non-oxygenated conditions by blocking an inflow of ambient air so as to prevent the reduced ore being re-oxidized. Since the reduced ore obtained by Page 2 l reducing nickel ore has a high degree of activity and a high iron content, if the reduced ore is exposed to air, the reduced ore may be re-oxidized. In addition, heat generated by the re-oxidation may accelerate the re oxidation and may cause a fire. Therefore, slurry is made by mixing the reduced ore with water so as to prevent oxidation and a fire. The amount of water added to the reduced ore may be one to two times the amount of the reduced ore by weight. If the amount of water is less than the range, the slurry may be too thick to carry, and if the amount of water is too large, a very thin leachate may be formed in a leaching process. After the reduced ore is made into slurry, an acid leaching process for ionization of iron and nickel may be performed by adding an acid to the slurry so as to dissolve (leach) ferronickel included in the reduced ore of the slurry. The acid leaching process may be performed in a reactor maintained in a non-oxygenated state by adding an acid to the slurry of the reduced ore and agitating the acid and the slurry of the reduced ore to dissolve the reduced ore. Although the slurry of the reduced ore made as described above is not easily oxidized, if the slurry of the reduced ore is intensively agitated in an oxygen Page22 atmosphere (for example, in the air), the reduced ore may be oxidized by a type of hydration. Therefore, the acid leaching process may be performed in a non-oxygenated state. The acid used in the acid leaching process is not limited to a particular type of acid. For example, hydrochloric acid or sulfuric acid may be used. Generally, if nickel ore reduced as expressed by Formula 1 is leached with an acid, a reaction occurs as expressed by Formula 6 or 7, and ferronickel included in the reduced nickel ore is dissolved (leached) in the acid in the form of ions. (Nio.iFeo.

9 ) + 2Fe + 6HCl = (Nio.iFeo.

9 )Cl 2 + 2FeCl 2 + 3H 2 (6) (Nio.iFeo.

9 ) + 2Fe + 6H 2

SO

4 = (Nio.iFeo.

9

)SO

4 + 2FeSO 4 + 3H 2 (7) If hydrochloric acid is used as the acid for leaching the reduced ore, as shown in Formula 6, the number of moles of hydrochloric acid may be twice or more the number of moles of (Fe+Ni). However, if the number of moles of hydrochloric acid exceeds 4 times the number of moles of (Fe+Ni), the efficiency of leaching may not be further increased. Therefore, it may be preferable that the number of moles of hydrochloric acid range from two to four times the number of moles of (Fe+Ni). If sulfuric acid is used, Page 2 3 as shown in Formula 7, it may be preferable that the number of moles of sulfuric acid range from one to two times the number of moles of (Fe+Ni). Such a leaching reaction is exothermic, and thus the interior temperature of a reactor is increased during the leaching reaction. Therefore, the leaching reaction may occur at room temperature, and if the leaching reaction occurs at 20'C or higher, good leaching efficiency may be obtained. In addition, the reaching reaction may be induced under a heated condition. In this case, the rate of the leaching reaction may be increased, and thus the period of the leaching reaction may be shortened. The heating temperature for the leaching reaction is not limited to a particular value. For example, the heating temperature for the leaching reaction may be appropriately set according to the equipment conditions of the reactor. However, if the heat treatment of the leaching reaction exceeds 80'C, equipment costs may be increased. During such an acid dissolving reaction, if a reduced metal exists in an aqueous acid solution, the oxidation reduction potential (ORP) of the solution has a negative ( ) value, and if the metal is completely dissolved in the aqueous acid solution, the ORP becomes zero (0) and then a positive (+) value. Therefore, if the ORP is 0 or above, Page 2 4 the acid dissolving reaction may be terminated. That is, a time point for terminating the acid dissolving reaction may be checked by measuring the ORP. A leachate obtained in the leaching process may be filtered to separate solid residues, for example, by using a solid-liquid separator such as a filter press or decanter. As shown in Formulas 6 and 7, in a leaching process for dissolving nickel and iron of reduced ore in an acid, if the acid is hydrochloric acid, the stoichiometric number of moles of the acid is twice the number of moles of iron and nickel within the reduced ore, and if the acid is sulfuric acid, the stoichiometric number of moles of the acid is equal to the number of moles of iron and nickel within the reduced ore. If a greater amount of an acid than a stoichiometric amount is supplied to leach reduced ore having a nickel content of about 1.5%, a leachate having a relatively high content of nickel may be obtained, and highly-concentrated nickel may be extracted in a later precipitation process. For example, nickel ore produced in Indonesia has a low nickel content of about 1%. Particularly, limonite produced in Indonesia has a relative high SiO 2 content and relatively low nickel and iron contents. If such nickel ore having a low nickel content is leached, a leachate Page 2 5 having a low nickel content is obtained. In detail, if reduced nickel ore having a low nickel content is processed through a leaching process using an acid to leach nickel and iron, a leachate having a low nickel content is obtained, and thus it is difficult to extract nickel from the leachate through a precipitation process. That is, to precipitate nickel from a leachate obtained through a leaching process, reduced ore is added to the leachate to induce a type of battery cell reaction (precipitation reaction) between nickel ions of the leachate and iron metal within the reduced ore by a natural potential difference therebetween and thus to reduce and precipitate nickel ions into nickel metal. This precipitation reaction may be expressed by Formulas 8 and 9. (Nio.iFeo.

9 )Cl 2 + { (Nio.iFeo.

9 ) + 2Fe} = Nio.

2 Feo.

8 + 2Fe + FeCl 2 (8) (Nio.iFeo.

9

)SO

4 + { (Nio.iFeo.

9 ) + 2Fe} = Nio.

2 Feo.

8 + 2Fe + FeSO 4 (9) Since the precipitation occurs through a type of battery cell reaction caused by a natural potential difference between iron and nickel, the mechanism of the precipitation may be expressed as follows: Positive electrode reaction: Fe = Fe2+ + 2e E'=0.44 Negative electrode reaction: Ni2+ + 2e = Ni E'=-0.25 Page 2 6 Total reaction: Fe + Ni2 = Fe2 + Ni E =0.19 However, since the precipitation occurs in the form of a diffusion reaction, if the nickel content of the leachate is low, a lower amount of reduced ore may be used to precipitate nickel ions. Therefore, the diffusion rate of the precipitation may also be markedly lowered, and thus it may be difficult to precipitate nickel from the leachate having a low nickel content. Therefore, a leachate having a sufficiently high nickel content is required to smoothly perform a later precipitation process. To this end, when reduced ore having a low nickel content is leached to obtain a leachate, nickel may be concentrated in the leachate. For this end, a smaller amount of an acid than a stoichiometric amount for leaching nickel and iron from reduced ore may be supplied to the reduced ore before performing the above-described leaching process on the reduced ore, so as to concentrate nickel prior to the leaching process. If a stoichiometric amount of an acid is used to leach iron and nickel from reduced ore, a leachate having a low nickel content may be obtained, in which all the iron and nickel within the reduced ore are leached. However, if a smaller amount of an acid than the stoichiometric amount is used, nickel may be barely Page 2 7 dissolved but iron may be selectively dissolved in the acid. This will now be referred to as a concentration reaction for convenience's sake. That is, if a smaller amount of an acid than a stoichiometric amount is used to leach reduced ore, a portion of iron within the reduced ore is not dissolved, and a portion of nickel within the reduced ore is dissolved (leached) as ions. Then, a precipitation reaction occurs between the remaining portion of the iron in the reduced ore and the nickel ions as expressed by Formula 8 or 9, and thus the iron (metal) within the reduced ore is substituted with the nickel ions so that nickel metal may be re precipitated as metal on the reduced ore. As a result of using a smaller amount of an acid than a stoichiometric amount, most of the nickel metal may not be leached but remains in the reduced ore, and only some of the iron within the reduced ore may be dissolved (leached). Thereafter, if a solution remaining as a result of dissolution of iron ions in an acid is removed, the reduced ore having an increased nickel content remains as a nickel concentrate. In detail, referring to Formulas 6 and 7, if hydrochloric acid is used for concentrating nickel, it may be preferable that the number of moles of hydrochloric acid Page 2 8 range from 0.5 times to 1.5 times the number of moles of (Fe+Ni) of reduced ore, and if sulfuric acid is used for concentrating nickel, it may be preferable that the number of moles of sulfuric acid range from 0.25 times to 0.75 times the number of moles of (Fe+Ni) of reduced ore. If a smaller amount of acid than the above-mention range is used, an insufficient amount of iron may be leached, and thus the content of nickel may not be sufficiently increased. On the other hand, if a larger amount of acid than the above mentioned range is used, an excessive amount of nickel may be leached, and the effect of nickel concentration by substitution and precipitation reactions of nickel metal and iron ions may not be sufficiently obtained. Therefore, the amount of acid may be set to be within the above mentioned range. As described above, the nickel concentrate is obtained after removing the solution containing iron ions. For this, a washing process may be performed. The nickel concentrate obtained through the above described concentration process may be made as slurry, and a larger amount of acid than a stoichiometric amount may be added to the slurry so as to dissolve iron and nickel of the nickel concentrate slurry through a leaching reaction expressed by Formula 6 or 7. Page 2 9 As described above, if ore including a relatively high Si0 2 content and a relatively low nickel content is leached, silicon (Si) may be included in a leachate, and thus the iron and nickel contents in the leachate may be relatively lowered. That is, if a large amount of silicon (Si) is included in a leachate, metallic iron within reduced ore may be coated with silicon ions before the metallic iron is substituted with nickel ions of the leachate. That is, precipitation of nickel on the reduced ore by a substitution reaction may be hindered. In detail, silicon ions form a colloid having a negative charge known as an (Si0 2 *nH 2 0) silica gel, and the surface of iron (Fe) of reduced ore is partially hydrated into Fe(OH)V. Therefore, the silica gel having a negative charge may be strongly adsorbed onto positive Fe(OH)V, and due to such adsorption of silicon onto the surface of iron, nickel precipitation may be hindered. Due to this reason, silicon (Si) components may be removed from a leachate before removing residues from the leachate and performing a precipitation reaction. Such silicon components may be removed by using properties of a negative (Si0 2 *nH 2 0) colloid in an acid solution. In the leachate, residues such as compounds of Al, Cr, Fe having a positive charge may not be dissolved in the Page 30 acid. Thus, the silicon colloid which is formed by controlling the pH of the leachate, and the Al, Cr, and Fe residues may be adsorbed onto each other. Therefore, if the leachate is filtered to remove the residues, silicon may also be almost removed from the leachate containing nickel ions. Thereafter, if reduced precipitation ore is added to the leachate, a precipitation reaction may smoothly occur while metallic iron included in the reduced precipitation ore is substituted with nickel ions of the leachate. In the above, silicon ions of the leachate may be converted into a colloid, that is, (SiO 2 *nH 2 0), by mixing the leachate with a small amount of a hydrate of a metal such as iron, manganese, nickel, or magnesium, slaked lime, or caustic soda which is an alkali so as to increase the pH of the leachate to a range of 2.5 to 6. If the pH of the leachate is less than 1.5, silicon ions may be slowly converted into a colloid. On the other hand, if the pH of the leachate is greater than 6, some of nickel of the leachate may be precipitated and then removed when the leachate is filtered, and thus the extraction ratio of nickel in a later process may be lowered. Therefore, it may be preferable that the pH of the leachate be within the above-mentioned range. More preferably, the pH of the Page 31 leachate may be adjusted to be within the range of 2.5 to 5.5. Preferably, a silicon colloid may be formed in the leachate by adjusting the pH of the leachate to be within the above-mentioned range and then adjusting the temperature of the leachate to be 40'C or higher for reducing a process time. While the temperature of the leachate is lower than 40'C, a silicon colloid may be formed and adsorbed onto residues, and the silicon colloid and the residues may be removed as intended in the present disclosure. However, it may take a significant amount of time to form a silicon colloid and remove the silicon colloid attached to residues. In addition, when a silicon colloid is formed in the leachate at a temperature of 40 0 C or higher, the leachate may be agitated to rapidly induce adsorption of the silicon colloid and residues. In addition to maintaining the leachate at a temperature of 40 0 C or higher, when a silicon colloid is formed, the leachate may be kept under non oxygenated conditions as in the case of the leaching process. However, conditions for forming a colloid are not limited thereto. According to equipment conditions and operating costs, the leachate may be maintained at a proper temperature, for example, 80 0 C or below. Preferably, the Page 32 temperature of the leachate may be maintained within the range of 50 0 C to 80 0 C, more preferably, within the range of 60 0 C to 80 0 C. In the above-mentioned conditions, the silicon colloid forming process may be performed for 15 minutes to 5 hours so as to induce the formation of a silicon colloid and the adsorption of the silicon colloid and residues onto each other. If the silicon colloid forming process is performed for a period of time shorter than 15 minutes, the efficiency of adsorption between the silicon colloid and residues may be lowered, and thus the extraction ratio of nickel may be reduced. On the other hand, if the silicon colloid forming process is performed for a period of time longer than 5 hours, adsorption may further occur. However, silicon removing efficiency may not be improved. More preferably, the silicon colloid forming process be performed for 30 minutes to 4 hours. Next, a precipitation process is performed to precipitate iron and nickel ions, dissolved as expressed by Formula 6 or 7, into metals. The solubility of iron in a leachate obtained in the above-described leaching process is about 150g/l, and thus the content of nickel dissolved in the leachate by an acid may be 5 g/l or less. Therefore, the compound of nickel in a leachate obtained by a leaching Page 33 reaction expressed by Formula 2 and 3 may usually be in the range of 2 g/l to 5 g/l. Since the content of nickel is low, the substitution and precipitation reaction expressed by Formulas 8 and 9 may be unlikely to occur. That is, if atomized iron powder is added to a leachate having a low nickel content, nickel may be precipitated and extracted only at a very low precipitation extraction ratio. If the amount of atomized iron powder is increased to 20 times or more the amount of nickel, the precipitation extraction ratio of nickel may be somewhat increased. However, since the nickel content in an obtained precipitate is not high, the precipitate may not be economically used. However, if reduced ore obtained through a reducing reaction expressed by Formula 1 is added to the leachate, nickel may be effectively precipitated and extracted even though the amount within the reduced ore is small. In detail, reduced ore (reduced precipitation ore) obtained through a reaction expressed by Formula 1 may be added to the leachate to precipitate iron and nickel. In this case, reduced precipitation ore which is obtained through a separate reducing process may be added to the leachate to precipitate iron and nickel. If reduced precipitation ore is added to the leachate, a precipitation reaction as expressed by Formula 8 or 9 is induced. Page 34 Through the precipitation reaction, iron of the reduced precipitation ore is substituted with nickel of iron and nickel ions of the leachate, and thus ferronickel is precipitated as metal. As described above, the precipitation reaction occurs according to the mechanism of a battery cell reaction. That is, a battery cell is formed by a natural potential difference between nickel ions of the leachate and iron of the reduced precipitation ore, thereby resulting in oxidation and dissolution of iron at a positive electrode site and reduction and precipitation of nickel ions of the leachate at a negative electrode site. The reduced precipitation ore may have a specific surface area of 1 m2/g to 100 m 2 /g and a high degree of activity for allowing efficient precipitation and extraction of nickel. Particularly, 100% of nickel included in the reduced ore may be extracted through the precipitation reaction of nickel, and owing to iron included in the reduced ore, 90% or more of nickel included in the leachate may precipitate. That is, since the reduced ore is added to the leachate during the precipitation reaction, a high precipitation extraction ratio of nickel may be obtained, and the nickel content in an obtained precipitate may be high. Page 35 The amount of reduced precipitation ore added to the leachate for reducing nickel may be adjusted the used amount of reduced leaching ore and may function as a factor determining the precipitation extraction ratio of nickel and the nickel content of a final product. Preferably, the amount of reduced precipitation ore may be within the range of 10% to 40% of the total amount of raw materials used in extracting ferronickel by weight, that is, within the range of 10% to 40% of the total amount of reduced leaching ore and reduced precipitation ore by weight. If the amount of reduced precipitation ore is less than 10% of the total amount of raw materials by weight, nickel may be extracted from a leachate at a low precipitation extraction ratio, and if the amount of reduced precipitation ore is greater than 40% of the total amount of raw materials by weight, a finally obtained precipitate may have a very low nickel content of 4.5 weight% or less. As described above, reduced precipitation ore may be added to a leachate obtained through a leaching reaction as expressed by Formula 6 or 7 to induce a precipitation reaction as expressed by Formula 8 or 9 and thus to precipitate ferronickel. Then, a nickel concentrate having a high nickel Page 3 6 content may be obtained by filtering a solution obtained by the precipitation reaction to separate a precipitate including ferronickel from the solution including iron ions (precipitation residual solution). If the nickel concentrate has a nickel content of 4.5 weight% or above, the nickel concentrate may be used as a ferronickel raw material. For example, the nickel concentrate (ferronickel concentrate) in which ferronickel is concentrated by precipitation may be mixed with organic and inorganic binders such as cement, molasses and water, and may be agglomerated so as to produce a ferronickel raw material for stainless steel. Ore impurities such as Mg and Mn which are soluble in acid but do not participate in an electrochemical substitution reaction are removed together with iron ions from the precipitation residual solution. However, in the precipitation reaction, substances such SiO 2 , A1 2 0 3 , and Cr 2 0 3 may be concentrated together with the ferronickel concentrate. In addition, if the ferronickel concentrate is mixed with a reductant such as carbon or aluminum and is melted, nickel and iron agglomerated during a process may be entirely reduced into metals, and substances such as SiO 2 , A1 2 0 3 , and Cr 2 0 3 concentrated together with ferronickel may Page37 be converted into slag and separated from ferronickel. In this manner, ferronickel may be obtained. [Mode for Invention] Hereinafter, the present disclosure will be described more specifically according to examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the present disclosure. Example 1 Pretreatment of nickel ore Limonite having a composition as shown in Table 1 was dried at 150'C in a rotary kiln for 1 hour, and was pulverized into powder using a super mill. Thereafter, the powder was blown with a dust collector to separate the powder according to the particle sizes thereof. In this manner, powder having an average particle size of 0.8 mm was obtained. The powder was calcined for 1 hour in a calcination furnace maintained at 300 0 C so as to remove crystal water from the powder. Preparation of reduced ore The nickel ore (limonite powder) was taken out from Page 38 the calcination furnace and inserted into a rotary kiln (reducing furnace) maintained in non-oxygenated conditions. In the rotary kiln, reduced ore was prepared by reducing the nickel ore using hydrogen at 725'C. Here, the number of moles of the hydrogen was 4 times the number of moles of (Ni+Fe) included in the nickel ore. The composition of the reduced ore obtained in this manner was analyzed as shown in Table 1. [Table 1] Inventive Ni Fe Mg Si Al Example 1 Limonite 1.4 42.3 1.1 1.1 2.5 Reduced Ore 2.0 60.5 1.65 1.6 3.6 In Table 1, the content of each component is given in weight%, and the other components of the ore include oxygen and a small amount of manganese (Mn). The reduced ore was cooled in a tank filled with nitrogen gas and maintained in a non-oxygenated state, and slurry was prepared by adding 200 ml of water to 200 g of the reduced ore. Leaching reaction 1 L of solution was prepared by adding 20% hydrochloric acid to the slurry prepared as described above, Page 39 and was agitated to dissolve the reduced ore of the slurry and thus leach ferronickel ions from the reduced ore (a leaching reaction). At this time, a sample of the slurry maintained at room temperature (25'C) was subjected to the leaching reaction, and another sample of the slurry was heated to 73 0 C and subjected to the leaching reaction. In this manner, the (reduced ore) leaching reaction was performed on the two samples of the slurry, and along with this, the oxidation-reduction potential (ORP) values of the samples were measured to check reaction end times. If the ORP was varied from negative (-) to positive (+), the reaction was terminated. Measured ORP values are shown in FIG. 1. Referring to FIG. 1, when the leaching reaction was performed at room temperature, the ORP was varied from negative (-) to positive (+) after about 40 minutes as a result of dissolution of metal components within the reduced ore. From this, it may be understood that the leaching reaction finishes within 40 minutes. At this time, since the leaching reaction was exothermic, the slurry having an initial temperature of 25 0 C had a final temperature of 50 0 C after the leaching reaction. When the leaching reaction was performed on the slurry having an initial temperature of 50 0 C, the Page 4 0 temperature of the slurry was increased to 73'C and the ORP was varied from negative (-) to positive (+) after about 20 minutes as shown in FIG. 1. That is, the rate of leaching was increased. The nickel content of a leachate obtained by performing the leaching reaction on the slurry initially having room temperature was measured by an inductively coupled plasma (ICP) emission spectroscopy method. The nickel content of the leachate was measured as 3.95 g/L, and the leaching extraction ratio of nickel (the weight of nickel in the leachate/the weight of nickel in the ore) was calculated as 98.7%. From the results, it may be understood that nickel is very effectively leached, even at room temperature, within a very short period of time. Solid leaching residues were removed from the leachate obtained by the leaching reaction by a solid liquid separating method. Precipitation reaction To precipitate ferronickel from the leachate obtained as described above, iron powder having an average particle diameter of 70 pm was prepared as precipitation slurry, and the reduced ore obtained by reducing limonite was also made as precipitation slurry. Thereafter, the precipitation raw Page 4 l materials (the precipitation slurries) were added to the leachate as shown in Table 2 in which the amounts and ratios of the precipitation raw materials are specified, so as to induce a substitution and precipitation reaction of ferronickel. In Table 2, the precipitation raw material ratio (reduced precipitation ore ratio) is calculated from the amount of reduced precipitation raw material (reduced precipitation ore) and the amount of reduced leaching raw material (reduced leaching ore) as shown in the following formula. Reducedprecipitatonore ratio(%) Weightof reducedprecipitatonore x100 Weightof reducedleachingore + Weightof reducedprecipitatonore The substitution and precipitation reaction was performed for 2 hours, and components of resulting solutions were inspected by an inductively coupled plasma (ICP) emission spectroscopy method. Then, the ratios of nickel extracted by precipitation (nickel extraction ratios) were calculated by the following formula as shown in Table 2. Nickel collectiorratio (%) _Nickel contentinleachate- Nickel contentinprecipitatonsolution x100 Nickel contentinleachate The calculated extraction ratios of nickel extracted Page 42 by precipitation are shown in Table 2. Extraction of ferronickel metal Precipitation solutions obtained by the above described precipitation reaction were filtered using a solid-liquid separator to remove liquid components including iron ions from solid components including ferronickel. In this manner, nickel concentrates were obtained. In addition, the nickel concentrates were mixed with stoichiometric amounts of carbon and aluminum and heated to 1600'C to obtain ferronickel by smelting and agglomeration, and slag including SiO 2 , A1 2 0 3 , and Cr 2 0 3 was removed. Then, the nickel contents of ferronickel samples obtained as described above were measured as shown in Table 2. [Table 2] Precipitation Used Precipitation Nickel Product raw material amount raw material extraction nickel (g/L) ratio ratio content *cs1 General iron 40 20% 25% 2.3% powder cs2 General iron 60 30% 40% 2.7% powder cs3 General iron 100 50% 80% 3.2% powder **IS1 Reduced 10 5% 85% 33% Page 43 limonite IS2 Reduced 20 10% 92% 18% limonite IS3 Reduced 60 30% 99% 6.7% limonite IS4 Reduced 90 40% 99% 4.5% limonite *CS: Comparative Sample, **IS: Inventive Sample Referring to Table 2, Comparative Samples 1 to 3 obtained by precipitating ferronickel using iron powder have low nickel extraction ratios of 25%, 40%, and 80%, respectively, and the highest product nickel content thereof is as low as 3.2%. That is, Inventive Samples 1 to 3 are practically valueless. In addition, if a small amount of iron powder is used to induce a substitution and precipitation reaction as in the case of Comparative Samples 1 and 2, a low nickel extraction ratio is obtained because of low activity of the iron powder. If a large amount of iron powder is used as in the case of Comparative Sample 3, a low nickel content is obtained. However, Inventive Samples 2 to 5 formed by using reduced limonite in a substitution and precipitation reaction have high nickel extraction ratio values of 85%, 92%, and 99%. In addition, even in the case that a small amount of a precipitation material is used, nickel may be Page44 substituted and precipitated from a leachate. As a result, a high-quality precipitation having a nickel content of 4.5% or above may be obtained. As described above, nickel may be extracted at a high leaching extraction ratio and a high precipitation extraction ratio by reducing limonite using a hydrogen containing gas, leaching the reduced limonite, and performing a precipitation reaction using the reduced limonite. Example 2 Preparation of reduced ore Preliminary reducing reaction Nickel ore powder prepared from the same type of limonite through the same pretreatment as in Example 1 was taken out from a calcination furnace and directly inserted into a rotary reducing kiln maintained in non-oxygenated conditions, and hydrogen gas was supplied into the rotary reducing kiln until the number of moles of hydrogen gas became three times the number of moles of iron. Then, a preliminary reducing reaction was performed at 550 0 C for 1 hour. At this time, coke oven gas (COG) including 15 volume% of hydrogen, a reformed liquefied natural gas (LNG) Page 45 including 65 volume% of hydrogen, and a gas mixture including 29 volume% of nitrogen and 71 volume% of hydrogen were respectively used as preliminary reducing gases. After 1 hour from the start of the preliminary reducing reaction, the reduction ratios of reduced ore were measured. Measured reduction ratios were 30%, 33%, and 35%, respectively. When the gas mixture of nitrogen and hydrogen having a relatively high hydrogen content was used, the reduction ratio of iron was relatively high. In addition, when the COG and reformed LNG were used, the reduction ratios of iron were 30% or above. That is, even though a low-grade reducing gas was used, the effect of the preliminary reducing reaction was sufficient. Main reducing reaction The preliminarily reduced ore was reduced by continuously supplying 99.99% pure hydrogen at different temperatures as shown in Table 3 so as to obtain reduced leaching ore and reduced precipitation ore. At this time, the number of moles of 99.99% pure hydrogen used was twice the number of moles of iron. Leaching reaction Page 4 6 The reduced ore was cooled in a tank filled with nitrogen gas and maintained in a non-oxygenated state, and slurry was prepared by adding 200 ml of water to 200 g of the reduced ore. 1 L of solution was prepared by adding 20% acid to the slurry, and the solution was agitated at room temperature to induce a leaching reaction. After 40 minutes from the start of the leaching reaction, the ORP of the solution was varied from negative (-) to positive (+), and thus the leaching reaction was finished. A leachate including nickel ions was obtained by removing solid components from the slurry. The leachate was inspected using ICP to calculate leaching extraction ratios. Measure results are shown in Table 3. Precipitation reaction The process ore was added to the leachate in which 4g/L of nickel was dissolved, and nickel precipitation ratios were measured by ICP analysis. Measure results are shown in Table 3. [Table 3] Usage Reduction Reduction Nickel leaching Nickel Temp. ( C) ratio (%) extraction ratio precipitation extraction Page 47 ratio (% *CS 4 Leaching 550 35 56 **IS6 Leaching 650 55 90 IS7 Leaching 750 74 96 IS8 Leaching 850 88 98 IS9 Leaching 950 92 96 CS 5 Precipitation 650 55 64 IS10 Precipitation 750 74 91 IS11 Precipitation 850 88 94 IS12 Precipitation 950 92 95 IS13 Precipitation 1050 96 94 *CS: Comparative Sample, **IS: Inventive Sample As shown in Table 3, Comparative Sample 4 prepared at a low reducing temperature has a low reduction ratio of 35% and thus a low nickel leaching extraction ratio. On the other hand, Inventive Samples 6 to 9 prepared using reduced ore having a reduction ratio of 50% or above have a high nickel leaching extraction ratio of 90% or above. However, Inventive Sample 8 prepared at a reducing temperature of 950'C has a lower nickel leaching extraction ratio than that of Inventive Sample 7 even though Inventive Sample 8 has a reduction ratio greater than that of Inventive Sample 7. Therefore, it may be predicted that if a reducing reaction is performed at a temperature higher than 950'C, the nickel leaching ratio will be lowered. Inventive Samples 10 to 13 are prepared using Page 4 8 precipitation ore reduced at 700 0 C or higher and thus have a high iron reduction ratio of 70% or above. Therefore, Inventive Samples 10 to 13 prepared using the reduced precipitation ore and subjected to the precipitation reaction have a nickel precipitation extraction ratio of 90% or above. However, Comparative Sample 5 prepared using nickel ore reduced at a temperature lower than 700 0 C has a low iron reduction ratio and thus a low nickel precipitation extraction ratio. While Inventive Sample 13 prepared using precipitation ore reduced at a high reducing temperature has a high reduction ratio, the nickel precipitation extraction ratio thereof is reduced. That is, it may be understood that if reduced precipitation ore is prepared by reducing nickel ore at a temperature higher than the temperature, the nickel precipitation extraction ratio will be lowered. Reference Example 1 Preparation of reduced ore Limonite (nickel ore) produced in Indonesia and having a composition as shown in Table 4 was pretreated in the same manner as that used to pretreat Inventive Sample 1. Then, after removing the pretreated limonite from a Page 4 9 calcination furnace, the limonite was inserted into a rotary kiln maintained in non-oxygenated conditions and was reduced at 725 0 C by using as much hydrogen as 4 times the amount of (Ni+Fe) of the limonite (powder) in moles. In this was, reduced ore was prepared. [Table 4] Raw ore Ni Fe Mg Si Al IS1 New Caledonia 1.4 42.3 1.1 1.1 2.5 RS1 Indonesia 1.1 34 4.1 6.1 3.5 *IS: Inventive Sample, RS: Reference Sample In table 4, the content of each component is given in weight%, and the other components of the ore include oxygen and a small amount of manganese (Mn). The composition of the reduced ore obtained in this manner was analyzed, and analysis results are compared with the composition of Inventive Sample 1 in Table 5. [Table 5] Raw ore Reduced ore Ni Fe Mg Si Al *IS1 New Caledonia New 2.0 60.5 1.65 1.6 3.6 Caledonia *RS1 Indonesia Indonesia 1.5 48 5.7 8.5 4.9 *IS: Inventive Sample, RS: Reference Sample In table 5, the content of each component is given in weight%, and the other components of the ore include oxygen Page 50 and a small amount of manganese (Mn). As shown in Tables 4 and 5, limonite produced in Indonesia has relatively low Ni and Fe contents and relatively high Mg, Si, and Al contents. Leaching reaction The reduced ore obtained by reducing the limonite produced in Indonesia was leached in the same manner as in Example 1. After the leaching reaction, a leachate was obtained after removing solid components therefrom, and the nickel content in the leachate was measured. The nickel content in the leachate obtained from reduced ore of New Caledonia was 3.95 g/L, and the nickel concentrate in the leachate obtained from reduced ore of Indonesia was 2.93 g/L. Precipitation reaction 29.3 g of Indonesian limonite reduced in the same manner as that described above was added to each leachate as precipitation ore, and a precipitation reaction was performed for 2 hours. After the precipitation reaction, a precipitate was separated using a solid-liquid separator, and the precipitation extraction ratio of nickel was measured. Page 51 Then, in the case of using the reduced Indonesian limonite having low Ni and Fe contents, the precipitation extraction of nickel was 80% lower than that in the case of using New Caledonia limonite (Inventive Sample 1). Example 3 Concentration reaction Limonite produced in Indonesia was reduced in the same manner as in Reference Example 1, and then a concentration reaction was performed using the reduced limonite in the same manner as that used for the leaching reaction of Reference Example 1 except that the number of moles of hydrochloric acid added to the reduced limonite was 0.2 times to 1.75 times the number of moles of (Fe+Ni) of the reduced limonite as shown in Table 6. The concentration reaction was performed for 40 minutes, and then leached residues were analyzed using ICP so as to calculate a nickel extraction ratio (amount of nickel in concentrated ore/amount of nickel in initial ore) and the nickel content in a concentrate. Measure results are shown in Table 6. Leaching reaction A product obtained by the concentration reaction was Page 52 filtered to remove a solution therefrom and collect solid components (concentrate) . Then, water was added to the solid components at a weight ratio of 1:1 so as to form slurry. As much hydrochloric acid as twice the amount of (Ni+Fe) in the concentrate in moles was added to the slurry to perform a leaching reaction at room temperature (25'C). During the leaching reaction, the ORP of a leachate was measured, and when the ORP was varied from negative (-) to positive (+), the leaching reaction was finished. The leaching reaction was performed for about 40 minutes. Precipitation reaction The leachate was filtered to remove solid components, and 29.4 g of the reduced ore (reduced Indonesian limonite) used for the concentration and leaching reactions was added to the leachate to perform a precipitation reaction at 85 0 C for about 2 hours. After the precipitation reaction, solid components were removed by filtering, and the nickel content in a precipitated ore was measured by ICP analysis. Measure results are shown in Table 6. [Table 6] Mole ratio of Ni extraction Ni content in Page 53 HC1/(Fe+Ni) ratio (%) concentrate (weight%) *CS6 0.2 99% 1.6% **IS14 0.5 98% 2.2% IS15 1.0 97% 3.0% IS16 1.5 80% 3.6% CS7 1.75 35% 1.8% *CS: Comparative Sample, **IS: Inventive Sample As shown Table 6, when the amount of hydrochloric acid is less than 0.5 times the amount of (Fe+Ni) in moles during the concentration reaction (Comparative Sample 6), iron is not effectively removed from the nickel ore (reduced ore), and thus the nickel content in the concentrate is slightly increased as compared with the initial nickel content of 1.5% in the reduced ore. In addition, when the amount of hydrochloric acid is greater than 1.5 times the amount of (Fe+Ni) in moles (Comparative Sample 7), the nickel extraction ratio is very low, and the nickel content in the concentrate is also very low. The reason for this may be as follows. Since an excessive amount of iron is leached together with nickel during the concentration reaction, the amount of iron metal in the reduced ore is insufficient to be substituted with nickel ions by a precipitation reaction. Thus, the nickel extraction ratio of the concentrate may be lowered, and the nickel content of the concentrate may also be low. In Inventive Samples 14 to 16 prepared by using a Page 54 smaller amount of hydrochloric acid than a stoichiometric amount in the concentration reaction (the number of moles of hydrochloric acid used is 0.5 times to 1.5 times the number of moles of (Ni+Fe) in the concentrate), the nickel extraction ratios and high nickel contents of the concentrates are high. In addition, after the leaching reaction, the nickel content in leachate was in the range of 3 g/L to 6 g/L, and after the precipitation reaction, the precipitation extraction ratio of nickel was 95% or above. Example 4 Pretreatment of raw material and preparation of reduced ore Nickel ore was pretreated and reduced to prepare reduced ore in the same manner as in Example 1 except that limonite produced in Indonesia was used the nickel ore. The composition of the reduced ore was analyzed as shown in Table 7. [Table 7] Ni Fe Mg Si Al Indonesia limonite 1.1 34 1 6.1 3.5 Reduced ore 1.5 48 1.3 8.5 4.9 In Table 7, the content of each component is given in Page 55 weight%, and the other components of the reduced ore include oxygen and a small amount of manganese (Mn). Leaching reaction The reduced ore was leached in the same manner as in Example 1. After the leaching reaction, the composition of a leachate was analyzed by an ICP emission spectroscopy method. Then, the nickel and silicon contents in the leachate were 2.93 g/L and 2.5 g/L, respectively. That is, most of nickel included in the reduced ore was leached. In addition, small amounts of Cr and Al were detected (0.5 g/L). Conversion into colloid The leachate obtained as described above was aged under pH, temperature, and agitating time conditions shown in Table 8, and the leachate was filtered to remove solid components. At this time, the pH of the leachate was controlled using caustic soda, and no caustic soda was added to Comparative Sample 8. Then, the Ni and Si contents of the leachate were measured as shown in Table 8. Page 56 Precipitation reaction 29.3 g of reduced ore obtained by pretreating and reducing Indonesian limonite in the same manner as described above was added as reduced precipitation ore to the leachate, and a precipitation reaction was performed at 80'C for 2 hours. Then, a resulting produce was filtered to remove liquid components and collect solid components, and the solid components were analyzed using ICP to calculate a nickel extraction ratio (the amount of nickel in precipitate ore/the amount of nickel in initial ore). The results are shown in Table 8. [Table 8] pH Temp. Aging Ni content Si content Ni precipitation ('C) time in leachate in leachate extraction ratio (hours) (g/L) (g/L) (%) *CS8 0.8 60 0 2.93 2.5 66 CS9 1.5 60 1 hr 2.92 1.0 75 **IS17 2.5 60 1 hr 2.91 0.05 91 IS18 4 60 1 hr 2.89 0.03 95 IS19 6 60 1 hr 2.64 0.03 85 IS20 4 60 2 hr 2.91 0.02 96 CS21 4 40 1 hr 2.90 0.07 84 IS22 4 60 15 min 2.89 0.03 88 IS23 2.5 60 3 hr 2.91 0.03 92 IS24 2.5 60 5 hr 2.91 0.03 92 *CS: Comparative Sample, **IS: Inventive Sample Page 57 As shown in Table 8, if pH values are too low as in the case of Comparative Samples 8 and 9, silicon (Si) is not efficiently removed, and thus low nickel precipitation extraction ratios are obtained. On the other hand, if pH values are adjusted to be within the range of 2.5 to 6 as in the case of the Inventive Samples, relatively high nickel precipitation extraction ratios are obtained. Particularly, the Si contents of Inventive Sample 17 and 18 prepared by treating leachate in conditions proposed in the present disclosure are markedly decreased, and thus the nickel precipitation extraction ratios of Inventive Samples 17 and 18 are high. Furthermore, as shown by the measured values of Inventive Samples 18, 20, 21, and 22, if the aging time is increased, silicon (Si) is removed more effectively, and a higher nickel precipitation extraction ratio is obtained. However, as shown by the measured values of Inventive Samples 23 and 24, even in the case that the aging time is further increased, the effects of removing silicon (Si) and increasing the nickel precipitation extraction ratio are not further improved. Inventive Sample 19 having an excessively high pH value as compared with Inventive Samples 17 and 18 has a relatively low nickel precipitation extraction ratio. This Page 58 is because the nickel content in the leachate is decreased by nickel precipitated and filtered out. In addition, Inventive Sample 21 prepared at a relatively low temperature has a relatively low nickel precipitation extraction ratio. This is because the effect of removing silicon and the diffusion of a substitution and precipitation reaction are lowered due to a low temperature. In addition, Inventive Sample 22 having an excessively short aging time does not have a high nickel precipitation extraction ratio. Page 59