[DESCRIPTION] [Invention Title] METHOD FOR RECOVERING NICKEL FROM RAW MATERIAL CONTAINING NICKEL [Technical Field] [0001] The present invention relates to a method of effectively recovering nickel from a nickel-containing raw material, and more particularly, to a method of effectively recovering nickel from a nickel ore having a high metal content by acid leaching. [Background Art] [00021 Nickel-containing ores include limonite and saprolite, and since these ores have passive characteristics, acid dissolution reactions are slow due to a high resistance to acids. Therefore, various methods of recovering nickel by acid dissolution in an autoclave at high temperature and at high pressure have been suggested as means of effectively leaching nickel from ore and these methods are collectively known as "high pressure acid leaching (HPAL)". [00031 When a nickel leaching reaction is performed at room temperature, a nickel recovery rate may not be greater than about 85% even in the case that leaching is performed for a few months or more. However, when the HPAL method is used, nickel leaching having a nickel recovery rate of 90% or more may be possible within two hours, and thus, the HPAL method may be regarded as being a typical method for nickel oxide ore Page 1 4423336.4 (GHMattes) P93963 AU hydrometallurgy. [0004] Examples of a technique related to the recovery of nickel by using the HPAL method may be disclosed in Korean Patent Application Laid-Open Publication No. 2007-7020915 and Japanese Patent Application Laid-Open Publication No. 2010 031341. However, it is commonly known in the technical field to which the current invention pertains that the HPAL method must be performed at high temperature and at high pressure in an autoclave, and only titanium may be used therefor due to the strong resistance to acidity thereof. Therefore, HPAL equipment costs may be very high as well as maintenance costs therefor. [0005] In Korean Patent Application Laid-Open Publication No. 2009-0031321, the present inventors suggested a method of recovering nickel by acid leaching after a nickel-containing raw material is reduced by hydrogen. A technique of the foregoing patent discloses a method of preparing an iron (Fe) and nickel (Ni)-containing raw material for recycling a residue of a spent petrochemical desulfurization catalyst including: treating a residue remaining after the recovery of vanadium (V) and molybdenum (Mo) from a spent petrochemical desulfurization catalyst with an acid to remove alkaline elements therefrom; drying the residue having the alkaline elements removed therefrom and heating the residue to a temperature within a range of 600 0 C to 1300 0 C in a reducing atmosphere to reduce Ni and Fe existing in oxide forms in the Page 2 44233361 (GHMalters) P93983.AU residue to metals; leaching a reduced product thus obtained with an acid to selectively dissolve iron and nickel; filtering the solution to obtain a solution containing leached nickel and iron ions; neutralizing the solution containing Ni and Fe ions with alkali to prepare Fe and Ni hydroxide; and filtering and drying a product thus obtained to obtain an Fe and Ni-containing raw material. [0006] However, since a large amount of hydrogen is required when Ni is attempted to be recovered from a Ni ore by using the foregoing method, economic factors may be greatly limited. That is, a spent catalyst residue generally includes metal (Fe+Ni) in an amount of 15 wt% or less, but a content of metal (Fe+Ni) in a nickel ore may be very high, in a range of 15 wt% to 65 wt%, and thus, a large amount of hydrogen must be used. [0007] Therefore, there is a need for developing a more economical method of recovering Ni by promoting the minimization of the use of hydrogen in the recovery of Ni from a Ni ore. [00081 Also, since nickel ores may include a large amount of iron, iron may be oxidized by reacting with oxygen in air when samples are extracted after reduction, and thus, safety may not be secured. [Disclosure] [Technical Problem] [0009] An aspect of the present invention provides an improved method of recovering nickel (Ni), in which Ni recovery may be Page 3 4423336_1 (GHMatters) P93963.AU performed at a relatively low temperature range (250C to 80 0 C) and atmospheric pressure allowing for the use of equipment formed of a general material, and acid leaching may be performed therewith at a high speed. [0010] Another aspect of the present invention provides a method of effectively resolving safety limitations caused by oxidation generated during sampling after reduction due to a high content of iron in a nickel oxide ore. [0011] Another aspect of the present invention provides a method of recycling hydrogen in order to minimize the use of hydrogen in the recovery of Ni. [Technical Solution] [00123 According to an aspect of the present invention, there is provided a method of recovering nickel (Ni) from a nickel containing raw material including: reducing a nickel containing raw material within a temperature range of 5500 to 950 0 C by using a reduction gas containing an amount of moles equal to double or more that of moles of hydrogen, based on moles of (Fe+Ni) in the nickel-containing raw material; preparing a slurry from the reduced nickel-containing raw material; solid-liquid separating to obtain a nickel containing solution through filtering and removing a sludge residue from a solution obtained in the leaching by using a solid-liquid separator; and removing iron (Fe) from the nickel-containing solution. [0013] The nickel-containing raw material may be dust obtained Page 4 442333_1 {GHMatters) P93963AU in a nickel ore pyrometallurgical process or a nickel ore, and when the nickel-containing raw material is a nickel ore, the nickel-containing raw material may be obtained by drying the nickel ore, pulverizing the nickel ore into particles having a diameter of 1 mm or less, and calcinating the particles within a temperature range of 2500C to 8500C. [0014] Also, the reduction gas containing hydrogen may be pure hydrogen gas or a mixed nitrogen and hydrogen gas. [0015] The slurry may be prepared by immersing the reduced nickel-containing raw material in an oxygen-barriered tank containing water. [0016] The acid may be sulfuric acid or hydrochloric acid, and the sulfuric acid may be added in an amount of moles equal to or more than that of moles of (Fe+Ni) in the nickel-containing raw material and the hydrochloric acid may be added in an amount of moles equal to double or more that of the moles of (Fe+Ni) in the nickel-containing raw material. [0017] The leaching may be terminated when a pH of the solution is in a range of 0.1 to 1.0 and may be performed at a temperature within a reaction temperature range of 25 0 C to 800C for 0.5 hours to 2 hours. [00181 The removing of the iron may be performed by injecting an oxygen-containing gas to generate iron hydroxide while a pH of the nickel-containing solution is controlled to be within a range of 2.5 to 5.5 and filtering the generated iron hydroxide, or using a solvent extraction method. Page 5 44233383 (GHMatters P93963.AU [0019] Hydrogen may be captured from an exhaust gas discharged in the reducing of the nickel-containing raw material to be resupplied to the reducing of the nickel-containing raw material. The capturing of hydrogen from the exhaust gas may be performed by cooling the exhaust gas containing water vapor and hydrogen to remove dust containing water generated by condensation of the water vapor. [0020] Hydrogen generated in the leaching may be captured to be resupplied to the reducing of the nickel-containing raw material, and dust including hydrochloric acid mist may be removed from an exhaust gas including hydrochloric acid mist and hydrogen discharged in the leaching by using a scrubber, and hydrogen may be captured to be resupplied to the reducing of the nickel-containing raw material. [Advantageous Effects] [0021] According to the present invention, since there is no need for a recovery of nickel (Ni) to be performed at a high temperature and a high pressure in order to leach nickel from a nickel-containing raw material, high-speed acid leaching may be possible at a low temperature and a low atmospheric pressure. Therefore, using relatively expensive titanium able to withstand high-temperature and high-pressure states in a reactor is unnecessary. [0022] Also, since Ni may be stably and effectively recovered from nickel ores, the present invention may be appropriately used in nickel smelting. Page 6 4423336_1 (GHMatters) P93963.AU [0023] Further, according to the present invention, recovery of Ni from nickel ores may be economically preformed as a required amount of hydrogen may be reduced. [Best Model [0024] Hereinafter, the present invention will be described in detail. [0025] The present invention relates to a method of effectively recovering nickel (Ni) from a nickel-containing raw material, and in particular, a method of recovering nickel by effectively acid leaching nickel from nickel ores having high metal contents is provided. [0026] Nickel ores used for the present invention are not particularly limited so long as the nickel ores contain nickel and, for example, may include limonite and saprolite. Pretreatments, such as drying, pulverization, and calcination, may be performed in order to recover nickel from the nickel ores. Hereinafter, pretreatment operations, i.e., drying, pulverization, and calcination operations, will be described in detail. [00271 In general, leaching by a wet method has been used when nickel is recovered from nickel-containing ores and for this purpose, the nickel-containing ores have been typically pulverized in a state having moisture. However, since the present invention includes a subsequent heat treatment operation, a drying operation removing moisture in advance may be performed. Dry pulverization after the drying operation may Page 7 4423336.) (GHMnilers) P93963.AU further increase pulverization efficiency in comparison to a wet pulverization process. Further, when there is a need for uniformly controlling a particle size of the ore required for reduction and leaching reactions, air classification of particles may be performed for particles of various sizes by using wind speeds of a dust collector and thus, powder required for the reduction and leaching reactions having a uniform particle size may be obtained. [00282 In the present invention, ore powder having a particle diameter of 1 mm or less may be used. When the particle size of the ore powder is greater than 1 mm, reduction and leaching rates may be low and in particular, workability may also be poor because pump and pipe clogging may greatly occur during an acid leaching reaction. When the particle size of the powder is 1 mm or less, a lower limit thereof is not particularly limited. However, the pulverization process must be performed for an unnecessarily long period of time or multiple times in order to obtain powder having a particle size less than 10 pm. Therefore, powder having a particle size of 10 pm or more may be used. [0029] In general, nickel ores contain crystallization water, and when a calcination process is not undertaken, crystallization water included in the ores may be released in a subsequent reduction process to retard a reduction reaction. Therefore, the calcination process may be undertaken. Among the nickel ores, limonite and saprolite have characteristics Page 8 442333 1 (GHMaiIOS) P039B3AU of releasing crystallization water at temperatures within temperature ranges of about 2500C to 350 0 C and 650 0 C to 750 0 C, respectively. Ore powders obtained from the pulverization process are calcinated at a temperature within a temperature range of 2500C to 850 0 C and thus, crystallization water included in the nickel ores may be removed. [00301 Meanwhile, saprolite having a high content of nickel is mainly used as a raw material of nickel pyrometallurgy, and nickel may also be recovered from rotary kiln dust generated in a pyrometallurgical process by using the present invention. However, since a particle size of the dust is included in an appropriate range suitable for the present invention and the dust has been exposed in a high-temperature state during the pyrometallurgical process, pulverization and calcination processes as in the case of the nickel-containing ores are not required. However, in the case that the particle size deviates from the range required in the present invention due to a factor such as the dust being exposed to air to take on moisture, a pulverization or calcination process may be undertaken as needed. [0031) Nickel ores typically include 1 wt% to 2.5 wt% of Ni and 15 wt% to 55 wt% of iron (Fe) although the nickel ores may be different according to types thereof. Nickel may be recovered by reducing nickel from such nickel ores. [0032) A reducing operation is performed by using a reduction gas in order to recover the foregoing nickel-containing raw Page 9 4423336_1 (GHMatters) P93963.AU material. Hydrogen may be used as the reduction gas used in reducing nickel. Since excess hydrogen generated in the reduction reaction and hydrogen generated in the leaching reaction may be recovered and recycled by using hydrogen as the reduction gas, a reduction in costs due to the use of reduction gas may be promoted. [0033] In reducing the nickel-containing raw material by using hydrogen as a reduction gas, a theoretical reaction is expressed as the following Formula (1). [0034] (NiFe)OFe 2
O
3 +4H2 = (NiFe) + 2Fe + 4H20 (1) [0035] However, excess hydrogen in an amount of moles equal to double or more that which is required in a real reduction reaction may be expressed as the following Reaction Formula (2). [0036] (NiFe)OFe 2
O
3 +8H2 = (NiFe) + 2Fe + 4H20 + 4H2 (2) [0037] As described above, in recovering the nickel-containing raw material by using hydrogen as a reduction gas, a reduction gas containing an amount of moles equal to double or more that of moles of hydrogen, based on the moles of (Fe+Ni) included in the nickel-containing raw material may be used and an upper limit thereof is not particularly limited. However, since costs may increase due to an increase in the amount of hydrogen used, the amount of moles of hydrogen may be equal to 5 times on the amount of moles of (Fe+Ni) included in the nickel-containing raw material or less. [0038] At this time, a temperature of a reduction furnace may Page 10 4423336_1 (GHMatters) P93963.AU be within a range of 550 0 C to 9500C. When the reduction temperature is 550 0 C or less, a recovery rate may decrease during subsequent leaching because a reduction may occur insufficiently, and when the reduction temperature is 950 0 C or more, the reduction rate may not increase further and only sintering may occur between particles to thereby badly affect workability. [00393 Meanwhile, inert gas may be included in the reduction gas in order to remove oxygen in addition to hydrogen existing in the reduction furnace during the reduction reaction. Examples of the inert gas may be nitrogen and the inert gas may also be recovered and recycled. [0040] In recovering nickel from the nickel-containing raw material by a reducing process, since a large amount of hydrogen is required, limitations may be generated in terms of increasing costs due to hydrogen, and there is a need to resolve such limitations. Therefore, excess hydrogen obtained after the reaction may be recycled. [0041] Excess hydrogen and water vapor are generated due to the reduction reaction as in Formula (2), and separation of the water vapor and the hydrogen is required for recycling hydrogen therefrom. The separation of the water vapor and the hydrogen may be performed in such a manner that the water vapor may be separated from the excess hydrogen by cooling an exhaust gas discharged after the reaction to change the water vapor into water. That is, when the exhaust gas is cooled, the Page 11 4423336_1 (GHMaIlers) P93983,AU water vapor is condensed to water, and as a result, hydrogen may be recovered by being separated from the water vapor through separation between gas and liquid and recovery. £0042] Meanwhile, since the reduced nickel-containing raw material obtained during the reduction reaction is dust having a particle diameter of 1 mm or less, the dust must be separated from the exhaust gas. Therefore, the liquid water and hydrogen gas as well as the dust in a solid state must all be separated. For this purpose, a scrubber may be used. When the exhaust gas is cooled by using mist in the scrubber, dust and water vapor are discharged to a lower portion and hydrogen is discharged to an upper portion. Hydrogen may be recovered by separating and capturing the discharged hydrogen gas to be pressurized, and thereafter, the recovered hydrogen gas may be reinjected into the reduction furnace as a reduction gas. [0043] Meanwhile, since a content of an iron component is very high when the nickel ores are reduced, reoxidation occurs during extraction into air after the reduction. During the reoxidation, an oxidation reaction is accelerated due to the generation of heat to thus increase the risk of fire. Therefore, the reduced nickel-containing raw material is discharged into an oxygen-barriered tank containing water to make the reduced nickel-containing raw material into a slurry and thus, oxidation of the iron component may be prevented. [0044] The slurry thus obtained is transferred to a pump to undergo a subsequent leaching operation. In the leaching Page 12 4423336.1 (GHMalters) P93983.AU operation, the nickel-containing raw material slurry is introduced into a reactor in an oxygen-free state and an acid is added to dissolve the nickel-containing raw material, and thus, nickel is leached therefrom. [0045] Hydrochloric acid, sulfuric acid, and nitric acid as well as other various acids may be used as the acid used in the leaching operation, but the acid used in the leaching operation is not limited thereto. However, hydrochloric acid and sulfuric acid may be used in view of wastewater disposal and cost considerations. [0046] When the reduced nickel-containing raw material is leached by using sulfuric acid and hydrochloric acid, metal acid reactions, such as the following Formulas (3) and (4), are performed to generate hydrogen gas. [0047] (NiFe) + 2Fe + 6HCl -- (NiFe) C1 2 + 2FeCl 2 + 3H2 (3) [0048] (NiFe) + 2Fe + 3H2SO4 -> (NiFe) S0 4 + 2FeSO 4 + 3H 2 (4) [0049] Therefore, as shown in Formulas (3) and (4), equivalence ratios may be reached when hydrochloric acid among the foregoing acids must be added in an amount of twice of the moles of (Fe+Ni) and sulfuric acid must be added in an amount of moles equal to or more that of moles of (Fe+Ni) of the nickel-containing raw material. Amounts of the added acids may be the equivalence ratios or more, but upper limits thereof are not particularly limited. However, in consideration of economic factors in processing, hydrochloric acid and sulfuric acid, for example, may be added in amounts of moles equal to Page 13 4423330_1 (GHMalters) P93963.AU quadruple or double the amount of moles of (Fe+Ni), respectively. [00501 Meanwhile, when the reduced nickel-containing raw material is leached with acids, nickel and iron are selectively dissolved into ions by the reactions in Formulas (3) and (4), and A1 2 0 3 , SiO 2 , or Cr 2 0 3 contained in the nickel containing raw material are virtually undissolved by the acids, and thus, a solid phase residue is obtained. Therefore, the nickel-containing solution obtained in the leaching operation and the solid phase residue are very easily separated by filtration and may be separated by a solid-liquid separator, such as a filter press and a decanter, to obtain a nickel containing solution. [00513 The leaching operation may be performed at a temperature within a temperature range of 25 0 C to 80 0 C. In the case that the present invention is used for nickel leaching by an acid, leaching may be terminated with two hours even in the case that the leaching is performed at room temperature. A rate of the leaching operation increases as a reaction temperature is raised. However, energy costs may increase as the reaction temperature is raised and in particular, pressure control of hydrogen may be difficult because hydrogen gas is explosively generated when the leaching reaction is performed at a temperature of 800C or more, and thus, recovery and recycling of hydrogen may become problematic. Therefore, the leaching reaction may be performed at a temperature within the Page 14 44233361 (GHMattes) P93963AU foregoing temperature range. [0052] The termination of the leaching reaction may be identified through changes in a pH value. The pH of the solution in the reactor increases when free acid is removed by the leaching reaction and the leaching reaction may be terminated when the pH is in a range of 0.1 to 1.0. When the pH is less than 0.1, the free acid must be removed in a subsequent process and an amount of alkali used for this purpose is increased. Also, when the pH becomes higher than one because an amount of hydrochloric acid is less than the equivalence ratio, substitution and precipitation of Ni due to unreacted Fe metal occur, and thus, a recovery rate of Ni may decrease. Therefore, when the pH of the solution in the reactor reaches a range of 0.1 to 1.0, the leaching reaction may be terminated and the solution containing Ni ions and the sludge residue may be separated by filtration. [0053] When the leaching operation is performed by using the foregoing method, leaching is terminated within two hours. At this time, a leaching rate of Ni may be 90% or more. For example, when the leaching operation is performed for less than 30 minutes, nickel is insufficiently leached from the nickel-containing raw material, and thus, the leaching operation may be performed for 30 minutes or more. [00543 Hydrogen used in the reaction of Formula (1) is generated in the leaching operation as shown in Formulas (3) and (4). Therefore, an amount of hydrogen required may be Page 15 44233361 (GHMaLters) P93963.AU greatly reduced by recovering and recycling hydrogen generated in Formulas (3) and (4) . The recovery of hydrogen may be performed by removing dust including hydrochloric acid mist and capturing hydrogen from an exhaust gas including hydrogen and hydrochloric acid mist discharged in the leaching operation by using the scrubber, and the recovered hydrogen may be reused by being resupplied to the reducing operation. [0055] As a result of measuring an amount of hydrogen generated and an amount of hydrogen recovered by recovering hydrogen generated in the leaching operation according to the method of the present invention, an amount of hydrogen reaching 95% of a theoretical amount of hydrogen generated may be recovered. The reason for not obtaining a recovery rate of 100% is that metal leaching rates of nickel and iron do not reach 100% because the leaching rates may be rapidly reduced at a termination point of the reaction and reduction rates of iron and nickel also do not reach 100%. [0056] The method of recovering nickel from the nickel containing raw material of the present invention includes, after separating a nickel-containing solution containing nickel and iron from a solid phase residue in the leaching operation, an iron removing operation removing iron from the nickel-containing solution. (0057] The nickel-containing solution containing iron is obtained, and when air is injected while a pH of the solution is controlled to be in a range of 2.5 to 5.5 in order to Page 16 442333 1 (GHMatlers) P9393AU remove a Fe component, iron hydroxide having an orange color is then generated as Fe is changed into iron hydroxide, and nickel and iron may be separated by filtering the solution. Also, in addition, a solvent extraction method may be used for separating the iron ions and the nickel ions. [Mode for Invention] [0058] Hereinafter, the present invention will be described in detail, according to embodiments. [0059] Embodiment [0060] Embodiment 1 [0061] In order to measure reduction rates and nickel (Ni) leaching rates of nickel-containing raw materials according to pretreatment conditions, the following experiments were conducted by using nickel ores of limonite and saprolite having compositions as in Table 1. [0062] [Table 1] Ni Fe Mg Si Al Limonite 1.32 47.17 1.36 1.93 2.49 Saprolite 1.96 24.37 9.94 16.1 1.5 [0063] A unit of a content of each component in Table 1 was wt% and oxygen as well as a trace amount of manganese (Mn) being included as a remainder. [0064] The nickel ores in Table 1 were pulverized and calcinated by using pretreatment conditions as in Table 2 to Page 17 44233361 (GHMatters) P93963AU prepare samples. [0065] The nickel-containing raw materials were reduced at a temperature of 700 0 C by using an amount of moles of hydrogen double that of the moles of (Fe+Ni) included in each sample as a reduction gas. Water vapor and excess hydrogen generated in a reduction reaction were discharged as an exhaust gas. [0066] The reduced nickel-containing raw materials were provided to an oxygen-barriered tank containing water to make the reduced nickel-containing raw material into slurries. Hydrochloric acid was added in an amount equal to the moles of (Fe+Ni) included in each sample to each slurry thus obtained to dissolve the each sample at a temperature of 30 0 C and as a result, nickel was leached. The leaching reaction was performed until the pH of the solution became 0.5, and a duration time was one hour and forty five minutes. Hydrogen gas generated in the leaching reaction was discharged as an exhaust gas. [0067] A solid phase sludge residue was removed by using a solid-liquid separator after termination of the leaching reaction and a nickel-containing solution was obtained. Iron in the solution was converted into iron hydroxide by adding oxygen thereto while a pH of the nickel-containing solution obtained was controlled to be 3.0, and nickel was then recovered by filtering the iron hydroxide. [00681 Accordingly, reduction rates and nickel recovery rates of the samples were investigated and the results thereof are Page 18 442336_1 (GHMatters) P93963.AU presented in Table 2. [0069] [Table 2] Pulverized Calcination Leach rate Ore type particle temperature of Ni ( Remarks size (mm) (oC) comparative Limonite 2 500 87 Pump Example 1 clogging Inventive Limonite 0.8 500 95 Example 1 Invenive Limonite 0.4 500 95 Comparative Limonite 0.8 200 89 Unreduced Example 2 portion Comparative Saprolite 0.8 500 89 Unreduced Example 3 portion Inventive Saprolite 0.8 700 95 Example 3 comparative Limonite 0.8 900 95 Example 4 [0070] According to Table 2, it was confirmed that when a particle size of the ore is greater than 1 mm (Comparative Example 1) , the leaching rate of nickel was decreased due to slow dissolution rates in the acid during the reduction reaction and the leaching reaction, and in particular, clogging of a pump occurred during a wet treatment because settleability of the ore was too high due to the large particle size. [0071] Meanwhile, with respect to Comparative Examples 2 and 3, water of crystallization in the ores was insufficiently removed due to low calcination temperatures and it may be understood that when hydrogen reductions were performed in such states, the hydrogen reductions were not facilitated and Page 19 4423336_1 (GHMaters) P93963.AU leaching rates were low. With respect to Comparative Example 4, calcination was performed at a temperature higher than the calcination temperature range of the present invention, and high leach rate may also be obtained under such a condition. However, subsequent increases in reduction rate of hydrogen and leach rate of nickel may be insignificant and energy consumption may be only increased. [0072] In contrast, with respect to Inventive Examples 1 to 3 satisfying conditions of pulverized particle size and calcination temperature as the pretreatment conditions of the present invention, it was confirmed that hydrogen reductions and leaching reactions were facilitated. Further, it was confirmed that high leaching rates of nickel were obtained with two hours even in the case that the leaching were performed at room temperature. [0073] Embodiment 2 [0074] In the present embodiment, reduction rates, as shown in Table 3, when nickel ores were reduced for each reduction temperature and an ignition or combustion phenomenon according to a method during extraction after the reduction were investigated. [00751 [Table 31 Ni Fe Mg Si Al Limonite 1.32 47.17 1.36 1.93 2.49 Saprolite 1.96 24.37 9.94 16.10 1.50 Kiln dust from pyrometallurgical 2.27 18.51 14.60 16.80 0.90 process of nickel ore Page 20 4423336_1 (GHMatters) P93963.AU [0076] A unit of a content of each component in Table 3 was wt% and oxygen as well as a trace amount of manganese (Mn) was included as a remainder. [0077] Among samples in Table 3, limonite was pretreated as in Inventive Example 1 of Embodiment 1 to prepare samples and saprolite was pretreated as in Inventive Example 3 of Embodiment 1 to prepare samples. [0078) Each sample prepared from limonite, saprolite, and dust from a pyrometallurgical process of nickel ores (hereinafter, referred to as "dust") was reduced in the same manner as Embodiment 1 except that the reduction of the each sample was performed at a temperature as described in Table 4. [00791 Reduction rates of the samples obtained by the reduction processes were calculated from amounts of water vapor generated based on an input equivalence of FeNi by cooling and capturing water vapor generated from the reaction of Formula (1) . The results thereof are presented in Table 4. [0080] The reduced samples were provided to an oxygen barriered tank containing water to make the reduced samples into slurries or extract into air. As a result, presence of ignition of the samples according to the generation of heat due to oxidation of Fe during extraction outside a reduction furnace and flame spread due to the generation of heat was investigated and the results thereof are presented in Table 4. [00811 [Table 4] Page 21 442333._1 (GHMalters P93963AV Reduction Extraction of Ore type temperature Reduction rate reduced sample (11C) Comparative Limonite 500 35% Example 5 Comparative Limonite 625 88% Air extraction, Example 6 Ignition Comparative Limonite 750 97% Air extraction, Example 7 Ignition Comparative Limonite 825 98% Air extraction, Example 8 Ignition Comparative Limonite 960 98% Sintering Example 9 Comparative Saprolite 725 98% Air extraction, Example 10 Ignition Reference Dust 825 98% Air extraction, Example 1 Good Inventive Limonite 25 88% Water extraction, Example 4 Good Inventive Limonite 750 97% Water extraction, Example 5 Good Inventive Limonite 825 989 Water extraction, Example 6 L Good Inventive Dust 725 98% water extraction, Example 7 Good [0082] As shown in the results of Comparative Example 5 in Table 4, reductions of nickel and iron by hydrogen gas occurred at a temperature of 550 0 C or more and did not occur at a temperature of less than 5500C, and thus, it was confirmed that a reduction rate of Comparative Example 5 was considerably low. Meanwhile, as described in Comparative Example 9, a sintering reaction of the sample occurred in the case that the reduction temperature was greater than 9500C, and as a result, limitations, such as an attachment of the sample to equipment in the reduction furnace, were generated. [0083] With respect to Comparative Examples 6 to 8 and 10, in which the samples were extracted outside the furnace after the Page 22 44233361_ (GHMatlem) PG39S3.AU reductions, ignition phenomena of the samples occurred according to the generation of heat due to the oxidation of Fe during extraction processes and flame spread due to the generation of heat. It was confirmed that the foregoing ignition phenomena more severely occurred with respect to limonite including a large amount of Fe in the samples. [0084] As shown in Comparative Example 10, the ignition phenomenon generated during extraction into air was prevented when the reduction temperature was increased, but the sample was sintered to generate limitations in attachment to a piece of equipment, such as a rotary kiln. Further, a subsequent leaching process may be adversely affected. In Reference Example 1, when kiln dust was reduced within a temperature range of 825aC to 8500C, ignition of the sample did not occur even in the case that the reduced sample was extracted into air, because a content of Fe in the dust was low. However, if a sample having a high content of Fe was used with Reference Example 1, ignition could occur. [0085] In contrast, in Inventive Examples 4 to 7, reduction reactions were performed at a temperature within a temperature range defined by the present invention and thus, high reduction rates were obtained. Also, the reduced samples were extracted into an oxygen-barriered tank containing water and thus, ignition of the samples due to a high content of reduced Fe may be prevented. Oxidations of the reduced samples immersed in water were limited due to a low concentration of Page 23 442333_ (GHMalters) P93963.AU oxygen in water. Also, the samples may be provided as slurries to a subsequent leaching process. Further, the water storage tank at an extraction part of the reduction furnace may provide a so-called "water sealing effect" as a barrier to prevent a discharge of hydrogen into the furnace and the intrusion of oxygen, and thus, may provide a basis for recycling hydrogen. [0086] Embodiment 3 [0087] In order to verify hydrogen recycling according to the reactions in Formulas (1) and (3), 1 mole of nickel oxide and 1 mole of iron oxide were reduced in a tube furnace at 750 0 C by using hydrogen gas as a reduction gas according to reactions as in Formulas (5) and (6) below, and discharged amounts of water vapor were passed through a condenser and captured. Amounts of the captured water vapors were weighed. [0088] NiO + H2 = Ni + H20 (5) [0089] Fe 2 0 3 + H2 = 2Fe + 2H 2 0 (6) [0090] Amounts of water vapor generated after reducing the iron oxide and the nickel oxide were respectively 17.8 g and 35.9 g, and were almost match with theoretical values. [0091] Meanwhile, hydrochloric acid was added to 1 mole of reduced NiFe to generate hydrogen by dissolving the reduced NiFe according to a reaction as in Formula (7). [0092] NiFe + 4HCl = NiCl 2 + FeCl 2 + 2H2 (7) [0093] The reaction was terminated within one hour (a pH value was increased to 0.5, and visually, no generation of hydrogen Page 24 442333_1 (GHMatters) P93983.AU gas was witnessed). At this time, discharged hydrogen during the reaction was captured and an amount thereof was measured. The amount of the captured hydrogen was about 42.71 g. [0094] The foregoing value did not reach 44.8 liters corresponding to two moles of hydrogen, a theoretical value of Formula (7). The reason for this is that metal leaching rates were not 100% because the leaching rates were rapidly reduced at a termination point of the reaction and reduction rates of the iron and nickel used were not 100% as confirmed in Embodiment 1. [0095] While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims. [0096] It is to be understood that, if any prior art publication is referred to herein, such reference does not constitute an admission that the publication forms a part of the common general knowledge in the art, in Australia or any other country. [0097] In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word "comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e. Page 25 6529473_1 (GHMatters) P93963.AU JBECKER to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention. Page 26 6529473_1 (GHMatters) P93963.AU JBECKER