AU2009212947A1 - Hydrometallurgical process of nickel laterite ore - Google Patents

Description

P/00/011I Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Invention Title: Hydrometallurgical process of nickel laterite ore The following statement is a full description of this invention, including the best method of performing it known to us: SPECIFICATION HYDROMETALLURGICAL PROCESS OF NICKEL LATERITE ORE BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to a hydrometallurgical process of a nickel laterite ore, and in more detail, the present invention relates to a hydrometallurgical process of a nickel laterite ore to recover nickel and cobalt from the nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, which process enables the reduction of the wear of equipment such as a pipeline, a pump, caused by an ore slurry produced from the ore treatment step, and enhance durability thereof, and also reduce the amount of final neutralization residue produced from the final neutralization step. The present invention thus at least alleviates the problem of preventing cost and environmental risk by decreasing the volume of a tailing dam for storing a leach residue, neutralization precipitate etc. to be subjected to waste disposal, as well as separating and recovering impurity components which may be utilized effectively by resource recycling. DESCRIPTION OF THE PRIOR ART In recent years, with ever increasing oligopoly of mining right in mineral resources such as coal, iron, copper, nickel, cobalt, chromium, manganese, raw material cost in metal smelting 2 has increased to a large degree. Therefore, also in metal smelting, as a means for cost reduction, technological development has been carried out so as to use low content raw materials, which have not been an object conventionally, because of disadvantage in view of cost. For example, in nickel refining, also thanks to development of a material having excellent corrosion resistance under high temperature and high pressure, a hydrometallurgical process for smelting, based on a High Pressure Acid Leach is noticed, where a nickel laterite ore is subjected to acid leaching with sulfuric acid under high pressure. This High Pressure Acid Leach, different from a pyrometallurgical refining, which is a conventional general process for smelting a nickel laterite ore, does not include dry steps such as a reduction step, a drying step, and is thus advantageous in view of energy costs, and is therefore evaluated as a promising technology as a process for smelting a low content nickel laterite ore. Accordingly, various proposals have been made on enhancement of the leaching rate of nickel and cobalt, for purification of a leach solution, or the reduction of reagents usage, majoring in a leaching step under high temperature and high pressure, so as to enhance the completeness as a smelting process. Incidentally, as a process where leaching under high temperature and high pressure is utilized, for example, in recovering the metals from an oxide ore containing valuable metals such as nickel, cobalt, manganese, a method for 3 recovering the valuable metals from an oxide ore composed of the following steps (a) to (c), has been proposed (for example, refer to Patent Reference 1); Step (a): obtaining normal pressure leach solution and normal pressure leach residue, by subjecting laterite ore, converted to slurry in advance, to normal pressure leaching under acid condition of sulfuric acid, using a high pressure -leach solution obtained in step (b); Step (b) : obtaining a high pressure leach solution by subjecting the normal pressure leach residue obtained in step (a), to a reaction with sulfuric acid under an oxidation atmosphere under high temperature and high pressure; and Step (c): recovering nickel and cobalt in the leach solution as sulfides by the addition of a neutralizing agent into the normal pressure leach solution obtained in step (a) for neutralization, and the subsequent addition of an alkali sulfide compound. In this method, by carrying out the two-stage leaching, normal pressure leaching of an oxide slurry (step (a)), and then High Pressure Acid Leaching of the normal pressure leach residue (step (b) ) , the nickel leaching rate from the ore can be enhanced, and at the same time, load of the neutralization step (step (c)) can be reduced by neutralization of excess acid contained in the leach solution of the High Pressure Acid Leaching with the alkali component contained in the normal pressure leach residue. However, because of the two-stage leaching, it had problems of increased cost and time caused by an increase in the items of equipment, and the cost for treatment of a large quantity of 4 a thin solution generating in washing of the leach residue. In order to at least alleviate these problems, a method composed of the following steps (1) to (4), has been proposed, as other process for utilization of leaching under high temperature and high pressure (for example, refer to Patent Literature 2). (1) a leaching step: forming a leaching slurry by the addition of sulfuric acid to a nickel laterite ore, which was converted to slurry in advance, and by stirring treatment at a temperature of 220 to 280 *C. (2) a solid-liquid separation step: separation to a leach solution containing nickel and cobalt, and a leach residue, by washing of the above-described leaching slurry using a multi-stage thickener. (3) a first neutralization step: forming a neutralization precipitate containing ferric iron, by adjustment of pH to equal to or lower than 4 using calcium carbonate, under prevention of oxidation of the above-described leach solution, so as to separate to the neutralization precipitate slurry and a mother liquor for nickel and cobalt recovery. and (4) a sulfurization step: blowing hydrogen sulfide gas into the above-described mother liquor for nickel recovery, so as to generate a sulfide containing a nickel and a cobalt, and separate it from a barren liquor. Here, explanation will be given on outline of a practical plant based on the above method (Patent Literature 2) with reference to a drawing. Figure 2 is a process chart of smelting 5 )'J_ .LAA., showing one example of a practical plant based on the hydrometallurgical process of a nickel laterite ore (Patent Literature 2) In Figure 2, firstly a nickel laterite ore 8 is mixed with water in an ore treatment step 1, and then removal of foreign material and adjustment of ore particle size of the ore are carried out to form an ore slurry 9. Then, in a leaching step 2, the ore slurry 9 is subjected to High Pressure Acid Leach with sulfuric acid to form leaching slurry 10. The leaching slurry 10 is subjected to a solid-liquid separation step 3 for multi-stage washing, and then separated to a leach solution 11 containing a nickel and a cobalt, and a leach residue slurry 12. The leach solution 11 is subjected to a first neutralization step 4 and separated to a neutralization precipitate slurry containing a ferric iron hydroxide 13, and a mother liquor for nickel recovery (1) 14. The mother liquor (1) 14 is subjected to a zinc removal step 5, where a sulfurizing agent is added, so as to separate to a zinc sulfide precipitate 15 containing a zinc sulfide, and a mother liquor for nickel recovery (2) 16. Then, the mother liquor (2) 16 is subjected to a sulfurization step 6 and separated to a mixed sulfide 17 containing a nickel and a cobalt, and a barren liquor 18 removed nickel etc. It should be noted that, the barren liquor 18 is used as washing water of the leach residue in the solid-liquid separation step 3. Lastly, the leach residue slurry 12 is subjected to a final neutralization step 7 together with the excess barren liquor 18 for neutralization treatment, and a final neutralization residue 19 is stored in a tailing dam 20. 6 As features of this method, there are included that consumption amount of the neutralizing agent and amount of the precipitate in the neutralization step can be reduced, by multi-stage washing of the leaching slurry in the solid-liquid separation step; solid-liquid separation characteristics can be improved due to increasing ability of true density of the leach residue; and still more a process can be simplified by carrying out the leaching step only by leaching under high temperature and high pressure, and it is said to have advantage relative to the above-described method (Patent Literature 1). Still more, using a barren liquor as a washing solution to be used in the solid-liquid separation step, nickel adhered onto the leach residue can be recovered with leaching, by utilization of remaining sulfuric acid, and it is said to be capable of using repeatedly the water effectively and efficiently. Still more, by sending the neutralization precipitate slurry to the solid-liquid separation step, nickel loss can be reduced, therefore it is said to be more advantageous. However, the practical plant by this method had the following problems: (1) prevention of equipment wear: a nickel laterite ore is carried between the steps as slurry, which significantly accelerates the wear of an equipment material, in particular, repair frequency increases for equipment such as a pipeline, a pump in the leaching step, and it gave a serious cause for increase in maintenance cost, and decrease in plant operation rate. That is, chromite contained in the nickel laterite ore 7 3Y,_.UUU is particularly hard, and is a component extremely to accelerate the wear of the pipeline, the pump, and the like, in a hydrometallurgical process for smelting accompanying with carrying of slurry, therefore, it is desirable to remove it from a raw material ore to be treated in the leaching step. (2) increase in solid rate of an ore slurry: in general, the higher solid rate of slurry of a nickel laterite ore provides the less solution amount to be handled, which enables to simplify equipment such as a pipeline, a tank, therefore, it is preferable that the ore slurry is concentrated to such a degree as there is no trouble in liquid sending or the like by a pump, or such a degree as there is no generation of pipeline clogging, however, there was limitation accompanying with sedimentation property of the ore slurry. (3) decrease in content of impurity elements of the ore slurry: in the leaching step, because impurity elements such as magnesium, aluminum contained in the ore slurry give a big influence on consumption of sulfuric acid, content of these impurity elements is preferably to be as low as possible. (4) decrease in amount of final neutralization residue: the leach residue obtained in the solid-liquid separation step is combined together with an excess barren liquor produced from the sulfurization step, and is made harmless by the neutralization step where lime stone slurry or slaked lime slurry is added. The final neutralization residue produced in this final neutralization treatment step (hereafter may be 8 59_6.DOC referred to as a final neutralization step), is stored in a tailing dam. However, because the final neutralization residue contains impurity components such as hematite, chromite, a silica mineral, magnesium silicate ore in the leach residue, as well as gypsum formed by neutralization treatment, there was a large cost burden for construction of the tailing dam and maintenance management thereof. Therefore, effective material recycling of impurity components such as hematite, chromite, a silica mineral, magnesium silicate ore in the above-described leach residue is expected. For example, chromite is expected to be utilized as a raw material to produce ferrochromium to be used as an addition element of stainless steel. However, in production of ferrochromium, recovery thereof is desired, in view of treatment efficiency or cost, as a concentrate with a chromium content of, for example, equal to or higher than 5% by mass. In addition, hematite is expected to be utilized as a raw material of steel and stainless-steel. However, because many components other than hematite are contained in the above-described leach residue, separation from these components is desired. In particular, sulfur has a generation problem of sulfurous acid gas in a steel making step, therefore it is desired to contain sulfur as low as possible. Upper limit value of allowable sulfur content depends on a plant, which receives as a raw material of iron and steel, however, in general, it is said necessary to lower the content to equal to or lower than about 2 to 3% by mass. (5) repeated treatment of a neutralization precipitate slurry: As described above, treatment of the neutralization precipitate 9 J7 U.J'JL slurry in the solid-liquid separation step is effective to enhance nickel recovery, however, iron hydroxide in the neutralization precipitate is also re-dissolved here, which results in increase in consumption amount of a neutralizing reagent, as well as increase in amount of the leach residue. Therefore it is desirable that the neutralization precipitate to be recycled to the solid-liquid separation step is as low as possible. From the above circumstances, it has been required to at least alleviate the above problems in a practical plant using the hydrometallurgical process for smelting based on the above High Pressure Acid Leach. Still more, in order to at least alleviate the above problems effectively and economically, effective separation and recovery of impurity components contained in an ore or the leach residue is an effective means, and also effective utilization of these impurity components by material recycling has also been required. [Patent Literature 1] JP-A-6-1l6660 (page 1 and page 2) [Patent Literature 2] JP-A-2005-350766 (page 1 and page 2) Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment, or any form of suggestion, that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. 10 SUMMARY OF THE INVENTION In view of the above conventional technological problems, it is an object of the present invention to provide a hydrometallurgical process of a nickel laterite ore to recover nickel and cobalt from the nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step. One aspect of the invention seeks to reduce wear of equipment such as a pipeline, or a pump, as is caused by an ore slurry produced from the ore treatment step, and thus enhance the durability, and simplify the equipment of, the ore treatment step by an increase in the solid rate of the ore slurry, and to also reduce the amount of a final neutralization residue produced from the final neutralization step. In doing so, one aspect of the invention seeks to at least alleviate the problem of prevention of cost and environmental risk thanks to a decrease in the volume needed for a tailings dam for storing a leach residue, neutralization precipitate slurry or the like, to be subjected to waste disposal. In one aspect the invention also seeks to separate and recover impurity components which may be utilized effectively by resource recycling. The present inventors have intensively studied a way to at least alleviate the above problems in a hydrometallurgical process for smelting to recover nickel and cobalt from a nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a 11 59_6.1)UU sulfurization step, and a final neutralization step. The inventors have found that it is effective, as a means to at least alleviate one or more of the above problems, to carry out at least one step selected from the following: step of (A) for separating and recovering, by a specific method, the particles containing a silica mineral, chromite or a magnesium silicate ore in ore slurry produced from the ore treatment step; step of (B) for separating and recovering, by a specific method, the hematite particles in leach residue slurry produced from the solid-liquid separation step; or step (C) for subjecting a neutralization precipitate slurry, produced from the first neutralization step, to the final neutralization treatment separately, and have thus completed the present invention. That is, according to a first aspect of the present invention, there is provided a hydrometallurgical process to recover nickel and cobalt from a nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the process characterized by further including at least one step selected from the following steps (A) to (C); (A) step for separation and recovery, by a physical separation method, of particles including at least one kind selected from the group consisting of a silica mineral, chromite or a magnesium silicate ore in an ore slurry produced from the ore treatment step; (B) step for separation and recovery, by a physical separation 12 method, of hematite particles in a leach residue slurry produced from the solid-liquid separation step; and (C) step for subjecting a neutralization precipitate slurry produced from the first neutralization step to the final neutralization treatment separately from the leach residue slurry produced from the solid-liquid separation step. leach residueleach residue In addition, according to a second aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the first aspect, characterized in that, in step of the above-described (C), zinc sulfide precipitate slurry produced from the above-described zinc removal step is subjected to the final neutralization treatment together with the above-described neutralization precipitate slurry at the same time. In addition, according to a third aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the first or the second aspect, characterized in that: the above-described ore treatment step is a step for forming the ore slurry by carrying out removal of foreign material and adjustment of ore particle size of a raw material ore mined; the above-described leaching step is a step for forming a leaching slurry composed of leach residue and leach solution, by the addition of sulfuric acid to the ore slurry and by carrying out the stirring treatment under high temperature and high pressure; 13 9_6.DOC the above-described solid-liquid separation step is a step for obtaining leach solution containing nickel and cobalt, and a leach residue slurry, by multi-stage washing of the leaching slurry; the above-described neutralization step is a step for forming neutralization precipitate slurry containing ferric iron, and a mother liquor for nickel recovery, by the addition of calcium carbonate into the leach solution; the above-described zinc removal step is a step for forming zinc sulfide precipitate slurry and a mother liquor for nickel and cobalt recovery, by blowing hydrogen sulfide gas into the mother liquor; the above-described sulfurization step is a step for forming a mixed sulfide containing nickel and cobalt and, a barren liquor by blowing hydrogen sulfide into the mother liquor for nickel and cobalt recovery; and the above-described final neutralization step is a step for obtaining a final neutralization residue, by the addition of an excess barren liquor into the leach residue slurry, and adjusting pH to about 8 to 9. In addition, according to a fourth aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the third aspect, characterized in that, in the above-described ore treatment step, ore particle size adjustment is subjected to sieve treatment at a particle size of equal to or smaller than 2 mm. In addition, according to a fifth aspect of the present 14 59_6.DOC invention, there is provided the hydrometallurgical process of a nickel laterite ore according to any one of the first to the fourth aspects, characterized in that, in step of the above-described (A), the above-described ore slurry is subjected to a physical separation method by sieve classification or centrifugal classification, wherein the coarse particle part classified is recovered as a concentrate of silica mineral, chromite or a magnesium silicate ore. In addition, according to a sixth aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the fifth aspect, characterized in that the above-described classification particle size is selected from a range of 20 to 850 pm. In addition, according to a seventh aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the fifth aspect, characterized in that the above-described classification particle size is two particle sizes selected from a range of equal to or larger than 850 pm and a range of 20 to 850 pm, wherein firstly a coarse particle part classified at the particle size of the former range is recovered as a concentrate of a silica mineral or a magnesium silicate ore, and next a coarse particle part classified at the particle size of the latter range is recovered as a concentrate of chromite. In addition, according to an eighth aspect of the present invention, there is provided the hydrometallurgical process of 15 a nickel laterite ore according to any one of the first to the forth aspects, characterized in that, in step of the above-described (B) , the above-described leach residue slurry or the final neutralization residue slurry containing it is subjected to a physical separation method by sieve classification or centrifugal classification, wherein the fine particle part classified is recovered as a concentrate of hematite. In addition, according to a ninth aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to the eighth aspect, characterized in that the above-described classification particle size is selected from a range of 20 to 100 pm. In addition, according to a tenth aspect of the present invention, there is provided the hydrometallurgical process of a nickel laterite ore according to any one of the first to the forth aspects, characterized in that, in step of the above-described (B), the above-described leach residue slurry or the final neutralization residue slurry containing it is subjected to a physical separation method by magnetic separation, wherein a magnetized substance is recovered as a concentrate of hematite. The hydrometallurgical process of a nickel laterite ore of the present invention is capable of at least alleviating the above-described problems as follows, by adoption of steps of (A) to (C), in a hydrometallurgical process for smelting to 16 recover nickel and cobalt from a nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, therefore, industrial value thereof is extremely high. By adoption of the step of (A), it is possible to prevent the wear of equipment such as a pipeline, a pump caused by the ore slurry as well as increase solid rate of the slurry, by separation and recovery of particles containing a silica mineral, chromite and a magnesium silicate ore in ore slurry produced from the ore treatment step. Still more, by separation of these impurity components, amount of the final neutralization residue can be reduced owing to decrease in amount of the leach residue, as well as reduction of contents of impurity elements, which influences largely on use amount of sulfuric acid, can be attained. Here, these impurity components, in particular, chromite can be utilized effectively. In addition, by adoption of the step of (B), by separation and recovery of hematite in leach residue slurry produced from the solid-liquid separation step, it is possible to reduce amount of a final neutralization residue produced from the final neutralization step, and thus prevent cost and environmental risk thanks to decrease in volume of a tailing dam for storing a leach residue, neutralization precipitate or the like to be subjected to waste disposal, as well as separate and recover hematite which may be utilized effectively as iron resources. 17 In addition, by adoption of the step (C), by subjecting a neutralization precipitate slurry produced from the first neutralization step to a separate neutralization treatment divided from the final neutralization step, amount of the final neutralization residue can be reduced, which is particularly advantageous in separation and recovery of hematite in the leach residue. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a process chart of smelting showing one example of embodiments according to the hydrometallurgical process of a nickel laterite ore relevant to the present invention. Figure 2 is a process chart of smelting showing one example of a practical plant based on the hydrometallurgical process of a nickel laterite ore (Patent Literature 2). Figure 3 is a drawing for showing the relation between particle size and content of iron, chromium and silicon of the leach residue. Figure 4 is a drawing for showing the relation between particle size and distribution rate of iron, chromium and silicon of the leach residue. NOTATION 1 ore treatment step 2 leaching step 3 solid-liquid separation step 4 neutralization step 5 zinc removal step 18 6 sulfurization step 7 final neutralization step or final neutralization step (1) 8 nickel laterite ore 9 ore slurry 10 leaching slurry 11 leach solution 12 leach residue slurry 13 neutralization precipitate slurry 14 mother liquor (1) 15 zinc sulfide precipitate 16 mother liquor (2) 17 mixed sulfide 18 barren liquor 19 final neutralization residue or final neutralization residue (1) 20 tailing dam 21 step of (A) 22 chromite or the like 23 step of (B) 24 hematite precipitate 25 final neutralization step (2) (step (C)) 26final neutralization residue (2) DETAILED DESCRIPTION OF THE INVENTION The hydrometallurgical process of a nickel laterite ore of the present invention is a hydrometallurgical process of a nickel laterite ore to recover nickel and cobalt from the nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, 19 a first neutralization step, a zinc removal step, a sulfurizati.on step, and a final neutralization step, characterized by including at least one step selected from the following steps (A) to (C). (A) separation and recovery, by a physical separation method, of particles containing at least one kind selected from a silica mineral, chromite or a magnesium silicate ore in ore slurry produced from the above-described ore treatment step; (B) separation and recovery, by a physical separation method, of hematite particles in leach residue slurry produced from the above-described solid-liquid separation step; and (C) step for subjecting a neutralization precipitate slurry, produced from the above-described neutralization step, to the final neutralization treatment separately from the leach residue produced from the above-described solid-liquid separation step. In the method of the present invention, it is important to include at least one step selected from the above-described steps (A) to (C), in order to at least alleviate the problems. Here, by adoption of the step (A) , it is possible to prevent the wear of equipment such as a pipeline, a pump caused by the ore slurry, as well as increase solid rate of the ore slurry, by separation and recovery of particles containing the silica mineral, chromite and the magnesium silicate ore in ore slurry produced from the above-described ore treatment step. That is, by separation of chromite or a magnesium silicate (magnesium silicate) ore having extremely high hardness, which is generally contained in a nickel laterite ore, wear can be prevented, as 20 well as it is possible to eliminate one of the causes of obstructing increase in solid rate of ore slurry, by separation of low density cristobalite (amorphous silica) and viscous aggregated block (for example, montmorillonite: a hydrated silicate of iron and aluminum), which generally are included in the nickel laterite ore and give bad influence on sedimentation property. Still more, separation of these impurity components enables to reduce amount of final neutralization residue thanks to decrease in amount of the leach residue, as well as attain reduction of content of impurity components, which largely influence on use amount of sulfuric acid. Incidentally, these impurity components, in particular, chromite can be utilized effectively. It should be noted that because chromite is a valuable mineral containing a chromium of a component of stainless steel, it can be utilized as an effective resource, when it is separated and recovered. Here, in the use as a raw material in production of ferrochromium, which is used as an addition element in stainless steel production, in view of treatment efficiency or cost, separation is preferably at a chromium content of, for example, equal to or higher than 5% by mass. In addition, by adoption of the step (B), by separation and recovery of hematite particles in leach residue produced from the above-described solid-liquid separation step, it is possible to reduce amount of the final neutralization residue produced from the final neutralization step, and thus prevent cost and environmental risk thanks to decrease in volume of a tailing dam for storing the leach residue, neutralization 21 precipitate or the like to be subjected to waste disposal, as well as separate and recover hematite which may be utilized effectively as iron resource. That is, because iron in a nickel laterite ore is hydrolyzed at high temperature in the leaching step, and iron is contained in a hematite form in the final neutralization residue. However, because the final neutralization residue contains chromite, a magnesium silicate ore and the like in the leach residue, as well as gypsum formed by neutralization treatment, iron content is as low as in the order of 30 to 50% by mass, therefore it was difficult to be utilized effectively, as it is, as a raw material in iron production or the like, where a content of generally equal to or higher than 60% by mass is said to be preferable, in consideration of production efficiency or cost. This is because, sulfur, chromium, silicon or the like is a component giving influence on distribution of trace components into pig iron, quality of iron and steel products or the like, therefore it was required to prevent a content of these impurity components. In addition, by adoption of the step of (C), by subjecting a neutralization precipitate slurry produced from the above-described neutralization step to a separate neutralization treatment divided from the final neutralization step, amount of the above-described final neutralization residue can be reduced, which is particularly advantageous in separation and recovery of hematite in the leach residue. That is, in the solid-liquid separation step, treatment of the neutralization precipitate slurry, which had conventionally been repeated, increased consumption amount of a neutralizing 22 agent. Firstly, explanation will be given on embodiments of the hydrometallurgical process of a nickel laterite ore of the present invention, with reference to a drawing. Figure 1 is a process chart of smelting showing one example of embodiments of the hydrometallurgical process of a nickel laterite ore relevant to the present invention. In Figure 1, firstly a nickel laterite ore 8 is mixed with water in an ore treatment step 1, and then removal of foreign material and adjustment of ore particle size of the ore are carried out to form an ore slurry 9. In this step or after that, the ore slurry 9 is subjected to a newly added step 21 of (A) for separation and recovery of a silica mineral, a magnesium silicate ore or chromite or the like 22. The ore slurry 9 is subjected to the leaching step 2. Here, the ore slurry 9 is charged into an autoclave or the like for leaching valuable components such as nickel, cobalt, with sulfuric acid, and forming a leaching slurry 10. The leaching slurry 10 is subjected to the solid-liquid separation step 3 using a multi-stage thickener or the like, for separation to a leach solution containing nickel and cobalt 11 and the leach residue slurry 12. Subsequently, the leach solution 11 is subjected to the first neutralization step 4 for separation to the neutralization residue 13 containing mainly ferric iron hydroxide, and a mother liquor containing nickel (1) 14. The mother liquor (1) 14 is subjected to the zinc removal step 5, where a sulfurizing agent 23 is added, for separation to a zinc sulfide precipitate 15 containing zinc sulfide, and a mother liquor (2) 16 for nickel recovery. Then, the mother liquor (2) 16 is subjected to the sulfurization step 6, where a sulfurizing agent is added, for separation to a mixed sulfide 17 containing nickel and cobalt, and a barren liquor 18. It should be noted that, the barren liquor 18 is used as washing water of the leach residue in the solid-liquid separation step 3, and as washing water of the neutralization precipitate slurry 13 produced in the first neutralization step 4. Lastly, the leach residue slurry 12 is subjected to a final neutralization step (1) 7 together with the excess barren liquor 18 for neutralization treatment. In this step or after that, the leach residue slurry 12 is subjected to a newly added step 23 of (B) for separation to the final neutralization residue (1) 19 and the hematite precipitate 24. In addition, the neutralization precipitate slurry 13 is subjected to the final neutralization step (2) 25, which corresponds to a newly added step (C), together with zinc sulfide precipitate 15. The resulting final neutralization residue (2) 26 and a final neutralization residue (1) 19 are stored in a tailing dam 20. Explanation will be given below in still more detail on each step. (1) The ore treatment step and the step of (A) The above ore treatment step is a step for forming the ore slurry by carrying out the removal of foreign material and adjustment of ore particle size. Here, the nickel laterite ore 24 is subjected to sieving with a wet sieve or the like, for separation of a foreign material not dissoluble in the leaching step, an ore having a particle size giving difficulty in pump flow sending, or the like. Here, sieving particle size is usually about 2 mm, preferably 1. 4 mm, and an ore with a particle size equal to or larger than this range is subjected to crushing treatment. Slurry is formed by the ore, which passed this crushing-sieving treatment, and then it is subjected to concentration by sedimentation, for preparation of ore slurry adjusted with solid concentration in the slurry (slurry concentration). It should be noted that the slurry concentration is usually adjusted at about 25 to 45% by mass. The above nickel laterite ore is the mineral such as mainly a limonite ore and a saprolite ore. Nickel content of the above-described laterite ore is usually 0.8 to 2.5% by mass, and nickel is contained as a hydroxide or a hydrated magnesium silicate (magnesium silicate) ore. Iron content is 10 to 50% by mass, and iron is mainly in a trivalent hydroxide form (goethite), however, a part of divalent iron is contained in the hydrated magnesium silicate ore or the like. In addition, silicic acid component is contained in a silica mineral such as quartz, cristobalite (amorphous silica), and the hydrated magnesium silicate ore. In addition, most of chromium is contained as a chromite ore containing iron or magnesium. In addition, magnesium component is contained in the hydrated magnesium silicate ore, as well as in a magnesium silicate ore which contains little un-weathered and high hardness nickel. As described above, the silica mineral, the chromite ore and 25 the magnesium silicate ore in the laterite ore are, what is called, gangue components containing little nickel. Therefore, in an ore slurry produced from the above ore treatment step, there are contained cristobalite, which gives bad influence on sedimentation property generally in increasing solid concentration, chromite and the magnesium silicate ore, which give large influence on wear of equipment such as a pipeline, a pump, together with magnesium, which consumes sulfuric acid in the leaching step, and still more a magnesium silicate mineral having low nickel content. Therefore, it is desirable that the silica mineral such as cristobalite, chromite and the magnesium silicate ore are separated and recovered in advance in the ore treatment step from the ore slurry to be prepared in the ore treatment step. Now, explanation will be given on a distribution state of each of the components in ore particles composing the ore slurry. From EPMA observation of a nickel laterite ore, it is found that a part having high content of chromium, silicon and magnesium has high presence rate as a single phase independent from a part having high content of iron, and in many cases, it has a particle diameter of 20 to 1000 pm. This shows that an ore containing chromium, silicon and magnesium is contained, in a large quantity, in particles of equal to or larger than about 20 pm, and on the other hand, an ore containing nickel and iron is contained, in a large quantity, in particles of equal to or smaller than about 20 pm. 26 Therefore, for effective separation and recovery of the silica mineral, the chromite ore and the magnesium silicate ore from an ore slurry, it is important that the ore after removing a coarse block is converted to slurry, and a nickel laterite ore in this ore slurry is crushed so as to have suitable particle size, and suitable classification particle size is set. It should be noted that, the above-described crushing particle size is preferably equal to or smaller than 2 mm, more preferably equal to or smaller than 1.4 mm, although it is determined in consideration of original object in formation of the ore slurry, and property of the ore. Examples of ore particle size distribution of the above-described ore slurry, and content of each component in each particle size classification are shown in Table 1 and Table 2. It should be noted that, ores used in Table 1 and Table 2 are those having different ore deposit from where they are produced. Table 1 shows one example of ore particle size distribution of the ore slurry obtained by crushing to a particle size of equal to or smaller than 2 mm, and content of each component in each particle size classification. From Table 1, it is understood that chromium, silicon, magnesium and the like are concentrated in each particle size classification of a coarse part of equal to or larger than 75 pm, and in particular, silicon, magnesium and the like are concentrated in each particle size classification of a coarse part of equal to or larger than 355 pm. 27 Table 1 Particle Chemical composition size Distribution rate (% by mass) (pm) Fe Cr Si Mg -2000to 0.9 36 2 14 6 +1400 to -40 to 1.8 37 3 13 6 +850 -850 to 2.7 33 3 12 5 +355____ -355 to +75 5.3 42 5 9 3 -75 89.3 47 3 6 2 Average 100 45.7 2.7 6.6 2 In addition, Table 2 shows one example of ore particle size distribution of the ore slurry obtained by crushing to a particle size of equal to or smaller than 1.4 mm, and content of each component in each particle size classification. From Table 2, it is understood that chromium, silicon, magnesium and the like are concentrated in each particle size classification of a coarse part of equal to or larger than 75 pm, and in particular, silicon, magnesium and the like are concentrated in each particle size classification of a coarse part of equal to or larger than 100 pm. In addition, in Table 3, average analysis values are shown, when each particle size classification in Table 2 is summed up every predetermined particle size range. Table 2 Particle Distribution Chemical composition Calculated value size rate (% by mass) (% by mass) (pm) (% by mass) Ni Cr Fe Si M9 Cr 2 0 3 SiO 2 -1400 to 0.8 1.0 1.5 24.6 10.8 9.3 2.2 23.0 +1190 o -1191 to 0.1 0.6 5.6 30.9 8.0 5.0 8.2 17.1 +10 00 ______ ___ -1000 to 0.2 0.5 11.2 30.5 4.2 4.1 16.4 9.0 28 +850 -850 to 0.3 0.6 11.8 28.9 5.3 5.1 17.2 11.3 +590 o -590 to 0.5 0.4 19.3 27.6 2.6 4.4 28.2 5.6 +425 -425 to 2.3 0.5 20.8 29.3 1.5 3.8 30.4 3.3 +210 ______ _ -200 to 2.7 0.4 20.2 33.8 0.9 3.2 29.5 2.0 +100 o -100 to 0.9 0.8 10.5 44.2 1.2 1.9 15.3 2.5 +75 ___ -75 to +37 8.8 1.1 4.2 49.8 1.4 1.1 6.2 3.1 -37 83.4 1.2 1.4 51.4 1.4 0.4 2.0 3.0 Average 100 1.1 2.8 49.7 1.4 0.7 4.1 3.0 29 Table 3 Particle Amount Ni Cr Fe Si Mg Size range (% by (% by (% by (% by (% by (% by (pm) mass) mass) mass) mass) mass) mass) A +100 to -850 6 0.5 20.0 31.2 1.5 3.6 B +75 to -1000 7 0.5 18.5 33.0 1.5 3.4 C +37 to -850 16 0.8 10.5 42.5 1.5 2.1 D +37 to -1000 16 0.8 10.5 42.3 1.5 2.1 E -75 92 1.2 1.6 51.3 1.4 0.5 F -100 93 1.2 1.7 51.2 1.4 0.5 G +1000 to 1 1.0 1.9 25.1 10.6 9.0 -1400 H +590 to 1 0.8 5.3 26.7 8.6 7.5 -1400 T 1 .1 __I From the above results, by utilization of the fact that particles containing chromium, silicon and magnesium in high content are coarser particles than particles containing iron in high content, the coarse particle part containing chromium, silicon and magnesium in high content, and a fine particle part containing nickel and iron in high content, are separated by a selection means such as a classification method. Here, the coarse particle part is discharged outside a system and purified in the separate step for recovering the chromium or the like as a resource. In addition, in the above coarse particle part, because particles containing silicon and magnesium in high content, are distributed more in the coarse particle side than particles containing chromium in high content, it is possible to classify these by the predetermined particle size, and separate the particles containing silicon and magnesium in high content, so as to recover a concentrate with enhanced chromium content. 30 The step of the above (A) is a step for separation and recovery of at least one kind selected from a silica mineral, chromite or a magnesium silicate ore in ore slurry produced from the above ore treatment step. It should be noted that, the step of (A) may be carried out by being included in the above ore treatment step, or in the subsequent step thereto. A method for step of the above (A) is not especially limited, and methods using various physical separation means for separation of a silica mineral, chromite or a magnesium silicate ore from the ore slurry, may be applied, and among these, physical separation methods by wet process such as sieving classification, sedimentation classification, centrifugal classification, which enables to separate and recover these all together from analysis of a distribution state of each component in the ore particles composing the ore slurry, are simple and convenient as a rough separation means, and thus preferable. For example, there is adopted a method for subjecting the ore slurry to physical separation methods by sieving classification or centrifugal classification, for recovering thus classified coarse particle part as a concentrate of a silica mineral, chromite or a magnesium silicate ore. That is, in the above-classification, gangue components such as a silica mineral, chromite or a magnesium silicate ore are distributed in the classified coarse particle part, and on the other hand, goethite and a hydrated magnesium silicate ore containing a nickel are distributed in the classified fine particle part. 31 Classification particle size in the above classification is not especially limited, however, it is selected from a range of preferably 20 to 850 pm, more preferably 20 to 300 pm and particularly preferably 75 to 100 pm, in consideration of property of a raw material ore and nickel yield to the fine particle part, or the like. That is, lower limit of the classification point industrially applicable is about 20 pm, and further, the above-described classification particle size of below 20 pm provides insufficient concentration of a silica mineral, chromite or a magnesium silicate ore to the coarse particle part, as well as provides nickel loss in the ore slurry to be used in the leaching step. On the other hand, the above-described classification particle size of over 850 pm provides insufficient removal of a silica mineral, chromite or a magnesium silicate ore in the fine particle part. In addition, in recovery of a concentrate with enhanced chromium content, from the above coarse particle part of a silica mineral, chromite or a magnesium silicate ore, two particle sizes selected from a range of equal to or larger than 850 pm and a range of 20 to 850 pm, are used, as the above-described classification particle size. Here, firstly, the coarse particle part classified by the particle size of the former range is recovered as a concentrate of a silica mineral or a magnesium silicate ore, and then the coarse particle part classified by the particle size of the latter range is recovered as a concentrate of chromite having reduced entrainment of a silica mineral or a magnesium silicate ore. Alternatively, also it can be carried out that firstly the coarse particle part classified 32 by the particle size of the latter range, is obtained, and then, the coarse particle part classified by the particle size of the former range is separated. That is, a concentrate of a silica mineral or a magnesium silicate ore is separated by selection of suitable particle size between 850 pm and a crushing particle size of the ore as classification particle size. On the other hand, a concentrate of chromium is efficiently separated by selection of suitable particle size, within a range of preferably 20 to 850 pm, more preferably 20 to 300 pm and particularly preferably 75 to 100 pm, as classification particle size. (2) A leaching step The above leaching step is a step for forming a leaching slurry composed of leach residue and leach solution, by the addition of sulfuric acid to the ore slurry obtained in the above ore treatment step and the step of (A), and by carrying out stirring treatment under condition of a temperature of 220 to 280 0 C. In this step, a pre-heater, an autoclave and a flash tank are used as main equipment. In the leaching step, leaching as sulfates such as nickel, cobalt, and fixation as hematite of leached iron sulfate are performed, by a leaching reaction and a high-temperature thermal hydrolysis reaction represented by the following formulae (1) to (5) . However, because of incomplete proceeding of fixation of an iron ion, it is usual that nickel, cobalt or the like, as well as divalent and ferric iron ions are contained in a liquid part of the resulting leaching slurry. 33 [leach reaction]

MO+H

2

SO

4 -+ MSO 4

+H

2 0 --- (1) (wherein, M represents Ni, Co, Fe, Zn, Cu, Mg, Cr, Mn or the like.) 2Fe(OH) 3 +3H 2

SO

4 - Fe 2

(SO

4

)

3 +6H 2 0 --- (2) FeO+H 2

SO

4 -- FeSO 4

+H

2 0 --- (3) [high-temperature thermal hydrolysis reaction] 2FeSO 4

+H

2

SO

4 +1/20 2 - Fe 2

(SO

4

)

3

+H

2 0 --- (4) Fe 2 (SO4) 3 +3H 2 0 -+ Fe 2 0 3 +3H 2

SO

4 --- (5) Temperature to be used in the above leaching step is 220 to 280 0 C, and preferably 240 to 270'C. That is, iron is fixed as hematite, by performance of the reaction in this temperature range. In the temperature below 220*C, iron dissolves and remains in the reaction solution, due to low speed of the high-temperature thermal hydrolysis reaction, resulting in increase in the solution purification load for iron removal, which makes it very difficult to separate the iron from nickel. On the other hand, the temperature over 280*C is not suitable, because not only selection of a material of a reactor to be used for High Pressure Acid Leach is difficult but also steam cost for raising temperature increases, although the high-temperature thermal hydrolysis reaction itself is accelerated. The addition amount of sulfuric acid in the above leaching step is not especially limited, and a little excess amount than 34 amount of stoichiometry required to leach iron in an ore and convert it to hematite is used, for example, the amount of 300 to 400 kg per ton of the ore. That is , the addition amount of sulfuric acid over 400 kg per one ton of the ore, is not preferable, due to increased cost of the sulfuric acid and cost of a neutralizing agent to be used in the later step. Use amount of the above sulfuric acid is not especially limited, however, it is preferably 25 to 50 g/L, more preferably 35 to 45 g/L, as concentration of free sulfuric acid at the time of leaching completion. In this way, true density of the leach residue can be increased, the leach residue with true density can be produced stably, and solid-liquid separation performance of slurry can be enhanced, therefore simplification of equipment of the solid-liquid separation step, which is the next step, can be performed. That is, the concentration below 25 g/L provides insufficient sedimentation concentration of a solid part in sedimentation of slurry containing the leach residue, and makes a floating solid part remained in the supernatant. This is because reaction rate of thermal hydrolysis at high temperature becomes slow and dehydration of iron hydroxide proceeds insufficiently, and hematite with low true density is formed. On the other hand, the concentration over 50 g/L requires enhancement of durability of leaching equipment, and in addition, extremely increases use amount of a neutralizing agent to be required in neutralization of an acid, and is thus disadvantageous in view of cost. (3) A solid-liquid separation step 35 The above solid-liquid separation step is a step for obtaining a leach solution containing a nickel and a cobalt, and a leach residue slurry, by multi-stage washing of the leaching slurry formed in the above leaching step. By this step, nickel, which is adhered onto the leach residue and disposed, is recovered in the leach solution. (4) A first neutralization step The above neutralization step is a step for forming a neutralization precipitate slurry containing a ferric iron, and a mother liquor for nickel recovery, by the addition of calcium carbonate into the leach solution obtained in the above-described leaching step, under prevention of oxidation thereof, so that pH becomes equal to or lower than 4, preferably 3.2 to 3.8. By this step, the excess acid used in the above leaching step is neutralized, as well as removal of a ferric iron ion remained in a solution is carried out. That is, pH over 4 increases generation of nickel hydroxide. The resulting neutralization precipitate slurry is sent to the final neutralization step (2), which corresponds to the step of newly added (C), for further treatment. (5) A zinc removal step The above zinc removal step is a step for forming a zinc sulfide precipitate slurry and a mother liquor for nickel and cobalt recovery, by blowing a hydrogen sulfide gas into the above mother liquor in advance to the separation step of nickel and cobalt as sulfides. This is for selective removal of zinc, by prevention of sulfurization reaction rate by creating the weak 36 condition in the sulfurization reaction, and prevention of co-precipitation of coexisting nickel having higher concentration as compared with zinc. The resulting zinc sulfide precipitate slurry is sent to the final neutralization step (2), similarly as the neutralization precipitate slurry obtained in the above, for further treatment. (6) A sulfurization step The above-described sulfurization step is a step for forming a mixed sulfide containing a nickel and a cobalt, and a barren liquor, by blowing a hydrogen sulfide into the mother liquor for nickel and cobalt recovery obtained in the above zinc removal step. Here, the resulting barren liquor has a pH of about 1 to 3, and contains impurities such as iron, magnesium, manganese contained in a non-sulfurized state, as well as trace amount of nickel and cobalt, as recovery loss, therefore, it is used as washing water of the leach residue in the solid-liquid separation step, and as washing water of the neutralization residue produced in the first neutralization step. (7) A final neutralization step (1) and the step of (B) The above final neutralization step (1) is a step for obtaining a final neutralization residue (1) containing the leach residue, by the addition of an excess barren liquor into the above leach residue slurry, and by the addition of lime stone slurry and slaked lime slurry thereto, by adjustment of pH to about 8 to 9 and by precipitation of the metal ions in liquid. 37 The above leach residue contains hematite as a main component, and contains gangue component such as quartz, chromite, a magnesium silicate ore, which is not leached in the above leaching step. Here, explanation will be given on a distribution state of each of the components in the ore particles composing the above-described leach residue slurry. Firstly, Table 4 shows one example of ore particle size distribution and content of each component in each particle size classification, of the leach residue obtained in leaching of the ore slurry (refer to Table 1) obtained in advance by crushing to a particle size of equal to or smaller than about 2 mm. Table 4 Particle Chemical composition size Distribution rate(%bmas size (% by mass)(%bmas (pm) Fe Cr Si Mg -2000 to 0 +1400 -1400 to +850 0 - - - -850 to +355 0.1 28 2 24 0 -355 to +75 0.7 26 7 25 1 -75 99.1 45 2 8 1 Average 100 44.6 2.5 7.8 1 From Table 4, it is understood that iron is concentrated in the fine particle part of equal to or smaller than 75 pm, and silicon is separated in this part. It should be noted that, analysis of the leach residue was carried out on a sample from which adhered sulfuric acid was removed by washing of the leach residue slurry with water. 38 Next, by using a leach residue (iron content: 47.6% by mass, chromium content: 2.6% by mass, silicon content: 7.1% by mass) different from the above-described, content or distribution rate of iron, chromium and silicon by each particle size was determined. Figures 3 and 4 show the relation between particle size and content or distribution rate of iron, chromium and silicon. From these Figures 3 and 4, it is understood that the finer particle size has the higher iron content, and the higher distribution rate to the fine particle as compared with chromium and silicon. From the above results, by utilization of the fact that particles containing an iron in high content are finer particles than particles containing a chromium, a silicon and the like in high content, the coarse particle part containing a chromium, a silicon and the like in high content is separated by a selection means such as a classification method, and discharged outside a system, and hematite can be recovered as a resource. The step of the above (B) is a step for separation and recovery, by a physical separation method, of hematite particles in leach residue produced from the above solid-liquid separation step. It should be noted that, the step of (B) may be carried out by being included in the above final neutralization step (1), or in the subsequent step thereto. It should be noted that, introduction of the step of (B) before neutralization is desirable to avoid entrainment of gypsum to be described later, however, there is a problem of requiring a large quantity of 39 water for washing to remove adhered sulfuric acid. A method for step of the above (B) is not especially limited, and there may be applied the methods using physical separation means by various wet processes such as sieving classification, sedimentation classification, centrifugal classification, magnetic separation method, which enable to separate hematite from the ore slurry. For example, there is adopted a method for subjecting a leach residue slurry or the final neutralization residue slurry containing it to physical separation method by sieving classification or centrifugal classification, for recovering thus classified fine particle part as a concentrate of hematite. That is, in the above-described classification, hematite is distributed in the classified fine particle part, on the other hand, gangue components is distributed in the classified coarse particle part. Classification particle size in the above classification is not especially limited, however, it is preferably selected from a range of 20 to 100 pm. Here the classification particle size should be determined in consideration of iron content of hematite precipitate and yield or the like, however, the classification particle size below 20 pm decreases amount of the leach residue of this particle size classification, and thus deteriorates efficiency in view of iron recovery. On the other hand, the classification particle size over 100 pm provides insufficient concentration of hematite in the fine particle part, that is, increase in iron content. 40 Here, explanation will be given on an analysis of distribution state of each of the components in the ore particles composing the above-described final neutralization residue. Table 5 shows one example of ore particle size distribution and content of each component in each particle size classification, of the final neutralization residue obtained in leaching and subjecting to neutralization treatment of the ore slurry (refer to Table 4) obtained by crushing to a particle size of equal to or smaller than about 2 mm. Table 5 Particle Distribution rate Chemical composition size (%by mass) (% by mass) (pm) Fe Cr Si Ca -2000 to 0.3 - - - +1400 -1400 to 0.8 12 1 36 9 +850 -850 to +355 1.5 11 1 23 14 -355 to +75 14.6 9 1 6 19 -75 82.9 41 2 8 3 Average 100 35.7 2 8.1 5.9 From Table 5, it is understood that in the fine particle part of equal to or smaller than 75 pm, iron is concentrated and content of silicon, calcium or the like is decreased. That is, it is understood that, in this part, a gangue component and hematite are separated. It should be noted that, presence of calcium is brought about by generation and entrainment of gypsum in neutralization in the final neutralization step (1), and it is understood that this gypsum is distributed in the fine particle size part. 41 From the above results, by utilization of the fact that hematite particles are finer than other leach residue components and gypsum generated by a neutralization reaction, in separation and recovery of hematite from the final neutralization residue slurry containing the leach residue slurry as well, physical separation means by various wet processes, such as sieving classification, sedimentation classification, centrifugal classification may be applied, similarly as in the case of the leach residue slurry, which enables to separate to the fine particle size part containing a hematite, and the coarse particle size part containing other leach residue components and the gypsum. Here, the fine particle part is discharged outside a system and purified in the separate step for recovering a hematite as an iron resource. It should be noted that, the coarse particle part is stored in a tailing dam as a final neutralization residue (1). In addition, as a method of step of the above (B) , a magnetic selection method by utilization of magnetic separation may be applied, and in particular, as a method for enhancing the separation of the above-described gypsum, combined use with the above classification method may be carried out. That is, the magnetic selection method utilizes the fact that hematite is a weak magnetic substance, and on the other hand, gypsum is a non-magnetic substance, and this property difference is utilized in separation. It should be noted that, in order to prevent basically 42 entrainment of calcium to a hematite precipitate to be recovered, it is effective to remove adhered sulfuric acid so as to decrease sulfur content to equal to or lower than about 1% by mass, by adoption of a method for washing the leach residue slurry with water having a low calcium concentration, before treatment in the final neutralization step (1), however, there is a problem that water having a low calcium concentration cannot always be secured in a large quantity, depending on locational condition. (8) A final neutralization step (2) The above final neutralization step (2) is a step for obtaining a final neutralization residue (2), by the addition of lime stone slurry and slaked lime slurry to the neutralization precipitate slurry obtained in the above neutralization step or, if necessary, addition thereto of the zinc sulfide precipitate slurry obtained in the above zinc removal step, so as to adjust pH to about 8 to 9, for sedimentation of metal ions in a solution as a neutralization precipitate. It should be noted that, the resulting final neutralization residue (2) is stored in a tailing dam. It should be noted that, conventionally the neutralization precipitate slurry obtained in the above neutralization step has been sent to the solid-liquid separation step, if necessary, however, it increased consumption amount of a neutralizing agent, as well as increased amount of the leach residue. As in the method of the present invention, in separation and recovery of hematite from the leach residue, in order to increase hematite content in the leach residue, it is preferable to treat the 43 neutralization precipitate slurry in a separate system. EXAMPLES Explanation will be given below in still more detail on the present invention, with reference to Examples of the present invention, however, the present invention should not be limited to these Examples. It should be noted that, analysis of metals used in Examples was carried out by a fluorescent X ray analysis method or an ICP emission spectrometry. (Example 1) As the above-described step (A), a silica mineral, a chromite and a magnesium silicate ore were concentrated and separated from an ore slurry by centrifugal classification. As a classification apparatus, a Knelson concentrator (manufactured by Knelson Engineering and Manufacturing Division) having a centrifugal force of maximal 100 G was used to carry out classification of the ore slurry shown in the above-described Table 1. Here, the slurry concentration was set at 15% by mass, and solution temperature was set at normal temperature. Obtained results are shown in Table 6. 44 0) '-4 -H w C) 0 0~ C441 0 41 o0 4 C) Q() r.. v- COG 41) 0 C000 )0 41) '-.4Y) (Y 4M 0. 000 0 U 41 c* 4-, 41 v-0 E-1- It is shown from Table 6 that, by the centrifugal classification, content of chromium, silicon and magnesium in the resulting coarse particle part increased up to 5. 3% by mass relative to 2.7% by mass in the feeding, 12.5% by mass relative to 6.6% by mass in the feeding, as well as 4.6% by mass relative to 2.0% by mass in the feeding, respectively, and on the other hand, content of iron decreased down to 34.4% by mass relative to 45.7% by mass in the feeding. From the above, it is understood that the silica mineral, chromite and the magnesium silicate ore were concentrated and separated in the coarse particle part by classification of the ore slurry. (Example 2) As step of the above (B), hematite was concentrated and separated from a leach residue by centrifugal classification. Using the ore slurry shown in the above-described Table 1, sulfuric acid with a concentration of 45 g/L was added to the slurry with a concentration of 30% by mass, which was charged into an autoclave equipped with a stirrer, to carry out leaching for 60 minutes after a predetermined leaching temperature of 245*C was attained. Then, after completion of the leaching, leach residue and leach solution were separated by filtration, and the resulting leach residue (refer to the above-described Table 4) was classified using a similar classification apparatus as one used in Example 1. It should be noted that, composition of the leach solution was Ni:7.1 g/L, Co:0.6 g/L and Fe:5 g/L. 46 Obtained results are shown in Table 7. 47 (U 0. 0 ., w U ' 4Jd 0~ s 0d CD 0C 0C s 0d CD C 00 0) . 0. 0 0 0 0 o) U 5 U) 0 0 CD 0) C 0)..(J *0 Y oY CD,) q (U) o\ 0

C..

It is shown from Table 7 that content of iron in the resulting fine particle part increased up to 52.4% by mass relative to 44. 6% by mass in the feeding, and on the other hand, contents of chromium, silicon and magnesium decreased down to 2.2% by mass relative to 2.52% by mass in the feeding, down to 6.1% by mass relative to 7.8% by mass in the feeding, down to 0.97% by mass relative to 1.33% by mass in the feeding, respectively. From the above, it is understood that hematite is concentrated and separated in the fine particle part by classification of the leach residue. (Example 3) As step of the above (B), hematite was concentrated and separated from a final neutralization residue by centrifugal classification. Slaked lime slurry with a concentration of 25% by mass was added, as a neutralizing agent, into the above leach residue (refer to the above-described Table 4) for neutralization so as to attain a pH of 8.5 at 60 0 C. Still more, the resulting final neutralization residue (refer to the above Table 5) was classified using a similar classification apparatus as one used in Example 1. Obtained results are shown in Table 8. 49 0 0-I r V) 0 L) 4-) 0 "0) 0 0 r 4-' 4-' 0D C) 0 0 C) CLO *~~~r- a r 0Oi -i 00 u Hn -H 41 0. 00m 00)0 C)C :r 0) 00 1-, U) u 4 C. . t.0

'U'

-A a) CU) C0) 4J U E a) It is shown from Table 8 that content of iron in the resulting fine particle part increased up to 40.2% by mass relative to 35.7% by mass in the feeding, by centrifugal separation. From the above, it is understood that hematite is concentrated and separated in the fine particle part by classification of the final neutralization residue slurry. (Example 4) As step of the above (B), hematite was concentrated and separated from the final neutralization residue by magnetic selective separation. Using the final neutralization residue slurry (refer to the above Table 5), magnetic selection was carried out by using a high gradient magnetic separator (HGMS). It should be noted that, final neutralization condition was similar to that in Example 3. Obtained results are shown in Table 9. Table 9 Chemical composition (% by mass) Ore Non-magnetized Magnetized substance supplied substance Amount 51 49 (% by mass) Ni 0.08 0.08 0.08 Fe 35.7 48.5 41.0 Mg 1.42 - 1.40 Si 8.1 <0.1 8.1 Cr 1.8 2.6 0.8 Ca 5.9 0.6 5.3 It is shown from Table 9 that content of iron in the 51 resulting magnetized substance increased up to 48.5% by mass relative to 35.7% by mass in the feeding, and on the other hand, content of calcium decreased down to 0.6% by mass relative to 5.9% by mass in the feeding. Recovery rate of slurry here was 51%. From this, it is understood that concentration of hematite to the magnetized substance and decrease in gypsum proceed. (Example 5) As step of the above (B), hematite was concentrated and separated from the leach residue by sieving separation. Using the leach residue (iron content: 47.6% by mass, chromium content: 2.6% by mass, and silicon content: 7.1% by mass) shown in the above Figures 3 and 4, each wet-type sieving were carried out using sieves with a mesh opening of 20 pm and 75 pm, to determine contents of chromium and silicon of a fine particle part, and distribution rate thereof. Results obtained are shown in Table 10. 52 0 -H .4) 00 0 C)* 40 .0) -H0 S 00 M00 0 C-) 0 u 0 -1 N~ C)) LOL 4) From Table 10, it is understood that a hematite concentrate (iron content: 50.6 and 53.2% by mass) having low contents of chromium and silicon in the fine particle part, can be obtained, by wet-type sieving where classification particle size is set at a range of 20 pm and 75 pm. (Example 6) As step of the above (B), hematite was concentrated and separated from the leach residue by centrifugal classification. By using the leach residues obtained through the above Example 1 to Example 3, centrifugal classification was carried out. However, there was not carried out the separation of chromium and silica by classification before the leaching in Example 1, in order to confirm separation effect of chromium and silica by classification after the leach residue of the present invention. For the centrifugal separation, a hydro-cyclone (an SP-50 model, manufactured by Japan Separation Co., Ltd.) having a rated classification point of 50 pm was used. Here, by supplying an under-flow part of the first stage of the cyclone, where the leach residue slurry was supplied, into the second stage of the cyclone, crude coarse particles (under-flow) and crude fine particles (over-flow) were obtained. In addition, by supplying over-flow part of the first stage of the cyclone into the third stage of the cyclone, fine crude particles (under-flow) and sufficiently fine particles (over-flow) were obtained. After that, distribution rates and compositions of these products were determined. Results are shown in Table 11. 54 r- (N I Y)q3 U) x. 0 C) (N C). CD CJIC 0 N (N w Lo w 0nL y C-' 10 0- tr, HH u 0U 10 (N u UW 41 4 44 (N CN: D 10- 14 1 0 1 From Table 11, it is understood that sufficiently fine particle with an iron content of 61% by mass, showing a physical distribution rate of 70%, can be obtained. (Example 7) As the above (A), chromite was concentrated and separated from the ore slurry by sieving classification. By using the ore slurry shown in the above Table 2, contents of nickel, iron, chromium, silicon and magnesium, and distribution rate thereof were determined for particle size range A: 100 to 850 pm, particle size range B: 75 to 1000 pm, particle size range C: 37 to 850 pm, particle size range D: 37 to 1000 pm, and particle size range F: equal to or smaller than 100 pm, in the case where a wet-type sieving was carried out using sieves with each mesh opening of 37 pm, 75 pm, 100 pm, 850 pm, and 1000 pm. From the above Table 3, it is understood that a concentrate of chromite with a chromium content of equal to or more than 10% by mass can be obtained for the particle size range C: 37 to 850 pm, and particle size range D: 37 to 1000 pm. In addition, it is understood that, for the particle size range G: equal to or larger than 1000 pm, silicon content and magnesium content increase to 10.6% by mass and 9% by mass, respectively, and a silica mineral and a magnesium silicate ore are concentrated and separated into a coarse particle part .In particular, for the particle size range A: 100 to 850 pm and the particle size range B: 75 to 1000 pm, a concentrate of chromium with a chromium content of about 20% by mass can be obtained. Still more, it is understood that nickel content 56 in the concentrate is 0.5% by mass and thus nickel loss can be prevented to the minimum, and for the particle size range F: equal to or smaller than 100 pm, chromium content reduces down to 1.7% by mass, and on the other hand, iron and nickel are concentrated. (Example 8 and Reference Example 1) According to a process chart of smelting, shown in Figure. 1, a hydrometallurgical process of a nickel laterite ore containing the steps of (A), (B) and (C) was carried out to separate chromite, a silica mineral and a magnesium silicate ore and concentration and separation of hematite. Firstly, as the step of (A), by using the ore slurry shown in the above Table 2, it was subjected to wet-sieving classification with a sieve having a mesh opening of 75 pm, for separation of chromite, a silica mineral and a magnesium silicate ore as a coarse particle part. Then as the leaching step, by using the resulting fine particle part, sulfuric acid with a concentration of 45 g/L was added to the slurry with a concentration of 30% by mass, which was charged into an autoclave equipped with a stirrer, to carry out leaching for 60 minutes after a leaching temperature of 245'C, and the leach residue and leach solution were obtained. Subsequently, as the final neutralization step, slaked lime slurry with a concentration of 25% by mass was added as a neutralizing agent, into the resulting leach residue slurry, for neutralization so as to attain a pH of 8.5 at 60*C, and lastly, as the step of (B), by using the resulting neutralization residue, it was classified to a fine particle part concentrated with hematite and a coarse 57 particle part concentrated with gypsum, by a hydro-cyclone (a NHC-1 model, manufactured by Japan Chemical Engineering & Machinery Co., Ltd.) having a centrifugal force of maximal 24000 G, and contents of iron, calcium, sulfur, chromium, silicon and magnesium in the fine particle part were determined (Example 8) . Results are shown in Table 12. It should be noted that, as the step of (C), neutralization precipitate slurry obtained from the first neutralization step of the above-described leach solution, was subjected to final neutralization treatment separately from the above-described leach residue. On the other hand, similarly as in Example 8, except that the above leach solution was neutralized, under maintaining at 60*C, by the addition of 25% by mass slaked lime slurry, as a neutralizing agent, so that pH becomes 2.5, to obtain neutralization precipitate slurry containing ferric iron hydroxide, and by mixing this with the leach residue, contents of iron, calcium, sulfur, chromium, silicon and magnesium of the fine particle part were determined (Reference Example 1). Results are shown in Table 12. Table 12 Chemical composition(% by mass) Fe Ca S Cr Si Mg Example 8 57 1.6 2.4 1.6 1.5 0.10 Reference Example 1 48 4.2 4.8 1.5 1.2 0.15 From Table 12, it is understood that, in Example 8, iron content of the fine particle part enhances to 57%, and at the same time, calcium content decreases to 1.6% by mass, and a concentrate of hematite with quality usable as a raw material 58 of iron and steel can be obtained. On the other hand, in Reference Example 1, it is understood that separation of iron and calcium is insufficient. As is clear from the above, the hydrometallurgical process of a nickel laterite ore of the present invention is suitable as a smelting based on High Pressure Acid Leach to be utilized in the field of a hydrometallurgical process of a nickel laterite ore. 59

Claims (11)

1. A hydrometallurgical process to recover nickel and cobalt from a nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the process characterized by further including at least one step selected from the following steps (A) to (C); (A) step for separation and recovery, by a physical separation method, of particles including at least one kind selected from the group consisting of a silica mineral, chromite or a magnesium silicate ore in an ore slurry produced from the ore treatment step; (B) step for separation and recovery, by a physical separation method, of hematite particles in a leach residue slurry produced from the solid-liquid separation step; and (C) step for subjecting a neutralization precipitate slurry produced from the first neutralization step to the final neutralization treatment separately from the leach residue slurry produced from the solid-liquid separation step.

2. The hydrometallurgical process according to claim 1, characterized in that, in step (C), zinc sulfide precipitate slurry produced from the zinc removal step is subjected to the final neutralization treatment together with the neutralization precipitate slurry at the same time.

3. The hydrometallurgical process according to claim 1 or 2, 60 characterized in that: - the ore treatment step is a step for forming an ore slurry by carrying out the removal of foreign material and the adjustment of ore particle size of a raw material ore mined; - the leaching step is a step for forming a leaching slurry composed leach residue and leach solution, by the addition of sulfuric acid to said ore slurry and by carrying out stirring treatment under high temperature and high pressure; - the solid-liquid separation step is a step for obtaining a leach solution including a nickel and a cobalt, and a leach residue slurry, by multi-stage washing of said leaching slurry; - the first neutralization step is a step for forming a neutralization precipitate slurry including ferric iron, and a mother liquor for nickel recovery, by the addition of calcium carbonate into said leach solution; - the zinc removal step is a step for forming a zinc sulfide precipitate slurry, and a mother liquor for nickel and cobalt recovery, by blowing a hydrogen sulfide gas into said mother liquor; - the sulfurization step is a step for forming a mixed sulfide including a nickel and a cobalt, and a barren liquor, by blowing a hydrogen sulfide into said mother liquor for nickel and cobalt recovery; and - the final neutralization step is a step for obtaining a final neutralization residue, by the addition of an excess barren liquor into said leach residue slurry, and adjusting pH to about 8 to 9. 61

4. The hydrometallurgical process according to claim 3, characterized in that, in the ore treatment step, ore particle size adjustment is subjected to the sieve treatment at a particle size of equal to or smaller than 2 mm.

5. The hydrometallurgical process according to any one of claims 1 to 4, characterized in that, in step (A), the ore slurry is subjected to a physical separation method by sieve classification or centrifugal classification, wherein the coarse particle part classified is recovered as a concentrate of silica mineral, chromite or a magnesium silicate ore.

6. The hydrometallurgical process according to claim 5, characterized in that the classification particle size is selected from a range of 20 to 850 pm.

7. The hydrometallurgical process according to claim 5, characterized in that the classification particle size is two particle sizes selected from a range of equal to or larger than 850 pm and a range of 20 to 850 pm, wherein firstly a coarse particle part classified at the particle size of the former range is recovered as a concentrate of a silica mineral or a magnesium silicate ore, and next a coarse particle part classified at the particle size of the latter range is recovered as a concentrate of chromite.

8. The hydrometallurgical process according to any one of claims 1 to 4, characterized in that, in step (B), the above-described 62 leach residue slurry or the final neutralization residue slurry including it is subjected to a physical separation method by sieve classification or centrifugal classification, wherein the fine particle part classified is recovered as a concentrate of hematite.

9. The hydrometallurgical process according to claim 8, characterized in that the classification particle size is selected from a range of 20 to 100 pm.

10. The hydrometallurgical process according to any one of claims 1 to 4, characterized in that, in step (B), the above-described leach residue slurry or the final neutralization residue slurry including it is subjected to a physical separation method by magnetic separation, wherein a magnetized substance is recovered as a concentrate of hematite.

11. A hydrometallurgical process to recover nickel and cobalt from a nickel laterite ore by a High Pressure Acid Leach including an ore treatment step, a leaching step, a solid-liquid separation step, a first neutralization step, a zinc removal step, a sulfurization step, and a final neutralization step, the process characterized by further including at least one step selected from steps (A) to (C) substantially as described herein with reference to the accompanying Examples and Figures, excluding Figure 2. 63