Method for pretreating nickel oxide ore

Abstract

To provide a pretreatment method capable of stabilizing the slurry concentration of a high-concentration ore slurry after condensation by a thickener.SOLUTION: A pretreatment method for a nickel oxide ore used as a raw material for producing a nickel cobalt mixed sulfide through a hydrometallurgical process comprises: a classification step of executing wet-type classification at a screen having a prescribed opening by adding water to a plurality of kinds of nickel oxide ores; and a condensation step of depositing and condensing a low-concentration ore slurry including a nickel oxide ore recovered on the underside of the screen to acquire a high-concentration ore slurry. When the plurality of kinds of nickel oxide ores include one of iron grade 50 mass%, an anionic coagulant and a nonionic coagulant are used as coagulants to be added to the low-concentration ore slurry.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a method for pretreating nickel oxide ore used as a raw material ore in nickel hydrometallurgy, and in particular to a pretreatment method comprising a classification step of screening the nickel oxide ore using a wet sieve, and a concentration step of introducing the low-concentration ore slurry obtained in the classification step into a thickener together with a flocculant to settle and concentrate the ore. [Background technology]

[0002] In the field of nickel hydrometallurgy using nickel oxide ore as a raw material, a technology has been put into practical use for efficiently recovering valuable metals such as nickel from low-grade ore by high-pressure acid leaching (HPAL), which involves acid leaching with sulfuric acid under high temperature and pressure. In the HPAL process, in the ore pretreatment step, nickel oxide ore is screened using a wet sieve while water is being introduced to prepare an ore slurry with a uniform particle size. This ore slurry has a too low slurry concentration as it is, making the acid leaching process inefficient. Therefore, as disclosed in Patent Documents 1 and 2, for example, the ore slurry is generally concentrated by adding a flocculant and then introducing it into a thickener.

[0003] However, when nickel oxide ore is prepared in the form of an ore slurry as described above and introduced into a thickener, the properties that affect its settling property often differ depending on the mining site, and it may be necessary to adjust the operating conditions of the thickener accordingly. For example, the properties of nickel oxide ore that affect the settling property include ore components and electric charge. If it is possible to collect representative samples from the mining area to be mined in advance, it is possible to determine, to some extent, the optimum operating conditions of the thickener by measuring these properties in advance. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2020-033602 [Patent Document 2] Japanese Patent Application Publication No. 2019-044208 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the conventional ore pretreatment process, preparation was carried out using a single type of flocculant, which made it impossible to respond to variations in the properties of the ore slurry, and this could result in a significant decrease in the slurry concentration of the concentrated slurry discharged from the bottom of the thickener. In this case, the amount of nickel oxide ore processed per unit time in the subsequent acid leaching process decreases, resulting in a significant decrease in the production efficiency of the nickel hydrometallurgy plant.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a pretreatment method that can stabilize the slurry concentration of a high-concentration ore slurry after concentration in a thickener, even when a plurality of types of nickel oxide ores having different properties that affect the settling properties when an ore slurry prepared by adding water to classified nickel oxide ore is supplied to the thickener is used as raw materials. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the inventors have discovered that by understanding in advance the properties that affect the settling properties of an ore slurry prepared by adding water to classified nickel oxide ore in a thickener, and determining the type and amount of flocculant to be added based on this understanding, it is possible to stabilize the slurry concentration of the high-concentration ore slurry after concentration in the thickener, which led to the completion of the present invention.

[0008] That is, the method for pretreating nickel oxide ore according to the present invention is a method for pretreating nickel oxide ore used as a raw material when producing nickel-cobalt mixed sulfides by a hydrometallurgical method, and comprises a classification step of adding water to a plurality of types of nickel oxide ore and wet classifying them using a screen with a predetermined mesh size, and a concentration step of obtaining a high-concentration ore slurry by settling and concentrating a low-concentration ore slurry containing nickel oxide ore recovered on the underside of the screen, and when the plurality of types of nickel oxide ore contains one with an iron content of 50 mass % or more, For each of the representative samples taken from the plurality of types of nickel oxide ores, a nonionic flocculant is used for nickel oxide ores having an iron content of 50 mass% and an isoelectric point of 7.8 or less based on the measured iron content and isoelectric point, and an anionic flocculant is used for other nickel oxide ores, and the ratio of the anionic flocculant and the nonionic flocculant to be added is determined according to the mass ratio of each type of nickel oxide ore to the total mass of the plurality of types of nickel oxide ores. It is characterized by: [Effects of the Invention]

[0009] According to the present invention, it is possible to stabilize the slurry concentration of the concentrated high-concentration ore slurry obtained by settling and thickening in the thickener, thereby stabilizing the production efficiency of a nickel hydrometallurgy plant. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a process flow diagram of a nickel hydrometallurgy method using a pretreatment method according to an embodiment of the present invention and the ore slurry obtained by the pretreatment method as a raw material. [Figure 2] 1 is a graph showing the relationship between the iron content of nickel oxide ore and the solid content concentration of a high-concentration ore slurry after concentration when a low-concentration ore slurry prepared by adding water to the nickel oxide ore is sedimented and concentrated in a thickener. [Figure 3] 1 is a graph showing the change over time in the height of the solid-liquid interface when two types of flocculants are added separately to a low-concentration ore slurry prepared by adding water to nickel oxide ore. [Figure 4] 1 is a specific example of a flowchart used to determine the type of effective flocculant in a pretreatment method according to an embodiment of the present invention. [Figure 5]FIG. 1 is a graph showing the relationship between the iron content of a nickel oxide ore and the solid content concentration of a high-concentration ore slurry after concentration when a low-concentration ore slurry prepared by adding water to the nickel oxide ore is sedimented and concentrated in a thickener in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] 1. Nickel hydrometallurgy The ore slurry obtained after pretreatment by the nickel oxide ore pretreatment method according to the present invention is suitably used as a raw material for nickel hydrometallurgy. Therefore, first, a nickel hydrometallurgy method for producing mixed nickel-cobalt sulfides by the HPAL (High Pressure Acid Leaching) method will be described with reference to FIG. 1 .

[0012] The nickel hydrometallurgy process shown in FIG. 1 includes an acid leaching step S1 in which a high-concentration ore slurry prepared by a pretreatment method according to an embodiment of the present invention, which will be described later, is charged into an autoclave together with sulfuric acid, and then high-pressure steam is blown in to perform a leaching treatment under high temperature and pressure to leach the valuable metals nickel and cobalt; a preliminary neutralization step S2 in which a pH adjuster is added to the leached slurry containing the valuable metals obtained in the acid leaching step S1 to adjust the pH to within a predetermined range; and a multi-stage washing step in which the pH-adjusted leached slurry is introduced into the front of a series of thickeners and washed with wash water flowing countercurrently. The process is mainly comprised of a solid-liquid separation step S3 in which a leachate containing nickel and cobalt is separated from the leach residue while the leachate is being leached, a neutralization step S4 in which a neutralizing agent is added to the leachate to separate and remove impurity elements contained in the leachate as a neutralized precipitate, a dezincification step S5 in which a sulfiding agent is added at low pressure to the neutralization end liquor containing nickel and cobalt obtained in the neutralization step S4 to separate and remove zinc contained in the neutralization end liquor as zinc sulfide, and a nickel recovery step S6 in which a sulfiding agent is added at high pressure to the nickel recovery mother liquor containing nickel and cobalt obtained in the dezincification step S5 to produce a nickel-cobalt mixed sulfide. Next, a detailed description will be given of the pretreatment method according to an embodiment of the present invention, which is enclosed by a dashed line in FIG.

[0013] 2. Pretreatment method The pretreatment method according to an embodiment of the present invention comprises a classification step in which nickel oxide ore as a raw material is supplied to a screen with a predetermined mesh size together with water and subjected to wet classification, and a concentration step in which the low-concentration ore slurry recovered on the underside of the screen is concentrated by gravity sedimentation to obtain a high-concentration ore slurry. Specifically, the nickel oxide ore prepared as a raw material is first subjected to multiple stages of classification using fixed sieves and vibrating sieves until it is finally subjected to wet classification on a screen with a mesh size of approximately 1 mm. As a result, a low-concentration ore slurry containing nickel oxide ore having a predetermined particle size and having a solids concentration (also referred to as a slurry concentration) of approximately 10 to 20 mass % is recovered on the underside of the screen.

[0014] After measuring the specific gravity and solids concentration of the low-concentration ore slurry as necessary, the low-concentration ore slurry is introduced into a feedwell of a thickener via a slurry pump to be sedimented and thickened. A flocculant, the concentration of which has been adjusted by adding water and stirring for a predetermined period in a dissolution tank equipped with an agitator, is added to the low-concentration ore slurry using a flocculant pump. The flocculant is added while measuring the flow rate with a flow meter installed on the suction or discharge side of the flocculant pump so that the flocculant is supplied at a predetermined set flow rate.

[0015] The solids contained in the low-concentration ore slurry introduced together with the flocculant are deposited on the bottom of the thickener's sedimentation tank by gravity, then scraped up to the center by a rake rotating along the bottom, and discharged from the center of the bottom as a concentrated high-concentration ore slurry. Meanwhile, the supernatant liquid from which the solids have been separated overflows and is discharged from the top of the sedimentation tank.

[0016] The high-concentration ore slurry extracted from the center of the bottom in this way is sampled periodically or as needed, and its specific gravity and solids concentration are measured. The set flow rate of the flocculant to be added is changed based on the operating status of the thickener as determined from these measurements. For example, if the solids concentration of the high-concentration ore slurry tends to decrease even when the solids concentration of the low-concentration ore slurry remains unchanged, the set flow rate of the flocculant is changed to a higher value to manage the situation.

[0017] The concentration of the flocculant added to the thickener is preferably about 0.010 to 0.050% by mass. If the concentration is less than 0.010% by mass, the total amount of liquid introduced into the thickener's settling tank (i.e., the total amount of the flocculant diluted with water and the low-concentration ore slurry) may be too large, resulting in insufficient residence time. Conversely, if the concentration is higher than 0.050% by mass, the opportunity for the nickel oxide ore particles contained in the low-concentration ore slurry to come into contact with the flocculant decreases, which is undesirable.

[0018] However, free silica, which is pure silicon dioxide unbound with other components, generally has poor settling properties, so if the silicon contained in the nickel oxide ore as a raw ore is in the form of free silica, it is thought that as its quality increases, the settling properties will be poor when the ore is prepared into an ore slurry and introduced into a thickener as described above. However, since the silicon in the raw ore is not necessarily in the form of free silica, the settling properties of the ore cannot be determined unambiguously by the silicon quality.

[0019] We investigated the various components contained in the ore feedstock, other than silicon, and found that when the iron (Fe) content of the ore feedstock exceeds 50% by mass, the solids concentration of the concentrated slurry discharged from the bottom of the thickener begins to decrease significantly when the ore slurry is prepared using the ore feedstock and introduced into a thickener for sedimentation and concentration, as shown in Figure 2. In other words, we found that the settling properties of the ore slurry deteriorate significantly once the iron content of the ore feedstock exceeds 50% by mass. Anionic coagulants are generally used as coagulants in the sedimentation and separation of ore slurries containing nickel oxide ores, and anionic coagulants were also used in the thickener used for the measurements in Figure 2. Furthermore, the upper limit of the iron content of nickel oxide ores is generally approximately 55% by mass.

[0020] As mentioned above, ores with high iron content are generally found relatively close to the surface, and so weathering is thought to cause the particle size to become smaller, which is presumably responsible for the deterioration of sedimentation. In fact, it has been confirmed that such ores with poor sedimentation properties have a smaller median diameter than ores with good sedimentation properties. Therefore, in the sedimentation separation of ore slurries prepared using ores with iron content of 50% by mass or more, it is thought that sedimentation properties can be improved by promoting floc formation using a flocculant.

[0021] The flocculation action of particles by flocculants can be thought of as either neutralizing the charge by adding an ionic flocculant with an opposite sign to the surface charge of the particles and promoting coagulation, or physically bridging and adsorbing particles together through its adhesive action in the case of polymer flocculants. Of these, the surface charge of fine particles in the ore slurry that affects the former coagulation action is expressed as a zeta potential.

[0022] In other words, the zeta potential is the potential near the electric double layer formed by ion pairs adsorbed on the particle surface in a solvent, and it is said that the larger the absolute value of this potential, the stronger the electrostatic repulsion between particles, making them less likely to aggregate and resulting in lower sedimentation. Therefore, sedimentation can be evaluated by the absolute value of the zeta potential. Furthermore, it is presumed that the sedimentation rate is maximized at the so-called isoelectric point (isopotential point), which is expressed as the pH value at which the absolute value of the zeta potential becomes zero, because the electrostatic repulsion between particles is eliminated.

[0023] While there are various methods for measuring zeta potential, ultrasonic measurement is preferred for relatively concentrated slurries, such as the ore slurries used in the pretreatment method of the present invention. Ultrasonic measurement can also effectively measure the zeta potential of ore slurries containing various ore components, such as nickel oxide ores, which are prepared to a slurry concentration of several tens of percent by mass. For example, the pH of limonite ore, when prepared into an ore slurry, is approximately 5 to 8 depending on the composition of the mineral species, but the zeta potential varies widely from +200 mV to -150 mV, and the isoelectric point also varies widely from pH 5 to 9.

[0024] Based on the above findings, in order to determine the type of flocculant and conditions, such as isoelectric point, suitable for thickening ore slurry prepared in a pretreatment method for nickel hydrometallurgy in a thickener, a portion was taken from a lot of nickel oxide ore commonly used as a raw material for nickel hydrometallurgy and treated under the same conditions as the pretreatment method to prepare a low-concentration ore slurry sample. The isoelectric point of this low-concentration ore slurry sample was determined using ultrasonic zeta potential measurement, and was confirmed to be near neutral at 7.8. Furthermore, when the low-concentration ore slurry was divided into several beakers and subjected to a so-called jar test, it was found that nonionic flocculants were more effective at promoting floc formation than anionic flocculants, resulting in improved settling. The iron content of this nickel oxide ore was measured using X-ray fluorescence analysis and found to be 52% by mass.

[0025] That is, to determine the type and amount of flocculant suitable for the low-concentration ore slurry, the low-concentration ore slurry was divided into equal amounts and placed in several beakers, and various flocculants were added to each beaker in gradually increasing amounts, followed by stirring and then allowing to stand. The formation of flocs, their size, and their settling properties were then visually observed. The decrease in the height of the solid-liquid interface over time was measured.

[0026] As a result, it was found that the use of nonionic flocculants resulted in a faster time for the solid-liquid interface height to reach a specified level than the use of anionic flocculants, and was therefore superior in settling properties, as shown in Figure 3. Furthermore, when samples were taken from various lots of nickel oxide ore with iron contents varying within the range of 48 to 52 mass%, and a jar test similar to that described above was conducted, it was found that for nickel oxide ores with iron contents of 50 mass% or more, when the isoelectric point was neutral (approximately 6.5 to 7.8), the use of nonionic flocculants was more effective in improving settling properties than anionic flocculants.

[0027] However, in actual nickel hydrometallurgical plants, multiple lots of raw ore supplied from multiple mining sites are often mixed together for processing, and in this case, a low-concentration ore slurry prepared using multiple types of raw ore that differ in properties such as the iron grade and the isoelectric point when prepared into a low-concentration ore slurry is introduced into a thickener for sedimentation separation. Therefore, it is not always necessary to use a nonionic flocculant to thicken the low-concentration ore slurry in the thickener, and it is preferable to adjust the addition ratio of the nonionic flocculant and the anionic flocculant depending on the characteristics of the raw ore.

[0028] Specifically, when multiple types of ore are mixed and processed in a nickel hydrometallurgy plant, representative samples are collected from the mining area of ​​the ores and their iron content and isoelectric points are measured in advance to determine whether anionic or nonionic flocculants are effective. This determination can be made, for example, according to the flowchart in Figure 4. Specifically, if the isoelectric point is 7.8 or less, the sample is considered neutral and a nonionic flocculant is used; if the isoelectric point is greater than 7.8, an anionic flocculant is used. Generally, the lower limit of the isoelectric point when using nonionic flocculants is approximately 6.5, and when the isoelectric point is less than 6.5, it is often more effective to use a cationic flocculant. On the other hand, the upper limit of the isoelectric point when using anionic flocculants is approximately 9.0.

[0029] The ratio of the anionic and nonionic coagulants to be added is determined based on the mass ratio, i.e., the ratio of the mass of each type of raw ore to the total mass of the multiple types of raw ore to be processed in the actual plant. For example, in an actual plant, two types of raw ore A and B are treated by mass in W A :W B When the iron content and isoelectric point of ore raw materials A and B are measured and it is found that it is preferable to use an anionic coagulant and a nonionic coagulant, respectively, for the thickener that settles and thickens the low-concentration ore slurry prepared by mixing the two types of ore raw materials, the ratio of anionic coagulant to nonionic coagulant W is 1 part by mass. B / W A These flocculants are added in proportions of parts by mass.

[0030] The anionic and nonionic flocculants may be fed from separate hoppers to the dissolution tank equipped with the agitator so as to achieve a predetermined mass ratio, and then fed to the thickener in the form of a mixed flocculant via a flocculant pump. Alternatively, two sets of feed equipment consisting of a dissolution tank equipped with an agitator and a flocculant pump may be provided, and the anionic and nonionic flocculants may be fed to the thickener separately from each of these feed equipment. Alternatively, the flocculants may be fed to a hopper so as to achieve a predetermined ratio, and then dissolved and mixed in a dissolution tank equipped with an agitator.

[0031] In either case, the total amount of anionic and nonionic coagulants added to the low-concentration ore slurry to be fed to the thickener is preferably 180 g or more, more preferably 200 g or more. If the amount added is less than 180 g, the fine particles may not be sufficiently coarsened, resulting in a decrease in the settling rate.

[0032] The above anionic and nonionic flocculants have a molecular weight of 8 × 10 6 ~20×10 6 It is preferable to use a so-called polymer flocculant with a molecular weight of about 8 × 10 6 If the molecular weight is less than 20 × 10, the effect of flocculation will be reduced and gravitational settling in the thickener may take too long. 6 If the viscosity exceeds this value, the effect of concentration due to aggregation becomes too high, and the viscosity may not fall within an appropriate range.

[0033] Examples of such polymer flocculants include, but are not limited to, anionic flocculants such as sodium polyacrylate, maleic acid copolymer salts, and polyacrylamide partial hydrolysate salts, and nonionic flocculants such as polyacrylamide and polyoxyethylene. Next, the method for pretreating nickel oxide ore of the present invention will be specifically described with reference to examples and comparative examples, but the present invention is not limited in any way to the following examples. [Example]

[0034] (Example) To prepare a high-concentration ore slurry to be used as a raw material in a nickel hydrometallurgy plant using the HPAL process, pretreatment was carried out using the classification and concentration processes shown in Figure 1. Specifically, nickel oxide ore was wet classified using a screen with a mesh size of 1.4 mm to obtain an ore slurry containing nickel oxide ore with a particle size of 1.4 mm or less on the underside of the screen. Water was added to this ore slurry to obtain a slurry with a specific gravity of 1120 to 1140 kg / m. 3 Adjust to 1000~1200m 3 When the low-concentration ore slurry was fed to the thickener at a flow rate of 1000 to 1500 m / h, the high-concentration ore slurry was extracted from the bottom of the thickener at a flow rate of 400 to 470 m / h. 3 / h.

[0035] The nickel oxide ore used above was made from two different ore raw materials mined in different locations. Representative samples were obtained from each mining area and their properties were measured in advance. The iron content of each sample was found to be within the range of 52–54% by mass. The isoelectric points of the samples were 7.2 and 8.5, respectively. They were mixed in a mass ratio of approximately 2:1 and used as the raw material. Therefore, according to the flowchart in Figure 4, a nonionic flocculant was used for the nickel oxide ore with an isoelectric point of 7.2, while an anionic flocculant was used for the nickel oxide ore with an isoelectric point of 8.5.

[0036] The blending ratio of these nonionic and anionic coagulants was 2:1 by mass, matching the mixing ratio of the two types of ore raw materials. These coagulants were added in a total amount of 200 to 220 g per ton of ore in the ore slurry supplied to the thickener. All of these coagulants were polymer coagulants manufactured by Kurita Water Industries Ltd., and water was added to adjust the concentration to 0.36% by mass.

[0037] In addition, as a comparative example, operation was performed under the same conditions as above, except that only an anionic coagulant was used. During operation of the above examples and comparative examples, the iron content in the low-concentration ore slurry and the solids concentration of the high-concentration ore slurry after thickening using a thickener were periodically measured. A graph plotting these measurement results is shown in Figure 5. As can be seen from the graph in Figure 5, when a mixture of nonionic and anionic coagulants was added, the solids concentration of the high-concentration ore slurry was improved by approximately 0.5 mass% compared to the comparative example in which only anionic coagulant was added.

Claims

[Claim 1] 1. A method for pretreating nickel oxide ore to be used as a raw material for producing nickel-cobalt mixed sulfides by hydrometallurgy, the method comprising: a classification step of adding water to a plurality of types of nickel oxide ore and wet-classifying the ore using a screen having predetermined mesh openings; and a concentration step of obtaining a high-concentration ore slurry by sedimenting and concentrating a low-concentration ore slurry containing nickel oxide ore recovered on the underside of the screen, the method comprising: when the plurality of types of nickel oxide ore contains one having an iron content of 50% by mass or more, the method further comprises: a step of measuring the iron content and isoelectric point of each of representative samples taken from the plurality of types of nickel oxide ore; a step of using a nonionic coagulant for nickel oxide ore having an iron content of 50% by mass and an isoelectric point of 7.8 or less; and a step of using an anionic coagulant for other nickel oxide ores; and a step of determining the ratio of the anionic coagulant and the nonionic coagulant to be added depending on the mass ratio of each type of nickel oxide ore to the total mass of the plurality of types of nickel oxide ore.

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