Pressure oxidative leaching method for metal sulfide

Abstract

To provide a pressure oxidative leaching method for metal sulfide, capable of sustaining reactivity of the metal sulfide and lowering electricity costs for producing high-pressure air.SOLUTION: A pressure oxidative leaching method for metal sulfide, comprises a pressure oxidative leaching step in which a feed slurry containing a metal sulfide is supplied to an autoclave having a plurality of reaction chambers arranged in series, high-pressure air is supplied to some or all of the plurality of reaction chambers, and the metal sulfide is subjected to pressure oxidative leaching to obtain an aqueous solution of metal sulfate. The total supply amount of high-pressure air relative to the supply amount of metal sulfide is set to 3.6 to 4.1 Nm3 / kg. Reducing surplus high-pressure air not contributing to oxidation of the metal sulfide makes it possible to sustain reactivity of the metal sulfide and lower electricity costs for producing high-pressure air.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pressure oxidative leaching method for metal sulfides, and more particularly to a method for obtaining an aqueous metal sulfate solution by pressure oxidative leaching of metal sulfides. [Background technology]

[0002] A method for obtaining a metal sulfate aqueous solution by pressure oxidative leaching of a metal sulfide is known. For example, a raw material slurry containing nickel sulfide is continuously fed into an autoclave, and pressurized air is blown into the slurry in the autoclave to perform pressure oxidative leaching. This produces a nickel sulfate aqueous solution (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-143391 Summary of the Invention [Problem to be solved by the invention]

[0004] The oxidative leaching reaction of metal sulfides using oxygen has an extremely slow reaction rate at room temperature. Therefore, to speed up the reaction rate, oxidative leaching is carried out under high temperature and pressure using an autoclave. To maintain high pressure inside the autoclave, pressurized air is supplied to the autoclave. Because the pressurized air contributes to the reaction as an oxidizing agent, a large amount of pressurized air must be continuously supplied to the autoclave.

[0005] High-pressure air is produced by a multi-stage compressor. Compressors consume large amounts of electricity, and the electricity costs account for a large proportion of the plant's operating costs. Power costs can be reduced by reducing the amount of high-pressure air supplied to the autoclave. However, if the amount of high-pressure air supplied is reduced too much, there will be a shortage of oxidizing agent, and the reactivity of metal sulfides will deteriorate. Therefore, there is a need to reduce the amount of high-pressure air supplied to the autoclave and reduce power costs while maintaining the reactivity of metal sulfides.

[0006] In view of the above circumstances, an object of the present invention is to provide a pressure oxidative leaching method for metal sulfides that can reduce the electricity cost required to produce high-pressure air while maintaining the reactivity of metal sulfides. [Means for solving the problem]

[0007] A first aspect of the pressure oxidative leaching method for metal sulfides includes a pressure oxidative leaching step of supplying a raw material slurry containing metal sulfides to an autoclave having a plurality of reaction chambers arranged in series, supplying pressurized air to some or all of the plurality of reaction chambers, and subjecting the metal sulfides to pressure oxidative leaching to obtain an aqueous metal sulfate solution, and the total amount of pressurized air supplied to the autoclave is 3.6 to 4.1 Nm relative to the amount of metal sulfide supplied. 3 / kg. The pressure oxidative leaching method for metal sulfides of a second aspect is the same as that of the first aspect, except that the amount of the high-pressure air supplied to a first chamber, to which the raw slurry is first supplied, of the plurality of reaction chambers is 1.4 to 2.2 Nm3 relative to the amount of the metal sulfide supplied. 3 / kg. A third aspect of the pressure oxidative leaching method for metal sulfides is the same as that of the first or second aspect, and the amount of the high-pressure air supplied to a second chamber, which is disposed next to a first chamber to which the raw slurry is first supplied, among the plurality of reaction chambers is set to 1.4 to 1.7 Nm3 relative to the amount of the metal sulfide supplied. 3 / kg. A fourth aspect of the pressure oxidative leaching method for metal sulfides is characterized in that, in any one of the first to third aspects, the pressure in the gas phase in the autoclave is 1 to 2 MPaG in gauge pressure, and the temperature of the slurry in the autoclave is 140 to 200°C. A fifth aspect of the pressure oxidative leaching method for metal sulfides is the method of any one of the first to fourth aspects, characterized in that the metal sulfide is a nickel-cobalt mixed sulfide, and the solids concentration of the raw slurry is 200 to 300 g / L. [Effects of the Invention]

[0008] According to the present invention, by reducing the excess pressurized air that does not contribute to the oxidation of metal sulfides, it is possible to reduce the electricity costs required to produce pressurized air while maintaining the reactivity of metal sulfides. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a longitudinal cross-sectional view of an autoclave. [Figure 2] Figure (A) is a graph showing the change over time in the total amount of compressed air supplied and the redox potential of the leachate. Figure (B) is a graph showing the relationship between the total amount of compressed air supplied and the redox potential of the leachate. [Figure 3] 10 is a graph showing the relationship between the amount of high-pressure air supplied to each reaction chamber and the oxygen consumption rate of each reaction chamber. [Figure 4] 1 is a graph showing the relationship between the amount of high-pressure air supplied to each reaction chamber and the nickel leaching rate in each reaction chamber. [Figure 5] 10 is a graph showing the change over time in the total amount of high-pressure air supplied and the liquid temperature in each reaction chamber. [Figure 6] 1 is a graph showing the relationship between the liquid temperature in the first and second chambers and the nickel leaching rate. DETAILED DESCRIPTION OF THE INVENTION

[0010] Next, an embodiment of the present invention will be described with reference to the drawings. A pressure oxidative leaching method for metal sulfides according to one embodiment of the present invention is a method for obtaining a metal sulfate aqueous solution by pressure oxidative leaching a metal sulfide. Examples of metal sulfides that can be used include nickel sulfide, cobalt sulfide, zinc sulfide, and cadmium sulfide. One or more of these metal sulfides can be used as the raw material. For example, a nickel-cobalt mixed sulfide can be used as the raw material.

[0011] The following steps are taken to obtain a nickel sulfate solution from nickel-cobalt mixed sulfide. First, the raw material, nickel-cobalt mixed sulfide, is repulped to prepare a raw material slurry. Next, the raw material is subjected to pressure oxidation leaching to obtain a leached slurry containing a crude nickel sulfate solution. Next, the iron ions contained in the crude nickel sulfate solution are converted into iron hydroxide precipitates by oxidation neutralization treatment, and this is then subjected to solid-liquid separation together with the leaching residue contained in the leaching slurry. Next, heavy metals such as cobalt contained in the crude nickel sulfate solution are separated by solvent extraction to obtain a high-purity nickel sulfate solution. The obtained high-purity nickel sulfate solution is used for the production of nickel sulfate crystals, etc.

[0012] The pressure oxidative leaching method includes a pressure oxidative leaching step in which metal sulfides are subjected to pressure oxidative leaching. In the pressure oxidative leaching step, an autoclave 1 as shown in Figure 1 is used. The autoclave 1 has a liquid-tight, airtight, horizontally long vessel 10. One end of the vessel 10 is provided with a supply port 11 for supplying raw material slurry. The other end of the vessel 10 is provided with a discharge port 12 for discharging the leached slurry.

[0013] One or more partition walls 13 are erected inside the tank 10. These partition walls 13 divide the interior of the tank 10 into a plurality of reaction chambers 14a to 14e lined up in the longitudinal direction. The number of reaction chambers 14a to 14e is not particularly limited. The autoclave 1 shown in FIG. 1 has five reaction chambers 14a to 14e. The five reaction chambers 14a to 14e are referred to as the first chamber 14a, the second chamber 14b, the third chamber 14c, the fourth chamber 14d, and the fifth chamber 14e, respectively.

[0014] The supply port 11 is provided in the first chamber 14a. The raw material slurry is first supplied to the first chamber 14a. The slurry in the first chamber 14a overflows the partition wall 13 and is supplied to the second chamber 14b arranged next to the first chamber 14a. By repeating this overflow process, the slurry reaches the fifth chamber 14e. In this manner, the multiple reaction chambers 14a to 14e are arranged in series so that the slurry flows in sequence. The discharge port 12 is provided in the fifth chamber 14e. The leached slurry in the fifth chamber 14e is discharged from the discharge port 12.

[0015] An air inlet pipe 15 is inserted into each reaction chamber 14a to 14e. High-pressure air is blown into the slurry in each reaction chamber 14a to 14e through the air inlet pipe 15. The amount of high-pressure air supplied to each reaction chamber 14a to 14e can be adjusted individually. The high-pressure air acts as an oxidizing agent. When the raw material metal sulfide comes into contact with oxygen, the metal sulfide is oxidized, resulting in a metal sulfate aqueous solution. To promote contact between the metal sulfide and oxygen and to efficiently carry out the oxidation leaching reaction, each reaction chamber 14a to 14e is provided with an agitator 16.

[0016] The oxidation leaching reaction of metal sulfides is an exothermic reaction. Therefore, if left unchecked, the temperature of the slurry in the autoclave 1 will become too high. To adjust the temperature of the slurry in the autoclave 1 to an appropriate level, cooling water is added.

[0017] A cooling water supply pipe 17 is inserted into each of the reaction chambers 14a to 14e. Cooling water is added to the slurry in each of the reaction chambers 14a to 14e through the cooling water supply pipe 17. The amount of cooling water supplied to each of the reaction chambers 14a to 14e can be adjusted individually. By adjusting the amount of cooling water supplied to each of the reaction chambers 14a to 14e, the slurry in each of the reaction chambers 14a to 14e can be adjusted to an appropriate temperature.

[0018] The cooling water cools the slurry mainly by consuming the latent heat of evaporation during evaporation. Water vapor is generated by the evaporation of the cooling water. A pressure regulating valve 18 is provided in the gas phase of the tank 10. The pressure inside the autoclave 1 is maintained at a predetermined pressure by discharging excess water vapor from the pressure regulating valve 18. The pressure inside the autoclave 1 can also be adjusted by the pressure regulating valve 18.

[0019] Each of the reaction chambers 14a to 14e is provided with a thermometer 19. The thermometer 19 can measure the temperature of the slurry in each of the reaction chambers 14a to 14e.

[0020] The pressurized oxidative leaching process is carried out in the following manner. A raw material slurry containing metal sulfides is continuously supplied to the autoclave 1. High-pressure air and cooling water are also continuously supplied to the autoclave 1. Here, high-pressure air may be supplied to all or some of the multiple reaction chambers 14a-14e. Cooling water may be supplied to all or some of the multiple reaction chambers 14a-14e.

[0021] As the slurry flows from the first chamber 14a to the fifth chamber 14e inside the autoclave 1, the metal sulfides are subjected to pressure oxidative leaching to produce a metal sulfate aqueous solution. When a nickel-cobalt mixed sulfide is used as the raw material, a nickel sulfate-cobalt sulfate mixed aqueous solution is produced. The leached slurry is continuously discharged from the autoclave 1. The leached slurry is a slurry consisting of a leachate, which is a metal sulfate aqueous solution, and a leach residue, which is a solid content.

[0022] The reactivity of metal sulfides can be evaluated by the oxidation-reduction potential of the leachate and the metal leaching rate of the metal sulfide. The higher the reactivity of the metal sulfide, the higher the oxidation-reduction potential of the leachate and the higher the metal leaching rate of the metal sulfide. In order to suppress the generation of thiosulfate ions, it is preferable that the oxidation-reduction potential of the leachate (based on a silver / silver chloride electrode, the same applies hereinafter) be 410 mV or higher.

[0023] The target metal content of the raw material, the solids concentration of the raw material slurry, the feed rate of the raw material slurry, the temperature and pressure inside the autoclave 1, and other factors are adjusted taking into account operational efficiency. For example, the nickel content of nickel-cobalt mixed sulfide is typically 50-60% by weight. To prevent wear and tear on the diaphragm pump used to supply the raw material slurry to the autoclave 1, breakdowns, and blockages in the piping, the solids concentration of the raw material slurry is preferably 200-300 g / L. The temperature of the slurry inside the autoclave 1 is typically adjusted to 140-200°C, and the pressure of the gas phase inside the autoclave 1 is typically adjusted to 1-2 MPaG in gauge pressure.

[0024] The amount of pressurized air supplied to each of the reaction chambers 14a to 14e is adjusted based on the liquid temperature in each of the reaction chambers 14a to 14e, the metal ion concentration of the leachate, the redox potential of the leachate, etc. Increasing the amount of pressurized air supplied increases the oxygen partial pressure in the autoclave 1, accelerating the oxidation leaching reaction of metal sulfides. In addition, increasing the amount of pressurized air supplied increases the effectiveness of cooling the slurry by the pressurized air.

[0025] The present inventors have discovered that if an excess of high-pressure air is supplied to autoclave 1, the excess air does not contribute to the oxidative leaching reaction as an oxidant, but is used only to cool the slurry. In other words, supplying an excess of high-pressure air to autoclave 1 does not improve the reactivity of the metal sulfides; rather, the reactivity decreases as the slurry is cooled. Therefore, the present inventors have discovered that by reducing the excess of high-pressure air supplied to autoclave 1, the reactivity of the metal sulfides can be maintained while reducing the electricity cost required to produce high-pressure air.

[0026] Specifically, the total amount of high-pressure air supplied to the autoclave 1 relative to the amount of metal sulfide supplied (hereinafter simply referred to as the total amount of high-pressure air supplied V T ) is 3.6 to 4.1 Nm 3 / kg. Here, the total supply amount of high-pressure air V T is the supply amount [Nm m of high-pressure air supplied to each reaction chamber 14a to 14e of the autoclave 1. 3 / min] divided by the supply amount of metal sulfide supplied to autoclave 1 [kg / min].

[0027] Total supply of high-pressure air V T 4.1Nm 3 / kg or less, the excess compressed air that does not contribute to the oxidation of metal sulfides is reduced, and the electricity cost required to produce compressed air can be reduced. T 3.6Nm 3 By setting the concentration to 1 / kg or more, a necessary amount of high-pressure air is supplied as an oxidizing agent, and the reactivity of the metal sulfide can be maintained.

[0028] Furthermore, oxidation leaching is carried out in multiple stages in multiple reaction chambers 14a to 14e within the autoclave 1. To improve the overall efficiency of the oxidation leaching reaction, the amount and balance of high-pressure air supplied to each of the reaction chambers 14a to 14e are also important factors.

[0029] Therefore, the amount of high-pressure air supplied to the first chamber 14a relative to the amount of metal sulfide supplied (hereinafter referred to as the amount of high-pressure air supplied to the first chamber 14a, V1) is set to 1.4 to 2.2 Nm 3 / kg. Here, the supply amount V1 of the high-pressure air to the first chamber 14a is preferably set to the supply amount [Nm 3 / min] divided by the supply amount of metal sulfide supplied to autoclave 1 [kg / min].

[0030] The supply amount V1 of high-pressure air to the first chamber 14a is set to 2.2 Nm 3 By setting the supply amount V1 of the high-pressure air to the first chamber 14a to 1.4 Nm / kg or less, the excess high-pressure air that does not contribute to the oxidation of the metal sulfide in the first chamber 14a is reduced, and the power cost required for producing the high-pressure air can be reduced. 3 By setting the oxidizing agent concentration to 1 / kg or more, a necessary amount of high-pressure air is supplied as an oxidizing agent in the first chamber 14a, and the reactivity of the metal sulfide can be maintained.

[0031] The amount of high-pressure air supplied to the second chamber 14b relative to the amount of metal sulfide supplied (hereinafter referred to as the amount of high-pressure air supplied to the second chamber 14b V2) is set to 1.4 to 1.7 Nm 3 / kg. Here, the supply amount V2 of the high-pressure air to the second chamber 14b is preferably set to the supply amount [Nm 3 / min] divided by the supply amount of metal sulfide supplied to autoclave 1 [kg / min].

[0032] The supply amount V2 of high-pressure air to the second chamber 14b is set to 1.7 Nm 3 By setting the supply amount V2 of high-pressure air to the second chamber 14b to 1.4 Nm / kg or less, the excess high-pressure air that does not contribute to the oxidation of metal sulfides in the second chamber 14b is reduced, and the power cost required for producing the high-pressure air can be reduced. 3 By setting the oxidizing agent concentration to 1 / kg or more, a necessary amount of high-pressure air is supplied as an oxidizing agent in the second chamber 14b, and the reactivity of the metal sulfide can be maintained. [Example]

[0033] Next, an example will be described. Pressure oxidation leaching was carried out using the autoclave 1 shown in Figure 1. The operating conditions were as follows: Raw material: Nickel-cobalt mixed sulfide Nickel content of raw material: 50-60% by weight Solids concentration of raw slurry: 200-300g / L Raw material slurry supply rate: 90-105 L / min Gas phase pressure inside the autoclave (gauge pressure): 1.8 to 1.9 MPaG Slurry temperature in autoclave: 150-180°C

[0034] High-pressure air was supplied to each of the first chamber 14a to the fourth chamber 14d. Cooling water was supplied to each of the first chamber 14a to the fourth chamber 14d to adjust the temperature and concentration of the slurry in the autoclave 1. In addition, the oxidation-reduction potential of the leachate discharged from the autoclave 1 was measured.

[0035] Figure 2(A) shows the total supply of high-pressure air V T The graph shows the change over time in the oxidation-reduction potential of the leachate and the total amount of compressed air supplied, V. T If the total supply of high-pressure air V is reduced, the oxygen partial pressure in the autoclave 1 will decrease, which may lead to a decrease in the reactivity of the metal sulfide. However, as can be seen from FIG. 2(A), at least T 3.6~4.6Nm 3 / kg, the total supply of compressed air V T Even if the total supply of compressed air V is reduced, the oxidation-reduction potential of the leachate does not decrease, but rather tends to increase. T Reducing the amount does not decrease the reactivity of the metal sulfide.

[0036] Figure 2(B) shows the total supply of high-pressure air V T The figure shows the relationship between the total supply of compressed air V and the oxidation-reduction potential of the leachate. Note that ORP in Figure 2(B) stands for oxidation-reduction potential. As can be seen from Figure 2(B), T is 3.85Nm 3 / kg, the oxidation-reduction potential of the leachate is highest. T is 3.85Nm 3 / kg or more, the total supply of compressed air V T Even if the total supply of compressed air V is reduced, the oxidation-reduction potential of the leachate does not decrease, but rather tends to increase. T is 3.85Nm 3 / kg or less, the total supply of compressed air V T If the total supply of high-pressure air V is reduced, the oxidation-reduction potential of the leachate tends to be lower. T 3.6~4.1Nm 3 In the range of 0.1g / kg, the redox potential of the leachate is 440mV or higher.

[0037] Considering the above trends, from the viewpoint of reducing the supply amount of high-pressure air while maintaining the reactivity of metal sulfides, the total supply amount of high-pressure air V T is 3.6~4.1Nm 3 / kg is preferable, 3.7 to 4.0 Nm 3 / kg is more preferable, 3.8 to 3.9 Nm 3 / kg is more preferable.

[0038] To maintain the reactivity of metal sulfides, the total supply of high-pressure air V T is 4.4Nm 3 / kg is thought to be necessary. However, the total supply of compressed air V T 4.4Nm 3 / kg to 3.85Nm 3 It was confirmed that the reactivity of metal sulfides can be maintained even if the amount of compressed air is reduced to about 1 / kg. Furthermore, this reduction in the amount of compressed air can reduce the electricity costs required to produce compressed air.

[0039] Next, the total supply of high-pressure air V T In order to clarify the factor that enables the reactivity of metal sulfide to be maintained even when the amount of oxygen is reduced, the oxygen consumption rate of each of the reaction chambers 14a to 14e was determined. The oxygen consumption rate of each of the reaction chambers 14a to 14e can be determined from the heat balance.

[0040] When high-pressure air is supplied to each reaction chamber 14a-14e, the oxygen contained in the high-pressure air reacts with the metal sulfides to generate heat. The sensible heat of the air after the reaction and the latent heat and sensible heat of the evaporated water are removed from each reaction chamber 14a-14e. By carefully examining the heat balance of each reaction chamber 14a-14e, the amount of oxygen consumed in the oxidative leaching reaction of the metal sulfides can be determined. Based on this, the ratio of the amount of oxygen consumed in the oxidative leaching reaction of the metal sulfides to the amount of oxygen supplied to each reaction chamber 14a-14e can be calculated.

[0041] Since the law of conservation of energy holds true for each reaction chamber 14a-14e, the heat input into the system is equal to the heat output from the system, and a heat balance can be established by utilizing this. Here, the heat inputs assumed were the reaction heat from the oxidation leaching of metal sulfides, the heat carried in by the slurry, the heat carried in by the high-pressure air, and the heat carried in by the cooling water. The heat outputs assumed were the heat carried away by the slurry to the next reaction chamber, the heat carried away by the exhaust gas, and the heat dissipated on the surface of the autoclave 1. Once the reaction heat from the oxidation leaching of metal sulfides, which is a common variable, is determined, the heat balance can be determined by convergence calculation.

[0042] By determining the breakdown of the reaction heat quantity for each reaction chamber 14a to 14e, the proportion of the supplied oxygen consumed in the oxidative leaching reaction can be determined. This proportion is referred to as the oxygen consumption rate. A higher oxygen consumption rate indicates that a larger proportion of the supplied oxygen is consumed in the oxidative leaching reaction of metal sulfides. The oxygen consumption rate can be calculated using the following formula: Oxygen consumption rate [volume %] = Amount of oxygen consumed in the oxidation leaching reaction in the reaction chamber / (Amount of compressed air supplied to the reaction chamber × Oxygen fraction in the atmosphere [volume %]) × 100

[0043] The oxygen fraction in the atmosphere was assumed to be 21%. The amount of oxygen consumed in the oxidative leaching reaction in the reaction chamber was calculated by dividing the heat of reaction estimated from the heat balance by the standard reaction enthalpy, and then correcting for the mass balance.

[0044] Figure 3 shows the relationship between the amount of high-pressure air supplied to each reaction chamber 14a-14e and the oxygen consumption rate of each reaction chamber 14a-14e. It was found that the second chamber 14b had a low oxygen consumption rate of 15-35%, despite the relatively large amount of high-pressure air supplied. In other words, the ratio of the amount of high-pressure air consumed in the oxidative leaching reaction of metal sulfides to the amount of high-pressure air supplied to the second chamber 14b was small.

[0045] This suggests that some of the high-pressure air supplied to the second chamber 14b is used solely for cooling the slurry without contributing to the oxidation leaching reaction. Therefore, we attempted to reduce the excess high-pressure air supplied to the second chamber 14b that is used solely for cooling the slurry.

[0046] Pressure oxidation leaching was carried out under the three conditions of the supply amount of compressed air shown in Table 1, and the oxidation-reduction potential of the leachate was measured and the nickel leaching rate was calculated. The nickel leaching rate is the ratio of the amount of nickel leached in the leachate to the amount of nickel supplied to autoclave 1. The nickel leaching rate can be calculated using the following formula. Nickel leaching rate [wt%] = 100 - (weight of leaching residue in leaching slurry × insoluble nickel content in leaching residue [wt%]) / (supply amount of raw material slurry × solids concentration of raw material slurry × nickel content of raw material [wt%])

[0047] [Table 1]

[0048] Condition 1 is the total supply of high-pressure air V T is 4.38Nm 3 / kg, and the supply amount V1 of high-pressure air to the first chamber 14a is 1.83 Nm 3 / kg, and the supply amount V2 of high-pressure air to the second chamber 14b is 1.79 Nm 3 / kg. Condition 2 reduces the amount of high-pressure air supplied to all of the first chamber 14a to the fourth chamber 14d compared to condition 1. Condition 3 further reduces the amount V2 of high-pressure air supplied to the second chamber 14b compared to condition 2.

[0049] The oxidation-reduction potential of the leachate and the nickel leaching rate under each condition are shown in Table 1. As can be seen from Table 1, reducing the supply of compressed air does not lower the oxidation-reduction potential of the leachate or the nickel leaching rate. In other words, the reactivity of metal sulfides does not decrease.

[0050] The relationship between the amount of pressurized air supplied to each of the reaction chambers 14a to 14d and the nickel leaching rate in each of the reaction chambers 14a to 14d is shown in Figure 4. The nickel leaching rate in each of the reaction chambers 14a to 14d was calculated using the following formula based on the amount of nickel leached in each of the reaction chambers 14a to 14d, which was calculated by dividing the heat of reaction estimated from the heat balance by the standard reaction enthalpy and then correcting the value based on the mass balance. Nickel leaching rate in each reaction chamber [wt%] = (nickel leaching amount in each reaction chamber estimated by heat balance) / (supply amount of raw material slurry × solids concentration of raw material slurry × nickel content of raw material [wt%])

[0051] Under condition 3, only the amount of high-pressure air supplied to the second chamber 14b, V2, is reduced compared to condition 2. As can be seen from Figure 4, the nickel leaching rate in the second chamber 14b under conditions 2 and 3 is almost the same. In other words, even if the amount of high-pressure air supplied to the second chamber 14b, V2, is reduced, the nickel leaching rate in the second chamber 14b remains almost unchanged. From this, it can be considered that only the excess amount of high-pressure air supplied to the second chamber 14b, which is used only for cooling the slurry, is reduced.

[0052] Figure 5 shows the total supply of high-pressure air V T 5 shows the change over time in the liquid temperature of each reaction chamber 14a to 14e. T It can be seen that when the total supply amount of high-pressure air V is reduced, the liquid temperature in each reaction chamber 14a to 14e rises. This is thought to be because the effect of cooling the slurry by the high-pressure air is reduced. More specifically, when the total supply amount of high-pressure air V is increased while the supply amount of metal sulfide is kept constant, T When the temperature is reduced, the ratio of the heat removed by the exhaust gas to the heat of reaction due to the oxidation leaching of metal sulfides decreases, and the heat retained in the liquid phase increases. This is thought to be the reason why the liquid temperature in each of the reaction chambers 14a to 14e increases.

[0053] Figure 6 shows the relationship between the liquid temperature in the first chamber 14a and the second chamber 14b and the nickel leaching rate. The nickel leaching rate in each of the reaction chambers 14a to 14e can be estimated by heat balance analysis. According to reaction kinetics, the reaction rate of the oxidation leaching reaction of nickel sulfide (NiS) is expressed by the following equation: r = k × [NiS] × [O2] 2 k = A × exp(-E / RT) where r is the reaction rate, k is the rate constant, A is the frequency factor, E is the activation energy, R is the gas constant, T is the absolute temperature, [NiS] is the nickel sulfate concentration, and [O2] is the oxygen concentration.

[0054] As can be seen from Figure 6, the higher the liquid temperature in the first chamber 14a and the second chamber 14b, the faster the nickel leaching rate. Reducing the supply of pressurized air reduces the oxygen partial pressure, thereby decreasing [O2]. On the other hand, increasing the liquid temperature increases the rate constant k. It is believed that the effect of increasing the reaction rate due to an increase in the rate constant k was greater than the effect of decreasing the reaction rate due to a decrease in [O2].

[0055] This confirmed that it is possible to reduce the amount of excess pressurized air used to cool the slurry without contributing to the oxidation of metal sulfides, and that this also reduces the electricity costs required to produce pressurized air while maintaining the reactivity of metal sulfides. [Explanation of symbols]

[0056] 1. Autoclave 10 tanks 11 Supply port 12 Outlet 13 Bulkhead 14a~14e Reaction chamber 15 Air inlet pipe 16 Mixer 17 Cooling water supply pipe 18 Pressure Regulating Valve 19 Thermometer

Claims

1. a pressure oxidative leaching step of supplying a raw material slurry containing a metal sulfide to an autoclave having a plurality of reaction chambers arranged in series, supplying pressurized air to some or all of the plurality of reaction chambers, and subjecting the metal sulfide to pressure oxidative leaching to obtain an aqueous metal sulfate solution, The total amount of the high-pressure air supplied to the autoclave is 3.6 to 4.1 Nm3 relative to the amount of the metal sulfide supplied. ３ / kg A pressure oxidative leaching method for metal sulfides, comprising:

2. The amount of the high-pressure air supplied to a first chamber among the plurality of reaction chambers to which the raw material slurry is first supplied is set to 1.4 to 2.2 Nm3 relative to the amount of the metal sulfide supplied. ３ / kg 2. The method for pressure oxidative leaching of metal sulfides according to claim 1.

3. The amount of the high-pressure air supplied to a second chamber, which is disposed next to a first chamber to which the raw material slurry is first supplied, among the plurality of reaction chambers is set to 1.4 to 1.7 Nm3 relative to the amount of the metal sulfide supplied. ３ / kg 3. The pressure oxidative leaching method for metal sulfides according to claim 1 or 2.

4. The pressure in the gas phase inside the autoclave is 1 to 2 MPaG in gauge pressure, The temperature of the slurry in the autoclave is 140 to 200°C.

2. The method for pressure oxidative leaching of metal sulfides according to claim 1.

5. The metal sulfide is a nickel-cobalt mixed sulfide, The solid content of the raw material slurry is 200 to 300 g / L.

2. The method for pressure oxidative leaching of metal sulfides according to claim 1.

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