JP7087566B2 - Pressure oxidative leaching method and nickel sulfate manufacturing method - Google Patents

Description

The present invention relates to a pressure oxidative leaching method and a method for producing nickel sulfate. More specifically, the present invention relates to a pressure oxidative leaching method for obtaining a nickel sulfate aqueous solution by pressure oxidative leaching of nickel sulfide, and a method for producing nickel sulfate including a pressure oxidative leaching step.

Patent Document 1 discloses that a nickel sulfate aqueous solution is obtained by continuously supplying a raw material slurry containing nickel sulfide as a raw material to an autoclave and blowing high-pressure air into the autoclave to oxidize and leaching under pressure. There is.

Japanese Unexamined Patent Publication No. 2016-011442

If the oxidation reaction of nickel sulfide in the autoclave is insufficient, the oxidation of sulfur constituting nickel sulfide does not proceed completely, and the oxo acid of reducing sulfur such as thiosulfate (hereinafter, "reducing sulfur compound"). ") May be generated. Then, the nickel sulfate crystal produced by purifying the nickel sulfate aqueous solution also contains a trace amount of the reducing sulfur compound. Nickel sulfate crystals are used, for example, as a raw material for electroless Ni-P alloy plating. When the reducing sulfur compound is mixed in the nickel sulfate crystals, a small amount of sulfur is deposited inside the Ni-P alloy plating layer, which causes a problem that the acid resistance of the plating is lowered. Therefore, it is required to completely promote the oxidation of sulfur in the pressure oxidation leaching, in other words, to improve the leaching rate of nickel sulfide.

In view of the above circumstances, it is an object of the present invention to provide a pressure oxidative leaching method capable of improving the leaching rate of a raw material, and a method for producing nickel sulfate including the pressure oxidative leaching step.

In the pressure oxidative leaching method of the first invention, a raw material slurry containing nickel sulfide is supplied to an autoclave, and nickel sulfide is pressurized oxidatively leached to obtain a nickel sulfate aqueous solution. It is characterized in that the nickel concentration of the liquid phase of the raw material slurry is 10 g / L or less.
The pressure oxidative leaching method of the second invention is characterized in that, in the first invention, the nickel concentration of the liquid phase of the raw material slurry at the time of being supplied to the autoclave is 3 g / L or less.
The method for producing nickel sulfate of the third invention is a repelling step of mixing a raw material containing nickel sulfide and repulp water to obtain a raw material slurry, and supplying the raw material slurry to an autoclave and pressurizing and leaching the nickel sulfide. Then, the nickel thin liquid obtained in the pressurized oxidative leaching step to obtain the leachate which is the nickel sulfate aqueous solution and the subsequent step following the pressurized oxidative leaching step is diluted to obtain the repulp water used in the repulp step. It comprises a diluting step, and is characterized in that the nickel concentration of the repulp water is adjusted to 10 g / L or less in the diluting step .
The method for producing nickel sulfate of the fourth invention is the iron removal step of adding a neutralizing agent to the leachate to remove the iron contained in the leachate as a neutralizing starch, and the neutralizing starch in the third invention. It is characterized by comprising a dissolution step of dissolving a nickel hydroxide accompanying an object with a sulfuric acid aqueous solution to obtain the nickel thin liquid.
The method for producing nickel sulfate of the fifth invention is characterized in that, in the third or fourth invention, the nickel concentration of the repulp water is adjusted to 3 g / L or less in the dilution step.

According to the present invention, it is possible to prevent the nickel sulfate crystals from precipitating on the surface of the unreacted raw material in the autoclave and inhibiting the pressure oxidative leaching of the raw material. As a result, the leaching rate of the raw material in the pressure oxidative leaching can be improved.

It is a process diagram of the manufacturing process of nickel sulfate crystal. It is a vertical sectional view of an autoclave. It is a graph which shows the relationship between the nickel concentration of the repulp water and the redox potential of the leachate in an Example.

Next, an embodiment of the present invention will be described with reference to the drawings.
The method for producing nickel sulfate according to an embodiment of the present invention is not particularly limited, but is suitably used for the process for producing nickel sulfate crystals shown in FIG. Further, the pressure oxidative leaching method according to the embodiment of the present invention is not particularly limited, but is suitably used for the pressure oxidative leaching step which is one step of the nickel sulfate crystal manufacturing process. Hereinafter, the manufacturing process of nickel sulfate crystals will be described in order.

A raw material containing nickel sulfide is used in the process of producing nickel sulfate crystals. In addition to nickel sulfide, the raw material may contain other metal sulfides such as cobalt sulfide. Examples of this type of raw material include nickel-cobalt mixed sulfide (MS: Mixed Sulfide).

The nickel-cobalt mixed sulfide can be obtained, for example, by the following procedure. First, nickel oxide ore such as low-grade laterite ore is subjected to high pressure acid Leaching (HPAL) to obtain a leachate. Remove impurities such as iron from the leachate. Then, hydrogen sulfide gas is blown into the leachate to cause a sulfurization reaction. The sulfurization reaction gives a nickel-cobalt mixed sulfurized product.

The chemical composition of the nickel-cobalt mixed sulfide is 45 to 60% by weight for Ni, 4 to 6% by weight for Co, and 35 to 39% by weight for S (all based on the dry amount). Nickel-cobalt mixed sulfide contains impurities such as iron, copper and zinc.

In the repulp step, the raw material and repulp water are mixed to obtain a raw material slurry. The solid content concentration of the raw material slurry is adjusted to 200 to 300 g / L.

In the pressure oxidative leaching step, the raw material slurry is supplied to the autoclave and pressurized oxidative leaching to obtain a leachate. Pressurized oxidative leaching of nickel sulfide gives an aqueous solution of nickel sulfate. The main component of the leachate is an aqueous solution of nickel sulfate. In addition to nickel, the leachate contains cobalt and other impurities.

For example, the autoclave 1 shown in FIG. 2 is used in the pressure oxidation leaching step. The autoclave 1 has a horizontally long tank 10 having liquidtightness and airtightness. A supply port 11 for supplying the raw material slurry is provided at one end of the tank 10. The other end of the tank 10 is provided with a discharge port 12 for discharging the leachate. A plurality of partition walls 13 are erected inside the tank 10. The partition wall 13 divides the inside of the tank 10 into a plurality of reaction chambers 14a to 14e arranged in the longitudinal direction.

The number of reaction chambers 14a to 14e is not particularly limited. The autoclave 1 shown in FIG. 2 has five reaction chambers 14a to 14e. The five reaction chambers 14a to 14e are referred to as a first chamber 14a, a second chamber 14b, a third chamber 14c, a fourth chamber 14d, and a fifth chamber 14e, respectively.

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. By repeating such overflow, the slurry reaches the fifth chamber 14e. In this way, the plurality of reaction chambers 14a to 14e are arranged in series so that the slurry flows in order. The discharge port 12 is provided in the fifth chamber 14e. The slurry that has reached the fifth chamber 14e is discharged from the discharge port 12 as a leachate.

An air blow pipe (not shown) is inserted in each of the reaction chambers 14a to 14e. High-pressure air is blown into the slurry in each reaction chamber 14a to 14e through an air blowing pipe. The nickel sulfide and oxygen come into contact with each other and the nickel sulfide is oxidized to obtain a nickel sulfate aqueous solution. A stirrer 15 is provided in each of the reaction chambers 14a to 14e in order to promote the contact between the nickel sulfide and oxygen and efficiently carry out the oxidation reaction.

The oxidation reaction of nickel sulfide is an exothermic reaction. Therefore, the temperature of the slurry in the autoclave 1 becomes too high as it is. Cooling water is added to adjust the slurry in the autoclave 1 to an appropriate temperature.

A cooling water supply pipe 16 is inserted into each of the reaction chambers 14a to 14e. Cooling water can be added to the slurry in each reaction chamber 14a to 14e through the cooling water supply pipe 16. The addition of cooling water adjusts the slurry in the autoclave 1 to an appropriate temperature.

The cooling water cools the slurry mainly by the effect of consuming the latent heat of vaporization at the time of evaporation. The slurry is cooled by evaporating the water originally contained in the cooling water and the raw material slurry. Water vapor is generated by evaporation of cooling water. A pressure adjusting valve 17 is provided in the gas phase portion of the tank 10. By discharging excess steam from the pressure regulating valve 17, the pressure in the autoclave 1 is maintained at a predetermined pressure.

The autoclave 1 is provided with a thermometer 18 for measuring the liquid temperature of the slurry. The autoclave 1 shown in FIG. 2 is provided with a thermometer 18 in the first chamber 14a. Therefore, the liquid temperature of the slurry in the first chamber 14a can be measured by the thermometer 18.

The raw material slurry is continuously supplied to the autoclave 1. In the autoclave 1, while the slurry flows from the first chamber 14a to the fifth chamber 14e, nickel sulfide is pressurized and leached to generate an aqueous nickel sulfate solution. The leachate is continuously discharged from the autoclave 1. The leachate is a slurry composed of a liquid containing an aqueous solution of nickel sulfate as a main component and a solid content.

The supply amount of the raw material slurry, the supply amount of high-pressure air to each of the reaction chambers 14a to 14e, the temperature in the autoclave 1, the pressure, and the like are appropriately adjusted in consideration of the operating efficiency. For example, the temperature in the autoclave 1 (liquid temperature of the slurry) is generally adjusted to 140 to 200 ° C., and the pressure in the autoclave 1 is generally adjusted to 1 to 2 MPaG by gauge pressure.

The leachate discharged from the autoclave 1 is stepped down to atmospheric pressure by the flash tank, and is cooled to less than 60 ° C. in the cooling tank. The leachate has, for example, a pH of 1.0 to 2.0. The composition of the leachate is, for example, 110 to 150 g / L for Ni, 5 to 15 g / L for Co, and 0.5 to 1.5 g / L for Fe.

The redox potential of the leachate is measured in the cooling tank. The redox potential of the leaching solution is used as an index of the leaching rate in the autoclave 1. Here, the leaching rate means the ratio of the raw materials that contributed to oxidative leaching. The nickel leaching rate can be obtained by "nickel leaching rate [%] = (weight of nickel in leachate ÷ weight of nickel in charged raw material) x 100". If the raw material is not sufficiently oxidized in the autoclave 1, the redox potential of the leachate becomes low. When the redox potential of the leaching solution is lower than the control reference value, it is judged that the leaching rate has decreased.

Returning to FIG. 1, the manufacturing process of nickel sulfate crystals will be described. In the iron removal step, impurities contained in the leachate, mainly iron, are removed as a neutralizing starch by adding a neutralizing agent to the leachate to neutralize the leachate. As the neutralizing agent, for example, slaked lime is used. The iron-removing final liquid is obtained by the iron-removing step. In addition to nickel, cobalt-free final solution contains cobalt and the like.

In the solvent extraction step, cobalt and impurities are removed from the iron-removing final solution by solvent extraction to obtain a high-purity nickel sulfate aqueous solution. The solvent extraction step includes an extraction stage, a washing stage, an exchange stage, a nickel recovery stage, a cobalt recovery stage, and a back extraction stage. In the extraction stage, nickel in a high-purity nickel sulfate aqueous solution is extracted into an organic phase to obtain a nickel-retaining organic phase. In the washing stage, the nickel-retaining organic phase is washed with a washing liquid containing nickel. In the exchange stage, the nickel-retaining organic phase after washing is brought into contact with the iron-retaining final solution to replace the nickel in the nickel-retaining organic phase with impurities in the iron-removing final solution to obtain a high-purity nickel sulfate aqueous solution. By sending the organic phase obtained in the exchange stage to the nickel recovery stage, the cobalt recovery stage, and the back extraction stage, nickel carried on the organic phase can be recovered, cobalt can be recovered, and impurities can be removed. The organic phase from which the extracted metals have been desorbed and purified is repeated in the extraction stage.

In the crystallization step, a high-purity nickel sulfate aqueous solution is concentrated using a crystallization facility, and nickel sulfate crystals are precipitated and recovered.

On the other hand, the neutralized starch discharged from the iron removal step is accompanied by nickel hydroxide. Therefore, if the neutralized starch is discharged to the outside of the system as it is, nickel will be lost. Therefore, it is preferable to recover nickel from the neutralized starch and repeat the recovered nickel in the system.

In the dissolution step, a sulfuric acid aqueous solution is added to the neutralized starch discharged from the iron removal step. The nickel hydroxide accompanying the neutralized starch is dissolved in a sulfuric acid aqueous solution to obtain a nickel thin liquid. Nickel thin liquid is an aqueous solution containing nickel having a relatively low concentration. The nickel concentration of the nickel thin liquid is, for example, 10 to 30 g / L.

In the dilution step, a thin nickel solution is diluted to obtain repulp water. Dilution adjusts the repulp water to a lower nickel concentration. Here, it is preferable to adjust the nickel concentration of the repulp water to 10 g / L or less, and more preferably to 3 g / L or less.

The nickel thin solution is diluted by mixing with the diluent. A liquid having a lower nickel concentration than a nickel thin liquid is used as the diluting liquid. As the diluting liquid, industrial water may be used, or water discharged in the process of producing nickel sulfate crystals may be used. For example, in the crystallization step, water vapor is generated when concentrating a high-purity nickel sulfate aqueous solution in a crystallization facility. Condensed water obtained from the water vapor may be used as a diluent.

The repulp water obtained in the dilution step is used in the repulp step. As a result, the liquid phase of the raw material slurry is adjusted to have a low nickel concentration, as in the case of repulp water. Here, the nickel concentration of the liquid phase of the raw material slurry at the time of being supplied to the autoclave is preferably 10 g / L or less, more preferably 3 g / L or less.

Nickel loss can be reduced by reusing the nickel thin liquid derived from the neutralized starch discharged from the iron removal step as repulp water. The dissolution step is included in the "post-step" described in the claims. As the nickel thin liquid used for producing repulp water, a liquid obtained in a subsequent step following the pressure oxidation leaching step in addition to the dissolution step, for example, a nickel recovery liquid obtained from the nickel recovery step in the solvent extraction step is used. You may use it.

The dilution step and the repulp step may be performed separately or at the same time. In order to carry out the diluting step and the repulp step at the same time, the raw material, the nickel thin liquid and the diluting liquid may be mixed in a single tank.

As the repulp water used in the repulp step, for example, industrially commonly used industrial water may be used. It suffices if the nickel concentration in the liquid phase of the raw material slurry can be maintained at a desired concentration.

By the way, one of the causes of the decrease in the leaching rate in the pressurized oxidative leaching is an increase in the nickel concentration in the liquid phase of the raw material slurry. The higher the nickel concentration in the liquid phase of the raw material slurry, the lower the redox potential of the leachate. That is, the leaching rate decreases.

The reason for this is presumed to be as follows.
The higher the nickel concentration in the liquid phase of the raw material slurry, the higher the total concentration of nickel eluted in the first chamber 14a of the autoclave and nickel originally contained in the liquid phase of the raw material slurry. Then, crystals of nickel sulfate monohydrate are likely to precipitate. When nickel sulfate monohydrate precipitates on the surface of a raw material (nickel sulfide) that has not been reacted or is in the process of reaction, contact between the raw material and oxygen is hindered. Then, a part of the raw material is discharged from the autoclave without reacting, and the leaching rate is lowered.

Therefore, it is considered that the leaching rate in the pressurized oxidative leaching can be improved by reducing the nickel concentration of the repulp water, that is, the nickel concentration of the liquid phase of the raw material slurry. If the nickel concentration in the liquid phase of the raw material slurry is reduced, nickel sulfate monohydrate precipitates on the surface of the raw material that has not reacted and is in the process of reaction in the autoclave, and the pressure oxidation leaching of the raw material is hindered. Can be suppressed. As a result, the leaching rate in pressurized oxidative leaching can be improved.

Conventionally, when the redox potential of the leachate is lower than the control reference value, the supply amount of the raw material slurry to the autoclave has been reduced. As a result, the residence time of the slurry in the autoclave is lengthened, and the leaching rate is improved. However, since the supply amount of the raw material slurry is reduced, the production amount of nickel sulfate crystals is reduced. On the other hand, according to the present embodiment, it is not necessary to reduce the supply amount of the raw material slurry, so that it is possible to avoid a reduction in the production of nickel sulfate crystals.

Further, since the nickel sulfide is sufficiently oxidized in the autoclave, the formation of the reducing sulfur compound can be suppressed. Therefore, it is possible to prevent the reducing sulfur compound from being mixed into the nickel sulfate crystals.

Next, an embodiment will be described.
The operation of the nickel sulfate crystal manufacturing process shown in FIG. 1 was carried out.
Nickel-cobalt mixed sulfide was used as a raw material. The nickel content of the raw material is 57.6 to 58.2% by weight. The nickel concentration of the repulp water was adjusted to various conditions of 1.9 to 17.4 g / L. A raw material slurry was prepared by mixing the raw material and repulp water. The solid content concentration of the raw material slurry was adjusted to 220 to 250 g / L.

The raw material slurry was continuously supplied to the autoclave to perform pressure oxidation leaching. The supply amount of the raw material slurry to the autoclave was set to 80 to 88 L / min. The pressure in the autoclave was set to 1.8 MPaG in gauge pressure. The amount of high-pressure air supplied into the autoclave was set to 6,000 to 6,500 Nm ³ / hour. Cooling water was added to the autoclave at 50 to 52 L / min, and the temperature of the slurry in the autoclave was controlled to 140 to 180 ° C.

The leachate discharged from the autoclave was lowered to atmospheric pressure by a flash tank, and then cooled in a cooling tank. The redox potential of the leachate in the cooling tank was measured. The relationship between the nickel concentration of the repulp water and the redox potential of the leachate is shown in the graph of FIG. Here, the redox potential is a measured value based on the Ag / AgCl electrode.

From the graph of FIG. 3, it can be seen that the lower the nickel concentration of the repulp water, the higher the redox potential of the leachate. From this, it was confirmed that the leaching rate in the pressurized oxidative leaching can be improved by lowering the nickel concentration of the repulp water.

It was also found that if the nickel concentration of the repulp water was adjusted to 10 g / L or less, the redox potential of the leachate became 390 mV or more, and a sufficient leachate rate could be obtained. It was also found that if the nickel concentration of the repulp water was adjusted to 3 g / L or less, the redox potential of the leachate became 410 mV or more, and the leachate rate became higher. Further, when the nickel concentration of the repulp water was adjusted to 3 g / L or less, the reducing sulfur compound was not produced.

1 Autoclave 10 Tank 11 Supply port 12 Discharge port 13 Partition 14a-14e Reaction chamber 15 Stirrer 16 Cooling water supply pipe 17 Pressure control valve 18 Thermometer

Claims (5)

In supplying a raw material slurry containing nickel sulfide to an autoclave and pressurizing and leaching nickel sulfide to obtain a nickel sulfate aqueous solution.
A pressure oxidative leaching method, wherein the nickel concentration of the liquid phase of the raw material slurry at the time of being supplied to the autoclave is 10 g / L or less. The pressure oxidative leaching method according to claim 1, wherein the nickel concentration of the liquid phase of the raw material slurry at the time of being supplied to the autoclave is 3 g / L or less. A repulp process in which a raw material containing nickel sulfide and repulp water are mixed to obtain a raw material slurry, and
A pressure oxidative leaching step of supplying the raw material slurry to an autoclave and pressurizing oxidative leaching of nickel sulfide to obtain a leachate which is a nickel sulfate aqueous solution.
The present invention comprises a diluting step of diluting a nickel thin liquid obtained in a subsequent step following the pressure oxidative leaching step to obtain the repulp water used in the repulp step .
In the dilution step, the nickel concentration of the repulp water is adjusted to 10 g / L or less.
A method for producing nickel sulfate. An iron removal step of adding a neutralizing agent to the leachate to remove iron contained in the leachate as a neutralizing starch.
The method for producing nickel sulfate according to claim 3, further comprising a dissolution step of dissolving the nickel hydroxide accompanying the neutralized starch with an aqueous sulfuric acid solution to obtain the nickel thin liquid. The method for producing nickel sulfate according to claim 3 or 4, wherein the nickel concentration of the repulp water is adjusted to 3 g / L or less in the dilution step.

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