JP7459517B2 - Autoclaves and methods for operating autoclaves - Google Patents

Description

The present invention relates to an autoclave and a method of operating an autoclave. More particularly, the present invention relates to an autoclave used for pressurized oxidative leaching of metal sulfides, and a method of operating the autoclave.

A method of obtaining an aqueous metal sulfate solution by leaching metal sulfides under pressure is known. For example, a raw material slurry containing nickel sulfide is continuously supplied to an autoclave, and high pressure air is blown into the slurry in the autoclave to perform pressurized oxidation leaching. In this way, a nickel sulfate aqueous solution can be obtained (Patent Document 1).

JP2016-011442A

To cause the oxidation reaction of the metal sulfides, the slurry in the autoclave must be heated to a specific temperature. The temperature of the slurry is raised by blowing steam directly into it through a steam pipe. Because the oxidation reaction is an exothermic reaction, once the oxidation reaction begins, the temperature of the slurry rises due to the heat of reaction. Therefore, there is no need to blow steam into the slurry once the oxidation reaction has begun.

During operation of the autoclave after the oxidation reaction has started, solid matter may adhere to the inside of the steam piping, causing the steam piping to become clogged. Therefore, after stopping the autoclave and before restarting operation, it is necessary to clean the steam piping to remove substances that cause blockage. Removal of such blockage-causing substances requires time and effort.

In view of the above circumstances, an object of the present invention is to provide an autoclave and an autoclave operating method that can suppress blockage of steam piping.

The autoclave of the first invention comprises a tank for retaining a slurry, and a common pipe for selectively supplying steam for heating the slurry or cooling water for cooling the slurry into the tank, and is characterized in that the discharge end of the common pipe is positioned below the liquid surface of the slurry .
The autoclave of a second invention is the autoclave of the first invention, characterized in that it comprises a steam pipe connected to a connection end of the common pipe and supplying the steam , and a cooling water pipe connected to the connection end of the common pipe and supplying the cooling water, and the connection end of the common pipe is disposed above the liquid surface of the slurry.
The autoclave of a third invention is the autoclave of the first or second invention , characterized in that the common pipe allows the steam to flow before the start of the oxidation reaction, and allows the cooling water to flow after the start of the oxidation reaction.
The autoclave of a fourth invention is the autoclave of any one of the first to third inventions, characterized in that the slurry is a raw material slurry containing a metal sulfide, and is subjected to pressure oxidative leaching in the tank.
The method for operating an autoclave of the fifth invention is characterized in that, when a raw material slurry containing a metal sulfide is continuously supplied to an autoclave and the metal sulfide is subjected to pressure oxidative leaching to obtain an aqueous metal sulfate solution, steam is blown into the slurry through a common pipe before the start of the oxidation reaction, and cooling water is supplied to the slurry through the common pipe after the start of the oxidation reaction.
A sixth aspect of the present invention is a method for operating an autoclave according to the fifth aspect of the present invention, characterized in that the metal sulfide is nickel sulfide, and the aqueous metal sulfate solution is an aqueous nickel sulfate solution.

According to the first invention, since the common pipe is used for both steam supply and cooling water supply, cooling water flows through the common pipe even after the oxidation reaction starts. Therefore, it is difficult for solid matter to adhere to the inside of the common pipe, and blockage can be suppressed. Further, since the discharge end of the common pipe is arranged below the liquid level of the slurry, steam can be blown into the slurry, and the temperature of the slurry can be raised efficiently.
According to the second aspect of the invention, since the connecting end of the pipe is arranged above the liquid level of the slurry, the slurry does not flow back into the steam pipe and the cooling water pipe, thereby preventing the pipe from clogging.
According to the third invention, since steam and cooling water continue to flow alternatively through the common pipe, solid matter is less likely to adhere to the inside of the common pipe, and blockage can be suppressed.
According to the fourth aspect of the present invention, it is possible to reduce the time and labor required to remove substances that cause clogging of pipes when performing pressurized oxidative leaching of a raw material slurry containing metal sulfides.
According to the fifth invention, since steam and cooling water continue to flow alternatively through the common pipe, solid matter is less likely to adhere to the inside of the common pipe, and blockage can be suppressed.
According to the sixth invention, when producing a nickel sulfate aqueous solution by pressurized oxidative leaching of nickel sulfide, it is possible to reduce the time and labor required to remove substances that cause clogging of pipes.

FIG. 1 is a vertical cross-sectional view of an autoclave according to a first embodiment. FIG. 3 is a longitudinal cross-sectional view of an autoclave according to a second embodiment.

Next, an embodiment of the present invention will be described with reference to the drawings.
First Embodiment
The autoclave according to the first embodiment of the present invention is suitably used for obtaining an aqueous metal sulfate solution by pressure oxidative leaching of a metal sulfide.

(Autoclave)
As shown in Fig. 1, the autoclave 1 has a liquid-tight and airtight long tank 10. One end of the tank 10 is provided with a supply port 11 for supplying raw slurry. The other end of the tank 10 is provided with a discharge port 12 for discharging the leachate. The slurry remains inside the tank 10.

One or more partition walls 13 are erected inside the tank 10. The partition walls 13 divide the inside of the tank 10 into multiple reaction chambers 14a-14e arranged in the longitudinal direction. The number of reaction chambers 14a-14e is not particularly limited. The autoclave 1 of this embodiment has five reaction chambers 14a-14e. The five reaction chambers 14a-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. Note that the inside of the tank 10 does not have to be divided by the partition walls 13. In other words, the autoclave 1 may have only one reaction chamber.

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. After 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 sequence. 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. Note that the feeding method of the raw material slurry is not limited to the continuous method as described above, but may be a batch method.

An air blowing pipe 15 is inserted into each reaction chamber 14a to 14e. High pressure air is blown into the slurry in each of the reaction chambers 14a to 14e through the air blowing pipe 15. The amount of high pressure air supplied to each reaction chamber 14a to 14e can be adjusted individually. High pressure air acts as an oxidizing agent. A metal sulfide aqueous solution is obtained by bringing the raw material metal sulfide into contact with oxygen and oxidizing the metal sulfide. A stirrer 16 is provided in each of the reaction chambers 14a to 14e to promote contact between the metal sulfide and oxygen and to perform the oxidation reaction efficiently.

A pressure regulating valve 17 is provided in the gas phase of the tank 10. The pressure inside the autoclave 1 is maintained at a predetermined pressure by the pressure regulating valve 17. The pressure inside the autoclave 1 can also be adjusted by the pressure regulating valve 17.

In order to cause the oxidation reaction of the metal sulfide, it is necessary to heat the slurry to a specific temperature (140° C. in the case of nickel sulfide) or higher. The temperature of the slurry is increased by blowing in high pressure steam.

The oxidation reaction of metal sulfides is an exothermic reaction. For example, the oxidation reaction of nickel (II) sulfide is shown in the following reaction formula (1).
NiS+ _2O2 → _NiSO4 ΔH=-0.80 MJ/mol... (1)
Here, ΔH is the standard enthalpy of formation. When the reaction shown in reaction formula (1) occurs, 0.80 MJ of reaction heat is generated per mol of nickel (II) sulfide.

Thus, the oxidation reaction of metal sulfides is an exothermic reaction, but the reaction rate is so slow that the reaction hardly progresses at room temperature. To make the oxidation reaction proceed, the slurry must be heated to a specific temperature using high-pressure steam when the oxidation reaction begins. Once the oxidation reaction occurs with a sufficient reaction rate, the heat of reaction will raise the temperature of the slurry. For this reason, there is no need to blow steam into the slurry after the oxidation reaction begins. In fact, if left as is, the temperature of the slurry will become too high. Cooling water is added to adjust the slurry to an appropriate temperature.

In this way, steam is injected before the oxidation reaction starts, and cooling water is added after the oxidation reaction starts. If the injection of steam and the addition of cooling water are performed through separate pipes, the pipe supplying the steam may become clogged. After the oxidation reaction starts, that is, for most of the operation period of the autoclave 1, the pipe supplying the steam is immersed in the slurry without steam flowing through it. Therefore, the solids contained in the slurry tend to adhere to the inside of the pipe. In addition, metal sulfides generally contain iron, and iron oxide produced by the oxidation reaction tends to adhere to the inside of the pipe. If the solids that adhere to the inside of the pipe accumulate, the pipe will be clogged.

In the start-up operation at the start of the oxidation reaction, high-pressure steam is introduced into the tank 10 into which the raw material slurry has been introduced, and the pressure is increased to create a high-temperature, high-pressure atmosphere. When a specific temperature is reached, high-pressure air is blown into the tank 10. Here, since the specific temperature is lower than the temperature during steady operation after the start of the oxidation reaction, the pressure of the high-pressure steam is lower than the pressure inside the tank 10 during steady operation. For example, in the case of nickel sulfide, the specific temperature is 140°C, but the temperature can be increased with high-pressure steam at a gauge pressure of about 0.5 MPaG. On the other hand, the pressure during steady operation is about 1.8 MPaG at a gauge pressure. This pressure difference pushes the slurry into the steam pipe. The steam shutoff valve cannot be installed inside the tank 10, which is a high-pressure device. The slurry will backflow from the steam pipe to the shutoff valve installed outside the tank 10. On the other hand, since the cooling water is added at a pressure higher than the pressure inside the tank 10 during steady operation, the slurry will not backflow into the cooling water pipe.

To prevent blockage of the piping, the autoclave 1 of this embodiment has the piping for supplying steam and cooling water configured as follows:

The autoclave 1 has a steam pipe 21 that supplies steam. The steam pipe 21 branches out into the same number of reaction chambers 14a-14e (five in this embodiment) that the autoclave 1 has, and is led to the vicinity of each of the reaction chambers 14a-14e. The autoclave 1 also has a cooling water pipe 22 that supplies cooling water. The cooling water pipe 22 also branches out into the same number of reaction chambers 14a-14e that the autoclave 1 has, and is led to the vicinity of each of the reaction chambers 14a-14e.

A common pipe 23 is inserted into each of the reaction chambers 14a to 14e of the tank 10. The upstream end of each common pipe 23 is called a connection end 23a, and the downstream end is called a discharge end 23b. A branch pipe of the steam pipe 21 and a branch pipe of the cooling water pipe 22 are connected to a connecting end 23a of one of the common pipes 23. Therefore, the steam flowing through the steam pipe 21 is supplied into the tank 10 through the common pipe 23. Further, the cooling water flowing through the cooling water pipe 22 is supplied into the tank 10 through the common pipe 23.

A steam control valve 24 is provided on the branch pipe of the steam pipe 21. By operating the steam control valve 24, the flow rate of steam flowing through each common pipe 23 can be adjusted and the supply of steam can be stopped. In addition, a cooling water control valve 25 is provided on the branch pipe of the cooling water pipe 22. By operating the cooling water control valve 25, the flow rate of cooling water flowing through each common pipe 23 can be adjusted and the supply of cooling water can be stopped. Note that flow control valves, on-off valves, etc. can be used as the steam control valve 24 and the cooling water control valve 25.

By opening the steam control valve 24 and closing the cooling water control valve 25, steam can be supplied into the tank 10 via the common pipe 23. Conversely, if the steam control valve 24 is closed and the cooling water control valve 25 is opened, cooling water can be supplied into the tank 10 via the common pipe 23. In this way, the common pipe 23 is used to alternatively supply steam and cooling water into the tank 10.

It is preferable that the discharge end 23b of the common pipe 23 is disposed below the surface of the slurry in the tank 10. The liquid level of the slurry in the tank 10 is determined by the height of the upper end of the partition wall 13. Therefore, the discharge end 23b of the common pipe 23 is preferably arranged at a lower position than the upper end of the partition wall 13. In this way, steam can be blown into the slurry. For example, since the heat transfer coefficient is higher than when steam is sprayed onto the liquid surface of the slurry, the temperature of the slurry can be raised efficiently.

The connection end 23a of the common pipe 23, i.e., the connection between the steam pipe 21, the cooling water pipe 22 and the common pipe 23, is preferably placed above the liquid surface of the slurry in the tank 10. The connection of the pipes may be inside or outside the tank 10. Since the connection of the pipes is placed above the liquid surface of the slurry, the slurry does not flow back into the steam pipe 21 and the cooling water pipe 22, and clogging of the pipes can be prevented.

(Operating method)
Next, a method of operating the autoclave 1 will be explained.
First, raw materials are repulped to prepare a raw material slurry. Metal sulfides are used as raw materials. Examples of metal sulfides include nickel sulfide, cobalt sulfide, zinc sulfide, cadmium sulfide, and copper sulfide. One or more of these metal sulfides may be used as a raw material.

A raw material slurry containing metal sulfides is continuously supplied to an autoclave 1. In the autoclave 1, while the slurry flows from the first chamber 14a to the fifth chamber 14e, metal sulfides are oxidized and leached under pressure to produce a metal sulfate aqueous solution. For example, when the metal sulfide is nickel sulfide, a nickel sulfate aqueous solution is produced as the metal sulfate aqueous solution. The leachate is continuously discharged from the autoclave 1. The leachate is a slurry consisting of an aqueous metal sulfate solution and solids (leach residue).

Here, immediately after the autoclave 1 starts operating, i.e. immediately after new raw material slurry is supplied to the empty tank 10, the temperature of the slurry is low and no oxidation reaction occurs. Therefore, steam is blown into the slurry through the common pipe 23 to raise the temperature of the slurry until the oxidation reaction starts.

On the other hand, after the oxidation reaction starts, the blowing of steam is stopped and cooling water is supplied to the slurry through the common pipe 23. This cools the slurry. Note that it is preferable to continue supplying the cooling water until the autoclave 1 is stopped.

In this way, the common pipe 23 is used for both steam supply and cooling water supply. Then, steam and cooling water continue to flow alternatively through the common pipe 23. Steam flows through the common pipe 23 before the oxidation reaction starts, and cooling water flows through the common pipe 23 after the oxidation reaction starts. Since the cooling water flows through the common pipe 23 even after the oxidation reaction starts, solid matter is less likely to adhere to the inside of the common pipe 23, and blockage can be suppressed.

When the piping becomes clogged, it is necessary to clean the piping and remove the object causing the blockage. This work of removing the object causing the blockage takes time and effort. In addition, since the autoclave 1 must be stopped while the work of removing the object causing the blockage is being performed, the operating rate of the autoclave 1 decreases. In contrast, this embodiment can suppress blockage of the piping, so the time and effort required to remove the object causing the blockage can be reduced and the operating rate of the autoclave 1 can be increased.

In order to effectively suppress the adhesion of solid matter inside the common pipe 23, it is preferable that the cooling water flowing through the common pipe 23 has a certain flow rate. Specifically, it is preferable that the flow rate of the cooling water in the common pipe 23 be 0.005 m/sec or more. By doing so, the effect of suppressing solid matter from adhering to the inside of the common pipe 23 is high. Furthermore, since the flow rate control of the cooling water is stabilized, it is possible to prevent the cooling water from temporarily stopping flowing.

Second Embodiment
There is no particular limitation on the connection positions of the steam pipe 21, the cooling water pipe 22, and the common pipe 23. For example, as shown in Fig. 2, the steam pipe 21, the cooling water pipe 22, and the common pipe 23 may be connected upstream of the branch points to each of the reaction chambers 14a to 14e. The common pipe 23 is branched into the same number of reaction chambers 14a to 14e of the autoclave 1, and each branch pipe is inserted into one of the reaction chambers 14a to 14e.

The steam pipe 21 is provided with a steam control valve 24. The cooling water pipe 22 is provided with a cooling water control valve 25. By opening and closing the steam control valve 24 and the cooling water control valve 25, steam and cooling water can be selectively flowed through the common pipe 23.

In this configuration, it is preferable to provide a flow control valve 26 in each branch pipe of the common pipe 23. This allows the flow rate of steam and cooling water to be adjusted for each reaction chamber 14a to 14e.

Next, an embodiment will be described.
Example 1
Pressure oxidation leaching was carried out using an autoclave having the configuration shown in Figure 1. The operating conditions were as follows.
Raw material: Mixed sulfide of nickel and cobalt Nickel content of raw material: 57.0-58.5% by weight (dry basis)
Cobalt content of raw material: 4.0-6.0% by weight (dry basis)
Solid concentration of raw material slurry: 220 to 270 g/L
Supply rate of raw material slurry: 30 to 85 L/min Pressure inside the autoclave (gauge pressure): 1.6 to 1.9 MPaG

After the autoclave started operating, steam was injected through the common pipe before the oxidation reaction began. After the oxidation reaction began, cooling water was constantly supplied through the common pipe. After five months of operation, the common pipe was checked and no blockages were found.

(Comparative example 1)
Pressurized oxidation leaching was carried out using an autoclave configured to carry out steam injection and cooling water addition through separate piping. The operating conditions are the same as in the example. After 5 months of operation, the steam piping was checked and it was found that the steam piping inserted into the first and second chambers was clogged.

From the above, it was confirmed that by having a configuration in which steam and cooling water are selectively supplied via a common pipe, clogging of the pipe can be suppressed.

1 Autoclave 10 Tank 21 Steam pipe 22 Cooling water pipe 23 Common pipe

Claims (6)

A tank for retaining slurry;
A common piping that selectively supplies steam to raise the temperature of the slurry and cooling water to cool the slurry into the tank ,
The discharge end of the common pipe is located below the liquid level of the slurry.
An autoclave characterized by: a steam pipe connected to a connection end of the common pipe and supplying the steam;
a cooling water pipe connected to the connection end of the common pipe and supplying the cooling water,
The autoclave according to claim 1 , wherein the connection end of the common pipe is located above the liquid level of the slurry. 3. The autoclave according to claim 1, wherein the common pipe is used for flowing the steam before the start of the oxidation reaction and for flowing the cooling water after the start of the oxidation reaction. 4. The autoclave according to claim 1 , wherein the slurry is a raw material slurry containing metal sulfides, and is subjected to pressure oxidative leaching in the tank. A raw material slurry containing a metal sulfide is continuously fed to an autoclave, and the metal sulfide is subjected to pressure oxidative leaching to obtain an aqueous metal sulfate solution,
Before the oxidation reaction begins, steam is blown into the slurry through a common pipe,
A method for operating an autoclave, comprising the steps of: supplying cooling water to said slurry through said common pipe after the start of the oxidation reaction. 6. The method of claim 5 , wherein the metal sulfide is nickel sulfide, and the metal sulfate aqueous solution is an aqueous nickel sulfate solution.