JP7183750B2 - Method for starting up autoclave and method for producing nickel sulfate aqueous solution using same - Google Patents

Description

The present invention relates to a method for starting up an autoclave and a method for producing an aqueous nickel sulfate solution using the same, and in particular to a stable start-up of an autoclave in which high-pressure air is blown into a mixed slurry containing nickel matte and elemental sulfur for leaching. The present invention relates to a lifting method and a method for producing a nickel sulfate aqueous solution using the same.

In the smelting of non-ferrous metals, a slurry containing metal raw materials is charged into a cylindrical pressure vessel called an autoclave, and the valuable metals contained in the metal raw materials are leached into an aqueous solution at high temperature and high pressure. there is For example, in a nickel smelting plant, as described in Patent Document 1, a nickel matte containing finely powdered nickel sulfide as a main component and a mixed slurry containing finely powdered sulfur charged into an autoclave A so-called pressurized leaching is performed in which nickel contained in the nickel matte is leached as nickel sulfate by blowing high-pressure air.

As described above, in the pressure leaching process for leaching valuable metals from metal raw materials using an autoclave under high temperature and pressure conditions, the temperature and pressure conditions in the autoclave, the slurry concentration of the mixed slurry, and the nickel matte and sulfur contained therein and various conditions that affect the pressurized leaching reaction, such as the blending ratio of high-pressure air and the blowing position, are appropriately adjusted. It is possible to increase the leaching rate of

JP 2016-011442 A

In the above-mentioned nickel matte pressure leaching process using an autoclave, when starting up the autoclave that has been stopped due to periodic inspection etc. and shifting to steady operation, first, fine powder nickel matte and fine powder are placed in the autoclave. After introducing a mixed slurry containing sulfur in the form of liquid or introducing water to fill the slurry to a predetermined liquid level, high-pressure steam is introduced to create a high-temperature and high-pressure atmosphere. Next, the mixed slurry similar to the above is preliminarily heated and introduced into the autoclave, and high-pressure air is blown into the autoclave. As a result, nickel is leached from the nickel matte, which is the metal raw material.

Since the pressure leaching reaction is an exothermic reaction, after the autoclave is started up, the excess heat generated by the exothermic reaction can be removed with cooling water to stably shift to a steady operation. However, the temperature tended to decrease after the autoclave was started up, and it became difficult to stably continue the steady operation. In this case, it is necessary to stop the operation and start it up again, so the operating rate decreases and the processing cost increases.

More specifically, when the temperature shows a downward trend after starting up the autoclave, it is often due to the reactivity of the mixed slurry in the autoclave. After removing the slurry, the inside of the autoclave is cleaned, and the start-up operation is performed again. During the start-up operation after releasing the autoclave to the atmosphere, for an airtightness test, the pressure is increased stepwise over time to a pressure that is lower than the pressure resistance of the container and higher than the steady-state operating pressure and is maintained for a certain period of time. It is necessary to confirm that there is no leakage from the flanges of manhole covers and pipes. Therefore, including the start-up operation that accompanies this airtightness test, the shutdown period extends to one day or longer, which requires a great deal of time and effort.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. intended to provide

In order to achieve the above object, the method for starting up an autoclave provided by the present invention is to start up an autoclave in which high-pressure air is blown into a mixed slurry containing pulverized nickel matte and pulverized elemental sulfur for pressure leaching. The raising method is characterized in that, after the mixed slurry is charged into the autoclave without preheating, the high-pressure air is blown into the autoclave within at least 6 hours from the pulverization of the elemental sulfur.

According to the present invention, an autoclave that pressurizes nickel matte to produce nickel sulfate can be smoothly started up and stably shifted to steady operation, thereby preventing a significant decrease in the operating rate. can do.

4 is a graph showing liquid temperature trends in the autoclave when the autoclave is started up. It is a photograph of the mixed slurry and the solid content obtained by filtering it, (a) is the mixed slurry used when showing the temperature trend of the solid line in FIG. 1, and (b) is the temperature trend of the dotted line in FIG. It is a mixed slurry used when showing 4 is a photomicrograph of slurries containing nickel matte and/or elemental sulfur under various conditions.

Hereinafter, a method for starting up an autoclave and a method for producing an aqueous nickel sulfate solution using the same according to an embodiment of the present invention will be described. A method for producing an aqueous nickel sulfate solution according to an embodiment of the present invention includes a raw material pulverizing step of pulverizing raw material nickel matte and elemental sulfur, a raw material preparation step of preparing a mixed slurry containing the pulverized raw materials, and an autoclave. and a pressurized leaching step of producing a nickel sulfate aqueous solution from nickel contained in the nickel matte by pressurized leaching of the mixed slurry with high-pressure air, and the autoclave is smoothly started up in the pressurized leaching step. It is possible to prevent the operation rate from significantly decreasing by stably shifting to steady operation by Each of these steps will be described in detail below.

(1) Raw material pulverization step In the method for producing an aqueous nickel sulfate solution according to an embodiment of the present invention, nickel matte and elemental sulfur are used as raw materials. Nickel matte here means nickel sulfide obtained by melting nickel sulfide ore in a blast furnace, nickel sulfide obtained by adding sulfur to nickel oxide ore and melting in an electric furnace, etc. by pyrometallurgy. It refers to a nickel concentrate mainly composed of a nickel sulfide represented by nickel subsulfide (Ni ₃ S ₂ ) produced and metallic nickel. The chemical composition of general nickel matte is about 74 to 80% by mass of Ni, about 1% by mass of Co, about 0.1 to 0.4% by mass of Cu, and 0.1 to 0.7% by mass of Fe. %, and S is about 18 to 23% by mass.

In the raw material pulverization step, the nickel matte is introduced into a wet vibration mill together with water and pulverized to form a slurry containing finely powdered nickel matte. The particle size of the nickel matte after pulverization is not particularly limited, but it is preferably as small as possible from the viewpoint of increasing the speed of the pressure leaching reaction of nickel. Specifically, D50 (particle size The particle diameter at 50% of the volume integration of the particle amount in the distribution curve) is preferably less than 50 μm, more preferably less than 30 μm. Also, elemental sulfur, which is the other raw material, is similarly introduced into a wet vibration mill together with water and pulverized to form a slurry containing finely powdered elemental sulfur. The particle diameter of the elemental sulfur after pulverization is preferably less than 50 μm, more preferably less than 30 μm, in terms of D50 measured by laser diffraction and scattering method, like nickel matte.

(2) Raw material preparation step The slurry of nickel matte prepared in the raw material pulverization step and the slurry of elemental sulfur are mixed, and if necessary, water is further added to prepare a mixed slurry having a predetermined slurry concentration. The reason why elemental sulfur is used as the starting material for the aqueous nickel sulfate solution is to supplement the stoichiometric amount of sulfur necessary for producing nickel sulfate from nickel in the nickel matte. However, when the amount of elemental sulfur added to nickel exceeds the stoichiometric amount, the sulfuric acid generated by the oxidation reaction of the excess sulfur dissolves the metallic nickel in the nickel matte to generate hydrogen gas. I don't like it because

Therefore, in order to prevent the generation of hydrogen gas due to the generation of sulfuric acid, when the stoichiometric equivalent of sulfur required to generate sulfate from the metal components contained in nickel matte is 1, nickel matte It is preferable to adjust the mixing ratio of the nickel matte slurry and the elemental sulfur slurry so that the total amount of the sulfur contained in the raw material and the elemental sulfur mixed in the raw material preparation step is about 0.8. In addition, the slurry concentration of the mixed slurry is 100 to 400 g from the viewpoint of the liquid transferability to the autoclave by a slurry pump such as a mill flow pump, the diffusivity of high pressure air blown into the autoclave, the concentration of the resulting nickel sulfate aqueous solution, etc. /L is preferred.

(3) Pressure leaching process In the autoclave, nickel is pressure leached from the nickel matte by the pressure leaching reactions represented by chemical formulas 1 to 3 below. The pressure leaching reaction of nickel matte in this autoclave is generally carried out at a pressure of 1.6-1.9 MPaG and a temperature of 140-180.degree.
[Chemical Formula 1]
_{Ni3S2 +} S+ _6O2 = _3NiSO4
[Chemical Formula 2]
Ni+S+ _2O2 = _NiSO4
[Chemical Formula 3]
2Ni+ _{Ni3S2 +} 11/ _2O2 = _3NiO.2NiSO4

As described above, since the amount of sulfur is made smaller than the equivalent amount of nickel in the nickel matte, sulfuric acid is not produced or consumed as shown in the above chemical formulas 1 to 3, and an aqueous solution of nickel sulfate having a pH of about 4 to 6 and the above A post-pressurized leaching slurry consisting of the basic nickel sulfate (basic sulfate) produced by Formula 3 is produced. The pressure-leached slurry is decompressed to almost atmospheric pressure in a flash tank, and then subjected to dissolution treatment of basic nickel sulfate with sulfuric acid by the reaction of chemical formula 4 below to obtain an aqueous nickel sulfate solution. After this dissolution treatment, the treatment liquid is introduced into a filter press to separate undissolved residues.
[Chemical Formula 4]
_3NiO.2NiSO4 + _{3H2SO4 = 5NiSO4} + _3H2O

The autoclave in which the above-mentioned pressure leaching process is performed is divided into a plurality of compartments by weirs (partition walls) capable of overflowing. A gas blow-out pipe for blowing out compressed air toward the stirring blades of the lowermost stage is preferably provided in the machine. With such a configuration, the mixed slurry charged into the most upstream compartment in the autoclave is subjected to pressurized leaching by blowing high-pressure air while being stirred therein, and then overflows the partition wall and is sequentially adjacent. After being transferred to the compartment on the downstream side and subjected to the same leaching process, it is extracted from the extraction pipe provided in the most downstream compartment. In general, this autoclave is made of a clad steel plate body in which corrosion-resistant and wear-resistant metals such as titanium, nickel-based molybdenum, and chromium alloys are bonded to the inner surface of the pressure vessel steel material. It has a structure in which heat-resistant and corrosion-resistant materials such as acid-resistant bricks are laminated.

By the way, in order to start up an autoclave that has been in a stopped state due to a periodic inspection or the like and stably carry out the pressure leaching treatment, first, a mixed slurry or water is introduced into the autoclave to fill the autoclave to a predetermined liquid level, and then, For an airtightness test, the pressure is increased stepwise over time to a pressure that is lower than the pressure resistance of the container but higher than the steady-state operating pressure, and the pressure is maintained for a certain period of time. Confirmation is done. As a result of this airtightness test, if there is any problem, the pressure is lowered and the leakage part is repaired, etc., and then the airtightness test is performed again. On the other hand, if there is no problem, the voltage is lowered once and then the start-up operation is performed.

In this start-up operation, high-pressure steam is introduced into the autoclave to raise the pressure to create a high-temperature, high-pressure atmosphere, and when the predetermined temperature and pressure are reached, steam is directly blown into the mixed slurry in the slurry storage tank to preliminarily raise the temperature. After introducing the mixed slurry into the autoclave, high-pressure air is blown into the autoclave. As a result, the pressure leaching reactions represented by chemical formulas 1 to 3 described above occur, sulfur is oxidized to oxo acid ions, and nickel is leached from the metal raw material.

Since this pressurized leaching reaction is an exothermic reaction, water can be introduced directly into the autoclave, or cooling water can be supplied continuously or at regular time intervals into a corrugated tube provided in the autoclave. As indicated by the solid line in FIG. 1, it is possible to stably transition to steady operation. However, when the autoclave was started up and shifted to steady operation, the temperature sometimes decreased as indicated by the dotted line in FIG. The temperature trend shown in FIG. 1 is obtained by measuring the temperature of the slurry in the most upstream compartment of the autoclave.

The pressurized leaching reaction of nickel matte is an exothermic reaction, but the reaction rate is very low, so the reaction hardly progresses at room temperature. Therefore, in order to advance the reaction, the temperature must be raised to a certain constant temperature using high-pressure steam and high-pressure air at the start of operation. Once the pressure leaching reaction proceeds with a sufficient reaction rate, the temperature of the liquid rises due to the reaction heat, so the pressure leaching reaction proceeds continuously without supplying heat with steam. However, when the pressure leaching reaction has progressed once but the reaction rate is not sufficient, after the mixed slurry has been cooled by water injection, the liquid temperature cannot be raised only by the heat of reaction, and the reaction proceeds. The temperature drops below the minimum temperature, resulting in the trend indicated by the dotted line in FIG. The minimum temperature for this reaction to proceed has been found to be approximately 140°C.

As a result of investigating the cause of this temperature drop, the solid line in Fig. 1 successfully transitioned to steady operation (good condition), and the dotted line in Fig. 1 did not favorably transition to steady operation (defective condition). It was found that the colors of the slurries before charging into the autoclave were different from each other. Therefore, when both slurries were filtered and the solid contents were compared with each other, the solid contents obtained by filtering the mixed slurry in good condition were glossy gray nickel matte and yellow sulfur as shown in FIG. While it exhibited a relatively bright color mixed with, the solid content obtained by filtering the mixed slurry at the time of failure was hardly mixed with yellow sulfur, as shown in FIG. It had a blackish color with no luster as a whole.

Based on the above findings, we considered that the properties of the mixed slurry are related to the reactivity of the pressure leaching reaction, and investigated the composition of various slurries before and after the pressure leaching treatment. Then, as a result of observing a scanning electron microscope (SEM) photograph of the cross section of the solid content contained in the slurry and analyzing the cross section composition with an electron probe microanalyzer (EPMA), it was found that the nickel matte slurry and the sulfur slurry immediately after pulverization were 3(a) and 3(b), respectively, whereas the mixed slurry at the time of failure has a sulfurized particle surface of elemental sulfur as shown in FIG. 3(c). It was found that films composed of NiS ₂ and Ni ₃ S ₄ , which are substances, were formed.

When the surface of the elemental sulfur particles contained in the raw material mixture slurry is covered with a sulfide film in this way, the contact between the sulfur particles and the air is prevented by the sulfide film, so the oxidation reaction of the elemental sulfur occurs. does not proceed satisfactorily, and therefore it is considered that stable transition to steady operation after starting the autoclave becomes difficult. In the leaching residue obtained by filtering the slurry after the leaching treatment, particles of elemental sulfur having a sulfide film remained as shown in FIG. 3(d). In addition, it was thought that direct blowing of live steam into the mixed slurry stored in the slurry storage tank before charging the autoclave for preheating would promote the formation of the sulfide film.

Therefore, in order to suppress the film formation reaction on the surface of the elemental sulfur, the mixed slurry prepared in the raw material preparation step was directly charged into the autoclave without preheating the mixed slurry when the autoclave was started up. . Furthermore, in order to prevent the mixed slurry prepared in the raw material preparation step from being stored for a long time, the raw material crushing step and the raw material preparation step were respectively pulverized and mixed and charged into the autoclave immediately before starting the autoclave.

As a result, the problem of temperature drop at the time of transition from start-up to steady-state operation almost disappeared. A microphotograph of the mixed slurry immediately before charging into the autoclave in this case is shown in FIG. 3(e). The morphology of the particles observed in FIG. 3(e) has the same morphology as the nickel matte particles and elemental sulfur particles observed in FIGS. 3(a) and 3(b), respectively, and ) and FIG. 3(d).

That is, the autoclave start-up method of the embodiment of the present invention includes a liquid filling step of introducing mixed slurry or water into the autoclave, and the liquid filled autoclave is preferably 0.2 MPaG or more and 0.7 MPaG or less, more Preferably, high-pressure steam of about 0.5 MPaG is blown into a temperature rising step to create a high-temperature and high-pressure atmosphere, and the mixed slurry obtained by preparing the nickel matte and elemental sulfur pulverized in the raw material pulverizing step described above in the raw material preparation step described above. A slurry charging step of charging into the autoclave without preheating, and blowing high-pressure air into the mixed slurry in the autoclave within 8 hours, preferably within 4 hours after pulverizing the simple sulfur and a high-pressure air blowing step for pressurized leaching treatment.

In addition, in order to more reliably prevent the problem of temperature drop during start-up, it is preferable to increase the input amount of elemental sulfur at the time of start-up of the autoclave by about 60% compared to that during steady-state operation. preferable. Specifically, the pulverized nickel matte and the pulverized elemental sulfur contained in the mixed slurry are preferably blended so that elemental sulfur per ton of nickel matte is preferably 160 kg/ton.

After starting up the autoclave by the above method, the temperature inside the autoclave is maintained almost constant by injecting water directly into the autoclave, or by supplying cooling water to a cooling device such as a corrugated tube for indirect cooling. be able to. During this steady operation, in order to suppress the formation of sulfuric acid as described above, the mixing ratio of the pulverized nickel matte and the pulverized elemental sulfur contained in the mixed slurry is such that the amount of elemental sulfur per ton of nickel matte is 100 kg/. Tons are preferred. In addition, in order to increase the processing capacity of the autoclave, the mixed slurry may be preliminarily heated to about 90 to 100° C. and then continuously supplied to the autoclave during steady operation. Furthermore, at least elemental sulfur contained in the mixed slurry continuously supplied to the autoclave in steady operation after startup is preferably pulverized in the raw material pulverizing step within 8 hours, more preferably within 4 hours. It is preferable to use the

[Example 1]
After starting up the autoclave according to the following procedure, the autoclave was shifted to steady operation, and the slurry of nickel matte charged into the autoclave was subjected to pressure leaching treatment to produce an aqueous nickel sulfate solution. Specifically, nickel matte as a metal raw material was mixed with water, and pulverized using a rod mill to a D50 of 30 μm to prepare a nickel matte slurry. The nickel matte is a mixture of nickel subsulfide and metallic nickel obtained by dry smelting nickel oxide ore, and the chemical composition measured by electrogravimetry and ICP emission spectrometry is 78 masses of Ni. % and S was 20% by mass. Further, elemental sulfur was mixed with water and pulverized using a ball mill to a D50 of 30 μm to prepare a slurry of elemental sulfur. The resulting sulfur slurry was mixed with the nickel matte slurry so that the amount of sulfur per ton of nickel matte was 160 kg/ton, and water was added to prepare a mixed slurry having a slurry concentration of 210 g/L.

On the other hand, in an autoclave with a total effective capacity of 18.5 m ³ having four compartments separated by partitions with overflow parts, water was introduced into the most downstream compartment and the other most upstream compartments. The mixed slurry was introduced into a total of three compartments, ie, the second and third compartments from the upstream side, without preheating. After filling the autoclave with the liquid in this manner, high-pressure steam of 0.5 MPaG was blown into the filled autoclave while stirring to create a high-temperature, high-pressure atmosphere. Furthermore, high-pressure air of 1.8 MPaG was blown into the autoclave to pressurize it, and the temperature in the most upstream compartment was adjusted to 150°C. The same mixed slurry as described above was supplied to the uppermost compartment of the autoclave in this high-temperature, high-pressure atmosphere at a flow rate of 40 L/min without preheating.

About 1 hour after the start of supply of the mixed slurry, high-pressure air was blown into each compartment while continuing to stir. The amount of high-pressure air blown was 1800 Nm ³ /h, and the pressure inside the autoclave was controlled at 1.63 MPaG. The time from pulverization of elemental sulfur to the start of blowing high-pressure air into the autoclave was 6 hours. After confirming that the slurry temperature in the most upstream compartment in the autoclave tends to rise, cooling water is intermittently supplied to the autoclave to raise the slurry temperature in the most upstream compartment in the autoclave to 155 ± 2 ° C. can be stably controlled.

The slurry after pressure leaching in the autoclave is extracted from the most downstream compartment of the autoclave and transferred to a flash tank, where the pressure is reduced to atmospheric pressure, and then 70% by mass of sulfuric acid is added. Adjusted to pH 1.0. Thereafter, the residue was removed by filtration using a filter press to obtain an aqueous nickel sulfate solution. After 8 hours from the start of blowing high-pressure air into the autoclave, the blending ratio of nickel matte and elemental sulfur in the mixed slurry was adjusted to 100 kg/ton of elemental sulfur per ton of nickel matte, and this Steam was blown into the mixed slurry to preliminarily heat it to 95° C., and then the mixed slurry was continuously supplied to the autoclave. As a result, an aqueous nickel sulfate solution could be produced while the slurry temperature in the autoclave was stably controlled.

[Comparative Example 1]
The autoclave was started up in the same manner as in Example 1 except that the time from pulverization of elemental sulfur to the start of blowing high-pressure air into the autoclave was set to 72 hours. As a result, the slurry temperature in the most upstream compartment in the autoclave could not be stably controlled at about 155°C, and the temperature dropped at a rate of about 5°C/10 minutes, so the operation was stopped.

[Reference example]
The autoclave was started up in the same manner as in Example 1 above, except that the blending ratio of nickel matte and elemental sulfur in the mixed slurry at the time of starting the autoclave was changed from 160 kg/ton of elemental sulfur per ton of nickel matte to 260 kg/ton. rice field. As a result, as in Example 1, the slurry temperature in the most upstream compartment in the autoclave could be stably controlled at 155 ± 2 ° C., but the pH of the leached slurry extracted from the autoclave did not reach about 1. I stopped driving because it dropped.

Claims (5)

A method for starting up an autoclave for performing pressure leaching by blowing high-pressure air into a mixed slurry containing pulverized nickel matte and pulverized elemental sulfur, comprising:
A method for starting up an autoclave, characterized in that, after charging the mixed slurry into the autoclave without preheating, the high-pressure air is blown into the autoclave within at least 6 hours from pulverization of the elemental sulfur. A liquid filling step of introducing the mixed slurry or water into the autoclave before charging the mixed slurry, and a temperature raising step of blowing high pressure steam of 0.2 MPaG or more into the autoclave to create a high temperature and high pressure atmosphere are performed. The method for starting up an autoclave according to claim 1, characterized by: 3. The mixed slurry according to claim 1 or 2, characterized in that the slurry concentration is 100 to 400 g/L and the amount of elemental sulfur per 1 ton of nickel matte is 160 kg/ton. How to start up an autoclave. In steady operation after starting the autoclave by the starting method according to any one of claims 1 to 3, the crushed nickel matte and the crushed nickel matte are mixed at a mixing ratio of 100 kg / ton of elemental sulfur per 1 ton of nickel matte. The unitary sulfur is blended to prepare a steady state mixed slurry, the steady state mixed slurry is continuously supplied to the autoclave, and at least the unitary sulfur contained in the steady state mixed slurry is pulverized within 8 hours. A method for producing an aqueous nickel sulfate solution, characterized by using a nickel sulfate aqueous solution. 5. The method for producing an aqueous nickel sulfate solution according to claim 4, wherein the autoclave has a pressure of 1.6 to 1.9 MPaG and a temperature of 140 to 180.degree.

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