JP6135479B2 - Method for producing nickel powder - Google Patents

Description

  The present invention relates to a method for producing nickel powder. More specifically, the present invention relates to a method for producing fine, less connected particles and oxygen useful for electronic parts such as a multilayer ceramic capacitor (hereinafter referred to as MLCC), an external electrode, and an electromagnetic shield. The present invention relates to a nickel powder production method capable of efficiently obtaining nickel powder having a low concentration by a low-cost and simple process regardless of a special apparatus.

  In recent years, with the miniaturization and high performance of mobile phones and digital devices, MLCC, which is a chip component, is also becoming smaller and larger in capacity. With the miniaturization and increase in capacity of MLCCs, nickel powders used for internal electrodes are also required to be reduced in diameter and coarse particles, and various nickel powder production methods have been proposed.

  For example, a vapor phase reduction method that reduces nickel chloride vapor with a reducing gas, a spray pyrolysis method in which a solution containing a metal compound is made into fine droplets and thermally decomposed at a high temperature, and a nickel salt is reduced in water or an organic solvent. There are a wet reduction method in which reduction is carried out by a method, and a static hydrogen reduction method in which powder of a nickel compound such as nickel oxide, nickel hydroxide, nickel carbonate is reduced with hydrogen gas.

Among these methods, a method of producing nickel powder by producing nickel hydroxide by a wet method and using this as a raw material to produce nickel powder is a production method capable of obtaining nickel powder with high productivity and low cost. For example, while continuously adding a nickel-containing solution to a slurry in a reaction vessel maintained at a constant temperature, an alkali solution is added so as to maintain the slurry at a predetermined pH to produce nickel hydroxide, A method for producing nickel powder is disclosed in which the slurry is filtered, washed with water and dried to obtain nickel hydroxide powder, which is then heated and reduced at a reduction temperature of 400 to 550 ° C. in a hydrogen gas reducing atmosphere. (Patent Document 1).
This method uses nickel chloride as a raw material to obtain nickel powder that is inexpensive and has good productivity, but has a problem that the residual chlorine of the nickel powder is large. If there is a lot of residual chlorine in the nickel powder, it will not only inhibit the rust resistance of the nickel powder, but when used as a material for electronic parts, it generates hydrogen chloride gas in the process of firing, etc. There is a problem of adversely affecting

  In order to solve the above problems, a nickel oxide production method including a step of washing impurities in nickel hydroxide with a sodium hydroxide aqueous solution (Patent Document 2), a slurry after completion of the neutralization reaction in the nickel hydroxide production step A method for producing nickel oxide (Patent Document 3) including a step of raising the pH of the powder to 10 or more and a method for washing nickel powder with an organic acid (Patent Document 4) have been proposed.

  Patent Documents 2 and 3 do not describe the step of reducing the obtained nickel oxide, but after obtaining nickel hydroxide with a reduced chlorine concentration by these production methods, nickel oxide powder is produced by oxidation treatment. When nickel powder is produced by reduction treatment of this nickel oxide powder, the sintering inhibiting effect during the reduction treatment is reduced, and linked particles are easily generated. On the other hand, when the heat treatment temperature is lowered in order to reduce the connected particles, the reduction of the nickel powder does not proceed sufficiently, and the oxygen concentration of the nickel powder increases, which is not suitable as an electrode material.

In Patent Document 4, since an organic acid is used, it is necessary to treat the generated waste liquid, resulting in high costs.
Therefore, an inexpensive nickel powder with few connected particles and a low oxygen concentration has been eagerly desired in a nickel powder manufacturing method using nickel chloride as a raw material.

JP 2003-213310 A Japanese Patent No. 519476 JP 2011-42528 A JP 2009-108351 A

  In view of the above-described problems of the prior art, the present invention is useful for electronic components such as multilayer ceramic capacitors (hereinafter referred to as MLCC), external electrodes, electromagnetic wave shields, etc. It aims at providing the manufacturing method of the nickel powder which can obtain low nickel powder efficiently by a low-cost and simple process irrespective of a special apparatus.

  As a result of diligent investigations on reducing the connected particles and reducing the oxygen concentration of nickel powder obtained by reducing nickel hydroxide obtained by a reduction process using a wet method with high productivity and low cost, By cleaning nickel under specific conditions, controlling the chlorine concentration in nickel hydroxide to a specific value, and then heating and reducing the nickel oxide obtained by oxidation at a specific temperature, the oxygen concentration of the nickel powder As a result, the inventors have found that it is possible to produce nickel powder with few connected particles, and thus completed the present invention.

  That is, according to the first aspect of the present invention, a nickel hydroxide powder having a residual chlorine concentration of 5000 to 9000 mass ppm is obtained by neutralizing an aqueous nickel chloride solution with alkali to precipitate nickel hydroxide (A ), A step (B) of heat-treating the nickel hydroxide powder in an oxidizing atmosphere or an inert atmosphere to form a nickel oxide powder, and heat-treating the nickel oxide at 380 to 500 ° C. in a reducing atmosphere. And producing a nickel powder, and a nickel powder production method comprising a step (D) of washing the nickel powder, wherein the nickel chloride aqueous solution and the alkali are neutralized in the step (A). Is completed, the nickel hydroxide slurry is washed with a pH of 8.5 to 12.0, followed by filtration and pure water washing.

Further, according to the second invention of the present invention, in the first invention, in the step (A), after the neutralization reaction between the nickel chloride aqueous solution and the alkali is completed, the nickel hydroxide slurry is concentrated to a pH. Is produced as 8.5 to 12.0. A method for producing nickel powder is provided.
According to the third invention of the present invention, in the first invention, in the step (A), the pH of the nickel hydroxide slurry at the time of washing is the pH at the time of neutralization reaction between the nickel chloride aqueous solution and the alkali. The method for producing nickel powder is characterized by being higher than
According to the fourth aspect of the present invention, in any one of the first to third aspects, the alkali used for neutralization in the step (A) is at least one selected from sodium hydroxide and potassium hydroxide. The method for producing nickel powder characterized by the above is provided.

According to the fifth invention of the present invention, in any one of the first to fourth inventions, the alkali used for washing in the step (A) is the same alkali used for neutralization. A nickel powder production method is provided.
According to a sixth aspect of the present invention, there is provided the nickel powder manufacturing method according to any one of the first to fifth aspects, wherein D90 of the obtained nickel powder is 1.5 μm or less. Is done.
Moreover, according to the seventh invention of the present invention, in any one of the first to sixth inventions, the nickel powder obtained has an oxygen concentration of 1.8% by mass or less. A method is provided.

According to the present invention, after the neutralization reaction between the nickel chloride aqueous solution and the alkali is completed, the pH of the nickel hydroxide slurry is washed to 8.5 to 12.0, and the resulting nickel hydroxide has a residual chlorine concentration of 5000. Since it is a simple process of heat treating (reducing) nickel oxide obtained by oxidizing nickel hydroxide, and then oxidizing nickel hydroxide at a specific temperature, without special equipment, Fine nickel powder can be produced efficiently.
In addition, the nickel powder obtained by the present invention is suitable for use in electronic parts such as MLCC internal parts, external electrodes, and electromagnetic wave shields because it has few connected particles and has a low oxygen concentration, and its industrial value is great.

  Hereinafter, an embodiment is described in detail about a manufacturing method of nickel powder of the present invention.

  The method for producing nickel powder of the present invention comprises a step (A) of neutralizing a nickel chloride aqueous solution with an alkali to precipitate nickel hydroxide to obtain a nickel hydroxide powder having a residual chlorine concentration of 5000 to 9000 mass ppm, Step (B) in which the nickel hydroxide powder is heat-treated in an oxidizing atmosphere or in an inert atmosphere to form nickel oxide powder, and the nickel oxide is heat-treated at 380 to 500 ° C. in a reducing atmosphere. A method for producing nickel powder comprising a step (C) for producing powder and a step (D) for washing the nickel powder, wherein the neutralization reaction between the aqueous nickel chloride solution and the alkali in the step (A) is completed. Thereafter, the pH of the nickel hydroxide slurry is washed to 8.5 to 12.0, followed by filtration and pure water washing.

(1) Process A
Step A of the present invention is a step of producing nickel hydroxide by neutralizing an aqueous nickel chloride solution with an alkaline aqueous solution. Known techniques can be applied to the concentration of the aqueous solution, neutralization conditions, and the like, and the cleaning apparatus is not particularly limited, and a reaction tank equipped with a mechanical stirring apparatus can be used.

  At this time, in order to obtain nickel hydroxide having uniform characteristics, it is preferable to add the nickel hydroxide aqueous solution and the alkaline aqueous solution while keeping the pH of the nickel hydroxide aqueous solution and the alkaline aqueous solution constant in a sufficiently stirred reaction vessel. The alkaline aqueous solution used for neutralization is preferably at least one selected from sodium hydroxide and potassium hydroxide, but sodium hydroxide is particularly preferred from the viewpoint of cost.

  In the present invention, after the formation of nickel hydroxide, the alkali is added to the reaction solution to adjust the pH to the range of 8.5 to 12.0 and the nickel hydroxide is washed. The pH during washing is preferably 8.5 or more and less than 10.0, and preferably pH 9.0 or more and less than 10.0. If the pH at the time of washing is less than 8.5, the nickel hydroxide washing will not proceed sufficiently and the chlorine concentration will increase, adversely affecting the production equipment. If the pH exceeds 12.0, the chlorine concentration of the nickel hydroxide will be reduced. Since it becomes too low and it becomes easy to produce | generate connection particle | grains by the heat processing process, it is unpreferable. In order to reduce the chlorine concentration by washing, the pH at the time of neutralization and the pH at the time of washing are preferably set such that the pH at the time of alkali washing is higher than that at the time of neutralization, and an aqueous alkali solution is further added at the time of washing.

  The reaction solution after neutralization is washed by adding the alkaline aqueous solution to the nickel hydroxide slurry after the produced nickel hydroxide is once settled to remove the amount of waste liquid after washing, removing the supernatant liquid and concentrating. Is preferred. The slurry concentration of nickel hydroxide after removing the supernatant is preferably 250 to 1000 g / L. When the slurry concentration before alkali cleaning is less than 250 g / L, the amount of waste liquid increases. When the slurry concentration is higher than 1000 g / L, the impurity concentration in the filtrate increases and the amount of impurities brought into the repulping process increases. Get higher. The alkali cleaning time and temperature may be appropriately set, but are preferably 20 to 70 ° C. and 15 minutes to 2 hours. Outside this range, sufficient alkali cleaning may not be performed.

  Since the cleaning degree of nickel hydroxide can be grasped by the residual chlorine concentration, it is preferable to control the residual chlorine after cleaning to 5000 to 9000 mass ppm. If the residual chlorine is less than 5000 ppm by mass, connected particles are likely to be generated in the heat treatment step, and if it exceeds 9000 ppm by mass, the chlorine concentration increases and adversely affects production equipment.

Conventionally, cleaning is performed with pure water instead of alkali cleaning. However, pure water requires multiple cleanings to reduce the chlorine concentration, which is not preferable in terms of waste liquid and productivity. The alkaline aqueous solution added at the time of alkaline cleaning is preferably sodium hydroxide or potassium hydroxide that is the same as that used during neutralization so as not to increase the impurity concentration of the nickel powder. Particularly preferred.
The nickel hydroxide thus produced is solid-liquid separated by filtration to obtain a cake. Although the obtained cake can be used directly in the next step, it is preferably washed with water in order to reduce the concentration of the element derived from the alkaline aqueous solution. An arbitrary method can be used as the washing method, and a method of passing water through the cake separated into solid and liquid, a method of re-slurry in pure water (repulping), or the like is used.

  Next, the nickel hydroxide powder obtained by washing is dried. For drying, a general dryer such as an air dryer or a vacuum dryer can be used, and the drying temperature is preferably 200 ° C. or lower. When dried at a temperature higher than 200 ° C., nickel hydroxide is decomposed, which may affect physical properties.

(2) Process (B)
The step (B) of the present invention is a step of obtaining nickel oxide powder by heat-treating the nickel hydroxide obtained in the step (A) in an oxidizing atmosphere or an inert atmosphere. Treatment conditions such as heating temperature and time can be appropriately set according to the nickel oxide powder to be obtained.

  This heat treatment is preferably performed in a state where gas exchange can be performed in order to perform uniform treatment. If the gas exchange is insufficient, the characteristics of the resulting nickel oxide powder may become non-uniform due to the influence of the generated water vapor. For the heat treatment, a general heating furnace can be used. For example, a stationary electric furnace, a rolling furnace, a burner furnace, a conveying continuous furnace, or the like can be used. The type of gas used is not limited as long as it is a non-reducing atmosphere, but an atmosphere containing oxygen is excellent in terms of cost and ease of handling.

(3) Process (C)
Step (C) of the present invention is a step of obtaining nickel powder by reducing the nickel oxide powder obtained in the step (B) in a reducing atmosphere.

Regarding this reduction condition, the reduction temperature is set to 380 to 500 ° C. A preferable reduction temperature is 380 to 450 ° C, and more preferably 380 to 400 ° C. The heating time is preferably 1 to 5 hours, for example, although it depends on the reduction temperature.
When the reduction temperature is less than 380 ° C., the nickel oxide powder may not be sufficiently reduced or may take a long time for the reduction. On the other hand, when the reduction temperature exceeds 500 ° C., the nickel particles may be coarsened. The reducing atmosphere can be selected as appropriate, but it is preferably a hydrogen-containing gas atmosphere in consideration of environmental influences. Further, during the reduction, it is preferably performed in a gas exchange atmosphere for the same reason as in the step (B). Other factors relating to reduction can be arbitrarily set according to the required scale. The type of gas used for making the reducing atmosphere is not limited, but a hydrogen-containing gas such as a hydrogen-containing nitrogen gas is preferred from the viewpoint of availability and the degree of influence on the environment.

(4) Process (D)
The step (D) of the present invention is a step of washing the nickel powder obtained in the step (C). For the washing here, pure water, an inorganic acid such as sulfuric acid, or an organic acid such as citric acid can be used, but it is preferable to use pure water because of the ease of wastewater treatment.

  Moreover, although washing | cleaning can be performed at arbitrary temperature, it is preferable to carry out at 10 to 50 degreeC. When the temperature is low, the cleaning effect is lowered, and it takes a long time to remove impurities, which causes a problem in productivity. Increasing the cleaning temperature increases the effect of removing impurities, but there is a problem that the change to nickel hydroxide advances, the surface state of nickel powder changes, and the oxygen concentration increases.

  The concentration of the slurry for washing is not particularly limited, but the slurry concentration is preferably 30 to 500 g / L, more preferably 30 to 300 g / L. When the slurry concentration is less than 30 g / L, productivity is low and a large amount of waste liquid is generated. On the other hand, when the slurry concentration exceeds 500 g / L, the dispersibility of nickel may be deteriorated, or impurities remaining in the cake may increase, and cleaning may not be performed sufficiently. The washing device is not particularly limited, and a reaction vessel equipped with a mechanical stirring device can be used as in the step (A).

  Finally, the nickel slurry is solid-liquid separated by filtration or the like, and the resulting nickel powder is dried. Although drying can use a general dryer similarly to a process (A), as for drying temperature, 180 degrees C or less is preferable. When drying is performed at a temperature higher than 180 ° C., particles are connected, and the dispersibility of the nickel powder may be affected. The lower limit of the drying temperature is not particularly limited, but if it is less than 100 ° C., it takes time to reach a desired dry state, so that productivity is lowered.

(5) Obtained nickel powder By passing through said process (A)-(D), D90 is 1.5 micrometers or less and nickel concentration whose oxygen concentration is 1.8 mass% or less can be obtained. When D90 exceeds 1.5 μm, the particles are connected, and thus the dispersibility of the nickel powder deteriorates. Further, nickel powder having an oxygen concentration exceeding 1.8% by mass is difficult to use as an electrode material.
Since the nickel powder obtained by the production method of the present invention has the above-described characteristics, it can be used as a nickel paste applied to the inside of the MLL, external electrodes, electromagnetic wave shields, and the like.

  EXAMPLES Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. The chlorine concentration in the nickel hydroxide powder, the particle diameter of the nickel powder and the oxygen concentration were measured and evaluated in the following manner.

(Chlorine concentration in nickel hydroxide powder)
The chlorine concentration in the nickel hydroxide powder was evaluated by a calibration curve method using a fluorescent X-ray quantitative analyzer. (Magic manufactured by PANalytical)
(Nickel powder particle size)
The particle size of the nickel powder was measured by a laser diffusion method, and the particle size D90 with a volume integration of 90% was determined from the particle size distribution. In addition, since the value of D90 increases when the ratio of connected particles increases even with the same particle size, the value of D90 is an indicator of the number of connected particles.
(Oxygen concentration in nickel powder)
The oxygen concentration in the nickel powder was evaluated by resistance heating infrared absorption analysis using an analyzer (TC-336 manufactured by LECO).

(Comprehensive evaluation)
Nickel powder with D90 of 1.5 μm or less, oxygen concentration of 1.8% or less, productivity: nickel hydroxide cleaning frequency of 2 times or less is good (◯), and it exceeds 3 times, it is impossible (×). Only those satisfying all of the criteria were judged as good (◯).

Example 1
Sodium hydroxide was dissolved in pure water in a 10 L beaker to prepare 1.5 L of an aqueous sodium hydroxide solution adjusted to pH 8.3. To this aqueous sodium hydroxide solution, a nickel chloride aqueous solution with a nickel concentration of 60 g / L and a 24% by mass aqueous sodium hydroxide solution were continuously added to the reaction vessel while adjusting the pH to 8.3, thereby adding water. Nickel oxide was produced.
At that time, the nickel chloride aqueous solution was added at a rate of 24 mL / min. Moreover, liquid temperature was hold | maintained at 60 degreeC and it mixed at 200 rpm with the stirring blade. After adding 3 L of nickel chloride aqueous solution, stirring was continued for 3 hours to produce nickel hydroxide.
Next, the obtained nickel hydroxide slurry was once settled, and the supernatant was removed so that the slurry concentration became 500 g / L. Thereafter, an aqueous sodium hydroxide solution was added to the slurry, and the pH was adjusted to 8.5 and the liquid temperature was adjusted to 50 ° C., followed by washing for 30 minutes. Then, it filtered and isolate | separated the nickel hydroxide cake, Furthermore, the pure water repulp and filtration were performed for 30 minutes with the slurry density | concentration of 200 g / L, and the nickel hydroxide filter cake was obtained. The obtained filter cake was put into an air dryer and dried at 120 ° C. for 24 hours to obtain nickel hydroxide powder. Moreover, the chlorine concentration of the obtained nickel hydroxide powder was measured.
Subsequently, 10 g of the obtained nickel hydroxide was heated in air at 460 ° C. for 2 hours to synthesize nickel oxide, and the obtained nickel oxide was reduced in hydrogen atmosphere at 400 ° C. for 3 hours to obtain nickel powder.
Finally, the obtained nickel powder was washed by stirring with pure water having a slurry concentration of 40 g / L for 30 minutes, and was subjected to solid-liquid separation by suction filtration. Thereafter, it was dried at 120 ° C. for 12 hours in an air dryer and passed through a # 100 sieve to obtain nickel powder. The results are shown in Table 1.

(Example 2)
Nickel powder was produced in the same manner as in Example 1 except that the pH at the time of washing nickel hydroxide was changed to 9.8. The results are shown in Table 1.

(Example 3)
Nickel powder was prepared in the same manner as in Example 1 except that the pH at the time of washing nickel hydroxide was changed to 12.0. The results are shown in Table 1.

(Comparative Example 1)
In Example 1, the nickel hydroxide slurry was once settled, and instead of adding the aqueous sodium hydroxide solution as the washing liquid after removing the supernatant liquid, the nickel hydroxide was washed with pure water, and the filtered pure water repulped and filtered. Nickel powder was produced in the same manner as in Example 1 except that the number of times was three. The pH at the first pure water washing was 7.5. The results are shown in Table 2.

(Comparative Example 2)
In the same manner as in Example 1, except that nickel hydroxide slurry was once settled in Example 1, and instead of adding a sodium hydroxide aqueous solution as a cleaning solution after removing the supernatant, nickel hydroxide was washed with pure water. Nickel hydroxide was produced. Due to the high residual chlorine content of nickel hydroxide, the work after nickel oxide generation was not performed. The pH at the first pure water washing was 7.5. The results are shown in Table 2.

(Comparative Example 3)
Nickel powder was prepared in the same manner as in Example 1 except that the pH at the time of washing nickel hydroxide was changed to 12.3. The results are shown in Table 2.

(Comparative Example 4)
Nickel powder was prepared in the same manner as in Example 1 except that the pH during the nickel hydroxide washing was changed to 12.3 and the heating temperature in the hydrogen atmosphere was changed to 370 ° C. in the reduction treatment of nickel oxide. The results are shown in Table 1.

(Evaluation)
As is apparent from Table 1 showing the above results, Examples 1 to 3 have excellent nickel powder productivity, few coarse particles, and low oxygen concentration. The nickel powder obtained in Example 3 has a large D90 and a slight increase in the number of connected particles, but at a level where there is no practical problem.

  On the other hand, as is apparent from Table 2, Comparative Example 1 did not use an alkali for the cleaning of nickel hydroxide, so that the number of cleanings was increased and the productivity became impossible. In Comparative Example 2, the cleaning with pure water was performed twice, so that the chlorine concentration of nickel hydroxide was high, and the influence on the equipment was large, which was not possible. In Comparative Example 3, since the pH was higher than 12.0 during the washing of nickel hydroxide, the chlorine concentration of nickel hydroxide became too low, and the connection of particles progressed, making it impossible. In Comparative Example 4, since the pH at the time of washing nickel hydroxide was higher than 12.0, the chlorine concentration of nickel hydroxide was lowered, and as a result of lowering the heat treatment temperature to prevent particle connection, the oxygen concentration was Highly impossible.

  According to the method for producing nickel powder of the present invention, nickel powder with few connected particles and reduced oxygen concentration can be obtained. The obtained nickel powder is suitable as an electronic component material such as a wiring material or an electrode material in MLCC or electromagnetic wave shield.

Claims (7)

A step (A) of neutralizing a nickel chloride aqueous solution with an alkali to precipitate nickel hydroxide to obtain nickel hydroxide powder having a residual chlorine concentration of 5000 to 9000 mass ppm; and the nickel hydroxide powder in an oxidizing atmosphere. Or the process (B) which heat-processes in inert atmosphere and makes nickel oxide powder, the process (C) which heat-processes this nickel oxide at 380-500 degreeC in a reducing atmosphere, and (C), A method for producing nickel powder comprising the step (D) of washing the nickel powder,
After the neutralization reaction between the aqueous nickel chloride solution and the alkali in the step (A) is completed, the nickel hydroxide slurry is washed with a pH of 8.5 to 12.0, and then filtered and washed with pure water. A method for producing nickel powder.   In the step (A), after completion of the neutralization reaction between the aqueous nickel chloride solution and the alkali, the nickel hydroxide slurry is concentrated and washed with a pH of 8.5 to 12.0. The manufacturing method of the nickel powder as described in 2.   In the step (A), the pH of the nickel hydroxide slurry at the time of washing is higher than the pH during the neutralization reaction between the aqueous nickel chloride solution and the alkali. Production method.   In the said process (A), the alkali used for neutralization is at least 1 sort (s) chosen from sodium hydroxide and potassium hydroxide, The manufacture of the nickel powder in any one of Claims 1-3 characterized by the above-mentioned. Method.   In the said process (A), the alkali used for washing | cleaning shall be the same alkali as what was used for neutralization, The manufacturing method of the nickel powder in any one of Claims 1-4 characterized by the above-mentioned.   D90 of the nickel powder obtained is 1.5 micrometers or less, The manufacturing method of the nickel powder in any one of Claims 1-5 characterized by the above-mentioned.   The oxygen concentration of the obtained nickel powder is 1.8 mass% or less, The manufacturing method of the nickel powder in any one of Claims 1-6 characterized by the above-mentioned.