RU2560901C1 - Method of metal fine disperse powder production - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: salt of appropriate metal is precipitated from solution with the help of solution settling agent composed by alkaline metal carbonate with excess concentration of 40-60% of stoichiometrically required amount at 40-60°C and pH of 7.0-9.5.Produced suspension is filtered and sediment flushed as carbonate of appropriate metal. Flushed precipitate is dehydrated and prepared for reduction at increase in temperature from 50°C to 150°C. Then carbonate is reduced at metal reduction temperature for 60-120 minutes with hydrogen at dew point equal to 0°C. Hydrogen is fed counter stream in powder motion direction. Produced powder is passivated in nitrogen medium at oxygen content of 0.05-1.0% for 30-60 minutes at gradual decrease in gas medium temperature to ambient temperature.

EFFECT: uniform size of fine metal powder particles.

2 cl, 8 dwg, 5 tbl, 4 ex

Description

The claimed technical solution relates to the field of powder metallurgy, in particular to a method for producing metal powders by chemical deposition and thermal reduction of metal-containing substances.

One of the chemical methods that make it possible to obtain finely dispersed powders (from 0.1 to 1 μm) and to regulate their particle size distribution is the method of chemical deposition based on the theory of mass crystallization from solution. The deposition process includes two main stages: the formation of crystalline nuclei and their further growth. A general condition for the formation of finely dispersed and finely dispersed precipitates is the combination of a high rate of nucleation with a low growth rate (Morokhov I.D., Trusov L.I., Chizhik S.P., "Ultrafine metallic media", Moscow, Atomizdat, 1977 ) [one].

A number of methods are known for producing metal powders (iron, copper, nickel, cobalt, tungsten, molybdenum, silver and metal alloys) by chemical methods consisting in chemical deposition, thermal decomposition of metal-containing compounds and described in RF patents for invention No. 2048977 "Method for producing ultrafine metal-containing powder "(class IPC B22F 9/26, priority date 08/30/1993) [2], No. 2356697" Method for producing silver powder "(class IPC B22F 9/24, C25C 5/02, priority date 10/17/2007) [ 3]. Upon receipt of metal powders by these methods, at least one metal hydroxide is precipitated with an alkali solution. Chlorides, nitrates and / or metal sulfates are taken as the starting salt. During the precipitation process, the hydrated salt is treated with an alkaline solution in a 1.5-2 fold excess of stoichiometric. The precipitate is separated, washed and dried to form a suspension, diafiltration of the resulting suspension is carried out with the separation of the solution of at least one metal hydroxide, its dehydration and reduction in a hydrogen atmosphere to obtain a metal powder and subsequent passivation of the specified powder. In most patents, to increase the completeness of the deposition of metal hydroxides with an alkali solution and to shift the direction of the redox process towards reaction products, it is necessary to use parameters such as heating the reaction mixture, maintaining excess pressure, or using catalysts and special reducing agents (reducing agents).

The disadvantages of these methods are:

- the need for heating the reaction mixture, maintaining excess pressure and the use of special autoclave equipment;

- the lack of effectiveness of the method due to the side process of the formation of metal hydroxide;

- multi-stage washing operation to neutral pH;

- increased measures to control processes in the operations of drying precipitation and restoring them to metal powders due to the dispersion of hydroxides.

A number of methods for producing metal powders by chemical methods are known, consisting in the chemical interaction of solutions of metal salts with alkalis (NaOH or KOH) in the presence of reducing agents (hydrazine hydrate, glucose, elemental phosphorus, sodium hypophosphite) during liquid-phase reduction and precipitation of finely dispersed nanopowders of metal-containing compounds described in the patent of the Russian Federation for invention No. 2428494 "Nanostructured agglomerate of metallic cobalt and the method for its production" (class IPC C22B 23/00, B22F 9/24, B82B 3/00, priority date and 28.12.2009) [4]. Before the interaction of solutions of cobalt salt with hydrazine hydrate, a stabilizing agent is introduced into the solution. As the stabilizing agent, potassium sodium tartrate is used. The technical result is to obtain new nanostructured fractal agglomerates of metal cobalt in a simple way, under mild technological conditions, to obtain the target product of high purity (99.9%). In the RF patent for the invention No. 2426805 “Method for producing nanodispersed copper powder” (CL IPC C22B 15/00, B22F 9/24, priority date 12/21/2009) [5] describes the preparation of nanosized copper powders by mixing, restoring the copper salt with a glucose solution . The introduction of sodium hydroxide is carried out after the copper sulfate is completely dissolved and the solution is heated to a temperature of 70 ° C and the pH is maintained during the reaction of restoration, equal to 6-11, preferably 8-9, first until the formation of monovalent copper oxide and then metallic copper. EFFECT: simplification and cost reduction of the technology for producing nanosized copper powders by reducing the number of technological synthesis operations.

The disadvantage of these methods for producing powders is their low productivity.

There are a number of methods for producing metal powders by chemical methods, consisting in the chemical interaction of solutions of metal salts with alkalis in the presence of catalysts described in RF patent for the invention No. 2143960 "Method for the extraction of nickel from aqueous solutions in the form of a metal powder" (class IPC B22F 9/24 , C22B 23/00, priority date 10.27.1998) [6], which consists in the precipitation of nickel (II) by dispersed aluminum with a particle size of 2-250 microns at a pH of 12.0-13.0 in the presence of aqueous ammonia and in a molar ratio: nickel: aluminum: aqueous ammonia, equal to 1: (1- 2.5) :( 15-50), respectively, washing and drying the precipitate. The method allows to obtain nickel powders from spent industrial and aqueous solutions with a wide range of concentrations of nickel (II) ions (mol / l): 10-3-1.0 in 25-60 minutes. The purity of the obtained Nickel is 98-99%.

Similar to the above RF patent for invention No. 2236475 “Method for nickel reduction by precipitation” (CL IPC C22B 23/00, C22B 3/44, priority date 10.27.2000) [7], which consists in obtaining nickel from an aqueous solution of a nickel-containing compound in as a metal powder by neutralizing the solution with an alkali or alkaline earth metal compound and precipitating nickel hydroxide in the presence of a catalyst (ferrous iron Fe ²⁺ , at least partially dissolved divalent chromium Cr ²⁺ can also be used). Ferrous iron in solution (in ionic form) is a strong catalyst for the recovery process from pulp containing nickel hydroxide, and is so strong that the reduction proceeds quickly at temperatures even below 100 ° C and at atmospheric pressure. To isolate nickel in the form of nickel hydroxide or a nickel salt (obtained by alkaline reaction), a neutralizing reagent, for example, CaO, Ca (OH) ₂ , NaOH, MgO or another suitable alkaline or alkaline earth metal compound, is added to the nickel sulfate solution, and in an amount slightly smaller than the stoichiometric, namely 70-98% of the stoichiometric, preferably 95-98%. If necessary, ammonia can also be used as a catalyst.

The disadvantage of this method is:

- multi-stage operation of washing from introduced reducing agents, catalysts;

- increased control measures of the chemical composition of metal powders in the operations of drying precipitation, recovery.

In the reduction of metal-containing compounds to metal powders, both inorganic and organic reducing agents in gaseous, solid-phase and liquid forms can be used in redox reactions.

Known RF patent for the invention No. 2468892 "Method for producing ultrafine metal powders by thermal decomposition of oxalates in saturated hydrocarbons" (CL IPC B22F 9/30, priority date 09/20/2011) [8], which consists in mixing, the interaction of a suspension of oxalates with preheated to 90-95 ° C with ceresin and thermal decomposition of oxalates at temperatures from 280 to 350 ° C and atmospheric pressure. The invention relates to a technology for producing ultrafine powders of copper, nickel, cobalt, other metals and alloys.

The disadvantages of these methods are:

- deposition of related impurities with the metal during treatment with hydrocarbon reducing agents (ceresin, glucose) and, as a result, deterioration of the chemical composition of metal powders.

Gaseous reagents (hydrogen) are also used as reducing agents.

Known RF patent No. 2030972 "Method for producing dispersed metal powder" (CL IPC B22F 9/22, priority date 10.26.1992) [9], which consists in the initial preparation of an aqueous solution of the reagent, which is used as an alkali, then cooked the solution is injected in portions with a salt of the corresponding metal; at room temperature, under stirring, treatment is carried out to obtain hydroxide. The resulting metal hydroxide is subjected to filtration and washing, during which it is crushed. Then, the resulting product, after drying in air, is reduced to metal using hydrogen passed through it when heated to a temperature above the threshold of reduction of metal hydroxide.

The closest in technical essence and therefore selected as a prototype is a method of producing finely dispersed metal powder according to the patent of the Russian Federation for invention No. 2170647 "Method for producing ultrafine metal powder" (CL IPC B22F 9/22, priority date 02.11.2000) [10], including chemical precipitation of at least one metal hydroxide with an alkali solution to form a suspension, filtering the resulting suspension with the separation of at least one metal hydroxide, its dehydration, preheating at least one metal hydroxide and its restoration to obtain the metal powder and the subsequent passivation of said powder.

The disadvantages of the prototype are:

- deposition of concomitant impurities simultaneously with the metal in the absence of the “washing” operation in this method and, as a result, deterioration of the chemical composition of the obtained metal powders;

- the recovery of metal hydroxides in the preparation of fine powders to prevent the sintering of particles requires the use of dried hydrogen to a dew point equal to or lower than -70 ° C, which means that the use of additional equipment for drying gases and additional costs for its maintenance in this method;

- subsequent passivation without gradually reducing the processing temperature increases the pyrophoricity of the specified powder and the complexity of the subsequent processes for producing finely divided powder of the desired particle size distribution.

The objective of the proposed technical solution is to create a method that allows you to get fine metal powder uniform in particle size, narrow fractional composition and a given morphology; providing the ability to control dispersion at all stages of the method of manufacturing a finely divided metal powder.

This problem in the present method for producing finely dispersed metal powder is solved due to the fact that in the known method, including chemical precipitation of the salt of the corresponding metal with a precipitant to form a suspension, filtering the resulting suspension to separate the precipitate of the metal salt, dehydration, drying the precipitate of the metal salt and restoring it to obtain metal powder and subsequent passivation of the powder, according to the claimed technical solution, chemical precipitation of a salt of the corresponding metal, for example cell or cobalt, is carried out using a solution of carbon dioxide of an alkali metal, such as sodium carbonate, with an excessive concentration of from 40 to 60% of the stoichiometrically necessary amount, at a deposition temperature of 40 to 60 ° C and a pH of 7.0 to 9.5 , with the formation of a suspension, moreover, the operation of filtering the suspension is combined with the washing operation, dehydration is carried out simultaneously with the preparation for reduction of the carbonate of the corresponding metal with increasing temperature from 50 to 150 ° C, which is restored by hydrogen and a temperature reduction of the corresponding starting metal carbonate for 60 to 120 min, hydrogen is fed countercurrent to the direction of movement of the powder, with a dew point of 0 ° C. The passivation process is carried out in a nitrogen medium with an oxygen content in the range of 0.05-1.0% for 30 to 60 minutes with a gradual decrease in the temperature of the gas atmosphere to ambient temperature.

In the inventive method for producing a finely divided metal powder in the first stage, chemical precipitation is carried out, for example, of a sulfate solution of the corresponding metal with a solution of sodium carbonate. Desalted water is used to prepare aqueous solutions of sodium carbonate and the corresponding metal sulfate. With vigorous stirring, sodium carbonate and the corresponding metal sulfate are poured into the water in the form of a salt. In order to create the optimal reaction flow for the formation of carbonate of the corresponding metal, solutions of sodium carbonate and sulfate of the corresponding metal are fed into the reactor in the form of jets with stirring.

In the claimed technical solution, the optimal deposition conditions are achieved by a combination of a number of parameters. An aqueous solution of sodium carbonate (precipitant) must meet a certain concentration: its excess is in the range from 40 to 60% of the stoichiometrically necessary amount. It was experimentally established that an excess of sodium carbonate leads to contamination of the product with impurities, and a lack of sodium carbonate, from the stoichiometrically necessary amount, leads to incomplete precipitation of salt and metal loss in the mother liquor.

The deposition temperature should be in the range from 40 to 60 ° C, since it was experimentally established that under these conditions, well-filtered, compact precipitates of the carbonate of the corresponding metal are obtained and a high degree of deposition of the corresponding metal from the solution is achieved. At temperatures less than 40 ° C, more humid carbonate deposits form and the degree of precipitation decreases. An increase in the process temperature above 60 ° C is accompanied by foaming of the solution due to the beginning decomposition of soda, which leads to a decrease in the rate of nickel deposition.

The pH of the medium must be maintained from 7.0 to 9.5. A decrease in pH increases the loss of metal with the mother liquor during filtration.

The resulting suspension is filtered, and the precipitate in the form of a metal carbonate is washed with demineralized water. Simultaneous filtration and washing of the precipitate of metal carbonate eliminates the long-term effect of the mother liquor on the dispersion of the precipitate particles, completely removes the excess of sodium carbonate and the formed sodium sulfate, and also eliminates the loss of metal.

The dehydration of the washed precipitate is carried out simultaneously with the preparation for recovery, with a gradual increase in temperature from 50 to 150 ° C, which ensures complete removal of adsorption and chemically bound moisture, residual moisture is from 1 to 5%. A decrease in temperature below the indicated is impractical due to an increase in the fraction of residual moisture in the precipitate, and an increase in temperature leads to enlargement of the particles of the precipitate during drying.

The material thus prepared is subjected to reduction of the corresponding starting material. The duration of the recovery process ranges from 60 to 120 minutes. The reducing gas, which is used as hydrogen with a dew point of 0 ° C, is supplied countercurrent in the direction of movement of the powder. It was experimentally established that if the duration of the recovery process was less than 60 minutes, the washed precipitate was not completely restored, but an increase in the duration of the process more than 120 minutes led to the enlargement of powder particles.

In order to reduce the pyrophoricity of the powders after reduction, they are transferred to a nitrogen medium. This is achieved through the use of nitrogen with an oxygen content in the range of 0.05-1.0%. The oxygen content below the specified limit does not provide coverage of the particles with an oxide film, exceeding the specified limit increases the oxygen content in the powder. The passivation process is carried out for 30-60 minutes With a shorter passivation time, the stabilization of powder particles is not fully ensured; a longer passivation process is simply not practical, since it increases nitrogen consumption.

Using the proposed method for producing finely divided metal powder allows to obtain not only pure metal powders, but also powders of a multicomponent composition. The method for producing finely divided powders of a multicomponent composition based on iron, nickel, copper, cobalt of different compositions does not fundamentally differ from the above-described production of single-component powders. The starting materials are carbonates obtained by co-precipitation of sodium carbonate from solutions of metal salts with subsequent reduction.

It is advisable to use pure starting basic and auxiliary materials to obtain powders of high purity, namely the use of chemically pure metal salts.

Thus, the main advantage of the proposed method is that due to the control of the technological parameters of the methods of chemical deposition and thermal reduction of metal-containing substances and the use of pure starting materials, one-component metal powders and multicomponent powders with a dispersion of 0.5-1.0 μm can be obtained.

The use of the claimed method for producing finely divided metal powder of the optimal concentration of sodium carbonate allowed us to obtain the value of the degree of extraction of the corresponding metal from the mother liquor in the range of 99.95-99.99%.

The proposed technical solution is used to obtain, for example, one-component powders of nickel, cobalt and powders of a multicomponent composition, for example, based on iron, nickel, cobalt, copper, where the concentration of components varied in the range from 1 to 90%.

In examples of specific applications No. 1 and 2, the ability to control the dispersion of a single-component nickel powder at the stage of chemical deposition is shown. In the specific application example No. 3, it is possible to control the dispersion of a single-component cobalt powder at the stage of thermal reduction. In the specific application example No. 4, the possibility of controlling the technological parameters of the methods of chemical deposition, thermal reduction and obtaining a powder of a multicomponent composition based on iron, nickel, cobalt is demonstrated.

Case Studies

Example 1

According to the claimed method, the preparation of a one-component nickel powder with a conditional particle size according to Fisher, D _f = 0.95 μm, was carried out as follows.

Chemical precipitation of a solution of nickel sulfate was carried out using a solution of sodium carbonate with an excess concentration of 60% of the stoichiometrically required amount.

Precipitation was carried out at a temperature of 50-55 ° C; the pH of the medium was 8.8.

Obtained by the claimed method, the suspension was subjected to filtration at the same time as washing. The precipitate of Nickel carbonate was separated from the mother liquor and washed with water. The dehydration of nickel carbonate was carried out simultaneously with preparation for reduction with a gradual increase in temperature from 50 to 150 ° C; reduction was carried out at a temperature of 450-500 ° C for 60 minutes with hydrogen flowing countercurrently in the direction of movement of the powder, with a dew point of 0 ° C and passivation in a nitrogen medium with an oxygen content of 0.10% for 40 minutes with a gradual decrease in the temperature of the gas atmosphere to ambient temperature.

Nickel powder PNT-31 obtained by this method has the characteristics presented in table 1, the morphology of the particles is shown in figure 1, the particle size distribution is shown in figure 2.

According to sedimentation analysis, the distribution of particles of nickel powder is in the range from 1 to 49 microns. The average particle size is 8.64 microns.

The mass concentration of metal nickel in the mother liquor is 0.025 g / l. The degree of extraction of Nickel in this way is 99.97%.

Example 2

According to the claimed method for producing finely dispersed metal powder, the preparation of a single-component nickel powder with a conditional particle size according to Fischer, D _f = 0.48 μm, was carried out as follows.

Chemical precipitation of a solution of Nickel sulfate was carried out using a solution of sodium carbonate with an excessive concentration of 40% of the stoichiometrically required amount.

Precipitation was carried out at a temperature of 50-55 ° C, while the pH of the medium was 8.5.

The resulting suspension was subjected to filtration simultaneously with washing. The precipitate of Nickel carbonate was separated from the mother liquor and washed with water. The dehydration of nickel carbonate was carried out simultaneously with the preparation for reduction with a gradual increase in temperature from 50 to 150 ° C, reduction was carried out at a temperature of 450-500 ° C, for 60 minutes with hydrogen flowing countercurrent in the direction of movement of the powder, with a dew point of 0 ° C, and passivation for 40 minutes in a nitrogen atmosphere with an oxygen content of 0.10% with a gradual decrease in the temperature of the gas atmosphere to ambient temperature.

Nickel powder PNT-9 obtained by this method has the characteristics presented in table 2, the morphology of the particles is shown in figure 3, the particle size distribution is shown in figure 4.

The mass concentration of metal nickel in the mother liquor is 0.043 g / l. The degree of extraction of Nickel in this way is 99.95%.

Example 3

According to the claimed method, a single-component cobalt powder was obtained with a range of variation in the conditional particle size according to Fischer D _f = 0.82-1.09 μm.

Chemical precipitation of a solution of cobalt sulfate was carried out using a solution of sodium carbonate with an excessive concentration of 40% of the stoichiometrically required amount.

Precipitation was carried out at a temperature of 50-55 ° C, while the pH of the medium was 8.5.

The resulting suspension was subjected to filtration simultaneously with washing. The cobalt carbonate precipitate was separated from the mother liquor and washed with water. The dehydration of cobalt carbonate was carried out simultaneously with the preparation for recovery with a gradual increase in temperature from 50 to 150 ° C, the recovery was carried out at a temperature of 550 and 600 ° C for 120 minutes with hydrogen flowing countercurrent in the direction of movement of the powder, with a dew point of 0 ° C , passivation was carried out for 50 minutes in a nitrogen medium with an oxygen content of 0.10% simultaneously with cooling while gradually reducing the temperature of the gas atmosphere to ambient temperature.

The cobalt powder obtained by this method has the characteristics shown in table 3, the particle morphology is shown in figure 5, the particle size distribution is shown in figure 6.

Example 4

When using the proposed method, a multicomponent composition powder was obtained based on iron, nickel, cobalt.

Joint chemical precipitation of solutions of nickel sulfate, iron, cobalt was carried out using a solution of sodium carbonate with an excess concentration of 60% of the stoichiometrically necessary amount.

Precipitation was carried out at a temperature of 50-55 ° C, the pH of the medium was 8.2.

The mass concentration of the corresponding metal in the mother liquor is presented in table 4.

The total degree of extraction of the components in this way is 99.99%.

The resulting suspension was subjected to filtration simultaneously with washing. The precipitate of the carbonate mixture was separated from the mother liquor and washed with water. The dehydration of the mixture of carbonates was carried out simultaneously with the preparation for reduction with a gradual increase in temperature from 50 to 150 ° C, reduction was carried out at a temperature of 400-450 ° C, for 60 minutes, with hydrogen flowing countercurrent in the direction of movement of the powder, with a dew point of 0 ° C, and passivation for 40 minutes in a nitrogen atmosphere with an oxygen content of 0.10% with a gradual decrease in the temperature of the gas atmosphere to ambient temperature.

The mixture of iron powder (base) - nickel (20-25%) - cobalt (7-9%) obtained by this method has the elemental composition shown in table 5, the electron microscopic view of the particles of powders PNTS-1 (particle morphology) - in figure 7 and particle size distribution - in figure 8.

The inventive method for producing finely dispersed metal powder provides the ability to control the dispersion of metal powders at all stages of the process and to obtain metal powders in a finely dispersed state of a narrow fractional composition with a given morphology.

In addition, the use of the proposed method allows to achieve the degree of extraction of the corresponding deposited metal from the mother liquor at the level of 99.95-99.99%, which improves the environmental performance of the process and reduces the requirements for cleaning wash water.

The claimed technical solution combines the production of high-quality finely divided metal powders with technological simplicity and cost-effectiveness of the process, which are ensured by the possibility of complete mechanization of the process from loading the carbonate of the corresponding metal to unloading the final product.

The proposed method at all stages of the process is carried out at relatively low temperatures, which does not require the use of special heat-resistant equipment.

The inventive method provides the possibility of obtaining finely divided one-component metal powders and powders of multicomponent composition, which can be used in powder metallurgy as components of metal-cutting and drilling hard alloys, in the manufacture of magnets, batteries, filter elements, electrical contacts, special coatings, dyes, catalysts, welding electrodes, composite adhesives, ferrites, for cold spraying, in modern systems of 3D modeling from metal by alloy Lenia laser metal powders.

Information sources

1. Morokhov I.D., Trusov L.I., Chizhik S.P., "Ultrafine metallic media", M., Atomizdat, 1977.

2. RF patent for the invention No. 2048977 "Method for producing ultrafine metal-containing powder."

3. RF patent for the invention No. 2356697 "Method for producing silver powder."

4. RF patent for the invention No. 2428494 "Nanostructured agglomerate of metallic cobalt and method for its preparation."

5. RF patent for the invention No. 2426805 "Method for producing nanosized copper powder."

6. RF patent for the invention No. 2143960 "Method for the extraction of Nickel from aqueous solutions in the form of a metal powder."

7. RF patent for the invention No. 2236475 "Method for the recovery of Nickel by deposition."

8. RF patent for the invention No. 2468892 "Method for producing ultrafine metal powders by thermal decomposition of oxalates in saturated hydrocarbons."

9. RF patent for the invention No. 2030972 "Method for producing dispersed metal powder."

10. RF patent for the invention No. 2170647 "Method for producing ultrafine metal powder."

Claims (2)

1. A method of producing a finely divided metal powder, including chemical precipitation of the salt of the corresponding metal with a precipitant to form a suspension, filtering the resulting suspension to separate the metal salt precipitate, its dehydration, drying and reduction to obtain a metal powder and subsequent passivation of the powder, characterized in that the chemical precipitation of salt the corresponding metal is carried out using a solution of carbon dioxide alkali metal with an excessive concentration of 40-60% of the stoich as a precipitant of the required amount at a temperature from 40 to 60 ° C and a pH value of the solution from 7.0 to 9.5, the filtration of the resulting suspension is combined with the washing operation with the separation of the precipitate in the form of carbonate of the corresponding metal, and the dehydration of the washed precipitate is carried out simultaneously with preparation for recovery metal carbonate with increasing temperature from 50 to 150 ° C, and the reduction of metal carbonate is carried out at a reduction temperature of the corresponding metal carbonate for 60 to 120 minutes with hydrogen with a dew point of 0 ° C, supplied countercurrent in the direction of movement of the powder, and passivation is carried out in a nitrogen medium with an oxygen content in the range of 0.05-1.0% for 30 to 60 minutes with a gradual decrease in the temperature of the gas atmosphere to ambient temperature. 2. The method according to p. 1, characterized in that as a precipitant use a solution of sodium carbonate.

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