RU2177447C1 - Method of preparing nickel (ii) hydroxide - Google Patents

Abstract

FIELD: technology of preparing nickel compounds, particularly, nickel II hydroxide used for current stocks. SUBSTANCE: method comprises preparing original solution of alkali metal hydroxide, nickel (II) salt and barium hydroxide, mixing thereof, precipitating nickel (II) hydroxide, separating mother liquor, treating deposit with alkali in autoclave at temperatures from 130 to 200 C, washing deposit and drying thereof. Treatment with alkali is carried out at hydroxide-ion concentration of 0.05-0.3 g-ion/l. Washing of deposit is carried out in three stages: in first stage, with water, in second stage with barium hydroxide solution with 2-6% concentration and in amount which maintains solution to deposit weight ratio at (1-2):1, and in third stage, once again with water. Method is simple, it does not involve prolonged and power consuming drying operation of deposit prior to washing operation. Content of water-soluble impurities such as SO $\genfrac{}{}{0ex}{}{\text{2-}}{\text{4}}$ Cl anions is reduced in product. EFFECT: more efficient preparation method. 3 cl

Description

Technical field
The invention relates to the field of producing nickel compounds, in particular to a technology for producing nickel (II) hydroxide used for current sources, for example, as part of the active mass of positive electrodes of alkaline batteries.

State of the art
A known method for producing nickel (II) hydroxide used for alkaline batteries (M. A. Dasoyan, V. V. Novoderezhkin and F. F. Tomashevsky "Production of electric batteries", M., "Higher School", 1977, p. 260 -277). The method involves the preparation of stock solutions of sodium hydroxide, nickel (II) sulfate and barium hydroxide as an activating additive and mixing them. The precipitate obtained is separated by filtration, then passes the first drying, washing from sulfate ions, the second drying and grinding. The disadvantages of the method are its duration and high energy consumption associated with the need to dry the resulting product twice.

 A known method of producing Nickel (II) hydroxide, including pouring a solution of Nickel sulfate in an alkali solution, filtering and drying the precipitate, washing off sodium sulfate, re-drying, treatment with alkali during boiling, washing with water and final drying (ed. SU 51380, 1937 g.). Three drying operations make the process very long, labor and energy intensive.

 There is also known a method for producing nickel (II) hydroxide, including the preparation of stock solutions, mixing them with an activating additive containing barium ions. This is followed by precipitation, separation of the mother liquor, the extraction of the precipitate, the first drying to a certain moisture content, washing from impurities and the second drying. After the first drying, a solution containing cobalt ions is introduced into the resulting paste (patent RU N 2138447). The method has the same disadvantages as in the previous case. In particular, each of the two drying stages lasts about 24 hours.

SUMMARY OF THE INVENTION
The proposed method can significantly reduce the duration of the process and reduce the cost of obtaining Nickel (II) hydroxide with a simultaneous increase in its quality.

A method for producing nickel (II) hydroxide for current sources includes preparing initial solutions of an alkali metal hydroxide, nickel (II) salt and barium hydroxide (activating additive), mixing them, precipitating and separating the mother liquor, followed by washing and drying the precipitate. In this case, the precipitate is subjected to alkali treatment in an autoclave (hydrothermal treatment) before washing. Processing is carried out at T = 130-200 ^o C, maintaining the concentration of hydroxyl ions in the liquid phase of the pulp of 0.1-0.5 g-ion / L.

 It is advisable to wash the precipitate in three stages: in the first stage with water, in the second stage with a solution of barium hydroxide with a concentration of 2-6% and in an amount providing a weight ratio of solution to precipitate (1-2): 1, and in the third stage again with water.

 In the first stage of washing, the bulk of soluble salts and impurity metals are separated, in the second stage, additional sulfate ions remaining in the liquid phase in the pores of the precipitate are extracted into the solid phase due to the formation of poorly soluble barium sulfate, and in the third stage, the precipitate is washed from barium cations and soluble salts.

The positive effect of hydrothermal treatment according to the proposed method is associated with a change in the composition and structure of the precipitate and the properties caused by it (specific volume, electrochemical capacity, content of impurity anions included in the structure of the precipitate in the form of basic sulfates of the type (3-6) Ni (OH) ₂ • NiSO ₄ and basic chlorides of the type (1-3) Ni (OH) ₂ • NiCl ₂ , as well as in the form of soluble sulfates and chlorides adsorbed by the precipitate). Presumably, this change occurs by the following mechanisms: ordering of the precipitate structure (transition from an X-ray amorphous to crystalline state), collective recrystallization and dehydration with the release of adsorbed salts and water and the hydrolysis of basic salts with the release of structural sulfate and chloride ions into the liquid phase.

Thanks to hydrothermal treatment and a three-stage washing, the present invention allows to reduce the content of water-soluble impurities of SO ₄ ^2- and Cl ^- anions in Ni (II) hydroxide and its specific volume, as well as to increase the electrochemical capacity of the product. In addition, the production of Ni (II) hydroxide, according to the invention, reduces the cost of the process by eliminating the drying operation before washing the precipitate of Ni (II) hydroxide from impurities.

Information confirming the possibility of carrying out the invention
To precipitate nickel (II) hydroxide by the known methods, the following solutions were prepared:
a solution of sodium hydroxide with a concentration of 26.5%, the specific gravity of the solution is 1295 kg / m ³ at T = 15 ^o C;
a solution of nickel sulfate (II) with a concentration of 15.5%, the specific gravity of the solution is 1175 kg / m ³ at T = 15 ^o C;
a solution of barium hydroxide (activating additive) with a concentration of 4%, the specific gravity of the solution is 1100 kg / m ³ at T = 70 ^o C.

The prepared sodium hydroxide solution in a volume of 150 l was poured into a reactor with a capacity of 1.2 m ³ equipped with a mechanical stirrer and a heater and heated to 50 ^° C. Then, while stirring for 1 hour, a sulfate solution preheated to 50 ^° C was simultaneously fed into the reactor nickel and up to 75 ^o C a solution of barium hydroxide in quantities of 460 l and 25 l, respectively. After draining the solution, the pulp containing the precipitate of nickel (II) hydroxide was stirred for another 30 minutes and the sodium hydroxide content in the liquid phase was determined, which should be at the level of 4-10 g / l. Under the indicated deposition conditions, it amounted to 6.2 g / l.

At the end of the deposition, the pulp with a temperature of 60 ^o C was sent to a filtering centrifuge, in which the mother liquor was separated from the precipitate. The precipitate, squeezed out in a centrifuge with a moisture content of 15-20%, was collected in a recovery tank V = 1 m ³ , where an aqueous solution of sodium hydroxide with a concentration of 0.2 g-eq / l was applied until the ratio T: W = 1: (5-6 ) After stirring for 10 minutes, a pulp sample was taken and the concentration of hydroxyl ions in the liquid phase was determined, which under these conditions was 0.18 g-ion / L. Next, the pulp from the tank-repulpator was pumped into an autoclave (V = 0.385 m ³ ) equipped with mixing and heating devices. In the autoclave, the pulp was treated with alkali at T = 170 ^° C for 1 hour.

After treatment with alkali, the nickel hydroxide pulp was cooled to 80-90 ^° C and transferred to a supply tank (V = 1 m ³ ) before separation of the solid and liquid phases. Separation of the mother liquor from the precipitate was carried out in a filtering centrifuge, where a pulp cooled to 70-80 ^° C was fed from a supply tank.

 The precipitate, squeezed in a centrifuge with a moisture content of 15-20%, was washed from impurities by feeding three washing solutions in series to the same centrifuge. In the first stage, washing was carried out with purified water at the rate of 2 kg per 1 kg of dry sludge, in the second stage with a solution of 4% barium hydroxide in an amount of 1.5 kg of solution per 1 kg of dry sludge, and in the third stage, again purified with water at the rate of 1.5 kg per 1 kg of dry sediment.

The washed precipitate with a moisture content of 15-20% from the centrifuge was transferred to a vibratory dryer, where it was dried at T = 120 ^o C to a moisture content of less than 2%. The dried product was analyzed for indicators regulated by the requirements for nickel (II) hydroxide used for the manufacture of current sources. According to the results of physical and chemical control, the obtained product had the following indicators: mass fraction of the amount of nickel and cobalt - 57.8%, nickel oxide - absent, mass fraction of barium, referred to the mass fraction of the amount of nickel and cobalt - 2.1%; mass fraction of the sum of Cl ^- and SO ₄ ^2- (free) anions, referred to the mass fraction of nickel and cobalt - 0.34%, no amorphous phase, specific volume 0.65 cm ³ / g, electrochemical capacity 0.166 A / h for 1 g.

The preparation of Ni (II) hydroxide by the proposed method accelerates and reduces the cost of the process, since it eliminates the long and energy-intensive operation of drying the precipitate before washing the Ni (II) hydroxide from impurities. In addition, the content of water-soluble impurities of SO ₄ ^2- and Cl ^- anions is reduced in the final product.

Claims (3)

1. A method of producing nickel (II) hydroxide for current sources, comprising preparing stock solutions of alkali metal hydroxide, nickel (II) salt and barium hydroxide, mixing them, precipitating nickel (II) hydroxide, separating the mother liquor, washing and drying the precipitate, characterized in that before washing the precipitate is treated with alkali in an autoclave at a temperature of 130-200 ^o C.  2. The method according to claim 1, characterized in that the alkali treatment is carried out at a concentration of hydroxyl ions in the liquid phase of the pulp equal to 0.05-0.3 g-ion / L.  3. The method according to claim 1, characterized in that the washing of the precipitate is carried out in three stages: in the first stage with water, in the second stage with a solution of barium hydroxide with a concentration of 2-6% and in an amount providing a mass ratio of solution to precipitate (1-2 ): 1, and in the third stage again with water.