CA2137762C

CA2137762C - Process for preparing metal hydroxides

Info

Publication number: CA2137762C
Application number: CA002137762A
Authority: CA
Inventors: Wilfried Gutknecht; Dirk Naumann; Armin Olbrich; Thomas Richter; Josef Schmoll
Original assignee: HC Starck GmbH
Current assignee: HC Starck GmbH
Priority date: 1993-12-14
Filing date: 1994-12-09
Publication date: 2005-05-24
Anticipated expiration: 2014-12-09
Also published as: DE59406270D1; CN1107440A; RU94043800A; FI945841A0; JPH07206438A; FI107445B; FI945841L; EP0658514B1; ES2118303T3; CN1041706C; KR950017738A; DE4342620C1; NO944825D0; NO314991B1; NO944825L; KR100347284B1; ATE167461T1; JP3529115B2; CA2137762A1; EP0658514A1

Abstract

Process for preparing low solubility metal hydroxides of the general formula M(x)(OH)x, where M = Co, Zn, Ni and/or Cu and x is the valence of the metal.

Description

213~'~62 Process for preparing metal hvdroxides BACKGROUND OF THE INVENTION
The present invention relates to a process for preparing low solubility metal hydroxides having the general formula M~"~ (OX) X, where M - Co, Zn, Ni and/or Cu, and x is the valence of the metal.
The metal hydroxides of cobalt, zinc, nickel and copper are valuable intermediates for the preparation of inorganic or organic salts of said metals and for the preparation of the corresponding oxides or the pure metals themselves. Starting from cobalt hydroxide, cobalt oxide of defined composition can be prepared by calcination, for example for application in electronics for the production of varistors or in storage batteries.
Also a cobalt metal powder of defined particle-size distribution can be prepared by reduction. Nickel hydroxides serve as pigments or are used with various dopings and particle structures for battery applications.
Zinc hydroxides serve as precursors for pigments and the copper compounds can be converted into catalytically active materials.
In the preparation of hydroxides for various appli-cations, the objective of preparing as compact and flow-able material as possible for further processing is uppermost. As a result of its particle-size distribution and particle structure, cobalt metal powder prepared from cobalt hydroxide yields after being sintered together with tungsten carbide, for example, Special hard-metal tools.
For the newly developed foam anodes, which are used, in particular, in nickel hydride storage cells, a nickel hydroxide is needed whose physical properties are optimized both in relation to the application purpose and also to the processing procedure applied. While the application in high-performance storage batteries re-quires a high packing density of the active material, the pasting process used for foam anodes requires a material with high flowability, compact particle shape, narrow particle-size distribution and constant quality.
STA 67-Foreign Countries - 1 -Furthermore, the product should be capable of being mixed well with the additives normally used, such as, for example, cobalt metal powder and cobalt oxide.
A suitable material and basic features of the preparation process are disclosed in the Japanese Patent JP Hei 4-80513. In this process, nickel hydroxide particles having a diameter of between 1 and 140 ~,m are crystallized by continuously feeding a nickel salt solution and an alkali-metal hydroxide in solid or liquid form into a reaction vessel at a constant pH and at constant temperature while stirring vigorously. A pH of 11 and a temperature of 48°C are specified as favorable experimental conditions. w It is furthermore known that a sufficiently compact nickel hydroxide can be prepared by precipitation in the presence of ammonia or an ammonium salt. 3'hus, according to Trans. Faraday Soc. 51 (1955), 961, a nickelamine complex solution is prepared from nickel nitrate and aqueous ammonia solution. A nickel hydroxide is obtained from said complex solution by boiling at normal or reduced pressure or by treatment with steam, which nickel hydroxide, compared with those nickel hydroxides which are precipitated in the absence of ammonia, has a substantially lower specific surface (13 to 20 m2Jg).
The preparation of compact nickel hydroxiøe~ in the presence of ammonia or an ammonium salt is known, ~.g., by the precipitation of nickel hydroxide by adding an alkali-metal hydroxide solution to a suitable solution having a pH of at least 3Ø Electrochemical investigations on material prepared in this way yielded particularly high specific charging capacities compared with commercial nickel hydroxides.
However, products of this type still do not fulfil the above-mentioned requirements in relation to .particle shape, particle-size distribution and flowability.
Essential features of the process for preparing a compact nickel hydroxide and~its use in alkaline batteries are disclosed in European patent document (EP-A) 353 837. A
nickel(II)tetramine salt solution is prepared by dissolv-ing nickel nitrate or nickel sulphate in dilute ammonia solution and a decomposition is carried out by controlled addition of sodium hydroxide solution in accordance with the following reaction:
( I ) NI (NH3 ) 4S04 + 2 NaOH => Ni (OH) 2 + Na2S04 + 4 NH3 The reaction proceeds at temperatures between 40 and 50°C
in the pH range between 11 and 13. In this process, the pore volume decreases with decreasing pH. It is expressly found that a pore-free product can be crystallized only at sufficiently low reaction rates.
Furthermore, the nickel hydroxide prepared by this process has a high crystallinity, a low specific surface, a low pore volume and, therefore, a high physical density. The disadvantages of this product, which are attributable to the high density, are also described.
The low specific surface results in a relatively low proton conductivity and in a relatively high current density which promotes the formation of the undesirable Y-Ni00H, which leads to swelling of the electrode.
Although the nickel hydroxide crystallized at low pHs has a high density, it has a greater tendency to form y-Ni00H. A compromise between the required high density and the porosity necessary to a certain degree can be found by the choice of a medium pH. A nickel hydroxide containing 3 to loo zinc or 1 to 3o magnesium in solid solution is prepared by this process. These dopings counteract the formation of 'y-Ni00H.
Japanese Patent JP Hei 4-68249 reveals a continuous process for crystallizing a nickel hydroxide having spherical particle shape. In this process, a nickel salt solution (0.5 to 3.5 mol/1), dilute alkali-metal hydroxide solution (1.25 to 10 mol/1) and an ammonia and/or ammonium salt solution are continuously pumped by means of a metering pump into a heated cylindrical container provided with an overflow pipe while stirring vigorously, in which process the ammonia can also be supplied in gaseous form. The ammonia concentration is specified as 10 to 28o by weight and the ammonium salt concentration as 3 to 7.5 mol/1. In order to complex the nickel, between 0.1 and 1.5 mol of ammonia per mol of nickel salt solution are added. After about 10 to 30 hours, the system reaches a steady state, and then a STA 67-Foreign Countries - 3 -product having a constant quality can be continuously drained off. The dwell time in the container is between 0.5 and 5 hours.
An essential feature of this process is that the reaction is carried out at a defined pH which is kept constant to within ~ 0.1 pH steps in the range between 9 and 12 by pH-controlled addition of alkali-metal hydroxide solution, and at a constant temperature in the range between 20 and 80°C, in which connection the temperature deviations should not be more than ~ 2 K. Under these conditions, the compact spherical particles having a particle size of between 2 and 50 ~,m are obtained. The particle size can be adjusted, in particular, by varying the supply of NH3, the dwell time and the stirring speed.
As the stirring speed decreases or the supply of NH3 increases, the particle size increases. As the dwell time in the container increases, the product becomes coarser and the particle-size distribution narrower. The crystalline product is then filtered, washed with water and dried. The product prepared by this process has the properties mentioned at the outset, and it does not need to be ground.
EP A 462 889 discloses a process for preparing nickel hydroxide. In this case, the temperature range of the crystallization is above 80°C. Nitrate or sulphate solutions doped with cobalt, cadmium and/or zinc are used. The cobalt content is between 1 and 8 o by weight and the contents of cadmium and/or zinc are between 3 and 10°s by weight. Complexing is carried out with the aid of an ammonium salt, the NH3/Ni molar ratio being between 0.3 and 0.6. In this process, a pH of 9.2 ~ 0.1 is maintained. Furthermore, a three-paddle stirrer whose diameter is half the container diameter and whose speed is between 300 and 1000 min-1 is used.
As in the processes already described, the product is filtered, washed and dried.
The disadvantages of these processes are, on the one hand, the large amounts of neutral salts which are inevitably produced and which are present in at least twice the stoichiometric amount of the nickel hydroxide and take the form of waste water. On the other hand, STA 67-Foreign Countries - 4 --231$9-7724 said waste water contains, in addition to small amounts of complexly dissolved nickel, also large amounts of ammonia which have to be disposed of.
SUMMARY OF THE INDENTION
The invention provides a process for preparing low solubility metal hydroxides of the general formula M{x) fOH)x, where M = Co, Zn, Ni and/or Cu, and x is the valence of the metal, in which process reactive metal hydroxide is reacted, in a first step, with a complexing agent L in the presence of alkali-metal salts AY (e.g. NaCl., KC1, NaBr, KBr) to form the metal complex salt of the general formula MLnYm and alkali-metal hydroxide solution, and the metal complex salt is decomposed, in a second step, by reaction with alkali-metal hydroxide solution at pHs of > 7 to form sparingly soluble metal hydroxides and complexing agent and alkali-metal salt.
In the process according to the invention, ammonia and/or organic mono- and/or diamines having a chain length of 1 to 6 are preferably used as complexing agents (L).
The process according to the invention makes it possible to avoid the waste-water problem in that reactive hydroxides of the said metals are used as starting materials and these are in turn converted into a solubi~ form. This is done by complexing with a suitable complexing agent such as ammonia or amines. Thug, for example, nickel hydroxide can be reacted almost completely with the aid of ammonia to form the hexamine complex in the presence of neutral salts in accordance with the following equation.

(II) Ni(OH)2 + 6 NH3 + 2 NaCl => [Ni(NH3)61C12 + 2 NaOH.
The solid nickelhexamine chloride oan readily be separated by filtering or decanting.
5a Particularly good results are achieved if the process according to the invention is carried out at temperatures in the range from 30 to 85°C, preferably 45 to 80°C.
An essential feature of the process according to the invention is that the metal hydroxide,.used.is in reactive form since it is only in that case that it is dissolved completely during the complexing. A particularly suitable reactive metal hydroxide is a freshly precipitated metal hydroxide. Also advantageous is the use of a reactive metal hydroxide which has been obtained by anodic _ oxidation of metal.
A process for preparing a suitable reactive nickel hydroxide is disclosed in German Patent DE 4 239 295 C2. This is a process for preparing pure nickel hydroxide by anodic oxidation of metallic nickel in aqueous electrolyte solution in the presence of sulfate ions and separation of the nickel hydroxide formed, in which process a chloride- and sulfate-containing nickel hydroxide is prepared which is then converted into pure nickel hydroxide as a result of the subsequent treatment with alkali-metal hydroxide solutions.
If, in the process according to the present invention, the reactive metal hydroxide is to contain doping elements such as, for example, is sometimes required in relation to nickel hydroxide for the production of batteries, the process according to the invention can be carried out in the presence of cadmium, cobalt, magnesium, calcium and/or zinc salts, these preferably being used as sulfate and/or chloride salts.
It is also advantageously possible to carry out the preparation of the reactive metal hydroxide in the case of anodic oxidation in the presence of cadmium, cobalt, magnesium and/or zinc, said elements being connected as metal anodes.
BRIEF DESCRIPTION OF THE DRAWING
The invention is further illustrated by a single figure of drawing.

~7ETAILED DES~tIPTI~N OF PREFERRED EMBODIMENTS
In a preferred embodiment of the process according to the invention, the metal hydroxides are doped with one or more of the elements Co, Zn, Mg, Ca and Cd in a total amount of up to 10~ by weight.
The mother liquor produced in the process according to the invention contains exactly the stoichiometric amount of sodium hydroxide solution which is necessary for the reaction to form compact, spherical metal hydroxide. It is therefore preferred to carry out the process continuously. In this case, the complexing agent and the alkali-metal salt can advantageously be fed back to the first step. The decomposition of the metal complex salt can, for its part, be carried out with the alkali-metal hydroxide solution formed in the first step.
The reaction of the initial stage proceeds with high yield and rate if the components are vigorously mixed.
Particularly advantageously, the metal complex salts are decomposed in a strongly turbulent flow which is generated by vigorous stirring, by passive or active mixing components or by flow nozzles. The decomposition in a reactor is carried out with a defined dwell time of 0.5 to 10 hours, preferably of 1 to 4 hours.
A loop reactor has proved particularly advantageous as reactor. The products ammonia and common salt produced in the reaction to form metal hydroxide are fed back to the first step and are again used therein to prepare the metalamine complex, with the result that the entire process can be run without waste water.
A loop reactor is described in its general embodiment in Ullmann, vol. B4, pages 172-179. It is shown diagrammatically in the drawing and comprises a reactor vessel R, a heat exchanger H, a nozzle N and flow piping F. Here, A denotes reactant feed and B denotes product discharge. If the reactor is designed as a loop, a continuous operation is possible and this allows, the reaction of the solid amine complexes with the alkaline mother liquor to be adjusted for the various metals as a result of the choice of circulation speed so that the 2~~77s~
required physical properties of the products can be adjusted by means of the dwell time, temperature and pH.
A stirred tank reactor of a given volume with a specified stirring apparatus cannot, on the other hand, be adapted flexibly enough for various metal hydroxides having different morphology to be capable of being produced in a reactor. The choice of circulation speed in the loop reactor and the incorporation of various mixers such as static mixers, active in-line mixers or nozzles (in addition to, or in line of, item nozzle drawing) offer the guarantee that the requisite mixing of the reactants with the reaction medium takes place in a very short time, which is not possible with the mixing intensity in other embodiments of a reaction system having the desired flexibility.
A nickel hydroxide obtainable by the process according to the invention is suitable, in particular, for use in foam anodes. Its typical characteristic data are:
- tap density (ASTM B 212): > 2.0 g/cm3 - BET specific surface (DIN 66232): 10 to 20 m2/g - mean particle size D50: 10 to 20 um - porosity: 47 to 53~
- swelling in 3-molar KOH solution: < 10~
- specific charging capacity in a foam anode (AA
cell): > 250 mAh/g - water content: < 1~
The invention is described by way of example below without any restriction having to be perceived therein.
STA 67-Foreign Countries - 8 -Examt~les 1. Preparatiori of a reactive nickel hydroxide a) Electrolysis An electrolysis reactor comprising an electrolysis cell (70 1) was filled with 200 1 of common salt solution (50 g NaCl/1) and the electrolyte solution was circulated between two containers by means of a centrifugal pump. Two tantalum baskets whose side surfaces were formed as a sieve and filled with Ni briquettes were suspended in the electrolysis cell. The tantalum baskets were connected as anode and a pure-nickel sheet connected as cathode was arranged opposite the side surfaces so that the total electrode area was 0.5 m2. Electrolysis was carried out at 4.2 V and 500 A, with a current density of 1000 A/m2. During the electrolysis, 200 ml of a solution of nickel sulfate and cobalt sulfate (250 g NiS04 7H20/l; 250 g/1 CoS04 ~ 7H20) per hour were continuously fed into the electrolysis cell.

After 5 h, 40 1/h of the suspension produced were continuously discharged from the circulation vessel and fresh common salt solution was simultaneously pumped into the electrolysis cell so that the liquid volume in the electrolysis reactor remained constant.

The suspension was then filtered batchwise and in the further course of the electrolysis, this filtrate was fed back into the electrolysis cell instead of the fresh common salt solution.

Consequently, the additional common salt solution was used only in the initial phase of the continuous operation, after which a closed circuit was then established during the steady-state operation of the reactor. The suspension was capable of being filtered well and a gel-like primary product was obtained which had a water content of 90~ on average. The water entrained therewith was fed back again into the system as wash water for the gel-like primary STA 67-Foreign Countries - 9 -2137?6~
product. Chemical analysis yielded on average a sulfate content of 1.8o and a chloride content of 2o in the dried gel. The duration of the experiment was 105 h in total. During the continuous operation a total of 870 kg of gel-like primary product was obtained during this time.
b) Conditioning in NaOH
200 kg of the moist gel-like primary product from the electrolysis reactor were finely dispersed by vigorous stirring into a heated double-jacket reactor containing 200 1 of water. A pH of 13.7 was then established with NaOH and the suspension was heated to 80°C
while stirring and kept at this temperature for 6 h.
Filtering was then carried out via the nutsch filter and the product from the nutsch filter was washed with water. After drying in a drying oven, 19.7 kg of nickel hydroxide having a Co content of to were obtained. The anionic contaminants were less than 500 ppm. The bulk density was 1.3 g/cm3 and the tap density was 1.8 g/cm3. The specific BET surface (measured by the N2 one-point method) exhibited the very high value of 88 m2/g. The half width of the (101) reflection was 2Ø
2. Preparation of nickelhexamine chloride a) Discontinuously using NHS (25%-strength) 1 kg of ammonia (25o-strength) was added to 1 1 of a suspension of 100 g/1 of highly active nickel hydroxide gel prepared electrolytically in accordance with Example 1 and 280 g/1 common salt and stirred for 1 h while cooling. The reaction mixture was filtered off by suction via a laboratory nutsch and washed out portionwise with a little concentrated NH3.
226 g of [Ni (NH3) ~] C12 were obtained with a yield of 90.50.
STA 67-Foreign Countries - 10 -z1377sz The mother liquor contained 9.5 g of complexly bound nickel hydroxide and 78 g~ of NaOH and excess ammonia. The excess ammonia was distilled off via a short packed column as 250-strength aqueous solution.
In this process, 'the 9.5 g of complexly bound nickel hydroxide was precipitated as a filterable product which sedimented well.
After filtration and washing out with a little water, 1.5 1 of filtrate containing 280 g of NaCl (3.2 mol/1) and 78 g NaOH (1.3 mol/1) were obtained.
b) Continuously with NH3 (25%-strength) 0.5 1/h of a suspension of 100 g/1 highly active nickel hydroxide gel and 280 g/1 NaCl, and also 0.5 1 of ammonia (25%-strength) was pumped continuously while stirring and cooling into a 21 beaker having an overflow. The overflow was fed via a dip pipe into an elutriator in which the nickelhexamine chloride formed sedimented. The filtrate draining from the elutriator contained 2 g/1 complexly bound nickel hydroxide and 40 g/1 sodium hydroxide, and also 140 g/1 NaCl and excess ammonia. For a mean dwell time of 4 h, this corresponds to a degree of conversion of the highly active nickel hydroxide gel to nickelhexamine chloride of 920. 1 1 of the filtrate containing 190 g/1 NaCl and 40 g/1 NH3 was worked up as in paragraph al) using a short packed column.

25o-strength ammonia was obtained as condensate and, after separating the precipitated nickel hydroxide, 700 ml of process liquor containing 140 g NaCl (3.4 mol/1) and 40 g NaOH (1.4 mol/1).

c) Continuously with NH3 (50o-strength) as vapor The reaction of highly active nickel hydroxide gel and common salt with ammonia was carried out continuously in a cooled 10 1 propulsive jet reactor.
STA 67-Foreign Countries - 11 -213??62 Ammonia was obtained from dilute process solutions by evaporation via a packed column and fed directly, without prior condensation, as a 50%-strength NH3/H20 vapor mixture to the propulsive jet reactor. 3 1/h of a suspension of 100 g/1 highly active nickel hydroxide gel were fed continuously into the propulsive jet reactor along with 280 g/1 common salt and 600 g/h NH3 and 600 g/h H20 as a vapor mixture.
The overflow of the propulsive jet reactor was connected via a dip pipe to an elutriator in which the nickelhexammine chloride formed sedimented. The clear filtrate draining off (4 1/h) contained 3 g/1 complexly bound nickel hydroxide, 210 g of NaCl, 49 g of NaOH and 70 g/1 NH3. This corresponds to a degree of conversion of 960.

3. Preparation of compact nickel hydroxide a) Continuously in a 5 1 continuous-flow stirred tank reactor.
A viscous suspension of nickelhexamine chloride (400 g to 600 g of NH3, 7o-strength) was kept pumpable into a feedstock container by stirring. Of this suspension, 500 g/h was continuously pumped into a 5 1 continuous-flow stirred-tank reactor heated to 70°C. As a second component, approximately 1.2 1/h pH-controlled process liquor containing 60 g/1 NaOH and 140 g/1 NaCl were added.
The mean dwell time in the reactor was approximately 3 h. After 21 h, a compact, very readily filterable nickel hydroxide having a packing density of 1.6 g/cm3 was obtained from the suspension draining off after filtration and washing with H20.
b) Continuously in a 100 1 propulsive jet reactor A propulsive jet reactor in which optimum mixing of the reactors and generation of high shearing forces were ensured by means of mixing nozzles and a high-capacity circulating pump STA 67-Foreign Countries - 12 -was used for the reaction of nickelhexamine chloride and sodium hydroxide to form compact nickel hydroxide. A suspension of 400 g of nickelhexamine chloride in 600 g of NH3, 70-strength, was kept pumpable in a feedstock container by stirring. 20 kg/h of this suspension were fed via a hose pump into the propulsive jet reactor which was kept at a temperature of 73°C. Approximately 43 1 hour process liquor containing 65 g/1 NaOH and 200 g/1 NaCl were fed in continuously as reaction components. The process liquor was added in a pH-controlled manner, the pH being kept between 11.4 and 11.6. The mean dwell time was on average approximately 1.6 hours.
After 16 h a very rapidly sedimenting, compact nickel hydroxide which was extremely readily filterable and was capable of being washed out with approximately 7 1/kg of warm water to a chloride content of < 500 ppm was obtained from the overflow of the propulsive jet reactor.
The packing density of the nickel hydroxide was on average 1.9 g/cm3 and the tap density 2.1 g/cm3. The mean particle size of the spherical particles was on average 12 ~.m.
a STA 67-Foreign Countries - 13 -

Claims

CLAIMS:

1. A process for preparing a low solubility metal hydroxide of the general formula M(x)(OH)x, where M = a metal selected from the group consisting of Co, Zn, Ni and Cu and x is the valence of the metal, which process comprises reacting a metal hydroxide in reactive form in a first step, with a complexing agent (L) in the presence of an alkali-metal salt (AY) to form a metal complex salt of the general formula ML n Y m and an alkali-metal hydroxide solution, and decomposing the metal complex salt in a second step, to form a low solubility metal hydroxide and complexing agent and alkali-metal salt by reaction with an alkali-metal hydroxide solution at a pH of greater than about 7.

2. A process according to claim 1, wherein the complexing agent is selected from the group consisting of ammonia, and organic mono-amines and organic diamines having a chain length of 1 to 6.

3. A process according to claim 1 or 2, wherein the metal hydroxide is doped with one or more elements selected from the group consisting of Co, Zn, Mg, Ca and Cd in a total amount of up to 10% by weight.

4. A process according to claim 1, 2 or 3, wherein the process is carried out at a temperature in the range from 30 to 85°C.

5. A process according to claim 4, wherein the temperature range is from 45 to 80°C.

6. A process according to any one of claims 1 to 5, wherein the metal hydroxide is a freshly precipitated metal hydroxide.

7. A process according to any one of claims 1 to 6, wherein the metal hydroxide is a metal hydroxide obtained by anodic oxidation of a metal.

8. A process according to any one of claims 1 to 7, wherein the process is carried out continuously.

9. A process according to claim 8, wherein the complexing agent and the alkali metal salt are fed back to the first step.

10. A process according to claim 8, wherein the decomposition of the metal complex salt is carried out with the alkali metal hydroxide solution formed in the first step.

11. A process according to any one of claims 1 to 10, wherein the decomposition of the metal complex salt is carried out in a strongly turbulent flow which is generated by vigorous stirring, by passive or active mixing elements or by flow jets.

12. A process according to any one of claims 1 to 11, wherein the decomposition is carried out in a reactor with a defined dwell time of 0.5 to 10 hours.

13. A process according to claim 12, wherein the decomposition is carried out in a reactor with a defined dwell time of 1 to 4 hours.

14. A process according to any one of claims 1 to 13, wherein the process is carried out in a loop reactor.

15. A process according to claim 1 or 2, wherein:

(a) the metal hydroxide is doped with one or more elements selected from the group consisting of Co, Zn, Mg, Ca and Cd in a total amount of up to 10% by weight;
(b) the process is carried out at a temperature in the range of from 30 to 85°C;
(c) the metal hydroxide is a freshly precipitated metal hydroxide;
(d) the process is carried out continuously in a loop reactor with feedback of complexing agent and alkali metal salt to the first step; and (e) the decomposition of the metal complex salt is carried out in a strongly turbulent flow which is generated by vigorous stirring, by passive or active mixing elements or by flow jets.