GB1600750A

GB1600750A - Process and apparatus for the production of hydroxides of metallic or semi-conductor elements

Info

Publication number: GB1600750A
Application number: GB3226877A
Authority: GB
Original assignee: Assoun C D
Current assignee: Assoun C D
Priority date: 1978-05-24
Filing date: 1978-05-24
Publication date: 1981-10-21

Description

(54) PROCESS AND APPARATUS FOR THE PRODUCTION OF HYDROXIDES OF METALLIC OR SEMI-CONDUCTOR ELEMENTS (71) I, CHRISTIAN DANIEL ASSOUN, a French national of Hydro-trade Metals, 9 Avenue C. Fachatte, Yerres 91330, France, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a process and a plant for the production of hydroxides of metallic or semi-conductor elements.

It is well known that Industry uses metal hydroxides in large quantities and that their industrial applications are numerous.

Metal hydroxides are generally produced by chemical reaction with a salt of the metal of the hydroxide which it is intended to produce.

The standard method consists of precipitating metal hydroxide, by double decomposition, in an aqueous medium, between a soluble salt and an alkaline hydroxide, according to the following formula:

(hydroxide precipitate) where MX is the soluble salt of the metal, M(OH)n its hydroxide which it is wished to obtain, N(OH)n is the alkaline hydroxide, and n is a whole number denoting the valency of the element N.

This standard method has the advantage that it demands only a low expenditure of energy, but has several undesirable features related to the precipitation of metal hydroxide in a very basic medium (pH approximately 13).

To obtain metal hydroxides which can be used industrially, repeated cleansing of the hydroxide precipitate is necessary and, despite this cleansing, it is still not possible to rid the hydroxide entirely of the alkaline ions which were introduced by the alkaline base used.

In addition, serious problems of pollution are caused by the disposal of the cleansing water referred to above.

The object of this invention is to provide a process which produces the metal hydroxide directly, in a pure state, ready for industrial use, without the need to introduce the laborious and polluting cleansing operations referred to above.

According to the present invention in a process for the production of the hydroxides, alcoholates or hydrates or metallic or semi-conductor elements including carbon, a voltage in excess of 30 volts is applied between an anode consisting of the metallic or semi-conductor element of the hydroxide it is intended to produce and a cathode, both of which are immersed in an aqueous medium whose pH lies between 6 and 8 at the beginning of the process, and the aqueous medium is then separated from the hydroxide which has formed.

The process can be used for transition and refractory metals, as well as for semi-conductor elements.

The process according to the invention differs from the standard electrolytic processes principally by the use of a significantly higher voltage (in excess of 30 volts) than that used in electrolytic treatment processes. The voltages used in electrolysis do not exceed 12 volts.

The invention is based on the discovery that, in electrolysis carried out in a neutral medium, a small amount of hydroxide is formed which adversely affects the conditions required for the efficient transfer of metal from the anode to the cathode.

Experience has yielded the surprising result that it is possible to considerably increase the quantity of hydroxide produced by employing much higher voltages, particularly in excess of 30 volts.

It was also found that the conversion of the metal of the anode into hydroxide largely followed Faraday's law.

The hydroxide of the metal or semi-conductor element thus formed is sufficiently pure and, after separation from the medium, requires no cleansing, since the pH of the medium is effectively neutral.

In a preferred form of the process, the value of the applied voltage lies between approximately 50 and 380 volts, the current being between approximately 2 and 100 amperes, depending on the nature of the metallic or semi-conductor element constituting the anode, the distance between the electrodes, and the dimensions of the latter. Other characteristics and advantages of the process will be apparent in the description which follows.

The invention may be put into practice in various ways and certain examples of the process and one specific embodiment of apparatus for carrying out the process will be described to illustrate the invention with reference to the accompanying drawing of the apparatus.

The drawing shows an anode 1 and a cathode 2, immersed in an aqueous medium 3, which has a pH which is effectively neutral and consists, for example, of ordinary water.

A current supply 4 (d.c. or rectified a.c.) is connected to the anode 1 and the cathode 2, and produces a voltage across them of between approximately 50 and 380 volts. The current flowing is preferably between approximately 2 and 100 amps.

To increase the conductivity of the aqueous medium 3, small quantities of an acid, such as hydrochloric acid, or of a base, such as sodium hydroxide, may be added. The pH of the medium 3 is close to neutral and at the beginning of the process is between 6 and 8. The conductivity of the medium can also be increased by adding a small quantity of the hydroxide it is intended to produce. It will at the same time constitute nucleii which will encourage the production of the hydroxide to be produced.

In order further to encourage the formation of the hydroxide, it is preferable that the medium 3 be continuously agitated, e.g. by means of a mechanical agitator 5 as shown in the drawing.

Some time after the voltage is first applied between the anode 1 and the cathode 2 a deposit will be observed on the surface of the medium 3, consisting of the hydroxide of the anode element.

It will also be noted that hydrogen is produced at the cathode 2, as in a standard electrolysis. Diminution of the anode 1 Is also observed, due to the formation of the hydroxide.

Without linking the invention to this interpretation, the formation of the metal hydroxide can be explained by the combination of the +ve M ions of the anode with the -ve OH ions formed in the medium 3, by dissociation of the water molecules.

This combination occurs equally in a normal electrolysis,but at a much slower rate than in the process of this invention.

Experience has also shown that the reduction in the bulk of the electrodes is much more pronounced at the bottom than it is in the middle or at the top. For this reason, the bottoms of the electrodes are, when possible, enlarged, as shown in the figure.

At the end of the operation, the particles of metal hydroxide 7 are deposited at the bottom of the tank 6, and can then be separated from the medium by decanting.

To facilitate this latter operation, a series of valves 8 are fitted to the side wall of the tank 6 at regular intervals. To separate the hydroxide deposit from the water, the valve 8 situated immediately above the level of the hydroxide deposit is opened. The position of the level itself is determined by means of the transparent strip 9 or by the transparent windows fitted alongside the valves 8.

The metal hydroxide recovered after the water has been decanted can then be separated from the rest of the water in a centrifuge.

Example 1- Nickel hydroxide: Ni(OH)2 Characteristics of the Plant used: Tank: of plastic, 80 cm in diameter, 80 cm high Electrodes: nickel, surface area 7 to 10 dm2, height 60 cm, thickness 3 to 5 mm.

Aqueous Medium: 160 litres of water.

Supply voltage: 180 to 260 volts d.c.

Current: 8 to 12 amperes.

To increase the conductivity of the water, 20 g of Ni(OH)2 or several c.c., e.g 1 to 5 c.c., of hydrochloric acid or sodium hydroxide e.g. (1M) may be added.

In all cases, the nickel hydroxide formed is found to be very pure, at the end of the operation the pH of the medium being between 7.8 and 8.7, or practically free from ions which could pollute the nickel hydroxide or create pollution problems when the aqueous medium was disposed of.

The nickel hydroxide obtained consists essentially of Ni(OH)2, but a small deposit of NiO2 will be found on the anode, and sometimes, especially when the voltage is low, NiOH and hydrated peroxide NiOOH is formed.

The nickel hydroxide obtained by this process can be used in electroplating, for the treatment of metal surfaces, in nickel-cadmium batteries, in atomic fuel piles, as a catalyst, in the hydrogenation of fats, and in the preparation of nickel salts.

Example 11 - Ferrous hydroxide: Fe(OH)2 and Fe(OH)3 The process of Example I was repeated using iron electrodes. Fe(OH)2, of a greenish colour, is obtained first, then Fe(OH)3, of a rusty colour, is obtained as the temperature of the medium increases. To prevent the medium overheating and the hydroxide being transformed into FeO, the former is cooled by the addition of cold water which is slightly alkaline.

These hydroxides are used notably in the preparation of ferrous salts.

Example 111 - Aluminium hydroxide : Al(OH)3 The process of Example I was repeated using aluminium electrodes. The process produces a very high quality aluminium hydroxide when the temperature of the medium reaches 70"C. A greyish deposit of ,B - aluminium will be found on the cathode.

The aluminium hydroxide obtained by this process is used in particular as a catalyst in the petro-chemical field, for the treatment of solvents, for the preparation of activated aluminium, for pharmaceutical preparations and for the preparation of stearates and fats.

Example IV - Lead hydroxide : Pb(OH)2 The process of Example I was repeated using lead electrodes. A period of 48 hours is required to produce this lead hydroxide. It is necessary ta monitor the temperature rise carefully to prevent the Pb(OH)2 being transtormed into PbO.

This hydroxide is used particularly as a catalyst and a pigment, in the electrochemical field and for the manufacture of stearates.

Example V - Tin hydroxide : Sn(OH)2 The process of Example I was repeated using tin electrodes. This hydroxide can be obtained without difficulty.

A greyish deposit of SnO and/or SnO2 is also found on the electrodes.

Tin hydroxide is used particularly in electroplating, pharmacy, in agricultural scientific products and for the treatment of fats.

Example VI - Zinc hydroxide: Zn(OH)2 The process of Example I was repeated using zinc electrodes. After 48 hours, a gelatinous and stable zinc hydroxide precipitate is obtained. A deposit of ZnO2 and/or ZnOOH will be found on the electrodes.

Example VII - Cobalt hydroxide: Co(OH)2 The process of Example I was repeated using cobalt electrodes. The green divalent cobalt hydroxide is produced without difficulty by the process. This compound oxidises slowly into a nomohydrous cobalt oxide. The formation of this oxide can be prevented by the presence of a weak reducing agent such as glucose.

Example VIII -Cobalt hydroxide: Co(OH)2 This hydroxide can be obtained by the oxidising of the medium produced in Example VII containing Co(OH)2, for example, by bubbling oxygen through it.

These cobalt hydroxides are used for the preparation of complex salts, in pharmacy and metallurgy, for the manufacture of drying agents, for the preparation of cobalt napthamate, in surface treatments and in the glass and porcelain industry.

Exaple IX- Cadmium hydroxide: Cd(OH)2 The process of Example I was repeated using Cadmium electrodes. This hydroxide is obtained in the form of a jelly.

The oxide CdO, and sometimes a hydrated peroxide, is formed on the electrodes.

The product is used in particular for surface treatments (cadmium-plating).

Example X - Copper hydroxide: Cu(OH)2 The process of Example I was repeated using copper electrodes. During the preparation of this compound, it is advisable to monitor carefully the rise in the temperature of the medium, to prevent the transformation of the Cu(OH)2, greenish-blue in colour, into CuO, Cu(OH)2, which is brown.

This compound has numerous applications, including catalysis, pharmacy, agricultural science and surface treatments.

Example XI - Magnesium hydroxide: Mg(OH)2 The process of Example I was repeated using magnesium electrodes. Magnesium hydroxide is white in colour and can be produced without difficulty. A deposit of hydrated oxide, Mg(OH)2 nH2O, will be found on the electrodes, with diminution of the cathode.

This hydroxide can be used as a mineral filler for elastomers and in the paper industry.

Example XII - Manganese hydroxide: Mn(OH)2 The process of Example I was repeated using manganese electrodes. This compound is easily produced and is used notably in catalysis.

Example XIII - Titanium hydroxide: Ti(OH)4 The process of Example I was repeated using titanium electrodes. The normal application of the process results in Ti(OH)4.

This compound can then easily be converted into TiO2, a product which has numerous applications.

Thus, the process allows titanium oxide to be produced directly from titanium metal, without causing pollution problems.

Example XIV to XVI The process of Example I was repeated using Zirconium, Hafnium, and Thorium electrodes respectively. The process allows the easy production of: Zirconium hydroxide : Zr(OH)4 Hafnium hydroxide : Hf(OH)4 Thorium hydroxide : Th(OH)4 Example XVII - Silver hydroxide: AgOH The process of Example I was repeated using silver electrodes. The process produces a stable precipitate of silver hydroxide. An increase in the temperature of the solution results in the formation of the oxide Ag2O. It will be noted that chemistry text books state that the production of silver hydroxide is a very critical process. Certain even treat the existance of this compound as theoretical, since the reactions used always result in Ag2O.

Example XVIII - Gold hydroxide: AuOH The process of Example I was repeated using gold electrodes. This compound can be used in electroplating to replace the toxic gold cyanide baths.

Example XIX - Gold hydroxide: Au(OH)3 This compound is obtained when very small quantities of an alkaline hydroxide. such as NaOH, are present in the reactive medium.

The process can also be used to produce the following metal hydroxide from the appropriate metals: - mercury hydroxide : Hg(OH)2 - the complex : RbOH, Sn(OH)2, LiOH - the chrome hydroxides : Cr(OH)2 and Cr(OH)3 - platinum hydroxide : Pt(OH)2 - palladium, ruthenium, rhenium, osmium and iridium hydroxides.

- tungsten hydroxide W(OH)4, vanadium hydroxide V(OH)4, tantalum hydroxide Ta(OH)2 and niobium hydroxide Nb(OH)2.

The process has also been used to produce a uranium hydroxide U(OH)4, UO2, H2O, which can be used in homogeneous reactors.

The process can also be used to produce hydroxides from electrodes composed of semi-conductors.

Example XX - Hydrated carbon, colloidal : nC, iH2O A compound such as this has useful applications, particularly in the field of electrodialysis or electrical filtration.

Examples XXI to XXIII The proceeds can also be used to produce bismuth, arsenic, and antimony hydroxides: Bi(OH)3, As(OH)3 and Sb(OH)3.

Example XXIV The process can be used to produce silicon hydroxide: Si(OH)4, from which silicon-based polymers can be produced.

Example XXV The process can also be used in the production of germanium hydroxide: Ge(OH)4, which can be used in the manufacture of semi-conductors and germanium-based polymers.

The process is also applicable to the preparation of metallic alcoholates.

Example XXVI - Aluminium alcoholate.

Aluminium electrodes are used, and a quantity of ethyl alcohol, varying between 1 and 20% in volume, is added to the aqueous medium.

A precipitate of aluminium alcoholate, is obtained above 70"C.

The examples given above show that the process allows hydroxides to be produced from the majority of transition or refractory metals and even from certain semi-conductor elements.

The process is remarkable in that it uses as the direct starting material the metallic or semi-conductor element whose hydroxide it is wished to obtain.

In all cases the hydroxide produced has a high degree of purity, the latter depending solely on the purity of the metallic or semi-conductor element which existed at the start and on the purity of the aqueous medium used.

The hydroxide produced is usable directly with no intermediate purifying process required.

In addition, the aqueous medium used in this process can, thanks to its neutrality, be disposed of without being a cause of pollution.

Naturally, the process is not limited to the examples which have been described.

Instead of the single anode, a series of anodes of different metals may be used, and thus mixed hydroxides of various metals can be produced. Mixed hydroxides can also be produced by using a single anode made of an alloy of several metals.

The water of the medium can be replaced by heavy water for the production of deuterium hydroxides which can be used in nuclear applications.

The process can, of course, be made continuous and automated, in a plant in which the replacement of the electrodes, the pH level of the medium, the voltage and the current, the temperature, etc are all controlled automatically.

In the table on Page 15 are given specific operating conditions for the examples.

When the process is being started and the bath is cold one may have to apply a higher voltage to initate the process than is necessary when the bath has warmed up. The initial voltage is quoted as a range V1 to V2 and the working voltage is quoted as a range V3 to V4.

The temperature should also be controlled and the temperature is quoted as a range T1 to T2 in degrees celsius.

Example Compound V V2 V3 V4 T1 T2 Produced I Ni(OH)2 120 180 80 120 60 75 NiOOH 60 80 60 80 30 40 II FE(OH)2 80 100 80 100 35 45 Fe(OH)3 80 100 80 100 50 60 III Al(OH)3 80 120 80 100 60 70 AlOOH 120 140 120 130 70 85 IV Pb(OH)2 80 100 110 110 50 60 V Sn(OH)2 80 100 80 100 50 65 VI Zn(OH)2 80 100 80 100 50 60 VII Co(OH)2 100 120 80 100 40 50 CoOOH 100 120 100 120 60 70 VIII Co(OH)3 100 120 100 120 60 70 IX Cd(OH)2 80 100 100 110 50 70 X Cu(OH)2 60 80 80 80 35 45 XI Mg(OH)2 80 100 80 100 50 50 XII Mn(OH2) 80 90 80 80 40 50 XIII Ti(OH)4 100 120 100 110 50 60 XVII AgOH 60 80 60 70 15 25 XIX U(OH)4 60 100 60 100 45 55 XXIV Si(OH)4 120 180 120 180 XXV Ge(OH)4 100 140 110 140 WHAT I CLAIM IS: 1.A process for the production of hydroxide, alcoholates or hydrates of metallic or semi-conductor elements or carbon, in which a voltage in excess of 30 volts is applied between an anode consisting of the metallic or semi-conductor element, the hydroxide of which it is intended to produce, and a cathode, both of which are immersed in an aqueous medium or an aqueous alcoholic medium the pH of which lies between 6 and 8 at the beginning of the process, the aqueous medium then being separated from the hydroxide which has formed.

2. A process as claimed in Claim 1, in which the value of the applied voltage is between 50 and 380 volts.

3. A process as claimed in Claim 1 or Claim 2 in which a small quantity of the hydroxide it is intended to produce is added to the medium as a nucleating agent.

4. A process as claimed in any one of Claims 1 to 3 in which the aqueous medium is agitated.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

voltage to initate the process than is necessary when the bath has warmed up. The initial voltage is quoted as a range V1 to V2 and the working voltage is quoted as a range V3 to V4.

The temperature should also be controlled and the temperature is quoted as a range T1 to T2 in degrees celsius.

Example Compound V V2 V3 V4 T1 T2 Produced I Ni(OH)2 120 180 80 120 60 75 NiOOH 60 80 60 80 30 40 II FE(OH)2 80 100 80 100 35 45 Fe(OH)3 80 100 80 100 50 60 III Al(OH)3 80 120 80 100 60 70 AlOOH 120 140 120 130 70 85 IV Pb(OH)2 80 100 110 110 50 60 V Sn(OH)2 80 100 80 100 50 65 VI Zn(OH)2 80 100 80 100 50 60 VII Co(OH)2 100 120 80 100 40 50 CoOOH 100 120 100 120 60 70 VIII Co(OH)3 100 120 100 120 60 70 IX Cd(OH)2 80 100 100 110 50 70 X Cu(OH)2 60 80 80 80 35 45 XI Mg(OH)2 80 100 80 100 50 50 XII Mn(OH2) 80 90 80 80 40 50 XIII Ti(OH)4 100 120 100 110 50 60 XVII AgOH 60 80 60 70 15 25 XIX U(OH)4 60 100 60 100 45 55 XXIV Si(OH)4 120 180 120 180 XXV Ge(OH)4 100 140 110 140 WHAT I CLAIM IS: 1.A process for the production of hydroxide, alcoholates or hydrates of metallic or semi-conductor elements or carbon, in which a voltage in excess of 30 volts is applied between an anode consisting of the metallic or semi-conductor element, the hydroxide of which it is intended to produce, and a cathode, both of which are immersed in an aqueous medium or an aqueous alcoholic medium the pH of which lies between 6 and 8 at the beginning of the process, the aqueous medium then being separated from the hydroxide which has formed.
2. A process as claimed in Claim 1, in which the value of the applied voltage is between 50 and 380 volts.
3. A process as claimed in Claim 1 or Claim 2 in which a small quantity of the hydroxide it is intended to produce is added to the medium as a nucleating agent.
4. A process as claimed in any one of Claims 1 to 3 in which the aqueous medium is agitated.
5. A process as claimed in any one of Claims 1 to 4 in which the medium is separated

from the hydroxide by decanting.
6. A process as claimed in Claim 5 in which after the supernatent liquid medium has been decanted from the solid hydroxide, the hydroxide is subjected to centrifuging to remove more of the aqueous medium.
7. A process as claimed in any one of Claims 1 to 6 in which the cross section of the electrodes is greater at their lower end than at their upper end.
8. A process as claimed in any one of Claims 1 to 7 in which two or more anodes of differing metals are used to prepare a mixture of metallic hydroxides.
9. A process as claimed in any one of Claims 1 to 8 in which an anode consisting of an alloy of different elements is used.
10. A process as claimed in any one of Claims 1 to 9 in which the aqueous medium contains or consists of D2O (heavy water) in order to produce deuterium hydroxides.
11. A process as claimed in any one of Claims 1 to 9 in which the aqueous medium contains between 1 and 20% by volume of alcohol whereby metallic alcoholates are produced.
12. A process as claimed in Claim 1 substantially as specifically described herein with reference to any one of the Examples.
13. A metallic or semi-conductor or carbon hydroxide, alcoholate or hydrate whenever produced by a process as claimed in any one of Claims 1 to 12.