WO2000075071A1

WO2000075071A1 - Method of manufacturing metal oxides

Info

Publication number: WO2000075071A1
Application number: PCT/GB2000/002140
Authority: WO
Inventors: Richard Lewis Warren
Original assignee: Bayer Aktiengesellschaft
Priority date: 1999-06-05
Filing date: 2000-06-02
Publication date: 2000-12-14
Also published as: GB9913041D0; AU5233000A

Abstract

A method for manufacturing metal oxides comprises feeding a slurry of metal salt to a reactor under oxidising conditions. The slurry includes an oxidant which may be selected from one or more of sodium nitrate, nitric acid and hydrogen peroxide. The metal salt may comprise one or more ferrous chloride, ferrous sulphate and ferric chloride.

Description

Method of Manufacturing Metal Oxides

This invention relates to the preparation of metal oxides. In particular, but not exclusively, the invention relates to the production of iron oxides, for example black and red iron oxides.

Conventional methods for the manufacture of black and red iron oxides of pigment grade are usually carried out as batch processes in large vats, typically of 10,000 litres capacity. In one process, an alkaline mixture of sodium hydroxide solution and a ferrous salt is heated to 90°C and partially oxidised by passing air slowly through the stirred mixture for about 48 hours. The disadvantages of this process are that large volumes of air and large quantities of reactants and energy are used. Also, the plant occupies large amount of space and reaction takes a considerable time. ~

According to one aspect of this invention, there is provided a method for preparing metal oxides comprising feeding a slurry of a metal salt to a reactor under oxidising conditions.

The reactor is preferably a tubular reactor.

The metal salt may be a precipitated metal salt, suitably a fully or partially precipitated metal salt. The said conditions are preferably fully or partially oxidising, and the process is preferably continuous.

In one embodiment of the invention, the slurry is alkaline, and may contain an alkali which may comprise an alkaline earth, for example calcium hydroxide. Alternatively, or in addition, the alkali may be ammonia, and/or sodium hydroxide.

The metal salt is preferably mixed with the alkali to cause precipitation and preferably form said slurry. The slurry preferably also includes an oxidant. The metal salt may be ferrous chloride, ferrous sulphate, and/or ferric chloride. The oxidant may be sodium nitrate, nitric acid, and/or hydrogen peroxide.

In one particular form of the invention, the slurry may contain substantially 100 parts of the alkali, for example calcium hydroxide, substantially 500 parts water, substantially 650 parts of the metal salt, for example ferrous chloride, and substantially 16 parts of the oxidant, for example sodium nitrate. The yield is advantageously 100 parts of dry metal oxide. The slurry is preferably heated to 140°C to 180°C and pressure may be applied thereto. Preferably, the pressure so applied is of a sufficient level to prevent the slurry boiling. Preferably, the reaction occurs to produce the metal oxide in a period less than substantially 3 minutes, desirably in about 10 seconds.

The ferrous chloride solution may contain up to 33% ferrous chloride, and may have been obtained as the by-product of a steel manufacturing process.

Embodiments of the invention will now be described by way of example only.

In a first example, 143g of ferrous sulphate septahydrate was dissolved in 700 ml of water. The resulting solution was added to a vigorously stirred solution of 40g sodium hydroxide in 300 ml of water. 6.8g of sodium nitrate was added to this solution and the stirring was continued for 5 minutes. The ferrous sulphate was precipitated out of the solution and a slurry formed. This slurry was then pumped into a tubular reactor and heated to a temperature of 100°C. The temperature was maintained for 10 seconds and the slurry then cooled and discharged from the reactor through a pressure relief valve. The pressure relief valve maintained the pressure in the tubular reactor during the reaction time at a sufficient level to prevent the slurry from boiling.

The precipitated product was then separated from the liquid and washed by any convenient known filtration of settling process. 38.5g of pigment grade black iron oxide was produced from the process. The tubular reactor is manufactured from material that will not corrode at the operating temperature. An example of such a material is inconel but it would be appreciated that other alloys or materials are likely also to be suitable. The heating and cooling may be carried out by any suitable known method. For example, the heating can be carried out by electrical heating or by the use of high pressure steam. A heat exchanger may also be used to reduce the amount of energy required to heat the slurry.

In a second example, the above example was repeated but this time using different ingredients with the same reactor to produce red iron oxide. In this second example, 102g ferric chloride and 60g ferrous chloride, with 66g ammonia and 2.8g nitric acid mixed together in the process as described above produced a pigment grade red iron oxide.

The advantages of the above described embodiments include the fact that the reaction is continuous which enables smaller quantities of reactants to be used at any given time. In view of the fact that the reaction is carried out at high temperature and pressure with an oxidant results in a short reaction time. Consequently, the cost of the reactants is reduced as is the capital cost and the size of the plant. The above described embodiment allows the production of a range of high quality pigment grade products with improved uniformity of crystal growth and particle size.

Various modifications can be made without departing from the scope of the invention.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A method for preparing metal oxides comprising feeding a slurry of a metal salt to a reactor under oxidising conditions and thereafter allowing the metal salt to react to produce the metal oxide.

2. A method according to claim 1, wherein the slurry includes an oxidant comprising one or more of sodium nitrate, nitric acid and hydrogen peroxide.

3. A method according to claim 1 or 2, wherein the metal salt comprises one or more of ferrous chloride, ferrous sulphate and ferric chloride.

4. A method according to claim 1, 2 or 3, wherein the metal salt is a precipitated metal salt.

5. A method according to any preceding claim, wherein the method is continuous.

6. A method according to any preceding claim, wherein the slurry is alkaline, containing an alkali.

7. A method according to claim 6, wherein the alkali comprises an alkaline earth.

8. A method according to claim 7, wherein the alkaline earth comprises one or more of calcium hydroxide, ammonia, and sodium hydroxide.

9. A method according to claims 6 to 8, wherein the metal salt is mixed with the alkali to cause precipitation and form said slurry.

10. A method according to any preceding claim, wherein the slurry includes an oxidant. The slurry contains substantially 100 parts of an alkali, substantially 500 parts water, substantially 650 parts of the metal salt, and substantially 16 parts of an oxidant

11. A method according to any preceding claim, wherein the reaction occurs to produce the metal oxide in a period less than substantially 3 minutes.

12. A method according to claim 11, wherein the reaction occurs to induce the metal oxide in a period of about 10 seconds.

13. A method according to any preceding claim, wherein the method includes the steps of heating the slurry to a temperature in the range of 140°C to 180°C, and applying pressure thereto to a sufficient level to prevent the slurry boiling.

14. A method according to claim 3, wherein a solution of the metal oxide is provided, and where the metal oxide ferrous chloride, the solution of said ferrous chloride contains up to 33% of ferrous chloride.

15. A method according to any preceding claim, wherein the reactor is a tubular reactor.

16. A method according to any preceding claim substantially as herein described.

17. Any novel subject matter or combination including novel subject matter disclosed herein, whether or not within the scope of or relating to the same invention as any of the preceding claims.