AU2012203902B2

AU2012203902B2 - Metal hydroxide formulation

Info

Publication number: AU2012203902B2
Application number: AU2012203902A
Authority: AU
Inventors: Gary Ernest James
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-07-02
Filing date: 2012-07-02
Publication date: 2015-12-17
Anticipated expiration: 2032-07-02
Also published as: AU2012203902A1

Abstract

A method for the manufacture of a stabilised metal hydroxide slurry is described. A pre-cursor formulation comprising a mixture of the metal oxide such as magnesium oxide, a monohydroxyalkanol such as methanol and a 5 dihydroxyalkanol such as ethylene glycol is prepared. This formulation can be transported to a site for use where it is added to an aqueous medium to generate the metal hydroxide slurry. The aqueous medium can be the waste liquid from a sewerage well of a sewerage lift station and the resultant slurry finds use to reduce the levels of obnoxious gases in the waste liquid within the 10 sewerage well

Description

1 METAL HYDROXIDE FORMULATION THIS INVENTION relates to a metal hydroxide formulation. In particular, it is directed to, although not limited to, a metal hydroxide formulation, such as a 5 magnesium hydroxide slurry, which is stable for an extended period. Throughout this specification., unless the contrary is expressly stated, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or 10 any combination thereof was, at the priority date, publicly available, known to the public, part of the common general knowledge, or known to be relevant to an attempt to solve any problem with which this specification is concerned. Magnesium hydroxide, as an aqueous slurry, is used in various chemical 15 processes, including for pH adjustment in the treatment of waste water and sewage, scrubbing and neutralization of acidic vapours in flue gases, and in the production of other specific magnesium-containing compounds such as magnesium sulphate, magnesium nitrate and magnesium chloride. 20 With particular reference to the waste water / sewerage industry, a magnesium hydroxide slurry is used to raise the pH of the sewage to inhibit the formation of the obnoxious gas hydrogen sulphide. A typical rate of addition is 100 gallons of slurry per 100,000 gallons of waste water / sewage. This slurry is preferred as, presently, it represents the safest and most effective commercially available 25 product. Commercially, magnesium hydroxide is manufactured by hydrating magnesium oxide and then transporting the resultant slurry for on-site use. 30 Currently, a magnesium hydroxide slurry is derived from three basic sources: seawater, well brines and magnesite ore. Typically, a magnesium hydroxide aqueous slurry is obtained containing 40-55% solids and having a relatively high viscosity as much as between 3,000 and 4,000 centipoise.

2 One advantage of such a magnesium slurry is that a reliable and accurate dosing in its subsequent use can be ensured. Further, by undertaking the hydration off-site, the potential danger of the exothermic reaction of magnesium oxide with water can be reduced. 5 Nevertheless, there remain significant disadvantages to the prior art production of a magnesium hydroxide slurry which include (i) production is limited to close proximity to sources of brine or seawater which may be remote from the intended use of the slurry; (ii) the cost of subsequently transporting (usually by 10 road or rail) a product which is at least 50% water is relatively high; (iii) such a slurry requires relatively frequent agitation to prevent the settling out and agglomeration of the suspended solids; if settling and agglomeration occurs, the resultant mass is extremely hard which, after a period of time, is virtually impossible to re-suspend; consequently, customers for the slurry, rarely being 15 aware of the date of initial production of any particular slurry, only hold relatively small supplies of the slurry to avoid this agglomeration which leads to a greater than ideal frequency of delivery which, in turn, raises the cost of the treatment; and (iv) in industries such as waste water and sewage treatment, these imported slurries are adding extra water to a process where the disposal of 20 unwanted water from that site is already a significant major aim of the industries. It is thus a general object of the present invention to overcome, or at least ameliorate, one or more of the above-mentioned disadvantages to provide a 25 stable, high solid content metal hydroxide slurry, especially a magnesium hydroxide slurry, that can readily be prepared at the site of its intended use. According to a first aspect of the present invention, there is provided a method for producing magnesium hydroxide slurry including: agitating magnesium oxide 30 with alcohol to form a coated oxide in a container; adding a stoichiometric excess of water to said container, sufficient to form a substantially uniform suspension with said coated oxide while maintaining said agitation; reacting 3 said suspension to completion with continuing agitation at a reaction temperature of at least 500C to form a magnesium hydroxide suspension; and diluting in said container with continuing agitation, said magnesium hydroxide suspension with water to form a stable suspension. 5 Preferably, the reaction temperature may be provided by heat of reaction of said oxide with said stoichiometric-excess of water. Alternatively, the reaction temperature may be provided in part by heat of reaction of said oxide with said stoichiometric-excess of water, and in part by external heating. 10 Preferably, the stable suspension may be allowed to cool to ambient temperature. Preferably, the stable suspension may be filtered to remove agglomerates 15 before use. Preferably, the stable suspension may be homogenized before use. Preferably, the oxide may be technical grade soft MgO. 20 Preferably, the alcohol may be at least one selected from lower alkanols. Alternatively, the alcohol may be a mixture of a monohydric alcohol and a dihydric alcohol. The ratio of said monohydric alcohol : dihydric alcohol may be approximately 1.5 : 1, by weight. 25 Preferably, the alcohols may be methanol and ethylene glycol. Preferably, the water used in the method may be waste water. 30 Preferably, the method may be performed at a sewage treatment plant.

4 The instant inventor has determined that, if a slurry is prepared as hereinbefore described, said slurry resists agglomeration for an extended period of several weeks, has a relatively low viscosity and maintains a high pH for an equally extended period. 5 Therefore, a second aspect of the present invention is a stabilised slurry prepared by the method as hereinbefore described. As hereinbefore described, the slurry of the present invention finds particular 10 use at sites which can readily access and utilise said aqueous media, such as council-operated sewage treatment sites. At such sites, there is already available the required said aqueous media in the form of treated or untreated waste water. Further, if said raising temperature is required, such sites can utilise the waste gases, such as methane, which are generated thereat to 15 supply the required heat. Therefore, as a third aspect of the present invention, there is provided a method of desulphurizing waste water from sewage including the steps of: producing magnesium hydroxide slurry at a sewage treatment plant by agitating 20 magnesium oxide with alcohol to form a coated oxide in a pot adding a stoichiometric-excess of said waste water to said pot, sufficient to form a substantially uniform suspension with said coted oxide while maintaining said agitation, sufficient to form a substantially uniform suspension to completion with continuing agitation at a reaction temperature of at least 500C to form a 25 magnesium hydroxide suspension, and diluting in said pot, with continuing agitation, said magnesium hydroxide suspension with more said waste water sufficient to form a stable suspension; and dosing a bulk amount of said waste water with said stable suspension. 30 The instant inventor has also determined that a pre-cursor to said slurry can be prepared off-site which reduces the workload required by a user of said slurry while still offering one or more advantages of the present invention.

5 Therefore, as a fourth aspect of the present invention, there is provided a formulation for use in the production of a slurry of magnesium hydroxide, said formulation including: a magnesium oxide; 5 a said first alcohol; and a said second alcohol. Preferred embodiments of the present invention will now be described with reference to the following examples. 10 EXAMPLE 1 Bagged magnesium oxide is delivered to a sewage treatment site. Typically, the magnesium oxide is technical grade readily available in the art and comprises 15 approximately 97% by weight oxide, with the balance essentially being oxides of calcium, silica, iron and aluminium. Supplies of methanol and ethylene glycol are also delivered to the site. Readily available technical grade methanol and ethylene glycol solvents are sufficient for the present invention. 20 These supplies are stored at the site by any convenient means known in the art until required for use. For every 15 litres of magnesium hydroxide slurry required: 25 360 mIs of methanol and 128 mIs of ethylene glycol are mixed together to a homogenous solution; 25g of magnesium oxide is added to the solution and agitation continued until a coated oxide is obtained; 30 7.5 litres of water is added to the coated oxide, sufficient to form a substantially uniform suspension with the coated oxide while maintaining 6 agitation; (conveniently, this water is that reclaimed from the sewage treatment facility) the temperature of the suspension is monitored while agitating; if the 5 temperature fails to reach 70'C before the uniform suspension is obtained, heat is applied to the suspension (from the burning of the methane gas in the digesters of the sewage treatment facility), stirring the suspension until the temperature is reached; 10 agitation is continued for a further 1 hour; a further 7.5 litres of water is added to the suspension; (conveniently, this water is that reclaimed from the sewage treatment facility) 15 agitation is continued for a further 30 minutes; remove heat if applied, maintain agitation and allow the slurry to cool to ambient temperature; 20 if required, dependent on the grade of reagents used, it may be necessary to filter the slurry to remove any particulate matter of unwanted size; if it is necessary to use a slurry of a required particulate size, pass 25 through a homogenizer; and the slurry is either pumped to a storage tank for later use or is passed to one or more sewerage wells of a sewerage lift station for use in the reduction of obnoxious gases such as hydrogen sulphide in the waste liquid within the well(s). 30 Typically, the viscosity of the slurry is 50 to 400 centipoise with a particulate size of 1 to 3 microns.

7 The slurry of the typically maintains a pH of 10.8 for at least four (4) weeks and also remains stable, and thus pumpable, for at least four (4) weeks. EXAMPLE 2 5 For every 100 kgs of magnesium hydroxide slurry to be prepared subsequently: 710g of methanol and 540g of ethylene glycol are mixed together to a homogenous solution; and 10 30kg of magnesium oxide is added to the solution and agitation continued until a substantially uniform suspension is obtained. The present invention thus provides a number of advantages which include (i) 15 can be manufactured partially or entirely at the site of intended use of the slurry; (ii) the expected life time of the slurry is known directly by the user; (iii) can be manufactured as required in the quantities required thus saving on transport costs; and (iv) when used in waste water and sewage treatment facilities or similar, it can use the onsite treated water rather than adding an outside water 20 source. It will be appreciated that the above described embodiments are only exemplifications of the various aspects of the present invention and that modifications and alterations can be made thereto without departing from the 25 inventive concept as defined in the following claims.

Claims

1. A method for producing magnesium hydroxide slurry including: agitating magnesium oxide with alcohol to form a coated oxide in a 5 container; adding a stoichiometric-excess of water to said container, sufficient to form a substantially uniform suspension with said coated oxide while maintaining said agitation; reacting said suspension to completion with continuing agitation at a 10 reaction temperature of at least 500C to form a magnesium hydroxide suspension; and diluting in said container with continuing agitation, said magnesium hydroxide suspension with water to form a stable suspension. 15

2. A method according to claim 1, wherein the reaction temperature is provided by heat of reaction of said oxide with said stoichiometric-excess of water.

3. A method according to claim 1, wherein the reaction temperature is 20 provided in part by heat of reaction of said oxide with said stoichiometric-excess of water, and in part by external heating.

4. A method according to any one of the preceding claims, wherein the stable suspension is allowed to cool to ambient temperature. 25

5. A method according to any one of the preceding claims, wherein the stable suspension is filtered to remove agglomerates before use.

6. A method according to any one of the preceding claims, wherein the 30 stable suspension is homogenized before use. 9

7. A method according to any one of the preceding claims, wherein the oxide is technical grade soft MgO.

8. A method according to any one of the preceding claims, wherein the 5 alcohol is at least one selected from lower alkanols.

9. A method according to claim 8 wherein the alcohol is a mixture of a monohydric alcohol and a dihydric alcohol.

10 10. A method according to claim 9 wherein the ratio of said monohydric alcohol : dihydric alcohol is approximately 1.5 : 1, by weight.

11. A method according to any one of claims 9 and 10, wherein the alcohols are methanol and ethylene glycol. 15

12. A method according any one of the preceding claim, wherein the water used in the method is waste water.

13. A method according to claim 12, when performed at a sewage treatment 20 plant.

14. A stabilised slurry prepared by a method as defined in any one of claims 1 to 13. 25

15. A method of desulphurizing waste water from sewage including the steps of: producing magnesium hydroxide slurry at a sewage treatment plant by agitating magnesium oxide with alcohol to form a coated oxide in a pot adding a stoichiometric-excess of said waste water to said pot, sufficient to form a 30 substantially uniform suspension with said coted oxide while maintaining said agitation, sufficient to form a substantially uniform suspension to completion with continuing agitation at a reaction temperature of at least 500C to form a 10 magnesium hydroxide suspension, and diluting in said pot, with continuing agitation, said magnesium hydroxide suspension with more said waste water sufficient to form a stable suspension; and dosing a bulk amount of said waste water with said stable suspension. 5