AU2764002A

AU2764002A - Liquid calcium hydroxide

Info

Publication number: AU2764002A
Application number: AU27640/02A
Authority: AU
Inventors: Peter Charles Leach; Glen Stuart McDonald; Graham George Strachan
Original assignee: Ultimate Nominees Pty Ltd
Current assignee: Ultimate Nominees Pty Ltd
Priority date: 2001-03-29
Filing date: 2002-03-25
Publication date: 2002-10-03

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT S. Invention Title: Liquid calcium hydroxide The following statement is a full description of this invention, including the best method of performing it known to us: Freehills Carter Smith Beadle Melbourne\004020538 Printed 25 March 2002 (9:51) Freehills Carter Smith Beadle Melbourne\004020538 Printed 25 March 2002 (9:51) LIQUID CALCIUM HYDROXIDE Technical Field of the Invention This invention relates to stable aqueous suspensions of calcium hydroxide particles. The invention also relates to methods of preparing such aqueous suspensions.

Background to the Invention Calcium hydroxide is formed by the reaction of calcium oxide with water.

Calcium oxide is also known as lime, quicklime, burnt lime and unslaked lime.

Calcium oxide is usually prepared by heat treatment of calcium carbonate (limestone). Calcium hydroxide is also referred to as calcium hydrate, hydrated lime, caustic lime and slaked lime. It is widely used in the building industry in mortars, plasters and cements as well as in many other industries. These other uses S"include water purification, road stabilisation, steel making and metals extraction.

In water treatment, hydrated lime neutralises the acid wastes from many S industrial processes, and also aids the flocculation of particles which are suspended in the water. It makes mortar more pliable and hence easier to apply, as well as minimising any cracking of the cured mortar due to movement.

Hydrated lime is caustic, causing burning of the skin and inflammation of the eyes. It has a TLV of 5 mg/m 3 of air. It is recommended that goggles, gloves and protective clothing are worn during handling. If applied as a bulk product, care must also be taken to minimise wind-drift. If applied from bulk hoppers, it can also bridge within the hopper, requiring regular attention to keep it flowing freely.

"Slaking machines" are available which mix the bulk or bagged lime into a slurry before application, but they do not overcome the problem of handling the lime prior to adding to the machine. As set out above there are significant handling problems associated with using calcium hydroxide in powder form.

Aqueous slurries of calcium hydroxide are known. However, these tend to have relatively low concentrations of calcium and also their storage stability tends to be poor. These known suspensions require agitation to maintain the calcium hydroxide particles in suspension and avoid settling. The problem with having Melbourne\004014107 Printed 22 March 2002 (11:31) relatively low concentrations of calcium is that storage and transport costs are increased as significant amounts of water relative to calcium are required. Known suspensions generally have calcium hydroxide concentrations less than 400 g/litre.

Summary of the Invention This invention provides in one form a stable aqueous concentrated suspension of calcium hydroxide wherein the concentration of calcium hydroxide is at least 600 g/litre of aqueous suspension, more preferably at least 700 g/litre and most preferably 800 g/litre.

Preferably the concentrated suspension further includes 1 10% of a water S 10 soluble polymer having a molecular weight of at least 10,000.

Preferably the water soluble polymer has a viscosity, 2% in water 20 0 C, in i"°"the range 10,000 100,000 cps.

Preferably the water soluble polymer is a cellulosic ether derivative.

More preferably the water soluble polymer is hydroxy propyl methyl cellulose polymer.

Preferably the aqueous suspension includes a wetting agent.

Detailed Description of the Invention As well as the preferred hydroxy propyl methyl cellulose polymer other polymers may be used. Examples of suitable polymers are alkali swellable (meth)acrylic copolymers, polyvinyl alcohol and polyethers. It is important for the composition that the water soluble polymer is hydrolytically stable at the highly alkaline pHs that are inherent in aqueous suspensions of calcium hydroxide.

Preferred water soluble polymers are polyethers such as cellulose derivatives.

The preferred wetting agents are anionic or non-ionic.

Combinations of different water soluble polymers as well as combinations of different types of wetting agents may be used.

The invention will be further described by reference to preferred embodiments in the following Example where all parts are expressed as parts by weight.

Melbourne\004014107 Printed 22 March 2002 (11:31) Example This example illustrates the preparation and stability testing of an aqueous suspension prepared according to the present invention.

The following ingredients were slowly added to a two litre plastic beaker equipped with a mechanical stirrer.

water (potable) 500.0g hydroxy propyl methyl cellulose* calcium lignosulfonate 0.2g Terwet 3001 Methocel, Grade -S 240 ex Dow Chemical alkyl C 8 -Co 10 polyglucoside wetting agent ex Huntsman Chemicals After the ingredients were dissolved calcium hydroxide (690.0 max S"particle size 75 was slowly added. A fine aqueous suspension was formed with a calcium hydroxide concentration of approximately 850 g/litre. The pH of the 15 suspension was in the range 12.5 to 13.0 The viscosity of the water soluble polymer is typically determined using a Brookfield viscometer.

The suspension was storage stable for six weeks at room temperature and for seven days at 50 0 C. The term "stable" is used in its art recognised sense and refers to the colloidal stability of the composition or suspension. It means that after a storage time and temperature that equates to typical shelf life of the product there is no hard settling of the suspended material. However, it will be appreciated that the colloidal stability may be adversely effected if the suspensions are not chemically stable, for example if the water soluble polymer degrades or deteriorates when the suspension is stored. The aqueous suspension was readily pourable.

Since modifications within the spirit and scope of the invention may be readily effected by persons skilled in the art, it is to be understood that the invention is not limited to the particular embodiment described, by way of example, hereinabove.

Melbourne\004014107 Printed 22 March 2002 (11:31)

Claims

1. A stable aqueous concentrated suspension of calcium hydroxide wherein the concentration of calcium hydroxide is at least 600 g/litre.

2. A stable aqueous concentrated suspension as defined in claim 1 wherein the concentration of calcium hydroxide is at least 700 g/litre.

3. A stable aqueous concentrated suspension as defined in claim 2 wherein the concentration of calcium hydroxide is at least 800 g/litre.

4. A stable aqueous concentrated suspension as defined in any one of claims 1 to 3 wherein the suspension includes 1 10% of a water soluble polymer having a "molecular weight of at least 10,000. 15

5. A stable aqueous concentrated suspension as defined in claim 4 wherein the water soluble polymer has a viscosity, 2% in water 20°C, in the range 10,000 100,000 cps.

6. A stable aqueous concentrated suspension as defined in claim 4 or claim wherein the water soluble polymer is a cellulosic ether derivative.

7. A stable aqueous concentrated suspension as defined in claim 6 wherein the water soluble polymer is hydroxy propyl methyl cellulose polymer. Ultimate Nominees Pty Ltd Freehills Carter Smith Beadle Registered Patent Attorneys for the Applicant March 2002 Melboume\004014107 Printed 22 March 2002 (11:31)