Chemistry of inorganic compounds – With additive
Patent
1997-01-23
1999-05-25
Lovering, Richard D.
Chemistry of inorganic compounds
With additive
423635, 423636, 423637, 576 88, C01F 514, B01J 1300
Patent
active
059068043
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to magnesium hydroxide slurries and is particularly concerned with high solids content, stable, pumpable magnesium hydroxide slurries and processes for production of such magnesium hydroxide slurries.
BACKGROUND OF THE INVENTION
Magnesium hydroxide slurries may be produced from magnesia (MgO) as a feed stock. Magnesia may be obtained from the natural mineral magnesite (MgCO.sub.3) or from sea water or brine. Production of magnesium hydroxide from magnesite generally involves calcination to decompose MgCO.sub.3 to MgO with subsequent hydration in water to convert MgO to Mg(OH).sub.2. The production of magnesium hydroxide from sea water or brine entails direct precipitation with quicklime (CaO) or more preferably with dolime or dolomitic lime. Commercially this is usually a precursor to the production of "synthetic magnesia" by subsequent calcination of the precipitated magnesium hydroxide. The sea water is seeded with magnesium hydroxide to promote crystal growth and to improve settling and filtering characteristics of the magnesium hydroxide precipitate. A flocculating agent is also usually added. The resulting thickened slurry is vacuum-filtered to produce a filter cake containing about 50% magnesium hydroxide. Because nearly all the magnesium hydroxide produced in this way is presently calcined to MgO, the characteristics of the magnesium hydroxide precipitate are optimised for solid/liquid separation rather than for magnesium hydroxide production.
Conventional magnesium hydroxide slurries may be utilised for desirable applications which include: or organic contaminants.
In this context magnesium hydroxide slurries are preferred for use in applications such as (a) (b) (c) and (d) above rather than magnesia either to avoid complications that uncontrolled hydration can cause, such as heat generation and cement formation, or because conversion of MgO to Mg(OH).sub.2 is essential to the desired application. In this regard magnesia in its reactive form in an aqueous environment will become hydrated to Mg(OH).sub.2 relatively spontaneously and in some cases it is desirable to control the rate of hydration dependent upon the desired application.
Magnesia in its reactive form commonly known as caustic magnesia, caustic calcined magnesite or light burned magnesia has to be distinguished from a relatively inert form of magnesia known as dead burned or inert magnesia.
None of the commercially produced magnesium hydroxide slurries which have a relatively high solids content (i.e. 50-60 wt %) have been found to have a combination of high solids content, stability to settling and high overall reactivity which are characteristics of magnesium hydroxide slurries produced by the present invention as hereinafter described. It is common practice in some conventional slurries, as referred to in prior art hereinafter, to incorporate a polymeric viscosity modifying agent to thin and/or stabilise the slurry but this practice has undesirable side effects as described hereinafter.
Reference also may be made to conventional processes for producing magnesium hydroxide slurries which are described in the following patent specifications: burned magnesia which is introduced into a hydration tank equipped with a stirrer or agitator and which is simultaneously milled by steel balls or other form of abrading apparatus; as a hexagonal plate like crystal having a specific surface area (SSA) of 10m.sup.2 /g or less. A slurry of Mg(OH).sub.2 having a solids content of 5-70% wt % is formed as an intermediate in a hydration process at above 50.degree. C. under agitation and some slurry is periodically removed and replaced by hot water and magnesia to obtain a uniform slurry density. This slurry is used for producing high purity dry Mg(OH).sub.2 used for flame retardant applications; wherein magnesia having a mean particle diameter of less than 100 micron is hydrated in the presence of alkali metal ions and/or alkaline earth metal ions and also in the presence of the hydroxide ion, nitrate ion,
REFERENCES:
patent: 2193281 (1940-03-01), Hall
patent: 3692898 (1972-09-01), Gorman et al.
patent: 3957674 (1976-05-01), Sano et al.
patent: 5183648 (1993-02-01), Wolfert
patent: 5487879 (1996-01-01), Witkowski et al.
87-011677/02, Nov. 29, 1986, Derwent Abstract, JP,A, 61-270214 (Shin Nippon Kagaku).
87/052782/08, Jan. 1987, Derwent Absstract, JP, A, 62-007439 (Katayama Kagaku KOG).
89/188315/26, May 18, 1989, Derwent Abstract, JP, A, 63-277511 (Shin Nippon Kagaku).
89/002317/01, Nov. 15, 1988, Derwent Abstract, Class A60, JP, A, 63-277511 (Shin Nippon Kagaku).
93-297709, Aug. 1993, Derwent Abstract, JP,A,5-208810 (Rohm and Haas Company).
81-91984, Nov. 2, 1981, Derwent Abstracts, JP, A, 56-140025 (Mitsui Mining & Smelting).
Aral Halil
Bush Philip
Houchin Martin Richard
Merkestein Robert Van
Strode Phillip Robin
Lovering Richard D.
Orica Australia Pty Ltd.
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