High-purity magnesium hydroxide and process for its production

Details High-purity magnesium hydroxide and process for its production High-purity magnesium hydroxide and process for its production

1999-04-13

2001-04-10

Langel, Wayne (Department: 1754)

Chemistry of inorganic compounds

Oxygen or compound thereof

Metal containing

C423S243080, C423S519200, C423S554000

Reexamination Certificate

active

06214313

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to production of high-purity magnesium hydroxide from process slurry of a flue gas desulfurization operation utilizing magnesium-enhanced lime.
BACKGROUND OF THE INVENTION
Production of high-purity magnesium hydroxide (Mg(OH)
2
) for uses such as flame retardants and pharmaceuticals by known processes involves numerous energy-intensive steps as well as high cost chemical usage. Various processes for such production are described in U.S. Pat. No. 5,476,642; No. 5,286,285; No. 5,143,965; No. 4,698,379; and No. 4,695,445.
In a flue gas desulfurization process, controlling alkalinity of process slurry prevents the formation of scale which is detrimental to the system. Magnesium-enhanced lime is used to increase alkalinity of the process slurry through the formation of magnesium sulfite (MgSO
3
). Lime presenting a magnesium oxide (MgO) content is selected for such use to enable the formation of the magnesium sulfite. Such process slurry is a lime slurry containing magnesium ions. A portion of such magnesium sulfite laden slurry is bled from the desulfurization system to maintain slurry chemistry. Its disposal can present high costs and environmental concerns.
Such bleed-off slurry provides an economical source of feedstock for the production of high purity magnesium hydroxide.
SUMMARY OF THE INVENTION
The present invention provides for the production of high-purity magnesium hydroxide from process slurry of a flue gas desulfurization process. Such slurry is prepared using lime having a magnesium oxide content. Such magnesium presence enables formation of magnesium sulfite in the process slurry. Control of slurry chemistry during operation of the desulfurization system facilitates recovery of magnesium sulfite hexahydrate crystals (MgSO
3
.6H
2
O) presenting a low level of impurities. Such crystals are the source material for the high-purity magnesium hydroxide of the invention.
In the process of the invention magnesium sulfite hexahydrate crystals are converted to an aqueous solution of magnesium sulfate (MgSO
4
) by a reaction with water and an oxidizing agent. The resulting aqueous solution is then reacted with a caustic solution to precipitate a magnesium hydroxide solid. Such solid precipitate is then separated from the reaction medium solution by filtering means to obtain a magnesium hydroxide filter cake. Entrained solution in the cake is removed and a drying process is used to eliminate residual water from the high-purity magnesium hydroxide product.


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