Magnesium hydroxide

• Magnesium ( II) hydroxide
• Brucite
• E528

• A02AA04
• G04BX01

Colorless and odorless solid

Fixed

2.38 g · cm -3

350 ° C ( decomposition)

Very poor in water ( 9 mg · l-1 at 18 ° C )

8500 mg · kg -1 ( LD50, rat, oral)

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Magnesium hydroxide is a chemical compound of magnesium selected from the group of the hydroxides. It is a colorless salt and a strong base. Due to the low solubility in water, but only has an aqueous slurry has a pH value of pH ~ 10, and therefore magnesium hydroxide acts as a seemingly weak base.

Occurrence

In nature, it occurs as the mineral brucite.

Production and representation

Magnesium hydroxide can be recovered from waste liquors of potash by precipitation with lime (1) or from sea water by precipitation with calcined dolomite (2). The product is then filtered and dried at about 100 ° C. Particularly pure magnesium hydroxide is produced by the action of water to elemental magnesium (3).

(1)

(2)

(3)

Since chalk besides calcium sulfate and calcium carbonate may also contain magnesium oxide, magnesium hydroxide is also produced by wiping Tafelaufschrieben; Hydoxid the magnesium carbonate is converted to by the uptake of carbon dioxide contained in the air gradually.

Properties

The crystal lattice of magnesium hydroxide ( brucite ) consists of a hexagonal close packing of hydroxide ions. Every second octahedral layer gap is occupied by magnesium ions ( Mg2 ). In water and alkaline solutions of magnesium hydroxide is sparingly soluble, whereas in acidic solutions ( for example, hydrochloric acid, nitric acid) soluble. In ammonium salt solutions, magnesium hydroxide is readily soluble, as ammonia and water to a low hydroxide concentration is achieved by the neutralization of ammonium hydroxide and, thus the solubility product is not exceeded.

Magnesium hydroxide forms with acids basic and neutral salts.

At temperatures above 350 ° C decomposition occurs slowly to a magnesium oxide. At 600 ° C, the equilibrium is almost on the side of the oxide.

Use

The largest part of the magnesium hydroxide produced for industrial purposes is further processed by calcining (burning ) at 500-600 ° C to form magnesium oxide.

Magnesium hydroxide is used as a cooking oil additive ( for binding sulfur dioxide), as a flocculant for wastewater treatment, as a flame retardant in thermoplastic materials ( polyolefins and PVC) and elastomers, as well as an additive in cleaning agents.

In medicine it is used as antacid (drug to neutralize the stomach acid), and as a mild laxative for use.

Magnesium hydroxide is added to foods as an acidity regulator or release agents. It is approved in the EU as a food additive with the E number E 528.