How is aluminum oxide reacted to produce aluminum hydroxide flame retardant?

There are currently numerous methods for preparing aluminum hydroxide flame retardants. These include the Bayer process, the lime-alkali calcination method, and the ammonium bicarbonate method. Beyond these three common approaches, aluminum hydroxide can also be produced through an aluminum oxide reaction—a highly comprehensive chemical process. Mastery of certain reaction principles is essential throughout the preparation process. Below is an overview of the reaction sequence.

Since alumina is an amphoteric oxide that is poorly soluble in water, and aluminum hydroxide flame retardant is an amphoteric hydroxide that is poorly soluble in water, both can dissolve in strong acids and strong bases. However, they do not dissolve in ammonia water (weak base) or carbonic acid (weak acid). Therefore, they can be prepared using the following method:

1. Dissolve aluminum oxide in sulfuric acid to obtain aluminum sulfate solution. Then add excess ammonia water to the aluminum sulfate solution. This yields aluminum hydroxide precipitate, which can be filtered, washed, and dried.

Al₂O₃ + 3H₂SO₄ = Al₂(SO₄)₃ + 3H₂O

Al₂(SO₄)₃ + 6NH₃·H₂O = 2Al(OH)₃↓ + 3(NH₄)₂SO₄

2. Dissolve aluminum oxide in sodium hydroxide to obtain sodium metasilicate solution. Then pass excess carbon dioxide through the sodium metasilicate solution. This yields aluminum hydroxide, which is precipitated, filtered, washed, and dried.

A key consideration during preparation is adding excess ammonia solution and carbon dioxide. This ensures complete conversion of aluminum oxide into aluminum hydroxide flame retardant, yielding a purer product.

The above outlines the method for producing aluminum hydroxide flame retardant from aluminum oxide reactions. The entire process is relatively straightforward, primarily leveraging chemical principles to induce reactions between substances. This approach effectively yields high-purity products, facilitating their practical application in production.