Zirconium(IV) hydroxide
Zirconium(IV) hydroxide, often written as Zr(OH)4, is an inorganic compound and a hydroxide of zirconium in its +4 oxidation state. It is generally understood to be a gelatinous, white precipitate formed when a base, such as ammonium hydroxide or sodium hydroxide, is added to a solution containing a zirconium(IV) salt, like zirconium tetrachloride or zirconium oxychloride. However, the precise nature of the product is complex and often poorly defined.
The formula Zr(OH)4 is often used as a simplified representation, but the actual precipitate is typically hydrated and contains varying amounts of water. Therefore, a more accurate representation might be Zr(OH)4•nH2O or ZrO2•mH2O, where 'n' and 'm' represent variable hydration numbers. The resulting material is often considered an amorphous hydrous zirconium oxide or hydrous zirconia.
Due to its amphoteric nature, zirconium(IV) hydroxide can react with both acids and bases. It dissolves in strong acids to form zirconium(IV) salts and dissolves in strong bases to form hydroxo-zirconate complexes.
Zirconium(IV) hydroxide is used as a precursor in the preparation of various zirconium compounds, including zirconium oxide (ZrO2), catalysts, and ion exchangers. It finds applications in water treatment, catalysis, and the production of ceramics. The properties of the derived products are often strongly influenced by the method of preparation and the degree of hydration of the initial zirconium(IV) hydroxide precipitate.
The term "zirconium hydroxide" is also sometimes used loosely to refer to solutions or gels containing partially hydrolyzed zirconium(IV) species. These are often mixtures of polymeric zirconium-containing species with varying degrees of hydroxylation and polymerization. The exact composition and structure of these solutions and gels are highly dependent on the pH, concentration, and the presence of other ions.