The precipitation of magnesium hydroxoaluminate hydrate powders from sodium hydroxoaluminate solutions: Precipitate phases and precipitation mechanisms

Magnesium hydroxoaluminate hydrates were precipitated from different sodium hydroxoaluminate and hydroxoaluminate‐hydroxide solutions at ambient temperature, at C Al = 0.1 M, OH/Al ratios = 4–9 and XS OH/Al ratios = 1–6. The precipitations were monitored by potentiometric (pH) measurements while the final precipitate compositions were examined by chemical analysis, infra‐red spectrophotometry and thermal analysis. At solution OH/Al ratio = 4, the main precipitate phase at 20°C was Mg(H 2 O) n [Al(OH) 4 ] 2 admixed with some Al(OH) 3 ; at solution OH/Al ratio = 5, the main phase was Mg 2 (H 2 O) 4 [Al 2 (OH) 10 ]; at solution OH/Al ratio = 7, the main phase was Mg 4 (H 2 O) n (OH) 4 [Al 2 (OH) 10 ] while at solution OH/Al ratio = 9, the main phase was Mg 6 (H 2 O) n (OH) 8 [Al 2 (OH) 10 ] admixed with some Mg(OH) 2 . These hydrates were dehydrated at 60–100°C probably to the compounds Mg 2 [Al 2 O 3 (OH) 4 ], Mg 4 (OH) 4 [Al 2 O 3 (OH) 4 ] and Mg 6 (OH) 8 [Al 2 O 3 (OH) 4 ], respectively.