Abstract
AbstractMagnesium aluminium hydroxides were coprecipitated from different mixed metal cation solutions — at total CM = 0.1 M and Mg/Al2 ratios from 1 to 6 — with sodium hydroxide solution at ambient temperature, with different pre‐ageing conditions for the aluminium hydroxide pre‐precipitate. The coprecipitations were monitored by potentiometric (pH) titration and the final precipitate compositions were examined by chemical analysis, infrared spectrophotometry and thermal analysis.Magnesium hydroxide was coprecipitated onto completely recrystallised aluminium hydroxide as a simple mixture.Generally, with no to three days pre‐ageing, microcrystalline aluminium hydroxide was first precipitated at pH about 4; this then partially redissolved on further addition of sodium hydroxide (to form hydroxoaluminate anion) and magnesium aluminium hydroxide coprecipitates were formed continuously at pHs from 8.0–8.7 to 12.0–12.5. Their compositions were similar to the magnesium hydroxoaluminate hydrates formed by direct precipitation from high pH sodium hydroxoaluminate solutions. equation image
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