Aluminium magnesium hydroxy fatty acid cpds. of formula (I), and which are obtd. by reacting a soluble aluminium salt with a soluble magnesium salt under alkaline at pH of at least 8 and in the presence of an alkali or ammonium salt of 12-22C aliphatic mono-carboxylic acid(s) are new. The aq. solns. of the aluminium and magnesium salt are simultaneously added at 20-90 (60-85) deg.C and with stirring, to the alkaline alkali carbonate soln. ensuring that the pH is always at least 8. The ppte. obtd. is sepd. by known methods and washed with fully deionised water until no more anions of the original aluminium and magnesium salt can be detected in the washing water. AlnMgy(OH)3x+2y-zRznH2O (I); R = the residue of a 12-22C aliphatic monocarboxylic acid RCOO- or their mixts., n = 2; y is between 2 and 10; Z = 2.
