Mixed magnesium-aluminiun hydroxides. I. Preparation and characterization of compounds formed in dialysed systems

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Abstract
The materials formed by dialysis of the precipitates formed by the reaction of NaOH with mixed Mg-Al solutions are described. In addition to aluminium and magnesium hydroxides, two hydrocarbonates having Mg/Al ratios of about 5 : 1 and 2 : 1 are formed, essentially pure, from solutions with Mg/Mg + Al molar ratios of 0.8 and 0.7, respectively. X-ray powder data shows that they have partially ordered hexagonal layer structures with unit layer dimensions a = 3.048 Å, layer thickness 7.60 Å for the Al-rich compound and a = 3.072 Å, layer thickness 7.92 Å for the Al-poor compound. X-ray and chemical data show that the new compounds resemble the minerals hydrotalcite and manasseite and also the compounds described as Mg-Al hydroxides by Feitknecht.
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