Syntheses of Disordered and Al-rich Hydrotalcite-Like Compounds

I. Pausch, H.-H. Lohse, K. Schürmann and R. Allmann
Fachbereich Geowissenschaften, Lahnberge, D-3550 Marburg Federal Republic of Germany

Abstract: Hydrotalcite-like compounds, [Mg1−xAlx(OH)2]x+ [xX · n H2O], where X = ½ CO32- or OH, were prepared by hydrothermal syntheses at PH2O = 100 MPa and T = 100°–350°C. Starting materials were MgO, γ-Al2O3, H2O, and MgC2O4·2H2O. The synthesis depended on temperature, pressure, the Al/(Al + Mg) ratio x, and the CO2 content of the starting material. Previously an Al content of x = 0.33 was thought to be the upper limit in these double-layer compounds, but by using pressure the Al-content was increased to x = 0.44. Up to x = 0.33, a0 decreased linearly to about 3.04 Å, but for x ≥0.33, a0 remained nearly constant at this value. For the synthesized products the layer thickness c′ varied between 7.40 and 7.57 Å in contrast to the natural phases wherein c' varies from 7.60 to 7.80 Å. At higher temperatures CO2-free syntheses, i.e., those without Mg-oxalate, resulted in a disordered hydrotalcite-like phase. The transition temperature between the ordered and the disordered hydrotalcite-like phase depended on the Al-content, x.

Clays and Clay Minerals; October 1986 v. 34; no. 5; p. 507-510; DOI: 10.1346/CCMN.1986.0340502
© 1986, The Clay Minerals Society
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