Synthetic solid solutions formed between goethite and diaspore

Authors:

• Emilia Wolska,
• Wojciech Szajda,
• Paweł Piszora

Abstract

The substitutional solid solutions of goethite (a‐FeOOH) and diaspore (α‐AlOOH) have been investigated by X‐ray powder diffraction and chemical analysis in order to establish the solubility limits of aluminium in the goethite structure. α‐Fe_1‐xAI_xOOH samples were obtained by ageing of coprecipitated amorphous (Fe,Al) hydroxides at pH 13 in NaOH and Na[Al(OH)₄] solutions at 25°C (G25 series) and 70°C (G70 series), respectively. Chemical analysis reveals that the aluminium content of Al goethites is consistent with Al concentration in the coprecipitated hydroxides up to about 10 mol% Al. In Al goethites obtained from (Fe,Al) hydroxides with higher Al:Fe ratios, the relative Al content is considerably lower. It was found that pure ferrihydrite stored in the aluminate solution is also transformed into Al goethite. The X‐ray diffraction results show a significant divergence of the unitcell parameters from Vegard's law. This points out the limited ranges of the solid solution between goethite and diaspore and suggests the formation of defect, cation‐deficient structures. Copyright © 1992 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim