Solid solution between Al-ettringite and Fe-ettringite (Ca_6[Al_(1 - x)Fe_x(OH)_6]_2(SO_4)_3 centre dot 26H_2O)

摘要

The solid solution between Al- and Fe-ettringite Ca_6[Al_(1 - x)Fe_x(OH)_6]_2(SO_4)_3 centre dot 26H_2O was investigated. Ettringite phases were synthesized at different Al/(Al + Fe)-ratios (= X_(Al.total)). so that X_(Al) increased from 0.0 to 1.0 in 0.1 unit steps. After 8 months of equilibration, the solid phases were analyzed by X-ray diffraction (XRD) and thermogravimetric analysis (TGA), while the aqueous solutions were analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). XRD analyses of the solid phases indicated the existence of a miscibility gap between X_(Al,total) = 03-0.6. Some of the XRD reflections showed two overlapping peaks at these molar ratios. The composition of the aqueous solutions, however, would have been in agreement with both, the existence of a miscibility gap or a continuous solid solution between Al- and Fe-ettringite, based on thermodynamic modeling, simulating the experimental conditions.