Crystallographic,Mössbauer and electrokinetic study of synthetic lipscombite

The transformation of vivianite and the direct synthesis starting from pure chemicals lead to the formation of lipscombite {Fe _x ²⁺ Fe _3?x ³⁺ [(OH)_3?x/(PO₄)₂]} with varying Fe²⁺/Fe³⁺ molar ratios. The influence of this ratio on the Mössbauer spectra, solubility, electrokinetic potential and infrared spectra has been studied. By means of Mössbauer spectroscopy, the distribution of the Fe²⁺ and Fe³⁺ ions between the octahedral sites I and II has been investigated. The unit cell dimensions have been determined from Guinier-Hägg X-ray diffraction patterns. The crystal system is tetragonal for synthetic lipscombite with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å. Lipscombite has been found to show a negative and time-dependent zeta-potential which, moreover, is influenced by the pH of the suspension and the Fe²⁺/Fe³⁺ molar ratio. An explanation of the time-dependence of the zeta-potential on variations of solubility is proposed. Infrared absorption spectrum only is characterized by two absorption bands: v _OH(3,500 cm^?1) and v _P?O(1,100-960 cm^?1). The density at 25° C is determined in toluene as 3.36±0.01 g·cm^?3.