The Structure and Thermal Properties of Solid Ternary Compounds Forming with Ca(2+), Al(3+) and Heptagluconate Ions †

In the present work, the structure and thermal stability of Ca–Al mixed-metal compounds, relevant in the Bayer process as intermediates, have been investigated. X-ray diffraction (XRD) measurements revealed the amorphous morphology of the compounds, which was corroborated by SEM-EDX measurements. The results of ICP-OES and UV-Vis experiments suggested the formation of three possible ternary calcium aluminum heptagluconate (Ca-Al-Hpgl) compounds, with the formulae of CaAlHpgl(OH)(4)(0), Ca(2)AlHpgl(2)(OH)(5)(0) and Ca(3)Al(2)Hpgl(3)(OH)(9)(0). Additional IR and Raman experiments revealed the centrally symmetric arrangement of heptagluconate around the metal ion. The increased thermal stability was demonstrated by thermal analysis of the solids and confirmed our findings.