The Structure and Thermal Properties of Solid Ternary Compounds Forming with Ca2+, Al3+ and Heptagluconate Ions.

Ákos Buckó,Ottó Berkesi,Ákos Kukovecz,Pál Sipos,István Pálinkó,Márton Szabados,Zsolt Kása,Bence Kutus,Zoltán Kónya

doi:10.3390/molecules25204715

Ákos Buckó, Ottó Berkesi + Show 7 more

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https://doi.org/10.3390/molecules25204715

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Abstract

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)40, Ca2AlHpgl2(OH)50 and Ca3Al2Hpgl3(OH)90. 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.

Highlights

Bauxite ores are the primary raw materials of the large-scale production of alumina, due to their high aluminum content, availability, as well as the relative simplicity of their refinement.During the Bayer process, i.e., the recrystallization of the aluminum content of bauxite in the form ofAl(OH)3, the causticity of the process liquor must be maximized to improve productivity
This so-called recausticization step is an integral part of most Bayer refineries operation; lime belongs to the primary raw materials of alumina production, and is essential for the causticization process to be a cost-effective operation of a Bayer refinery [1]
We report on the qualitative and quantitative analysis of the solid phases forming in solutions containing calcium, aluminate and heptagluconate (Hpgl− ) ions, with the latter serving as a model organic ligand (Scheme 1)

Summary

Introduction

Bauxite ores are the primary raw materials of the large-scale production of alumina, due to their high aluminum content, availability, as well as the relative simplicity of their refinement.During the Bayer process, i.e., the recrystallization of the aluminum content of bauxite in the form ofAl(OH) , the causticity of the process liquor must be maximized to improve productivity. Bauxite ores are the primary raw materials of the large-scale production of alumina, due to their high aluminum content, availability, as well as the relative simplicity of their refinement. Lime (Ca(OH)2 ) is added to the spent liquor to convert the in situ formed sodium carbonate to sodium hydroxide via the precipitation of calcium carbonate. This so-called recausticization step is an integral part of most Bayer refineries operation; lime belongs to the primary raw materials of alumina production, and is essential for the causticization process to be a cost-effective operation of a Bayer refinery [1]. The chemistry of calcium hydroxide in Bayer liquors has attracted considerable scientific as well as technological interest [2,3,4].

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