Abstract:It is necessary to clarify the influence of thermal history on the conversion of aluminate species in sodium aluminate solution in order to optimize Bayer alumina production. The interconversion of various solution species in the systems was investigated by measuring the infrared spectra of sodium aluminate solution with different compositions after separate heat treatment, dilution and concentration. The results show that increasing temperature or prolonging holding time favors the transformation of Al₂O(OH)₆^2- to Al—OH vibration (condensed AlO₄ tetrahedral aluminate ion) at about 880 cm^-1 and Al(OH)₄^-. A1₂O(OH)₆^2- and Al—OH tetrahedral dimer ions convert rapidly to Al(OH)₄^- during the dilution process; however, the back transformation of Al(OH)₄^- to the Al—OH tetrahedral dimer ions can occur in diluted sodium aluminate solution. As for the concentration process, the transformation of Al(OH)₄^- to A1₂O(OH)₆^2- and Al—OH tetrahedral dimer ions can take place, while it is relatively difficult to transform to A1₂O(OH)₆^2-.

Key words: aluminate ions; structural changes; infrared spectrum; thermal history