Application Of Raman Spectra In Structural Analysis Of Sodium Aluminate Solution

The structure and properties of sodium aluminate solution are the important theoretical basis for the production of alumina by alkali method,such as dissolution,settlement,seed separation and evaporation.Therefore,revealing and mastering the structure and properties of sodium aluminate solution can further clarify its characteristic in various processes,and provide a more reliable theoretical basis for optimizing the technological conditions.This paper simulated industrial sodium aluminate solution composition.The influence of process conditions and components on the Raman spectrum,viscosity and conductivity of sodium aluminate solution was systematically studied.The relationship between the ionic structure and physical properties of sodium aluminate solution was discussed.The main results obtained in this paper are as follows:The effects of solution temperature and time on the Raman spectra and physical properties of sodium aluminate solution were investigated,and the change rules of solution ionic structure were explored.In 25～100℃,The higher concentration of caustic alkali and the bigger molecular ratio would lead greater influence of temperature on the ionic structure and physical properties of the solution.The influence of molecular ratio on the ionic structure,viscosity and conductivity of sodium aluminate solution was greater at different temperatures and with the increase of the molecular ratio,the degree of influence increased gradually.With the increase of temperature,the dimers[(HO)3Al-O-Al(OH)3]2-of the circulating mother solution and the decomposed mother liquid were converted to the tetrahedrons Al(OH)4-,and the tetrahedrons Al(OH)4-in the solution were transformed to dimers[(HO)3Al-O-Al(OH)3]2-;When the solution was placed in 72h,a small amount of dimers[(HO)3Al-O-Al(OH)3]2-was converted to tetrahedrons Al(OH)4-.Due to the amount of ionic conversion was small,the increase of Al(OH)4-did not cause the change of solution viscosity.The electromigration ability of Al(OH)4-was stronger than[(HO)3Al-O-Al(OH)3]2-,and a small amount of ions in the solution would cause electrical conductivity change,so the conductivity of solution increased with the prolongation of storage time.The Raman spectral characteristics and physical properties of different caustic concentration,SiO2 concentration and molecular ratio of sodium aluminate solution were studied.The change rules of ionic structure of solution were explored,and the viscous activation energy of the solution was calculated.The stable ion form in sodium aluminate solution was tetrahedrons Al(OH)4-,and the Al(OH)4-was the basic form of aluminate ions in the medium and low concentration of sodium aluminate solution.The dimers[(HO)3Al-O-Al(OH)3]2-appeared with the increase of concentration of solution,and the number of two ions increased with the increase of the concentration of caustic alkali in solution.The increase of SiO2 concentration made the viscosity of the solution increase and the conductivity decrease.The Al-O-Al bond in solution gradually transforms into Al-O-Si bond,Si-O-Si bond or a more complex polymeric silicon acid complex.The structure of Al-O-Si or Si-O-Si was more stable than that of Al-O-Al in the maximum range of sodium aluminate solution that can dissolve sodium silicate.The increase of molecular ratio reduced the viscosity and electrical conductivity of the solution,and the Al(OH)4-gradually transformed into AbO(OH)62-.The effects of anion impurities CO32-,SO42-,C2O42-and CH3COO-on Raman spectra and physical properties of sodium aluminate solution were studied.The change rules of ionic structure of solution were explored,and the viscous activation energy of the solution was calculated.The presence of anionic impurities made the viscosity of the solution rise and the conductivity decrease.The increase of CO32-or SO42-concentration would lead to the transformation of Al(OH)4-into Al2O(OH)62-in solution,and CO32-was more conducive to the formation of the dimers[(HO)3Al-O-Al(OH)3]2-than SO42-.918 cm-1 and 931 cm-1 were the Raman characteristic peaks of C2O42-and CH3COO-,the presence of C2O42-or CH3COO-can make the Al2O(OH)62-transformed to the Al(OH)4-,but the effect of C2O42-on the ionic structure of the solution were more significant than CH3COO-.