Raman Spectroscopic Study of Aluminum Silicate Complexes at 20°C in Basic Solutions
Résumé
Raman spectroscopic measurements were performed at ambient temperature onaqueous silica-bearing solutions (0.005 < m Si < 0.02; 0 < pH < 14). The spectraare consistent with the formation of monomeric Si(OH)o 4, SiO(OH)– 3 andSiO2(OH)2– 2 species at acid to neutral, basic, and strongly basic pH, respectively.Raman spectra of aqueous Al-bearing solutions at basic pH confirm thepredominance of the Al(OH)– 4 species in a wide concentration range (0.01 < m Al < 0.1).Raman spectra of basic solutions (12.4 < pH < 14.3), containing both Al andSi, exhibit a strong decrease in intensities of SiO(OH)– 3, SiO2(OH)2– 2, andAl(OH)– 4 bands in comparison with Al-free Si-bearing and Si-free Al-bearingsolutions of the same metal concentration and pH, suggesting the formation ofsoluble Al—Si complexes. The amounts of complexed Al and Si derived fromthe measurements of the Al and Si band intensities in strongly basic solutions(pH sim 14) are consistent with the formation, between Al(OH)– 4 andSiO2(OH)2– 2, of the single Al—Si dimer SiAlO3(OH)3– 4 according to the reactionSiO2(OH)2– 2 + Al(OH)– 4 hArr SiAlO3(OH)3– 4 + H2OAt lower pH (sim 12.5) the changes in band intensities are consistent with theformation of several, likely more polymerized, Al—Si complexes.