Physical chemistry of aluminosilicate gels.: Part 2 -: Influence of the batch molar ratio SiO2/Al2O3 on chemical composition of the gels

The influence of the batch (bN: N=I, II) molar ratio, Y=[SiO2](bN)/[Al2O3](bN), and order of mixing of aluminate and silicate solutions (A: sodium silicate to sodium aluminate solution; B: sodium aluminate to sodium silicate solution) on the distributions of Na, Al and Si between the solid (S) and the liquid (L) phase of the sodium aluminosilicate hydrogels prepared at the constant batch concentrations of SiO2, i.e. [SiO2](bI)=0.20505 mol dm(-3) [System I(A,B)]; [SiO2](bII)=0.4101 mol dm(-3) [System II(A,B)I, were investigated by measuring the concentrations of Na, Al and Si in both solid and liquid phase by atomic absorption spectrometry. It was found that the amounts of Na2O and Al2O3 contained in the solid phase are directly proportional to the batch concentration [Al2O3](bN), and inversely proportional to the batch concentration [Na2O](bN), i.e. both the [Na2O](s) and [Al2O3](s) are linear functions of 1/(Y[Na2O](bN)). On the other hand, logarithms of the molar ratios [Al2O3](s)/[Al2O3](L), [SiO](s)/[SiO2](L) and [SiO2](L)/[Al2O3](L) are linear functions of the batch molar ratio 1/Y=[Al2O3](bN)/[SiO2](bN), while the molar ratio [SiO2](s)/[Al2O3](s) of SiO2 and Al2O3 in the precipitated amorphous aluminosilicate is in linear relationship with the batch molar ratio 1/Y in the region 2<Y<32. Based on these interrelations, it was found that the equation [SiO2](s)/[Al2O3](s)-0.18 In([SiO2](L)/[Al2O3](L))=2.554 satisfactorily describes the equilibrium distribution of SiO, and Al2O3 between the solid and the liquid phase of the investigated aluminosilicate hydrogels. (C) 1998 Elsevier Science B.V.