Physical chemistry of aluminosilicate gels. Part 2 Influence of the batch molar ratio SiO 2/Al 2O 3 on chemical composition of the gels

Abstract

The influence of the batch (b N: N = I, II) molar ratio. Y=[SiO 2] b N /[Al 2O 3] b N , 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 SiO 2, i.e. [SiO 2] bI = 0.20505 mol dm −3 [System I(A,B)]; [SiO 2] bII = 0.410l mol dm −3 [System II(A.B)], 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 Na 2O and Al 2O contained in the solid phase are directly proportional to the batch concentration [Al 2O 3] b N , and inversely proportional to the batch concentration [Na 2O] b N , i.e. both the [Na 2O] S and [Al 2O 3] S are linear functions of 1/( Y[Na 2O] b N ). On the other hand, logarithms of the molar ratios [Al 2O 3] S/[Al 2O 3] L, [SiO] S/[SiO 2] L and [SiO 2] L/[Al 2O 3] L are linear functions of the batch molar ratio 1/ Y=[Al 2O 3] b N /[SiO 2] b N , while the molar ratio [SiO 2] S/[Al 2O 3] S of SiO 2 and Al 2O 3 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 [SiO 2] S/[Al 2O 3] S-0.18 ln([SiO 2] L/[Al 2O 3] L) = 2.554 satisfactorily describes the equilibrium distribution of SiO 2 and Al 2O 3 between the solid and the liquid phase of the investigated aluminosilicate hydrogels.