27Al NMR Study on the Interaction between Aluminate and Silicate Ions in Alkaline Solution

Abstract

An interaction between aluminate and silicate ions in highly alkaline solution was investigated by a high-resolution 27Al NMR study. The interaction greatly varied with alkali concentration, and did not occur at 1.0 mol dm−3 NaOH. At 0.10 mol dm−3 NaOH, the formation of a monomeric species with an ≡Al–O–Si≡ bond (Si/Al=1) was suggested and the formation constant was estimated to be 22.8 dm3 mol−1. At 0.015 mol dm−3 NaOH, polynuclear species with ≡Al–O–Si≡ bond was expected to be formed.

Initial Stages of Self-Organization of Silica−Alumina Gels in Zeolite Synthesis

“…27 Al and 29 Si NMR spectroscopy, in contrast, can provide information about the species in solution at relevant zeolite-synthesis compositions. [31][32][33][34]51 These reports find that, for silica concentrations below SiO 2 :[OH -] 1:1 molar ratios in the synthesis gel (i.e., below the cac of an equivalent pure silica solution), all five possible aluminum coordination environments are observed: reaches a threshold value. After this point, the addition of more silica to the system changes the concentration of other species, but not the concentration of H 4 SiO 4 , which remains constant.…”

“…At lower pH, the concentration of q 1 to q 4 species increases, and at even lower pH, the intensity of the peaks decreases due to the formation of larger aluminosilicate oligomers that broaden the NMR peaks. 33,34,37 As with silica, 38 the cation type can have a marked effect on the species observed in solution. In the presence of small organic cations, the 27 Al NMR spectra can be stable for periods of days.…”

“…These results, however, were obtained at concentrations at least 10 times lower than typical zeolite synthesis conditions. 27 Al and 29 Si NMR spectroscopy, in contrast, can provide information about the species in solution at relevant zeolite-synthesis compositions. − , These reports find that, for silica concentrations below SiO 2 :[OH - ] 1:1 molar ratios in the synthesis gel (i.e., below the cac of an equivalent pure silica solution), all five possible aluminum coordination environments are observed: from the monomer q 0 (Al(OH) 4 - ) to the tetracoordinated species q 4 (q n = (HO) 4 - n Al(OSi(OH) 3 ) n - ) . Under selected conditions of pH and concentration, well-resolved 27 Al signals can be observed in the spectra, indicating that the broad peaks normally assigned to q 1 , q 2 , and q 3 species are probably a composite of various species.…”

Exchange reactions in aluminosilicate solutions

“…Moreover, the assignment of Bell and coworkers6 takes no obvious account of the exchange phen~menon.~ It is our belief that the earlier workers are correct and that the highest frequency peak arises from averaging of qo and q1 environments, the shift with time (and with Si:Al ratio) being a measure of changes in the 90: q1 ratio, as suggested in ref. 4 for shift variations with Si:Al ratio. Any q4 peak presumably relates to a potential Bronsted acid site.…”

Role of Aluminum and Lithium in Mitigating Alkali-Silica Reaction—A Review

“…Relatively low concentrations of Al (1-5 mM) can reduce the dissolution rate of silica by as much as 90%. However, the sorption of Al(OH) 4 on the surface of silica and the slowing down of silica dissolution silica is more distinct at intermediate pH values (<12), while at pH 13 and above the sorption of Al(OH) 4 on silica becomes weak resulting in only feeble suppression of the dissolution rate (Yokoyama et al, 1988;Chappex and Scrivener, 2012b;Nicoleau et al, 2014) as illustrated in Figure 3 (Bagheri et al, 2022). A comparison with the Al concentration in the pore solution of Portland cement and blended cements, show that blending of Portland cement with fly ash or metakaolin could in fact increase the Al concentration to 1 mM and above, i.e., to Al concentrations efficient in slowing down silica dissolution (see Figure 3).…”