The Dissolution of Amorphous Silica in the Presence of Tropolone Under Acidic Conditions

Abstract

Dissolution of amorphous silica or silicate is an important reaction to release silicic acid in natural water and this reaction is affected by several factors. The existence of a natural organic compound, tropolone, because of its abundance, is of particular importance. In the present study, the dissolution of amorphous silica in the presence of tropolone (HL) was investigated in an aqueous solution under acidic conditions. The dissolution is controlled by the reaction between silicic acid and tropolone (Si(OH)4 + 3HL + H+ ⇌ SiL3+ + 4H2O), where the conditional formation constant K = [SiL3+]/[Si(OH)4][HL]3[H+]). The solubility of amorphous silica in the presence of tropolone was significantly greater than that in pure water due to the formation of the Si-tropolonate complex in the solution. The acceleration of silica dissolution by tropolone depends on the reaction pH and tropolone concentration. The solubility of the amorphous silica in the tropolone solution at pH 1 was approximately ten times greater than in the 0.1 mol/dm3 HCl used as a reference. This increase in the solubility correlates to a K value of the Si-tropolone complex at each pH. From the solubility experiments, the conditional formation constants (log K) of the Si-tropolonate complex at each reaction pH 1, 2, and 3 were 6.39, 5.88, and 5.77, respectively. The significant acceleration of the dissolution of amorphous silica by tropolone at pH 1 can be attributed to the large formation constant of the Si-tropolonate complex.

Recent advances and future perspectives of sol–gel derived porous bioactive glasses: a review

“…387 The dissolution rate is generally increased with an increase in pH from 2 to 8.5 because when pH > 8.5, ions which are more soluble (SiO(OH) 3À ) are being developed. 388 The composition is also an equally important factor that helps in determining the dissolution rate of the glass. For example; Ma et al 60 reported that with partial substitution of MgO for CaO in the composition, the glass degradation rate decreases with the delay in HCA layer formation, which was ascribed to the effect of ionic eld strength and diverse bonding congurations of glass.…”

“…387 The dissolution rate is generally increased with an increase in pH from 2 to 8.5 because when pH > 8.5, ions which are more soluble (SiO(OH) 3− ) are being developed. 388…”

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“…The equilibrium concentration of Si(OH) 4 (in parts per million) is 70 ppm at 25 °C for massive amorphous silica. 57 It was reported that organic compounds can interact with Si(OH) 4 or a silica surface to notably increase the dissolution concentration in water, 59 and the organic contaminants adsorbed on the cantilever and sample surfaces may have such an effect. As can be seen from Figure 3e, the C peak intensity in the contact zone is high, while that outside the contact zone is low.…”