Clays and Clay Minerals, Vol. 58, No. 6, 757–765, 2010.
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Authors
Kawano, Motoharu
Hwang, Jinyeon
Issue Date
2010
Type
Article
Language
Keywords
Periodicals , Geology , Amorphous Silica , Dissolution Rate , Guanidine , Imidazole , Pyrazole , Pyrrole
Alternative Title
Influence Of Guanidine, Imidazole, And Some Heterocyclic Compounds On Dissolution Rates Of Amorphous Silica
Abstract
Guanidineand imidazoleareimporta nt functional molecules that constitutethe side chain of basic amino acids (arginine and histidine); these molecules are capable of interacting with mineral surfaces. However, little information is available about the effect of these molecules on mineral dissolution, including amorphous silica. In this study, to evaluate the effect of these organic molecules on the dissolution rates of amorphous silica, dissolution experiments were performed in solutions containing these molecules and other related heterocyclic compounds. The dissolution experiments were conducted by thebatch method using 0.1 g of amorphous silica and 100 mL of 0.1 mM NaCl solution with 0.0, 0.1, 1.0, and 10.0 mM of guanidine, imidazole, pyrazole, or pyrrole at pH values of 4, 5, and 6. The results demonstrated that these compounds can enhance the dissolution rate of amorphous silica, depending on their ionic speciation in thefollo wing order: guanidine= imidazole> pyrazole> pyrrole. When 10.0 mM solutions were used, both guanidine and imidazole greatly increased the dissolution rate with an enhancement factor of 5.5-6.5, pyrazolee xhibited a smaller change in thedis solution ratewith an enhancement factor of 1.5-2.4, and pyrrole exhibited no significant enhancement. ChemEQL calculations confirmed that guanidine(pK = 13.6) and imidazole(pK = 6.99) are fully protonated and mostly present as cationic species in a pH range of 4-6; therefore, these compounds are capable of interacting with the >SiO- sites of amorphous silica. Pyrazole (pK = 2.61) and pyrrole (pK = 0.4), however, existed mostly as neutral forms. The concentrations of cationic species of pyrazole and pyrrole were at least one and three orders of magnitude lower than those of fully protonated compounds, respectively; therefore, pyrazole and pyrrolewe rele ss reactivethan thefully protonated compounds on thesurface s of amorphous silica.
Description
gsccm58603-kaw.pdf -- 501KB
Citation
Clays and Clay Minerals, Vol. 58, No. 6, 757–765, 2010.
Publisher
The Clay Minerals Society
License
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