Analytical Sciences

Quantification Method of Size Distribution of Polysilicic Acid in Supersaturated Silicic Acid Solution

Emi OTSU,*1 Mayumi ETOU,*1 Hironori OHASHI,*2 Ikuko NISHIDA,*3 Shuquin BAI,*4 Yoshihiro OKAUE,*1 and Takushi YOKOYAMA*1

*1 Department of Chemistry, Faculty of Science, Kyushu University, 6-10-1 Hakozaki, Higashi, Fukuoka 812-8581, Japan
*2 Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi, Fukuoka 819-0395, Japan
*3 Kurita Water Industries Ltd., 1-1 Gochoyama, Kawada, Nogi, Shimotsuga, Tochigi 329-0105, Japan
*4 College of Environment and Resources, Inner Mongolia University, No. 235, West University Road, Saihan, Hohhot 010021, P. R. China

In order to estimate the absolute size distribution of polysilicic acid particles in geothermal waters, the distribution coefficient (K_av) of gel permeation chromatography (GPC) for polysilicic acid particles and the hydrodynamic radius for the same polysilicic acid particles from Dynamic Light Scattering (DLS) are combined to quantify the particle size. From the combination, a quantitative relationship between the K_av from GPC and the hydrodynamic radius for polysilicic acid from DLS was built up. Using this relationship, the change in particle size of polysilicic acid formed during the polymerization of silicic acid at pH 8 and 9 (initial silicic acid concentration: 800 ppm as SiO₂) was examined. The result showed that polysilicic acid grew to 500 and 1000 nm by 5 h at pH 9 and 8, respectively. It was found that aluminum affects the growth of polysilicic acid particles, and that the effect depends on the pH. The proposed method in this study has been proved to be valid to measure the size of polysilicic acid during the polymerization of silicic acid in solutions with relatively low silicic acid concentration, such as geothermal water.

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