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Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

No MeSH data available.


Related in: MedlinePlus

Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 (Al/Si-5.0, Fe/Si-5.0) and 8.0 (Al/Si-8.0, Fe/Si-8.0) under an electrolyte concentration of 0.01 M NaNO3.
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f1: Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 (Al/Si-5.0, Fe/Si-5.0) and 8.0 (Al/Si-8.0, Fe/Si-8.0) under an electrolyte concentration of 0.01 M NaNO3.

Mentions: Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 in 0.01 M NaNO3 (Al or Fe/Si-5.0 and -8.0) were shown in Fig. 1. In raw silica solids (SiO2), the silicate dissolution tended to increase with increasing pH, agreeing with the previous report9. There was a significant amount of dissolved Al or Fe under acidic conditions. However, only less than 0.15% of total added Al in Al/Si samples and 0.08% of total added Fe in Fe/Si samples was found at pH > 5.1 and 3.3, respectively (Figure S1). Such results indicated SiO2 was surrounded by AlO6 or FeO6. While SiO2 coprecipitated with Fe hydroxides, the amounts of silicate dissolution was general alleviated among all tested pH, especially for the Fe/Si samples coprecipitated at pH 5.0 (Fe/Si-5.0). Noteworthily, the silicate dissolution was essentially inhibited in Al/Si coprecipitates. For example, while 74%, 60%, and 62% of silicate was dissolved from SiO2, Fe/Si-5.0, and Fe/Si-8.0 at pH 10, no discernable silicate dissolution was found for Al/Si samples at alkaline condition. Furthermore, only 5 to 7% of silicate was dissolved from Al/Si-5.0 and Al/Si-8.0 at pH < 4.5.


Molecular Structures of Al/Si and Fe/Si Coprecipitates and the Implication for Selenite Removal.

Chan YT, Kuan WH, Tzou YM, Chen TY, Liu YT, Wang MK, Teah HY - Sci Rep (2016)

Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 (Al/Si-5.0, Fe/Si-5.0) and 8.0 (Al/Si-8.0, Fe/Si-8.0) under an electrolyte concentration of 0.01 M NaNO3.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4837376&req=5

f1: Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 (Al/Si-5.0, Fe/Si-5.0) and 8.0 (Al/Si-8.0, Fe/Si-8.0) under an electrolyte concentration of 0.01 M NaNO3.
Mentions: Trends of silicate dissolution from Al/Si and Fe/Si coprecipitates synthesized at pH 5.0 and 8.0 in 0.01 M NaNO3 (Al or Fe/Si-5.0 and -8.0) were shown in Fig. 1. In raw silica solids (SiO2), the silicate dissolution tended to increase with increasing pH, agreeing with the previous report9. There was a significant amount of dissolved Al or Fe under acidic conditions. However, only less than 0.15% of total added Al in Al/Si samples and 0.08% of total added Fe in Fe/Si samples was found at pH > 5.1 and 3.3, respectively (Figure S1). Such results indicated SiO2 was surrounded by AlO6 or FeO6. While SiO2 coprecipitated with Fe hydroxides, the amounts of silicate dissolution was general alleviated among all tested pH, especially for the Fe/Si samples coprecipitated at pH 5.0 (Fe/Si-5.0). Noteworthily, the silicate dissolution was essentially inhibited in Al/Si coprecipitates. For example, while 74%, 60%, and 62% of silicate was dissolved from SiO2, Fe/Si-5.0, and Fe/Si-8.0 at pH 10, no discernable silicate dissolution was found for Al/Si samples at alkaline condition. Furthermore, only 5 to 7% of silicate was dissolved from Al/Si-5.0 and Al/Si-8.0 at pH < 4.5.

Bottom Line: In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse.Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates.The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

View Article: PubMed Central - PubMed

Affiliation: Department of Soil and Environmental Sciences, National Chung Hsing University, 250 Kuo Kuang Rd., Taichung 40227, Taiwan, R.O.C.

ABSTRACT
Aluminum and iron oxides have been often used in the coagulation processes during water purification due to their unique surface properties toward anions. In the presence of silica, the coprecipitation of Al/Si or Fe/Si might decrease the efficiency of wastewater purification and reuse. In this study, surface properties and molecular structures of Al/Si and Fe/Si coprecipitates were characterized using spectroscopic techniques. Also, the selenite removal efficiency of Al/Si and Fe/Si coprecipitates in relation to their surface and structural properties was investigated. While dissolved silicate increased with increasing pH from Fe/Si coprecipitates, less than 7% of silicate was discernible from Al/Si samples over the range from acidic to alkaline conditions. Our spectroscopic results showed that the associations between Al and Si were relatively stronger than that between Fe and Si in coprecipitates. In Al/Si coprecipitates, core-shell structures were developed with AlO6/AlO4 domains as the shells and Si frameworks polymerized from the SiO2 as the cores. However, Si framework remained relatively unchanged upon coprecipitation with Fe hydroxides in Fe/Si samples. The Si core with Al shell structure of Al/Si coprecipitates shielded the negative charges from SiO2 and thereby resulted in a higher adsorption capacity of selenite than Fe/Si coprecipitates.

No MeSH data available.


Related in: MedlinePlus